CCITT group 4 (Fax4) decoding support

Cargo.toml

@@ -20,6 +20,7 @@ exclude = ["tests/images/*", "tests/fuzz_images/*"]
 weezl = "0.1.0"
 jpeg = { package = "jpeg-decoder", version = "0.3.0", default-features = false }
 flate2 = "1.0.20"
+fax = "0.2.2"
 
 [dev-dependencies]
 criterion = "0.3.1"

src/decoder/image.rs

@@ -7,6 +7,7 @@ use crate::tags::{
     CompressionMethod, PhotometricInterpretation, PlanarConfiguration, Predictor, SampleFormat, Tag,
 };
 use crate::{ColorType, TiffError, TiffFormatError, TiffResult, TiffUnsupportedError, UsageError};
+use fax;
 use std::io::{self, Cursor, Read, Seek};
 use std::sync::Arc;
 
@@ -368,6 +369,7 @@ impl Image {
     }
 
     fn create_reader<'r, R: 'r + Read>(
+        &self,
         reader: R,
         photometric_interpretation: PhotometricInterpretation,
         compression_method: CompressionMethod,
@@ -447,6 +449,25 @@ impl Image {
 
                 Box::new(Cursor::new(data))
             }
+            CompressionMethod::Fax4 => {
+                let width = u16::try_from(self.width)?;
+                let height = u16::try_from(self.height)?;
+                let mut out: Vec<u8> = Vec::with_capacity(usize::from(width) * usize::from(height));
+
+                let mut buffer = Vec::with_capacity(usize::try_from(compressed_length)?);
+                reader.take(compressed_length).read_to_end(&mut buffer)?;
+
+                // all extant tiff/fax4 decoders I've found always assume that the photometric interpretation
+                // is `WhiteIsZero`, ignoring the tag. ImageMagick appears to generate fax4-encoded tiffs
+                // with the tag incorrectly set to `BlackIsZero`.
+                fax::decoder::decode_g4(buffer.into_iter(), width, Some(height), |transitions| {
+                    out.extend(fax::decoder::pels(transitions, width).map(|c| match c {
+                        fax::Color::Black => 255,
+                        fax::Color::White => 0,
+                    }))
+                });
+                Box::new(Cursor::new(out))
+            }
             method => {
                 return Err(TiffError::UnsupportedError(
                     TiffUnsupportedError::UnsupportedCompressionMethod(method),
@@ -633,7 +654,7 @@ impl Image {
 
         let padding_right = chunk_dims.0 - data_dims.0;
 
-        let mut reader = Self::create_reader(
+        let mut reader = self.create_reader(
             reader,
             photometric_interpretation,
             compression_method,

tests/decode_images.rs

@@ -510,3 +510,8 @@ fn test_predictor_3_rgb_f32() {
 fn test_predictor_3_gray_f32() {
     test_image_sum_f32("predictor-3-gray-f32.tif", ColorType::Gray(32), 20008.275);
 }
+
+#[test]
+fn test_fax4() {
+    test_image_sum_u8("fax4.tiff", ColorType::Gray(1), 62384985);
+}