Re: Typical to/from EXIF conversions

You might also mention that if the JPEG/TIFF contains an
ICC profile, don't write cHRM or gAMA in steps 5 and 6.of TIFF->PNG;
just write an iCCP chunk containing the profile.

Glenn

On Sat, Mar 11, 2017 at 7:17 AM, Pavel Zlatovratskii <[email protected]> wrote:
> To make eXIf discussion more useful I tried to write my visions of "typical"
> scenarios to convert EXIF file to PNG.
>
> TIFF(JPEG/EXIF) to PNG conversion
>
> Read and parse EXIF header (and JPEG header for JPEG).
> Write PNG signature and IHDR chunk based on data from header.
> Write pHYs chunk if resolution present.
> Write tags "ImageDescription", "Model", "Software", "Artist", "Copyright",
> "UserComment", "DateTimeOriginal" (and it's subsec and timezone) as
> appropriate tEXt(iTXt; zTXt) chunk if any.
> Write cHRM chunk if "WhitePoint" and "PrimaryChromacies" tags present.
> Write gAMA chunk if "Gamma" tag present.
> Remove any tags that inapplicable to PNG (like PlanarConfiguration).
> Remove thumbnail.
> Write processed EXIF header as eXIf chunk.
> Convert image data and write IDAT and IEND chunks.
>
> PNG to JPEG/EXIF conversion
>
> Read IHDR and all chunks before IDAT.
> Parse eXIf chunk
> Remove any tags that marked as "J" or "N" in column "Compressed" of Table
> 17, Table 18, Table 19 or Table 20 of CIPA DC-008-2016
> Update(create) resolution tags with data of pHYs chunk.
> Update(create) tags "ImageDescription", "Model", "Software", "Artist",
> "Copyright", "UserComment", "DateTimeOriginal" (and it's subsec and
> timezone) with data from appropriate tEXt(iTXt; zTXt) chunks.
> Update(create) "Gamma" tag with data of gAMA chunk.
> Recreate thumbnail image.
> Write result EXIF as APP1 marker.
> If iCCP is present - use JFIF-designed(B.5 of ICC.1:2004-10) way to save it
> as APP2 marker.
> If both iTXt and tEXt(zTXt) with keyword "Comment" present - iTXt could be
> saved to "UserComment" of EXIF and tEXt(zTXt) could be saved to COM marker.
> Convert and write image data (SOI - EOI).
>
>
> What I missed? Any other visions?
>
> --
> Have a nice DOS.
>
> Pavel Zlatovratskii scondo-JGs/[email protected]; [email protected]
>
>
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