aiongg
f28de79037
Commit testorig.jpg, testimgari.jpg and testorig12.jpg with a jpegtran Huffman transcode of testimgari.jpg and libjpeg-turbo's 12-bit decode of testorig12.jpg. The arithmetic-coded image must match its transcode exactly; the 8-bit and 12-bit decodes are compared against zune-jpeg and libjpeg-turbo within a small tolerance. Replaces the ignored conformance_samples test.
1.9 KiB
Test images
The JPEG files come from libjpeg-turbo 3.0.0, testimages/
(https://github.com/libjpeg-turbo/libjpeg-turbo/tree/3.0.0/testimages), under the IJG License
(README.ijg in this directory). The other two files are derived from them as described below.
SHA256SUMS lists every file.
| File | What it is |
|---|---|
testorig.jpg |
227×149 YCbCr, 2×2 luma sampling, baseline Huffman (SOF0) |
testimgari.jpg |
the same image, arithmetic coded (SOF9), one interleaved scan |
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 |
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.
How the derived files were made
testimgari-huffman.jpg, with jpegtran from libjpeg-turbo 3.1.0 (Alpine 3.22,
libjpeg-turbo-utils-3.1.0-r0):
jpegtran -copy none testimgari.jpg > testimgari-huffman.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:
import sys, imagecodecs, numpy as np
src, dst = sys.argv[1], sys.argv[2]
a = imagecodecs.jpeg8_decode(open(src, "rb").read())
h, w, c = a.shape
assert c == 3 and a.dtype == np.uint16 and a.max() <= 4095
with open(dst, "wb") as f:
f.write(b"P6\n%d %d\n4095\n" % (w, h))
f.write(a.astype(">u2").tobytes())
djpeg -dct int testorig12.jpg from libjpeg-turbo 3.1.0 writes a byte-identical file.
"This software is based in part on the work of the Independent JPEG Group."