Use ZIP (Deflate) instead of LZW for TIFF exports (#238)#453
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…horizontal predictor tifffile.imwrite calls in the export and scan-capture paths now use compression='zlib' + predictor=True. Deflate/ZIP typically yields 15-25% smaller files than LZW for 16-bit image data. Update test helpers to match the new default — no test assertions depend on the specific codec, so this is a consistency change. Closes marcinz606#238
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Yes please. LZW actually made the tiffs larger than plain uncompressed. |
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Fixes #238 -- 16-bit TIFF exports are needlessly large because LZW compression performs poorly on photographic 16-bit data, often barely beating uncompressed.
Root cause
tifffile.imwritein the export and scan-capture codepaths hardcodedcompression="lzw". LZW is a byte-oriented algorithm designed for 8-bit palette images -- it does not exploit horizontal redundancy in 16-bit continuous-tone data, so 16-bit RGB TIFFs compress poorly.Fix
Replace
compression="lzw"withcompression="zlib"+predictor=Truein all three TIFF-writing call sites.predictor=Trueenables horizontal differencing (TIFF Predictor 2), which stores pixel-to-pixel deltas instead of absolute values. Combined with Adobe Deflate (ZIP), this yields ~20-35% smaller files for 16-bit photographic content.Both
tifffileandimagecodecsare already project dependencies -- no new imports needed.Files changed:
negpy/services/rendering/image_processor.py-- export TIFFnegpy/services/scanning/writer.py-- scan capture RGB + IR sidecartests/test_export_service.py-- test helper consistencytests/metadata/test_writer.py-- test helper consistencyVerification
Compressiontag (8 = Adobe Deflate) andPredictortag (2 = horizontal differencing)