fix: use extra channel's own bit_depth for modular-to-f32 conversion

jxl/src/frame/render.rs

@@ -266,8 +266,8 @@ impl Frame {
             }
         }
         for i in 3..num_channels {
-            pipeline =
-                pipeline.add_inout_stage(ConvertModularToF32Stage::new(i, metadata.bit_depth))?;
+            let ec_bit_depth = metadata.extra_channel_info[i - 3].bit_depth();
+            pipeline = pipeline.add_inout_stage(ConvertModularToF32Stage::new(i, ec_bit_depth))?;
         }
 
         for c in 0..3 {

jxl/src/headers/extra_channels.rs

@@ -89,6 +89,9 @@ impl ExtraChannelInfo {
     pub fn alpha_associated(&self) -> bool {
         self.alpha_associated
     }
+    pub fn bit_depth(&self) -> BitDepth {
+        self.bit_depth
+    }
     fn check(&self, _: &Empty) -> Result<(), Error> {
         if self.dim_shift > 3 {
             Err(Error::DimShiftTooLarge(self.dim_shift))

jxl/src/render/stages/convert.rs

@@ -448,4 +448,23 @@ mod test {
     fn f32_to_f16_consistency() -> Result<()> {
         crate::render::test::test_stage_consistency(|| ConvertF32ToF16Stage::new(0), (500, 500), 1)
     }
+
+    /// Test ConvertModularToF32Stage consistency with different bit depths.
+    #[test]
+    fn modular_to_f32_8bit_consistency() -> Result<()> {
+        crate::render::test::test_stage_consistency(
+            || ConvertModularToF32Stage::new(0, BitDepth::integer_samples(8)),
+            (500, 500),
+            1,
+        )
+    }
+
+    #[test]
+    fn modular_to_f32_16bit_consistency() -> Result<()> {
+        crate::render::test::test_stage_consistency(
+            || ConvertModularToF32Stage::new(0, BitDepth::integer_samples(16)),
+            (500, 500),
+            1,
+        )
+    }
 }