1 files changed, 74 insertions, 0 deletions
diff --git a/vendor/exr/examples/5b_extract_exr_layers_as_pngs.rs b/vendor/exr/examples/5b_extract_exr_layers_as_pngs.rs
new file mode 100644
index 0000000..1f14ea7
--- /dev/null
+++ b/vendor/exr/examples/5b_extract_exr_layers_as_pngs.rs
@@ -0,0 +1,74 @@
+extern crate image as png;
+use std::cmp::Ordering;
+
+extern crate exr;
+
+/// For each layer in the exr file,
+/// extract each channel as grayscale png,
+/// including all multi-resolution levels.
+//
+// FIXME throws "access denied" sometimes, simply trying again usually works.
+//
+pub fn main() {
+    use exr::prelude::*;
+
+    let path = "layers.exr";
+    let now = ::std::time::Instant::now();
+
+    // load the exr file from disk with multi-core decompression
+    let image = read()
+        .no_deep_data().largest_resolution_level().all_channels().all_layers().all_attributes()
+        .from_file(path).expect("run example `5a_write_multiple_layers` to generate this image file");
+
+    // warning: highly unscientific benchmarks ahead!
+    println!("\nloaded file in {:?}s", now.elapsed().as_secs_f32());
+    let _ = std::fs::create_dir_all("pngs/");
+    println!("writing images...");
+
+    for (layer_index, layer) in image.layer_data.iter().enumerate() {
+        let layer_name = layer.attributes.layer_name.as_ref()
+            .map_or(String::from("main_layer"), Text::to_string);
+
+        for channel in &layer.channel_data.list {
+            let data : Vec<f32> = channel.sample_data.values_as_f32().collect();
+            save_f32_image_as_png(&data, layer.size, format!(
+                "pngs/{} ({}) {}_{}x{}.png",
+                layer_index, layer_name, channel.name,
+                layer.size.width(), layer.size.height(),
+            ))
+        }
+    }
+
+    /// Save raw float data to a PNG file, doing automatic brightness adjustments per channel
+    fn save_f32_image_as_png(data: &[f32], size: Vec2<usize>, name: String) {
+        let mut png_buffer = png::GrayImage::new(size.width() as u32, size.height() as u32);
+        let mut sorted = Vec::from(data);
+        sorted.sort_by(|a, b| a.partial_cmp(b).unwrap_or(Ordering::Less));
+
+        // percentile normalization
+        let max = sorted[7 * sorted.len() / 8];
+        let min = sorted[1 * sorted.len() / 8];
+
+        // primitive tone mapping
+        let tone = |v: f32| (v - 0.5).tanh() * 0.5 + 0.5;
+        let max_toned = tone(*sorted.last().unwrap());
+        let min_toned = tone(*sorted.first().unwrap());
+
+        // for each pixel, tone map the value
+        for (x, y, pixel) in png_buffer.enumerate_pixels_mut() {
+            let v = data[y as usize * size.0 + x as usize];
+            let v = (v - min) / (max - min);
+            let v = tone(v);
+
+            let v = (v - min_toned) / (max_toned - min_toned);
+
+            // TODO does the `image` crate expect gamma corrected data?
+            *pixel = png::Luma([(v.max(0.0).min(1.0) * 255.0) as u8]);
+        }
+
+        png_buffer.save(&name).unwrap();
+    }
+
+    println!("extracted all layers to folder `./pngs/*.png`");
+}
+