Encoding of extra samples, roundtrip test

src/encoder/mod.rs

@@ -563,9 +563,6 @@ impl<'a, W: 'a + Write + Seek, T: ColorType, K: TiffKind> ImageEncoder<'a, W, T,
         encoder.write_tag(Tag::Compression, compression.tag().to_u16())?;
         encoder.write_tag(Tag::Predictor, predictor.to_u16())?;
 
-        encoder.write_tag(Tag::BitsPerSample, <T>::BITS_PER_SAMPLE)?;
-        let sample_format: Vec<_> = <T>::SAMPLE_FORMAT.iter().map(|s| s.to_u16()).collect();
-        encoder.write_tag(Tag::SampleFormat, &sample_format[..])?;
         encoder.write_tag(Tag::PhotometricInterpretation, <T>::TIFF_VALUE.to_u16())?;
 
         encoder.write_tag(Tag::RowsPerStrip, u32::try_from(rows_per_strip)?)?;
@@ -754,6 +751,39 @@ impl<'a, W: 'a + Write + Seek, T: ColorType, K: TiffKind> ImageEncoder<'a, W, T,
     }
 
     fn finish_internal(&mut self) -> TiffResult<DirectoryOffset<K>> {
+        if self.extra_samples.is_empty() {
+            self.encoder
+                .write_tag(Tag::BitsPerSample, <T>::BITS_PER_SAMPLE)?;
+        } else {
+            let mut sample_format: Vec<_> = <T>::BITS_PER_SAMPLE.to_vec();
+            let replicated =
+                core::iter::repeat(<T>::BITS_PER_SAMPLE[0]).take(self.extra_samples.len());
+            sample_format.extend(replicated);
+
+            self.encoder
+                .write_tag(Tag::BitsPerSample, &sample_format[..])?;
+
+            self.encoder.write_tag(
+                Tag::SamplesPerPixel,
+                u16::try_from(<T>::BITS_PER_SAMPLE.len() + self.extra_samples.len())?,
+            )?;
+        }
+
+        let mut sample_format: Vec<_> = <T>::SAMPLE_FORMAT.iter().map(|s| s.to_u16()).collect();
+        let extra_format = sample_format
+            .first()
+            .copied()
+            // Frankly should not occur, we have no sample format without at least one entry. We
+            // would need an interface upgrade to handle this however. Either decide to support
+            // heterogeneous sample formats or a way to provide fallback that is used for purely
+            // extra samples and not provided via a slice used for samples themselves.
+            .unwrap_or(SampleFormat::Void.to_u16());
+
+        sample_format.extend(core::iter::repeat(extra_format).take(self.extra_samples.len()));
+
+        self.encoder
+            .write_tag(Tag::SampleFormat, &sample_format[..])?;
+
         self.encoder
             .write_tag(Tag::StripOffsets, K::convert_slice(&self.strip_offsets))?;
         self.encoder.write_tag(

tests/decode_images.rs

@@ -686,19 +686,37 @@ fn test_fax4_white_is_min() {
 }
 
 #[test]
-fn extra_bits_image() {
+fn write_extra_bits_image() {
     use tiff::{encoder, tags::ExtraSamples};
 
-    let path = PathBuf::from(TEST_IMAGE_DIR).join("extra_bits_gray_4b.tiff");
+    let path = PathBuf::from(TEST_IMAGE_DIR).join("extra_bits_rgb_8b.tiff");
     let img_file = File::create(path).expect("Cannot find test image!");
 
     let mut encoder = encoder::TiffEncoder::new(img_file).expect("Cannot create encoder");
-    let mut img = encoder
-        .new_image::<encoder::colortype::Gray8>(8, 8)
-        .unwrap();
+    let mut img = encoder.new_image::<encoder::colortype::RGB8>(8, 8).unwrap();
 
     img.extra_samples(&[ExtraSamples::Unspecified]).unwrap();
 
-    let data: [u8; 128] = core::array::from_fn(|i| i as u8 % 2);
-    img.write_data(&data).expect("correct amount of data to write");
+    // all pixels are supposed to be 0, the extra is 1
+    let data: [u8; 256] = core::array::from_fn(|i| (i as u8 % 4).saturating_sub(2));
+
+    img.write_data(&data)
+        .expect("correct amount of data to write");
+}
+
+#[test]
+fn extra_bits_gray() {
+    test_image_sum_u8(
+        "extra_bits_gray_8b.tiff",
+        ColorType::Multiband {
+            bit_depth: 8,
+            num_samples: 2,
+        },
+        64,
+    );
+}
+
+#[test]
+fn extra_bits_rgb() {
+    test_image_sum_u8("extra_bits_rgb_8b.tiff", ColorType::RGB(8), 0);
 }

tests/encode_images.rs

@@ -57,7 +57,7 @@ fn encode_decode() {
                 ),
                 (Tag::Compression, ifd::Value::Short(1)),
                 (Tag::PhotometricInterpretation, ifd::Value::Short(2)),
-                (Tag::StripOffsets, ifd::Value::Unsigned(47)),
+                (Tag::StripOffsets, ifd::Value::Unsigned(35)),
                 (Tag::SamplesPerPixel, ifd::Value::Short(3)),
                 (Tag::RowsPerStrip, ifd::Value::Unsigned(3334)),
                 (Tag::StripByteCounts, ifd::Value::Unsigned(30000)),