Re: EXIF support in PNG [was: Modern compressor]
John Bowler <[email protected]>
| Newsgroups | gmane.comp.graphics.png.general |
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| Message-ID | <CAP7U39-Wh581KRbH6ng+nYd-Y_k1y3J+=ZAEqhH8wfEm=OsN5A@mail.gmail.com> |
The chunk needs to be unsafe-to-copy; it contains color space information so it behaves in a way similar to iCCP. Here's a modified proposal: ======================================================= PNG CHUNK PROPOSAL: eXIF SPECIFICATION ============= The four-byte chunk type field contains the decimal values 101 88 73 10 The eXIF chunk contains EXIF metadata with a length given by the chunk length. Such data shall be compatible with specifications issued by CIPA, "Exchangeable image file format for digital still cameras" [CIPA DC-008-2016] or its successors. At most one eXIF chunk shall occur in a PNG stream. The chunk has no chunk-specific positioning requirements; it may appear before or after the IDAT chunks. RATIONALE ========= EXIF metadata is commonly contained in the images produced by digital cameras. If such images are converted to PNG during processing some or all of the EXIF metadata is frequently lost. Existing image processing programs preserve the data using different non-approved chunks. Such images are rarely if ever distributed in PNG format, rather the format is used as an intermediate format during processing and the final images are distributed as JPEG or TIFF. The intent of this chunk is to prevent loss of data in this process by ensuring that EXIF can be preserved in PNG with minimal overhead on existing PNG using applications. The tag is marked 'unsafe-to-copy' because the metadata can contain information relating to the image data. Color conversions therefore invalidate the data, simple recompression of the image will not invalidate the EXIF data. ======================================================= ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ png-mng-misc mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/png-mng-misc
20170101 eXIF.txt
(text/plain, 1.4 KB)
PNG CHUNK PROPOSAL: eXIF SPECIFICATION ============= The four-byte chunk type field contains the decimal values 101 88 73 10 The eXIF chunk contains EXIF metadata with a length given by the chunk length. Such data shall be compatible with specifications issued by CIPA, "Exchangeable image file format for digital still cameras" [CIPA DC-008-2016] or its successors. At most one eXIF chunk shall occur in a PNG stream. The chunk has no chunk-specific positioning requirements; it may appear before or after the IDAT chunks. RATIONALE ========= EXIF metadata is commonly contained in the images produced by digital cameras. If such images are converted to PNG during processing some or all of the EXIF metadata is frequently lost. Existing image processing programs preserve the data using different non-approved chunks. Such images are rarely if ever distributed in PNG format, rather the format is used as an intermediate format during processing and the final images are distributed as JPEG or TIFF. The intent of this chunk is to prevent loss of data in this process by ensuring that EXIF can be preserved in PNG with minimal overhead on existing PNG using applications. The tag is marked 'unsafe-to-copy' because the metadata can contain information relating to the image data. Color conversions therefore invalidate the data, simple recompression of the image will not invalidate the EXIF data.