Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

1 files changed, 1493 insertions, 0 deletions

diff --git a/vendor/jpeg-decoder/src/decoder.rs b/vendor/jpeg-decoder/src/decoder.rs
new file mode 100644
index 0000000..795ad1e
--- /dev/null
+++ b/vendor/jpeg-decoder/src/decoder.rs
@@ -0,0 +1,1493 @@
+use crate::error::{Error, Result, UnsupportedFeature};
+use crate::huffman::{fill_default_mjpeg_tables, HuffmanDecoder, HuffmanTable};
+use crate::marker::Marker;
+use crate::parser::{
+    parse_app, parse_com, parse_dht, parse_dqt, parse_dri, parse_sof, parse_sos,
+    AdobeColorTransform, AppData, CodingProcess, Component, Dimensions, EntropyCoding, FrameInfo,
+    IccChunk, ScanInfo,
+};
+use crate::read_u8;
+use crate::upsampler::Upsampler;
+use crate::worker::{compute_image_parallel, PreferWorkerKind, RowData, Worker, WorkerScope};
+use alloc::borrow::ToOwned;
+use alloc::sync::Arc;
+use alloc::vec::Vec;
+use alloc::{format, vec};
+use core::cmp;
+use core::mem;
+use core::ops::Range;
+use std::convert::TryInto;
+use std::io::Read;
+
+pub const MAX_COMPONENTS: usize = 4;
+
+mod lossless;
+use self::lossless::compute_image_lossless;
+
+#[cfg_attr(rustfmt, rustfmt_skip)]
+static UNZIGZAG: [u8; 64] = [
+     0,  1,  8, 16,  9,  2,  3, 10,
+    17, 24, 32, 25, 18, 11,  4,  5,
+    12, 19, 26, 33, 40, 48, 41, 34,
+    27, 20, 13,  6,  7, 14, 21, 28,
+    35, 42, 49, 56, 57, 50, 43, 36,
+    29, 22, 15, 23, 30, 37, 44, 51,
+    58, 59, 52, 45, 38, 31, 39, 46,
+    53, 60, 61, 54, 47, 55, 62, 63,
+];
+
+/// An enumeration over combinations of color spaces and bit depths a pixel can have.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub enum PixelFormat {
+    /// Luminance (grayscale), 8 bits
+    L8,
+    /// Luminance (grayscale), 16 bits
+    L16,
+    /// RGB, 8 bits per channel
+    RGB24,
+    /// CMYK, 8 bits per channel
+    CMYK32,
+}
+
+impl PixelFormat {
+    /// Determine the size in bytes of each pixel in this format
+    pub fn pixel_bytes(&self) -> usize {
+        match self {
+            PixelFormat::L8 => 1,
+            PixelFormat::L16 => 2,
+            PixelFormat::RGB24 => 3,
+            PixelFormat::CMYK32 => 4,
+        }
+    }
+}
+
+/// Represents metadata of an image.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct ImageInfo {
+    /// The width of the image, in pixels.
+    pub width: u16,
+    /// The height of the image, in pixels.
+    pub height: u16,
+    /// The pixel format of the image.
+    pub pixel_format: PixelFormat,
+    /// The coding process of the image.
+    pub coding_process: CodingProcess,
+}
+
+/// Describes the colour transform to apply before binary data is returned
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[non_exhaustive]
+pub enum ColorTransform {
+    /// No transform should be applied and the data is returned as-is.
+    None,
+    /// Unknown colour transformation
+    Unknown,
+    /// Grayscale transform should be applied (expects 1 channel)
+    Grayscale,
+    /// RGB transform should be applied.
+    RGB,
+    /// YCbCr transform should be applied.
+    YCbCr,
+    /// CMYK transform should be applied.
+    CMYK,
+    /// YCCK transform should be applied.
+    YCCK,
+    /// big gamut Y/Cb/Cr, bg-sYCC
+    JcsBgYcc,
+    /// big gamut red/green/blue, bg-sRGB
+    JcsBgRgb,
+}
+
+/// JPEG decoder
+pub struct Decoder<R> {
+    reader: R,
+
+    frame: Option<FrameInfo>,
+    dc_huffman_tables: Vec<Option<HuffmanTable>>,
+    ac_huffman_tables: Vec<Option<HuffmanTable>>,
+    quantization_tables: [Option<Arc<[u16; 64]>>; 4],
+
+    restart_interval: u16,
+
+    adobe_color_transform: Option<AdobeColorTransform>,
+    color_transform: Option<ColorTransform>,
+
+    is_jfif: bool,
+    is_mjpeg: bool,
+
+    icc_markers: Vec<IccChunk>,
+
+    exif_data: Option<Vec<u8>>,
+
+    // Used for progressive JPEGs.
+    coefficients: Vec<Vec<i16>>,
+    // Bitmask of which coefficients has been completely decoded.
+    coefficients_finished: [u64; MAX_COMPONENTS],
+
+    // Maximum allowed size of decoded image buffer
+    decoding_buffer_size_limit: usize,
+}
+
+impl<R: Read> Decoder<R> {
+    /// Creates a new `Decoder` using the reader `reader`.
+    pub fn new(reader: R) -> Decoder<R> {
+        Decoder {
+            reader,
+            frame: None,
+            dc_huffman_tables: vec![None, None, None, None],
+            ac_huffman_tables: vec![None, None, None, None],
+            quantization_tables: [None, None, None, None],
+            restart_interval: 0,
+            adobe_color_transform: None,
+            color_transform: None,
+            is_jfif: false,
+            is_mjpeg: false,
+            icc_markers: Vec::new(),
+            exif_data: None,
+            coefficients: Vec::new(),
+            coefficients_finished: [0; MAX_COMPONENTS],
+            decoding_buffer_size_limit: usize::MAX,
+        }
+    }
+
+    /// Colour transform to use when decoding the image. App segments relating to colour transforms
+    /// will be ignored.
+    pub fn set_color_transform(&mut self, transform: ColorTransform) {
+        self.color_transform = Some(transform);
+    }
+
+    /// Set maximum buffer size allowed for decoded images
+    pub fn set_max_decoding_buffer_size(&mut self, max: usize) {
+        self.decoding_buffer_size_limit = max;
+    }
+
+    /// Returns metadata about the image.
+    ///
+    /// The returned value will be `None` until a call to either `read_info` or `decode` has
+    /// returned `Ok`.
+    pub fn info(&self) -> Option<ImageInfo> {
+        match self.frame {
+            Some(ref frame) => {
+                let pixel_format = match frame.components.len() {
+                    1 => match frame.precision {
+                        8 => PixelFormat::L8,
+                        16 => PixelFormat::L16,
+                        _ => panic!(),
+                    },
+                    3 => PixelFormat::RGB24,
+                    4 => PixelFormat::CMYK32,
+                    _ => panic!(),
+                };
+
+                Some(ImageInfo {
+                    width: frame.output_size.width,
+                    height: frame.output_size.height,
+                    pixel_format,
+                    coding_process: frame.coding_process,
+                })
+            }
+            None => None,
+        }
+    }
+
+    /// Returns raw exif data, starting at the TIFF header, if the image contains any.
+    ///
+    /// The returned value will be `None` until a call to `decode` has returned `Ok`.    
+    pub fn exif_data(&self) -> Option<&[u8]> {
+        self.exif_data.as_deref()
+    }
+
+    /// Returns the embeded icc profile if the image contains one.
+    pub fn icc_profile(&self) -> Option<Vec<u8>> {
+        let mut marker_present: [Option<&IccChunk>; 256] = [None; 256];
+        let num_markers = self.icc_markers.len();
+        if num_markers == 0 || num_markers >= 255 {
+            return None;
+        }
+        // check the validity of the markers
+        for chunk in &self.icc_markers {
+            if usize::from(chunk.num_markers) != num_markers {
+                // all the lengths must match
+                return None;
+            }
+            if chunk.seq_no == 0 {
+                return None;
+            }
+            if marker_present[usize::from(chunk.seq_no)].is_some() {
+                // duplicate seq_no
+                return None;
+            } else {
+                marker_present[usize::from(chunk.seq_no)] = Some(chunk);
+            }
+        }
+
+        // assemble them together by seq_no failing if any are missing
+        let mut data = Vec::new();
+        // seq_no's start at 1
+        for &chunk in marker_present.get(1..=num_markers)? {
+            data.extend_from_slice(&chunk?.data);
+        }
+        Some(data)
+    }
+
+    /// Heuristic to avoid starting thread, synchronization if we expect a small amount of
+    /// parallelism to be utilized.
+    fn select_worker(frame: &FrameInfo, worker_preference: PreferWorkerKind) -> PreferWorkerKind {
+        const PARALLELISM_THRESHOLD: u64 = 128 * 128;
+
+        match worker_preference {
+            PreferWorkerKind::Immediate => PreferWorkerKind::Immediate,
+            PreferWorkerKind::Multithreaded => {
+                let width: u64 = frame.output_size.width.into();
+                let height: u64 = frame.output_size.width.into();
+                if width * height > PARALLELISM_THRESHOLD {
+                    PreferWorkerKind::Multithreaded
+                } else {
+                    PreferWorkerKind::Immediate
+                }
+            }
+        }
+    }
+
+    /// Tries to read metadata from the image without decoding it.
+    ///
+    /// If successful, the metadata can be obtained using the `info` method.
+    pub fn read_info(&mut self) -> Result<()> {
+        WorkerScope::with(|worker| self.decode_internal(true, worker)).map(|_| ())
+    }
+
+    /// Configure the decoder to scale the image during decoding.
+    ///
+    /// This efficiently scales the image by the smallest supported scale
+    /// factor that produces an image larger than or equal to the requested
+    /// size in at least one axis. The currently implemented scale factors
+    /// are 1/8, 1/4, 1/2 and 1.
+    ///
+    /// To generate a thumbnail of an exact size, pass the desired size and
+    /// then scale to the final size using a traditional resampling algorithm.
+    pub fn scale(&mut self, requested_width: u16, requested_height: u16) -> Result<(u16, u16)> {
+        self.read_info()?;
+        let frame = self.frame.as_mut().unwrap();
+        let idct_size = crate::idct::choose_idct_size(
+            frame.image_size,
+            Dimensions {
+                width: requested_width,
+                height: requested_height,
+            },
+        );
+        frame.update_idct_size(idct_size)?;
+        Ok((frame.output_size.width, frame.output_size.height))
+    }
+
+    /// Decodes the image and returns the decoded pixels if successful.
+    pub fn decode(&mut self) -> Result<Vec<u8>> {
+        WorkerScope::with(|worker| self.decode_internal(false, worker))
+    }
+
+    fn decode_internal(
+        &mut self,
+        stop_after_metadata: bool,
+        worker_scope: &WorkerScope,
+    ) -> Result<Vec<u8>> {
+        if stop_after_metadata && self.frame.is_some() {
+            // The metadata has already been read.
+            return Ok(Vec::new());
+        } else if self.frame.is_none()
+            && (read_u8(&mut self.reader)? != 0xFF
+                || Marker::from_u8(read_u8(&mut self.reader)?) != Some(Marker::SOI))
+        {
+            return Err(Error::Format(
+                "first two bytes are not an SOI marker".to_owned(),
+            ));
+        }
+
+        let mut previous_marker = Marker::SOI;
+        let mut pending_marker = None;
+        let mut scans_processed = 0;
+        let mut planes = vec![
+            Vec::<u8>::new();
+            self.frame
+                .as_ref()
+                .map_or(0, |frame| frame.components.len())
+        ];
+        let mut planes_u16 = vec![
+            Vec::<u16>::new();
+            self.frame
+                .as_ref()
+                .map_or(0, |frame| frame.components.len())
+        ];
+
+        loop {
+            let marker = match pending_marker.take() {
+                Some(m) => m,
+                None => self.read_marker()?,
+            };
+
+            match marker {
+                // Frame header
+                Marker::SOF(..) => {
+                    // Section 4.10
+                    // "An image contains only one frame in the cases of sequential and
+                    //  progressive coding processes; an image contains multiple frames for the
+                    //  hierarchical mode."
+                    if self.frame.is_some() {
+                        return Err(Error::Unsupported(UnsupportedFeature::Hierarchical));
+                    }
+
+                    let frame = parse_sof(&mut self.reader, marker)?;
+                    let component_count = frame.components.len();
+
+                    if frame.is_differential {
+                        return Err(Error::Unsupported(UnsupportedFeature::Hierarchical));
+                    }
+                    if frame.entropy_coding == EntropyCoding::Arithmetic {
+                        return Err(Error::Unsupported(
+                            UnsupportedFeature::ArithmeticEntropyCoding,
+                        ));
+                    }
+                    if frame.precision != 8 && frame.coding_process != CodingProcess::Lossless {
+                        return Err(Error::Unsupported(UnsupportedFeature::SamplePrecision(
+                            frame.precision,
+                        )));
+                    }
+                    if frame.precision != 8 && frame.precision != 16 {
+                        return Err(Error::Unsupported(UnsupportedFeature::SamplePrecision(
+                            frame.precision,
+                        )));
+                    }
+                    if component_count != 1 && component_count != 3 && component_count != 4 {
+                        return Err(Error::Unsupported(UnsupportedFeature::ComponentCount(
+                            component_count as u8,
+                        )));
+                    }
+
+                    // Make sure we support the subsampling ratios used.
+                    let _ = Upsampler::new(
+                        &frame.components,
+                        frame.image_size.width,
+                        frame.image_size.height,
+                    )?;
+
+                    self.frame = Some(frame);
+
+                    if stop_after_metadata {
+                        return Ok(Vec::new());
+                    }
+
+                    planes = vec![Vec::new(); component_count];
+                    planes_u16 = vec![Vec::new(); component_count];
+                }
+
+                // Scan header
+                Marker::SOS => {
+                    if self.frame.is_none() {
+                        return Err(Error::Format("scan encountered before frame".to_owned()));
+                    }
+
+                    let frame = self.frame.clone().unwrap();
+                    let scan = parse_sos(&mut self.reader, &frame)?;
+
+                    if frame.coding_process == CodingProcess::DctProgressive
+                        && self.coefficients.is_empty()
+                    {
+                        self.coefficients = frame
+                            .components
+                            .iter()
+                            .map(|c| {
+                                let block_count =
+                                    c.block_size.width as usize * c.block_size.height as usize;
+                                vec![0; block_count * 64]
+                            })
+                            .collect();
+                    }
+
+                    if frame.coding_process == CodingProcess::Lossless {
+                        let (marker, data) = self.decode_scan_lossless(&frame, &scan)?;
+
+                        for (i, plane) in data
+                            .into_iter()
+                            .enumerate()
+                            .filter(|&(_, ref plane)| !plane.is_empty())
+                        {
+                            planes_u16[i] = plane;
+                        }
+                        pending_marker = marker;
+                    } else {
+                        // This was previously buggy, so let's explain the log here a bit. When a
+                        // progressive frame is encoded then the coefficients (DC, AC) of each
+                        // component (=color plane) can be split amongst scans. In particular it can
+                        // happen or at least occurs in the wild that a scan contains coefficient 0 of
+                        // all components. If now one but not all components had all other coefficients
+                        // delivered in previous scans then such a scan contains all components but
+                        // completes only some of them! (This is technically NOT permitted for all
+                        // other coefficients as the standard dictates that scans with coefficients
+                        // other than the 0th must only contain ONE component so we would either
+                        // complete it or not. We may want to detect and error in case more component
+                        // are part of a scan than allowed.) What a weird edge case.
+                        //
+                        // But this means we track precisely which components get completed here.
+                        let mut finished = [false; MAX_COMPONENTS];
+
+                        if scan.successive_approximation_low == 0 {
+                            for (&i, component_finished) in
+                                scan.component_indices.iter().zip(&mut finished)
+                            {
+                                if self.coefficients_finished[i] == !0 {
+                                    continue;
+                                }
+                                for j in scan.spectral_selection.clone() {
+                                    self.coefficients_finished[i] |= 1 << j;
+                                }
+                                if self.coefficients_finished[i] == !0 {
+                                    *component_finished = true;
+                                }
+                            }
+                        }
+
+                        let preference =
+                            Self::select_worker(&frame, PreferWorkerKind::Multithreaded);
+
+                        let (marker, data) = worker_scope
+                            .get_or_init_worker(preference, |worker| {
+                                self.decode_scan(&frame, &scan, worker, &finished)
+                            })?;
+
+                        if let Some(data) = data {
+                            for (i, plane) in data
+                                .into_iter()
+                                .enumerate()
+                                .filter(|&(_, ref plane)| !plane.is_empty())
+                            {
+                                if self.coefficients_finished[i] == !0 {
+                                    planes[i] = plane;
+                                }
+                            }
+                        }
+
+                        pending_marker = marker;
+                    }
+
+                    scans_processed += 1;
+                }
+
+                // Table-specification and miscellaneous markers
+                // Quantization table-specification
+                Marker::DQT => {
+                    let tables = parse_dqt(&mut self.reader)?;
+
+                    for (i, &table) in tables.iter().enumerate() {
+                        if let Some(table) = table {
+                            let mut unzigzagged_table = [0u16; 64];
+
+                            for j in 0..64 {
+                                unzigzagged_table[UNZIGZAG[j] as usize] = table[j];
+                            }
+
+                            self.quantization_tables[i] = Some(Arc::new(unzigzagged_table));
+                        }
+                    }
+                }
+                // Huffman table-specification
+                Marker::DHT => {
+                    let is_baseline = self.frame.as_ref().map(|frame| frame.is_baseline);
+                    let (dc_tables, ac_tables) = parse_dht(&mut self.reader, is_baseline)?;
+
+                    let current_dc_tables = mem::take(&mut self.dc_huffman_tables);
+                    self.dc_huffman_tables = dc_tables
+                        .into_iter()
+                        .zip(current_dc_tables.into_iter())
+                        .map(|(a, b)| a.or(b))
+                        .collect();
+
+                    let current_ac_tables = mem::take(&mut self.ac_huffman_tables);
+                    self.ac_huffman_tables = ac_tables
+                        .into_iter()
+                        .zip(current_ac_tables.into_iter())
+                        .map(|(a, b)| a.or(b))
+                        .collect();
+                }
+                // Arithmetic conditioning table-specification
+                Marker::DAC => {
+                    return Err(Error::Unsupported(
+                        UnsupportedFeature::ArithmeticEntropyCoding,
+                    ))
+                }
+                // Restart interval definition
+                Marker::DRI => self.restart_interval = parse_dri(&mut self.reader)?,
+                // Comment
+                Marker::COM => {
+                    let _comment = parse_com(&mut self.reader)?;
+                }
+                // Application data
+                Marker::APP(..) => {
+                    if let Some(data) = parse_app(&mut self.reader, marker)? {
+                        match data {
+                            AppData::Adobe(color_transform) => {
+                                self.adobe_color_transform = Some(color_transform)
+                            }
+                            AppData::Jfif => {
+                                // From the JFIF spec:
+                                // "The APP0 marker is used to identify a JPEG FIF file.
+                                //     The JPEG FIF APP0 marker is mandatory right after the SOI marker."
+                                // Some JPEGs in the wild does not follow this though, so we allow
+                                // JFIF headers anywhere APP0 markers are allowed.
+                                /*
+                                if previous_marker != Marker::SOI {
+                                    return Err(Error::Format("the JFIF APP0 marker must come right after the SOI marker".to_owned()));
+                                }
+                                */
+
+                                self.is_jfif = true;
+                            }
+                            AppData::Avi1 => self.is_mjpeg = true,
+                            AppData::Icc(icc) => self.icc_markers.push(icc),
+                            AppData::Exif(data) => self.exif_data = Some(data),
+                        }
+                    }
+                }
+                // Restart
+                Marker::RST(..) => {
+                    // Some encoders emit a final RST marker after entropy-coded data, which
+                    // decode_scan does not take care of. So if we encounter one, we ignore it.
+                    if previous_marker != Marker::SOS {
+                        return Err(Error::Format(
+                            "RST found outside of entropy-coded data".to_owned(),
+                        ));
+                    }
+                }
+
+                // Define number of lines
+                Marker::DNL => {
+                    // Section B.2.1
+                    // "If a DNL segment (see B.2.5) is present, it shall immediately follow the first scan."
+                    if previous_marker != Marker::SOS || scans_processed != 1 {
+                        return Err(Error::Format(
+                            "DNL is only allowed immediately after the first scan".to_owned(),
+                        ));
+                    }
+
+                    return Err(Error::Unsupported(UnsupportedFeature::DNL));
+                }
+
+                // Hierarchical mode markers
+                Marker::DHP | Marker::EXP => {
+                    return Err(Error::Unsupported(UnsupportedFeature::Hierarchical))
+                }
+
+                // End of image
+                Marker::EOI => break,
+
+                _ => {
+                    return Err(Error::Format(format!(
+                        "{:?} marker found where not allowed",
+                        marker
+                    )))
+                }
+            }
+
+            previous_marker = marker;
+        }
+
+        if self.frame.is_none() {
+            return Err(Error::Format(
+                "end of image encountered before frame".to_owned(),
+            ));
+        }
+
+        let frame = self.frame.as_ref().unwrap();
+        let preference = Self::select_worker(&frame, PreferWorkerKind::Multithreaded);
+
+        worker_scope.get_or_init_worker(preference, |worker| {
+            self.decode_planes(worker, planes, planes_u16)
+        })
+    }
+
+    fn decode_planes(
+        &mut self,
+        worker: &mut dyn Worker,
+        mut planes: Vec<Vec<u8>>,
+        planes_u16: Vec<Vec<u16>>,
+    ) -> Result<Vec<u8>> {
+        if self.frame.is_none() {
+            return Err(Error::Format(
+                "end of image encountered before frame".to_owned(),
+            ));
+        }
+
+        let frame = self.frame.as_ref().unwrap();
+
+        if {
+            let required_mem = frame
+                .components
+                .len()
+                .checked_mul(frame.output_size.width.into())
+                .and_then(|m| m.checked_mul(frame.output_size.height.into()));
+            required_mem.map_or(true, |m| self.decoding_buffer_size_limit < m)
+        } {
+            return Err(Error::Format(
+                "size of decoded image exceeds maximum allowed size".to_owned(),
+            ));
+        }
+
+        // If we're decoding a progressive jpeg and a component is unfinished, render what we've got
+        if frame.coding_process == CodingProcess::DctProgressive
+            && self.coefficients.len() == frame.components.len()
+        {
+            for (i, component) in frame.components.iter().enumerate() {
+                // Only dealing with unfinished components
+                if self.coefficients_finished[i] == !0 {
+                    continue;
+                }
+
+                let quantization_table =
+                    match self.quantization_tables[component.quantization_table_index].clone() {
+                        Some(quantization_table) => quantization_table,
+                        None => continue,
+                    };
+
+                // Get the worker prepared
+                let row_data = RowData {
+                    index: i,
+                    component: component.clone(),
+                    quantization_table,
+                };
+                worker.start(row_data)?;
+
+                // Send the rows over to the worker and collect the result
+                let coefficients_per_mcu_row = usize::from(component.block_size.width)
+                    * usize::from(component.vertical_sampling_factor)
+                    * 64;
+
+                let mut tasks = (0..frame.mcu_size.height).map(|mcu_y| {
+                    let offset = usize::from(mcu_y) * coefficients_per_mcu_row;
+                    let row_coefficients =
+                        self.coefficients[i][offset..offset + coefficients_per_mcu_row].to_vec();
+                    (i, row_coefficients)
+                });
+
+                // FIXME: additional potential work stealing opportunities for rayon case if we
+                // also internally can parallelize over components.
+                worker.append_rows(&mut tasks)?;
+                planes[i] = worker.get_result(i)?;
+            }
+        }
+
+        if frame.coding_process == CodingProcess::Lossless {
+            compute_image_lossless(frame, planes_u16)
+        } else {
+            compute_image(
+                &frame.components,
+                planes,
+                frame.output_size,
+                self.determine_color_transform(),
+            )
+        }
+    }
+
+    fn determine_color_transform(&self) -> ColorTransform {
+        if let Some(color_transform) = self.color_transform {
+            return color_transform;
+        }
+
+        let frame = self.frame.as_ref().unwrap();
+
+        if frame.components.len() == 1 {
+            return ColorTransform::Grayscale;
+        }
+
+        // Using logic for determining colour as described here: https://entropymine.wordpress.com/2018/10/22/how-is-a-jpeg-images-color-type-determined/
+
+        if frame.components.len() == 3 {
+            match (
+                frame.components[0].identifier,
+                frame.components[1].identifier,
+                frame.components[2].identifier,
+            ) {
+                (1, 2, 3) => {
+                    return ColorTransform::YCbCr;
+                }
+                (1, 34, 35) => {
+                    return ColorTransform::JcsBgYcc;
+                }
+                (82, 71, 66) => {
+                    return ColorTransform::RGB;
+                }
+                (114, 103, 98) => {
+                    return ColorTransform::JcsBgRgb;
+                }
+                _ => {}
+            }
+
+            if self.is_jfif {
+                return ColorTransform::YCbCr;
+            }
+        }
+
+        if let Some(colour_transform) = self.adobe_color_transform {
+            match colour_transform {
+                AdobeColorTransform::Unknown => {
+                    if frame.components.len() == 3 {
+                        return ColorTransform::RGB;
+                    } else if frame.components.len() == 4 {
+                        return ColorTransform::CMYK;
+                    }
+                }
+                AdobeColorTransform::YCbCr => {
+                    return ColorTransform::YCbCr;
+                }
+                AdobeColorTransform::YCCK => {
+                    return ColorTransform::YCCK;
+                }
+            }
+        } else if frame.components.len() == 4 {
+            return ColorTransform::CMYK;
+        }
+
+        if frame.components.len() == 4 {
+            ColorTransform::YCCK
+        } else if frame.components.len() == 3 {
+            ColorTransform::YCbCr
+        } else {
+            ColorTransform::Unknown
+        }
+    }
+
+    fn read_marker(&mut self) -> Result<Marker> {
+        loop {
+            // This should be an error as the JPEG spec doesn't allow extraneous data between marker segments.
+            // libjpeg allows this though and there are images in the wild utilising it, so we are
+            // forced to support this behavior.
+            // Sony Ericsson P990i is an example of a device which produce this sort of JPEGs.
+            while read_u8(&mut self.reader)? != 0xFF {}
+
+            // Section B.1.1.2
+            // All markers are assigned two-byte codes: an X’FF’ byte followed by a
+            // byte which is not equal to 0 or X’FF’ (see Table B.1). Any marker may
+            // optionally be preceded by any number of fill bytes, which are bytes
+            // assigned code X’FF’.
+            let mut byte = read_u8(&mut self.reader)?;
+
+            // Section B.1.1.2
+            // "Any marker may optionally be preceded by any number of fill bytes, which are bytes assigned code X’FF’."
+            while byte == 0xFF {
+                byte = read_u8(&mut self.reader)?;
+            }
+
+            if byte != 0x00 && byte != 0xFF {
+                return Ok(Marker::from_u8(byte).unwrap());
+            }
+        }
+    }
+
+    fn decode_scan(
+        &mut self,
+        frame: &FrameInfo,
+        scan: &ScanInfo,
+        worker: &mut dyn Worker,
+        finished: &[bool; MAX_COMPONENTS],
+    ) -> Result<(Option<Marker>, Option<Vec<Vec<u8>>>)> {
+        assert!(scan.component_indices.len() <= MAX_COMPONENTS);
+
+        let components: Vec<Component> = scan
+            .component_indices
+            .iter()
+            .map(|&i| frame.components[i].clone())
+            .collect();
+
+        // Verify that all required quantization tables has been set.
+        if components
+            .iter()
+            .any(|component| self.quantization_tables[component.quantization_table_index].is_none())
+        {
+            return Err(Error::Format("use of unset quantization table".to_owned()));
+        }
+
+        if self.is_mjpeg {
+            fill_default_mjpeg_tables(
+                scan,
+                &mut self.dc_huffman_tables,
+                &mut self.ac_huffman_tables,
+            );
+        }
+
+        // Verify that all required huffman tables has been set.
+        if scan.spectral_selection.start == 0
+            && scan
+                .dc_table_indices
+                .iter()
+                .any(|&i| self.dc_huffman_tables[i].is_none())
+        {
+            return Err(Error::Format(
+                "scan makes use of unset dc huffman table".to_owned(),
+            ));
+        }
+        if scan.spectral_selection.end > 1
+            && scan
+                .ac_table_indices
+                .iter()
+                .any(|&i| self.ac_huffman_tables[i].is_none())
+        {
+            return Err(Error::Format(
+                "scan makes use of unset ac huffman table".to_owned(),
+            ));
+        }
+
+        // Prepare the worker thread for the work to come.
+        for (i, component) in components.iter().enumerate() {
+            if finished[i] {
+                let row_data = RowData {
+                    index: i,
+                    component: component.clone(),
+                    quantization_table: self.quantization_tables
+                        [component.quantization_table_index]
+                        .clone()
+                        .unwrap(),
+                };
+
+                worker.start(row_data)?;
+            }
+        }
+
+        let is_progressive = frame.coding_process == CodingProcess::DctProgressive;
+        let is_interleaved = components.len() > 1;
+        let mut dummy_block = [0i16; 64];
+        let mut huffman = HuffmanDecoder::new();
+        let mut dc_predictors = [0i16; MAX_COMPONENTS];
+        let mut mcus_left_until_restart = self.restart_interval;
+        let mut expected_rst_num = 0;
+        let mut eob_run = 0;
+        let mut mcu_row_coefficients = vec![vec![]; components.len()];
+
+        if !is_progressive {
+            for (i, component) in components.iter().enumerate().filter(|&(i, _)| finished[i]) {
+                let coefficients_per_mcu_row = component.block_size.width as usize
+                    * component.vertical_sampling_factor as usize
+                    * 64;
+                mcu_row_coefficients[i] = vec![0i16; coefficients_per_mcu_row];
+            }
+        }
+
+        // 4.8.2
+        // When reading from the stream, if the data is non-interleaved then an MCU consists of
+        // exactly one block (effectively a 1x1 sample).
+        let (mcu_horizontal_samples, mcu_vertical_samples) = if is_interleaved {
+            let horizontal = components
+                .iter()
+                .map(|component| component.horizontal_sampling_factor as u16)
+                .collect::<Vec<_>>();
+            let vertical = components
+                .iter()
+                .map(|component| component.vertical_sampling_factor as u16)
+                .collect::<Vec<_>>();
+            (horizontal, vertical)
+        } else {
+            (vec![1], vec![1])
+        };
+
+        // This also affects how many MCU values we read from stream. If it's a non-interleaved stream,
+        // the MCUs will be exactly the block count.
+        let (max_mcu_x, max_mcu_y) = if is_interleaved {
+            (frame.mcu_size.width, frame.mcu_size.height)
+        } else {
+            (
+                components[0].block_size.width,
+                components[0].block_size.height,
+            )
+        };
+
+        for mcu_y in 0..max_mcu_y {
+            if mcu_y * 8 >= frame.image_size.height {
+                break;
+            }
+
+            for mcu_x in 0..max_mcu_x {
+                if mcu_x * 8 >= frame.image_size.width {
+                    break;
+                }
+
+                if self.restart_interval > 0 {
+                    if mcus_left_until_restart == 0 {
+                        match huffman.take_marker(&mut self.reader)? {
+                            Some(Marker::RST(n)) => {
+                                if n != expected_rst_num {
+                                    return Err(Error::Format(format!(
+                                        "found RST{} where RST{} was expected",
+                                        n, expected_rst_num
+                                    )));
+                                }
+
+                                huffman.reset();
+                                // Section F.2.1.3.1
+                                dc_predictors = [0i16; MAX_COMPONENTS];
+                                // Section G.1.2.2
+                                eob_run = 0;
+
+                                expected_rst_num = (expected_rst_num + 1) % 8;
+                                mcus_left_until_restart = self.restart_interval;
+                            }
+                            Some(marker) => {
+                                return Err(Error::Format(format!(
+                                    "found marker {:?} inside scan where RST{} was expected",
+                                    marker, expected_rst_num
+                                )))
+                            }
+                            None => {
+                                return Err(Error::Format(format!(
+                                    "no marker found where RST{} was expected",
+                                    expected_rst_num
+                                )))
+                            }
+                        }
+                    }
+
+                    mcus_left_until_restart -= 1;
+                }
+
+                for (i, component) in components.iter().enumerate() {
+                    for v_pos in 0..mcu_vertical_samples[i] {
+                        for h_pos in 0..mcu_horizontal_samples[i] {
+                            let coefficients = if is_progressive {
+                                let block_y = (mcu_y * mcu_vertical_samples[i] + v_pos) as usize;
+                                let block_x = (mcu_x * mcu_horizontal_samples[i] + h_pos) as usize;
+                                let block_offset =
+                                    (block_y * component.block_size.width as usize + block_x) * 64;
+                                &mut self.coefficients[scan.component_indices[i]]
+                                    [block_offset..block_offset + 64]
+                            } else if finished[i] {
+                                // Because the worker thread operates in batches as if we were always interleaved, we
+                                // need to distinguish between a single-shot buffer and one that's currently in process
+                                // (for a non-interleaved) stream
+                                let mcu_batch_current_row = if is_interleaved {
+                                    0
+                                } else {
+                                    mcu_y % component.vertical_sampling_factor as u16
+                                };
+
+                                let block_y = (mcu_batch_current_row * mcu_vertical_samples[i]
+                                    + v_pos) as usize;
+                                let block_x = (mcu_x * mcu_horizontal_samples[i] + h_pos) as usize;
+                                let block_offset =
+                                    (block_y * component.block_size.width as usize + block_x) * 64;
+                                &mut mcu_row_coefficients[i][block_offset..block_offset + 64]
+                            } else {
+                                &mut dummy_block[..64]
+                            }
+                            .try_into()
+                            .unwrap();
+
+                            if scan.successive_approximation_high == 0 {
+                                decode_block(
+                                    &mut self.reader,
+                                    coefficients,
+                                    &mut huffman,
+                                    self.dc_huffman_tables[scan.dc_table_indices[i]].as_ref(),
+                                    self.ac_huffman_tables[scan.ac_table_indices[i]].as_ref(),
+                                    scan.spectral_selection.clone(),
+                                    scan.successive_approximation_low,
+                                    &mut eob_run,
+                                    &mut dc_predictors[i],
+                                )?;
+                            } else {
+                                decode_block_successive_approximation(
+                                    &mut self.reader,
+                                    coefficients,
+                                    &mut huffman,
+                                    self.ac_huffman_tables[scan.ac_table_indices[i]].as_ref(),
+                                    scan.spectral_selection.clone(),
+                                    scan.successive_approximation_low,
+                                    &mut eob_run,
+                                )?;
+                            }
+                        }
+                    }
+                }
+            }
+
+            // Send the coefficients from this MCU row to the worker thread for dequantization and idct.
+            for (i, component) in components.iter().enumerate() {
+                if finished[i] {
+                    // In the event of non-interleaved streams, if we're still building the buffer out,
+                    // keep going; don't send it yet. We also need to ensure we don't skip over the last
+                    // row(s) of the image.
+                    if !is_interleaved && (mcu_y + 1) * 8 < frame.image_size.height {
+                        if (mcu_y + 1) % component.vertical_sampling_factor as u16 > 0 {
+                            continue;
+                        }
+                    }
+
+                    let coefficients_per_mcu_row = component.block_size.width as usize
+                        * component.vertical_sampling_factor as usize
+                        * 64;
+
+                    let row_coefficients = if is_progressive {
+                        // Because non-interleaved streams will have multiple MCU rows concatenated together,
+                        // the row for calculating the offset is different.
+                        let worker_mcu_y = if is_interleaved {
+                            mcu_y
+                        } else {
+                            // Explicitly doing floor-division here
+                            mcu_y / component.vertical_sampling_factor as u16
+                        };
+
+                        let offset = worker_mcu_y as usize * coefficients_per_mcu_row;
+                        self.coefficients[scan.component_indices[i]]
+                            [offset..offset + coefficients_per_mcu_row]
+                            .to_vec()
+                    } else {
+                        mem::replace(
+                            &mut mcu_row_coefficients[i],
+                            vec![0i16; coefficients_per_mcu_row],
+                        )
+                    };
+
+                    // FIXME: additional potential work stealing opportunities for rayon case if we
+                    // also internally can parallelize over components.
+                    worker.append_row((i, row_coefficients))?;
+                }
+            }
+        }
+
+        let mut marker = huffman.take_marker(&mut self.reader)?;
+        while let Some(Marker::RST(_)) = marker {
+            marker = self.read_marker().ok();
+        }
+
+        if finished.iter().any(|&c| c) {
+            // Retrieve all the data from the worker thread.
+            let mut data = vec![Vec::new(); frame.components.len()];
+
+            for (i, &component_index) in scan.component_indices.iter().enumerate() {
+                if finished[i] {
+                    data[component_index] = worker.get_result(i)?;
+                }
+            }
+
+            Ok((marker, Some(data)))
+        } else {
+            Ok((marker, None))
+        }
+    }
+}
+
+fn decode_block<R: Read>(
+    reader: &mut R,
+    coefficients: &mut [i16; 64],
+    huffman: &mut HuffmanDecoder,
+    dc_table: Option<&HuffmanTable>,
+    ac_table: Option<&HuffmanTable>,
+    spectral_selection: Range<u8>,
+    successive_approximation_low: u8,
+    eob_run: &mut u16,
+    dc_predictor: &mut i16,
+) -> Result<()> {
+    debug_assert_eq!(coefficients.len(), 64);
+
+    if spectral_selection.start == 0 {
+        // Section F.2.2.1
+        // Figure F.12
+        let value = huffman.decode(reader, dc_table.unwrap())?;
+        let diff = match value {
+            0 => 0,
+            1..=11 => huffman.receive_extend(reader, value)?,
+            _ => {
+                // Section F.1.2.1.1
+                // Table F.1
+                return Err(Error::Format(
+                    "invalid DC difference magnitude category".to_owned(),
+                ));
+            }
+        };
+
+        // Malicious JPEG files can cause this add to overflow, therefore we use wrapping_add.
+        // One example of such a file is tests/crashtest/images/dc-predictor-overflow.jpg
+        *dc_predictor = dc_predictor.wrapping_add(diff);
+        coefficients[0] = *dc_predictor << successive_approximation_low;
+    }
+
+    let mut index = cmp::max(spectral_selection.start, 1);
+
+    if index < spectral_selection.end && *eob_run > 0 {
+        *eob_run -= 1;
+        return Ok(());
+    }
+
+    // Section F.1.2.2.1
+    while index < spectral_selection.end {
+        if let Some((value, run)) = huffman.decode_fast_ac(reader, ac_table.unwrap())? {
+            index += run;
+
+            if index >= spectral_selection.end {
+                break;
+            }
+
+            coefficients[UNZIGZAG[index as usize] as usize] = value << successive_approximation_low;
+            index += 1;
+        } else {
+            let byte = huffman.decode(reader, ac_table.unwrap())?;
+            let r = byte >> 4;
+            let s = byte & 0x0f;
+
+            if s == 0 {
+                match r {
+                    15 => index += 16, // Run length of 16 zero coefficients.
+                    _ => {
+                        *eob_run = (1 << r) - 1;
+
+                        if r > 0 {
+                            *eob_run += huffman.get_bits(reader, r)?;
+                        }
+
+                        break;
+                    }
+                }
+            } else {
+                index += r;
+
+                if index >= spectral_selection.end {
+                    break;
+                }
+
+                coefficients[UNZIGZAG[index as usize] as usize] =
+                    huffman.receive_extend(reader, s)? << successive_approximation_low;
+                index += 1;
+            }
+        }
+    }
+
+    Ok(())
+}
+
+fn decode_block_successive_approximation<R: Read>(
+    reader: &mut R,
+    coefficients: &mut [i16; 64],
+    huffman: &mut HuffmanDecoder,
+    ac_table: Option<&HuffmanTable>,
+    spectral_selection: Range<u8>,
+    successive_approximation_low: u8,
+    eob_run: &mut u16,
+) -> Result<()> {
+    debug_assert_eq!(coefficients.len(), 64);
+
+    let bit = 1 << successive_approximation_low;
+
+    if spectral_selection.start == 0 {
+        // Section G.1.2.1
+
+        if huffman.get_bits(reader, 1)? == 1 {
+            coefficients[0] |= bit;
+        }
+    } else {
+        // Section G.1.2.3
+
+        if *eob_run > 0 {
+            *eob_run -= 1;
+            refine_non_zeroes(reader, coefficients, huffman, spectral_selection, 64, bit)?;
+            return Ok(());
+        }
+
+        let mut index = spectral_selection.start;
+
+        while index < spectral_selection.end {
+            let byte = huffman.decode(reader, ac_table.unwrap())?;
+            let r = byte >> 4;
+            let s = byte & 0x0f;
+
+            let mut zero_run_length = r;
+            let mut value = 0;
+
+            match s {
+                0 => {
+                    match r {
+                        15 => {
+                            // Run length of 16 zero coefficients.
+                            // We don't need to do anything special here, zero_run_length is 15
+                            // and then value (which is zero) gets written, resulting in 16
+                            // zero coefficients.
+                        }
+                        _ => {
+                            *eob_run = (1 << r) - 1;
+
+                            if r > 0 {
+                                *eob_run += huffman.get_bits(reader, r)?;
+                            }
+
+                            // Force end of block.
+                            zero_run_length = 64;
+                        }
+                    }
+                }
+                1 => {
+                    if huffman.get_bits(reader, 1)? == 1 {
+                        value = bit;
+                    } else {
+                        value = -bit;
+                    }
+                }
+                _ => return Err(Error::Format("unexpected huffman code".to_owned())),
+            }
+
+            let range = Range {
+                start: index,
+                end: spectral_selection.end,
+            };
+            index = refine_non_zeroes(reader, coefficients, huffman, range, zero_run_length, bit)?;
+
+            if value != 0 {
+                coefficients[UNZIGZAG[index as usize] as usize] = value;
+            }
+
+            index += 1;
+        }
+    }
+
+    Ok(())
+}
+
+fn refine_non_zeroes<R: Read>(
+    reader: &mut R,
+    coefficients: &mut [i16; 64],
+    huffman: &mut HuffmanDecoder,
+    range: Range<u8>,
+    zrl: u8,
+    bit: i16,
+) -> Result<u8> {
+    debug_assert_eq!(coefficients.len(), 64);
+
+    let last = range.end - 1;
+    let mut zero_run_length = zrl;
+
+    for i in range {
+        let index = UNZIGZAG[i as usize] as usize;
+
+        let coefficient = &mut coefficients[index];
+
+        if *coefficient == 0 {
+            if zero_run_length == 0 {
+                return Ok(i);
+            }
+
+            zero_run_length -= 1;
+        } else if huffman.get_bits(reader, 1)? == 1 && *coefficient & bit == 0 {
+            if *coefficient > 0 {
+                *coefficient = coefficient
+                    .checked_add(bit)
+                    .ok_or_else(|| Error::Format("Coefficient overflow".to_owned()))?;
+            } else {
+                *coefficient = coefficient
+                    .checked_sub(bit)
+                    .ok_or_else(|| Error::Format("Coefficient overflow".to_owned()))?;
+            }
+        }
+    }
+
+    Ok(last)
+}
+
+fn compute_image(
+    components: &[Component],
+    mut data: Vec<Vec<u8>>,
+    output_size: Dimensions,
+    color_transform: ColorTransform,
+) -> Result<Vec<u8>> {
+    if data.is_empty() || data.iter().any(Vec::is_empty) {
+        return Err(Error::Format("not all components have data".to_owned()));
+    }
+
+    if components.len() == 1 {
+        let component = &components[0];
+        let mut decoded: Vec<u8> = data.remove(0);
+
+        let width = component.size.width as usize;
+        let height = component.size.height as usize;
+        let size = width * height;
+        let line_stride = component.block_size.width as usize * component.dct_scale;
+
+        // if the image width is a multiple of the block size,
+        // then we don't have to move bytes in the decoded data
+        if usize::from(output_size.width) != line_stride {
+            // The first line already starts at index 0, so we need to move only lines 1..height
+            // We move from the top down because all lines are being moved backwards.
+            for y in 1..height {
+                let destination_idx = y * width;
+                let source_idx = y * line_stride;
+                let end = source_idx + width;
+                decoded.copy_within(source_idx..end, destination_idx);
+            }
+        }
+        decoded.resize(size, 0);
+        Ok(decoded)
+    } else {
+        compute_image_parallel(components, data, output_size, color_transform)
+    }
+}
+
+pub(crate) fn choose_color_convert_func(
+    component_count: usize,
+    color_transform: ColorTransform,
+) -> Result<fn(&[Vec<u8>], &mut [u8])> {
+    match component_count {
+        3 => match color_transform {
+            ColorTransform::None => Ok(color_no_convert),
+            ColorTransform::Grayscale => Err(Error::Format(
+                "Invalid number of channels (3) for Grayscale data".to_string(),
+            )),
+            ColorTransform::RGB => Ok(color_convert_line_rgb),
+            ColorTransform::YCbCr => Ok(color_convert_line_ycbcr),
+            ColorTransform::CMYK => Err(Error::Format(
+                "Invalid number of channels (3) for CMYK data".to_string(),
+            )),
+            ColorTransform::YCCK => Err(Error::Format(
+                "Invalid number of channels (3) for YCCK data".to_string(),
+            )),
+            ColorTransform::JcsBgYcc => Err(Error::Unsupported(
+                UnsupportedFeature::ColorTransform(ColorTransform::JcsBgYcc),
+            )),
+            ColorTransform::JcsBgRgb => Err(Error::Unsupported(
+                UnsupportedFeature::ColorTransform(ColorTransform::JcsBgRgb),
+            )),
+            ColorTransform::Unknown => Err(Error::Format("Unknown colour transform".to_string())),
+        },
+        4 => match color_transform {
+            ColorTransform::None => Ok(color_no_convert),
+            ColorTransform::Grayscale => Err(Error::Format(
+                "Invalid number of channels (4) for Grayscale data".to_string(),
+            )),
+            ColorTransform::RGB => Err(Error::Format(
+                "Invalid number of channels (4) for RGB data".to_string(),
+            )),
+            ColorTransform::YCbCr => Err(Error::Format(
+                "Invalid number of channels (4) for YCbCr data".to_string(),
+            )),
+            ColorTransform::CMYK => Ok(color_convert_line_cmyk),
+            ColorTransform::YCCK => Ok(color_convert_line_ycck),
+
+            ColorTransform::JcsBgYcc => Err(Error::Unsupported(
+                UnsupportedFeature::ColorTransform(ColorTransform::JcsBgYcc),
+            )),
+            ColorTransform::JcsBgRgb => Err(Error::Unsupported(
+                UnsupportedFeature::ColorTransform(ColorTransform::JcsBgRgb),
+            )),
+            ColorTransform::Unknown => Err(Error::Format("Unknown colour transform".to_string())),
+        },
+        _ => panic!(),
+    }
+}
+
+fn color_convert_line_rgb(data: &[Vec<u8>], output: &mut [u8]) {
+    assert!(data.len() == 3, "wrong number of components for rgb");
+    let [r, g, b]: &[Vec<u8>; 3] = data.try_into().unwrap();
+    for (((chunk, r), g), b) in output
+        .chunks_exact_mut(3)
+        .zip(r.iter())
+        .zip(g.iter())
+        .zip(b.iter())
+    {
+        chunk[0] = *r;
+        chunk[1] = *g;
+        chunk[2] = *b;
+    }
+}
+
+fn color_convert_line_ycbcr(data: &[Vec<u8>], output: &mut [u8]) {
+    assert!(data.len() == 3, "wrong number of components for ycbcr");
+    let [y, cb, cr]: &[_; 3] = data.try_into().unwrap();
+
+    #[cfg(not(feature = "platform_independent"))]
+    let arch_specific_pixels = {
+        if let Some(ycbcr) = crate::arch::get_color_convert_line_ycbcr() {
+            #[allow(unsafe_code)]
+            unsafe {
+                ycbcr(y, cb, cr, output)
+            }
+        } else {
+            0
+        }
+    };
+
+    #[cfg(feature = "platform_independent")]
+    let arch_specific_pixels = 0;
+
+    for (((chunk, y), cb), cr) in output
+        .chunks_exact_mut(3)
+        .zip(y.iter())
+        .zip(cb.iter())
+        .zip(cr.iter())
+        .skip(arch_specific_pixels)
+    {
+        let (r, g, b) = ycbcr_to_rgb(*y, *cb, *cr);
+        chunk[0] = r;
+        chunk[1] = g;
+        chunk[2] = b;
+    }
+}
+
+fn color_convert_line_ycck(data: &[Vec<u8>], output: &mut [u8]) {
+    assert!(data.len() == 4, "wrong number of components for ycck");
+    let [c, m, y, k]: &[Vec<u8>; 4] = data.try_into().unwrap();
+
+    for ((((chunk, c), m), y), k) in output
+        .chunks_exact_mut(4)
+        .zip(c.iter())
+        .zip(m.iter())
+        .zip(y.iter())
+        .zip(k.iter())
+    {
+        let (r, g, b) = ycbcr_to_rgb(*c, *m, *y);
+        chunk[0] = r;
+        chunk[1] = g;
+        chunk[2] = b;
+        chunk[3] = 255 - *k;
+    }
+}
+
+fn color_convert_line_cmyk(data: &[Vec<u8>], output: &mut [u8]) {
+    assert!(data.len() == 4, "wrong number of components for cmyk");
+    let [c, m, y, k]: &[Vec<u8>; 4] = data.try_into().unwrap();
+
+    for ((((chunk, c), m), y), k) in output
+        .chunks_exact_mut(4)
+        .zip(c.iter())
+        .zip(m.iter())
+        .zip(y.iter())
+        .zip(k.iter())
+    {
+        chunk[0] = 255 - c;
+        chunk[1] = 255 - m;
+        chunk[2] = 255 - y;
+        chunk[3] = 255 - k;
+    }
+}
+
+fn color_no_convert(data: &[Vec<u8>], output: &mut [u8]) {
+    let mut output_iter = output.iter_mut();
+
+    for pixel in data {
+        for d in pixel {
+            *(output_iter.next().unwrap()) = *d;
+        }
+    }
+}
+
+const FIXED_POINT_OFFSET: i32 = 20;
+const HALF: i32 = (1 << FIXED_POINT_OFFSET) / 2;
+
+// ITU-R BT.601
+// Based on libjpeg-turbo's jdcolext.c
+fn ycbcr_to_rgb(y: u8, cb: u8, cr: u8) -> (u8, u8, u8) {
+    let y = y as i32 * (1 << FIXED_POINT_OFFSET) + HALF;
+    let cb = cb as i32 - 128;
+    let cr = cr as i32 - 128;
+
+    let r = clamp_fixed_point(y + stbi_f2f(1.40200) * cr);
+    let g = clamp_fixed_point(y - stbi_f2f(0.34414) * cb - stbi_f2f(0.71414) * cr);
+    let b = clamp_fixed_point(y + stbi_f2f(1.77200) * cb);
+    (r, g, b)
+}
+
+fn stbi_f2f(x: f32) -> i32 {
+    (x * ((1 << FIXED_POINT_OFFSET) as f32) + 0.5) as i32
+}
+
+fn clamp_fixed_point(value: i32) -> u8 {
+    (value >> FIXED_POINT_OFFSET).min(255).max(0) as u8
+}