cross-codec-testing

name: cross-codec-testing description: 'Cross-codec interoperability testing between J2KSwift and OpenJPEG. Use for validating encode/decode compatibility, verifying lossless roundtrip, comparing outputs between codecs, testing multi-tile images, medical imaging interop.'

Cross-Codec Interoperability Testing

Test JPEG 2000 encode/decode compatibility between J2KSwift and OpenJPEG.

When to Use

• Verifying J2KSwift output can be decoded by OpenJPEG (and vice versa)
• Testing lossless roundtrip: encode → decode → compare
• Validating multi-tile, multi-component, or medical images
• Debugging interoperability failures

Prerequisites

• J2KSwift CLI built: swift build (produces .build/debug/j2k)
• OpenJPEG v2.5.4 at /opt/homebrew/bin/ (opj_compress, opj_decompress, opj_dump)
• Test images (create synthetic PGM/PPM if none available)

Procedure

1. Build J2KSwift CLI

swift build

2. Create Test Images (if needed)

Generate synthetic PGM (grayscale) or PPM (color) test images:

# 256x256 grayscale gradient
python3 -c "
import struct
with open('/tmp/test_gray.pgm', 'wb') as f:
    f.write(b'P5\n256 256\n255\n')
    for y in range(256):
        for x in range(256):
            f.write(struct.pack('B', (x + y) % 256))
"

3. Test Matrix

Run each combination:

4. Encode/Decode Commands

J2KSwift encode (lossless):

.build/debug/j2k encode /tmp/test_gray.pgm /tmp/j2k_lossless.j2k

J2KSwift encode (lossy):

.build/debug/j2k encode /tmp/test_gray.pgm /tmp/j2k_lossy.j2k --quality 0.5

OpenJPEG encode (lossless):

opj_compress -i /tmp/test_gray.pgm -o /tmp/opj_lossless.j2k -r 1

OpenJPEG decode:

opj_decompress -i /tmp/j2k_lossless.j2k -o /tmp/decoded.pgm

J2KSwift decode:

.build/debug/j2k decode /tmp/opj_lossless.j2k /tmp/decoded.pgm

5. Compare Results

.build/debug/j2k compare /tmp/test_gray.pgm /tmp/decoded.pgm

Or use Python for MAE calculation:

python3 -c "
import sys
a = open(sys.argv[1], 'rb').read()
b = open(sys.argv[2], 'rb').read()
# Skip PGM header (find data after third newline)
def skip_header(d):
    pos = 0
    for _ in range(3):
        pos = d.index(ord('\n'), pos) + 1
    return d[pos:]
da, db = skip_header(a), skip_header(b)
mae = sum(abs(x-y) for x,y in zip(da,db)) / len(da)
print(f'MAE: {mae:.4f}')
" /tmp/test_gray.pgm /tmp/decoded.pgm

6. Test Edge Cases

• 1x1 pixel image
• Non-power-of-2 dimensions (e.g., 253x127)
• Multi-tile (large images with small tile size)
• 16-bit depth images
• Multi-component (RGB) images

Troubleshooting

• If J2KSwift output fails in OpenJPEG: use opj_dump to inspect codestream markers
• If lossless MAE > 0: check DWT mode (must be 5/3 reversible) and quantization step sizes
• If multi-tile fails: verify tile boundaries match between encoder/decoder