jpeg/encoder: Fix DQT ordering

gufo-rs · Dec 31, 2024 · af67a20 · af67a20
1 parent 643be70
commit af67a20
Show file tree

Hide file tree

Showing 2 changed files with 35 additions and 7 deletions.
diff --git a/gufo-jpeg/src/encoder.rs b/gufo-jpeg/src/encoder.rs
@@ -1,14 +1,14 @@
-use crate::Error;
 use gufo_common::math::*;
+use jpeg_encoder::QuantizationTableType;
+
+use crate::Error;
 
 impl crate::Jpeg {
     pub fn encoder<W: jpeg_encoder::JfifWrite>(
         &self,
         w: W,
     ) -> Result<jpeg_encoder::Encoder<W>, EncoderError> {
-        let mut encoder = jpeg_encoder::Encoder::new(w, 50);
-
-        encoder.set_sampling_factor(self.sampling_factor()?);
+        let mut encoder = jpeg_encoder::Encoder::new(w, 100);
 
         let (luma, chroma) = self.quantization_tables()?;
 
@@ -61,11 +61,12 @@ impl crate::Jpeg {
 
         let luma_parameters = self.components_specification_parameters(0)?;
         let luma_table = dqts.get(&luma_parameters.tq).ok_or(Error::MissingDqt)?;
-        let luma = jpeg_encoder::QuantizationTableType::Custom(Box::new(luma_table.qk()));
+        let luma = jpeg_encoder::QuantizationTableType::Custom(Box::new(luma_table.qk_ordered()));
 
         let chroma_parameters = self.components_specification_parameters(1)?;
         let chroma_table = dqts.get(&chroma_parameters.tq).ok_or(Error::MissingDqt)?;
-        let chroma = jpeg_encoder::QuantizationTableType::Custom(Box::new(chroma_table.qk()));
+        let chroma: QuantizationTableType =
+            jpeg_encoder::QuantizationTableType::Custom(Box::new(chroma_table.qk_ordered()));
 
         Ok((luma, chroma))
     }

diff --git a/gufo-jpeg/src/segments.rs b/gufo-jpeg/src/segments.rs
@@ -29,7 +29,8 @@ impl Dqt {
 
     /// Quantization table elements in 16 bit
     ///
-    /// This resturns the data in 16 bit, even if defined as 8 bit.
+    /// This resturns the data in 16 bit, even if defined as 8 bit. The 8-bit
+    /// data is not scaled to 16-bit.
     pub fn qk(&self) -> [u16; 64] {
         match self {
             Self::Dqt8(dqt) => {
@@ -43,6 +44,32 @@ impl Dqt {
         }
     }
 
+    /// Quantization table in non-zig-zag order
+    ///
+    /// Otherwise same as `qk()`
+    pub fn qk_ordered(&self) -> [u16; 64] {
+        const IDX: [[usize; 8]; 8] = [
+            [0, 1, 5, 6, 14, 15, 27, 28],
+            [2, 4, 7, 13, 16, 26, 29, 42],
+            [3, 8, 12, 17, 25, 30, 41, 43],
+            [9, 11, 18, 24, 31, 40, 44, 53],
+            [10, 19, 23, 32, 39, 45, 52, 54],
+            [20, 22, 33, 38, 46, 51, 55, 60],
+            [21, 34, 37, 47, 50, 56, 59, 61],
+            [35, 36, 48, 49, 57, 58, 62, 63],
+        ];
+
+        let qk = self.qk();
+
+        let mut qk_ordered = [0; 64];
+
+        for (i, n) in IDX.into_iter().flatten().enumerate() {
+            qk_ordered[i] = qk[n];
+        }
+
+        qk_ordered
+    }
+
     pub fn from_data(mut value: &[u8]) -> Result<Vec<Self>, Error> {
         let mut dqts = Vec::new();
         while !value.is_empty() {