Merge pull request #3 from vstroebel/sequential_subsampling

Fix chroma subsampling in sequential encoding

Author: vstroebel

fuzz/Cargo.toml

@@ -41,3 +41,15 @@ name = "encode_rgb_custom_q_table"
 path = "fuzz_targets/encode_rgb_custom_q_table.rs"
 test = false
 doc = false
+
+[[bin]]
+name = "encode_rgb_subsampled"
+path = "fuzz_targets/encode_rgb_subsampled.rs"
+test = false
+doc = false
+
+[[bin]]
+name = "encode_rgb_progressive"
+path = "fuzz_targets/encode_rgb_progressive.rs"
+test = false
+doc = false

fuzz/fuzz_targets/encode_rgb_progressive.rs

@@ -0,0 +1,21 @@
+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+
+use jpeg_encoder::*;
+
+fuzz_target!(|data: &[u8]| {
+
+    let pixels = data.len() / 3;
+
+    let width = (pixels as f64).sqrt() as u16;
+    let height = width;
+
+    if width >0 && width < u16::MAX &&  height >0 && height < u16::MAX  {
+        let mut out = Vec::new();
+        let mut encoder = Encoder::new(&mut out, 80);
+        encoder.set_sampling_factor(SamplingFactor::F_2_2);
+        encoder.set_progressive(true);
+        encoder.encode(data, width as u16, height as u16, ColorType::Rgb).unwrap();
+    }
+});

fuzz/fuzz_targets/encode_rgb_subsampled.rs

@@ -0,0 +1,20 @@
+#![no_main]
+
+use libfuzzer_sys::fuzz_target;
+
+use jpeg_encoder::*;
+
+fuzz_target!(|data: &[u8]| {
+
+    let pixels = data.len() / 3;
+
+    let width = (pixels as f64).sqrt() as u16;
+    let height = width;
+
+    if width >0 && width < u16::MAX &&  height >0 && height < u16::MAX  {
+        let mut out = Vec::new();
+        let mut encoder = Encoder::new(&mut out, 80);
+        encoder.set_sampling_factor(SamplingFactor::F_4_2);
+        encoder.encode(data, width as u16, height as u16, ColorType::Rgb).unwrap();
+    }
+});

src/encoder.rs

@@ -969,14 +969,20 @@ impl<W: JfifWrite> Encoder<W> {
             }
         }
 
+        let num_cols = ceil_div(usize::from(width), 8);
+        let num_rows = ceil_div(usize::from(height), 8);
+
+        debug_assert!(num_cols > 0);
+        debug_assert!(num_rows > 0);
+
         let mut blocks: [Vec<_>; 4] = self.init_block_buffers(buffer_size / 64);
 
         for (i, component) in self.components.iter().enumerate() {
             let h_scale = max_h_sampling as usize / component.horizontal_sampling_factor as usize;
             let v_scale = max_v_sampling as usize / component.vertical_sampling_factor as usize;
 
-            let cols = num_cols as usize / h_scale;
-            let rows = num_rows as usize / v_scale;
+            let cols = ceil_div(num_cols as usize , h_scale);
+            let rows = ceil_div(num_rows as usize , v_scale);
 
             debug_assert!(cols > 0);
             debug_assert!(rows > 0);

src/lib.rs

@@ -59,13 +59,15 @@ mod tests {
     use alloc::vec::Vec;
 
     fn create_test_img_rgb() -> (Vec<u8>, u16, u16) {
-        let width = 255;
+        // Ensure size which which ensures an odd MCU count per row to test chroma subsampling
+        let width = 258;
         let height = 128;
 
         let mut data = Vec::with_capacity(width * height * 3);
 
         for y in 0..height {
             for x in 0..width {
+                let x = x.min(255);
                 data.push(x as u8);
                 data.push((y * 2) as u8);
                 data.push(((x + y * 2) / 2) as u8);
@@ -76,13 +78,14 @@ mod tests {
     }
 
     fn create_test_img_gray() -> (Vec<u8>, u16, u16) {
-        let width = 255;
+        let width = 258;
         let height = 128;
 
         let mut data = Vec::with_capacity(width * height);
 
         for y in 0..height {
             for x in 0..width {
+                let x = x.min(255);
                 let (y, _, _) = rgb_to_ycbcr(x as u8, (y * 2) as u8, ((x + y * 2) / 2) as u8);
                 data.push(y);
             }
@@ -92,13 +95,14 @@ mod tests {
     }
 
     fn create_test_img_cmyk() -> (Vec<u8>, u16, u16) {
-        let width = 255;
+        let width = 258;
         let height = 192;
 
         let mut data = Vec::with_capacity(width * height * 4);
 
         for y in 0..height {
             for x in 0..width {
+                let x = x.min(255);
                 data.push(x as u8);
                 data.push((y * 3 / 2) as u8);
                 data.push(((x + y * 3 / 2) / 2) as u8);