jpeg: conformance fixtures for jpegtran's progressive and 12-bit arithmetic transcodes

crates/jpeg/README.md

@@ -112,6 +112,8 @@ SOF11 (lossless) falls in that range and returns `Unsupported`.
 - `tests/conformance.rs`, on libjpeg-turbo's test images in `tests/data` (provenance and how
   the derived files were made: `tests/data/SOURCE.md`):
   - `testimgari.jpg` (SOF9) decodes to exactly the samples of its jpegtran Huffman transcode.
+  - jpegtran's arithmetic and progressive arithmetic transcodes of `testorig.jpg` (one with
+    restarts) and `testorig12.jpg` decode to exactly the samples of their sources.
   - `whitetail-ari.jpg` (SOF9 from cjpeg, a white lower part that decodes from the zeros
     supplied at EOI) decodes undamaged and equal to its Huffman transcode.
   - `testorig.jpg` matches `zune-jpeg`, and `testorig12.jpg` matches libjpeg-turbo's 12-bit

crates/jpeg/tests/conformance.rs

@@ -41,6 +41,21 @@ fn arithmetic_coded_image_matches_its_huffman_transcode() {
     assert!(huffman.samples == arithmetic.samples, "testimgari.jpg decodes differently from testimgari-huffman.jpg");
 }
 
+/// The arithmetic and progressive arithmetic transcodes jpegtran made of testorig.jpg and
+/// testorig12.jpg hold their coefficients, so they decode to exactly the same samples.
+#[test]
+fn arithmetic_transcodes_match_their_huffman_sources() {
+    for (source, transcodes) in [
+        ("testorig.jpg", &["testorig-ari-progressive.jpg", "testorig-ari-progressive-restart.jpg"]),
+        ("testorig12.jpg", &["testorig12-ari.jpg", "testorig12-ari-progressive.jpg"]),
+    ] {
+        let reference = decode_fixture(source);
+        for name in transcodes {
+            assert!(decode_fixture(name).samples == reference.samples, "{name} decodes differently from {source}");
+        }
+    }
+}
+
 /// libjpeg's arithmetic encoder drops the trailing zero bytes of a scan, so the white lower
 /// part of whitetail-ari.jpg decodes from zeros supplied at the EOI marker. It must decode
 /// whole and match its Huffman transcode.

crates/jpeg/tests/data/SHA256SUMS

@@ -5,3 +5,7 @@ acc6ec555d41d15b368320edaa3b20958ee6fa97cb6e4a18d1213d5ae8bec73b  testorig.jpg
 62d182ed042e243544d3d753c440ada1a6992464717311fe6efd546632f44dc4  testorig12.ppm
 0031b82a06300b5b5d19ef5553cc39d3fafafa4fbc474199e6cfbc7818312a87  whitetail-ari.jpg
 0f6e17a44be7a005d6610e66f91fa119388dc6b8438e95cb8816b6db58f8c365  whitetail-huffman.jpg
+7e7edd9d9825c2eca1e6ff6dfafeaddec39e2464fc5d6d1ce4a378a59ec3f716  testorig-ari-progressive.jpg
+cb0a2c60e6a89c68ef8cf48854dc09c77c26ffb27ac62e17d343d98f1424cc77  testorig-ari-progressive-restart.jpg
+c4942c4b704d20e27c4cd3e613c6ef975dd7cfe53a756e2c209fa3ad033d8b51  testorig12-ari.jpg
+18df0394115d9f8751939fb9f45a0d330df2ca849e9f8b07d0af76c09b90fcdb  testorig12-ari-progressive.jpg

crates/jpeg/tests/data/SOURCE.md

@@ -13,12 +13,17 @@ libjpeg-turbo's tools, as described below.
 | `testimgari-huffman.jpg` | `testimgari.jpg` losslessly transcoded to baseline Huffman (SOF0) |
 | `testorig12.jpg` | 227×149 YCbCr, 12-bit extended sequential Huffman (SOF1) |
 | `testorig12.ppm` | libjpeg-turbo's decode of `testorig12.jpg`: 12-bit RGB, binary PPM, maxval 4095 |
+| `testorig-ari-progressive.jpg` | `testorig.jpg` transcoded to progressive arithmetic (SOF10) |
+| `testorig-ari-progressive-restart.jpg` | the same with a restart interval of 3 MCU rows |
+| `testorig12-ari.jpg` | `testorig12.jpg` transcoded to 12-bit arithmetic (SOF9) |
+| `testorig12-ari-progressive.jpg` | `testorig12.jpg` transcoded to 12-bit progressive arithmetic (SOF10) |
 | `whitetail-ari.jpg` | 512×512 gray, arithmetic coded (SOF9), noise in the top 16 rows, white below |
 | `whitetail-huffman.jpg` | `whitetail-ari.jpg` losslessly transcoded to baseline Huffman (SOF0) |
 
 `testimgari.jpg` and `testorig.jpg` share their quantization tables but not their coefficients:
 libjpeg-turbo decodes them to different pixels. `testimgari-huffman.jpg` holds exactly the
-coefficients of `testimgari.jpg`, so the two must decode to identical samples.
+coefficients of `testimgari.jpg`, so the two must decode to identical samples. The same holds
+for each jpegtran transcode below and its source.
 
 ## How the derived files were made
 
@@ -29,6 +34,16 @@ coefficients of `testimgari.jpg`, so the two must decode to identical samples.
 jpegtran -copy none testimgari.jpg > testimgari-huffman.jpg
 ```
 
+The arithmetic transcodes of `testorig.jpg` and `testorig12.jpg`, with jpegtran from
+libjpeg-turbo 3.1.3 (Alpine 3.24, `libjpeg-turbo-utils`):
+
+```sh
+jpegtran -copy none -arithmetic -progressive testorig.jpg > testorig-ari-progressive.jpg
+jpegtran -copy none -arithmetic -progressive -restart 3 testorig.jpg > testorig-ari-progressive-restart.jpg
+jpegtran -copy none -arithmetic testorig12.jpg > testorig12-ari.jpg
+jpegtran -copy none -arithmetic -progressive testorig12.jpg > testorig12-ari-progressive.jpg
+```
+
 `testorig12.ppm`, with libjpeg-turbo 3.2.0 through imagecodecs 2026.10.10 (default settings:
 integer IDCT `JDCT_ISLOW`, fancy upsampling), run as
 `uv run --with imagecodecs --with numpy python make.py testorig12.jpg testorig12.ppm`: