#11279: Aspect ratio defined by the PNG resolution chunk “pHYs” is
misinterpreted
as its reciprocal
--------------------------------------+----------------------------------
Reporter: goodbye | Type: defect
Status: new | Priority: normal
Component: undetermined | Version: 7.1
Keywords: png | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
--------------------------------------+----------------------------------
The PNG {{{pHYs}}} chunk describes the resolution/pixel density of an
image, which can be in abstract units (in which case it only defines the
pixel aspect ratio) or in pixels per metre.
FFmpeg interprets the X:Y resolution ratio directly as a X:Y PAR, but in
actuality, it’s the reciprocal. This is because the resolution is
specified as a “pixels per unit” value and not “units per pixel”, as is
typically the case with PARs. The X:Y PAR is equal to the Y:X ratio of
resolutions specified in the chunk.
Both of these images, from the libpng test suite, are supposed to have a
DAR of 1:1, but FFmpeg misinterprets them to have DARs of 16:1 and 1:16:
* http://www.libpng.org/pub/png/PngSuite/cdhn2c08.png
* http://www.libpng.org/pub/png/PngSuite/cdfn2c08.png
--
Ticket URL: <https://trac.ffmpeg.org/ticket/11279>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker
_______________________________________________
FFmpeg-trac mailing list
FFmpeg-trac@avcodec.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-trac
To unsubscribe, visit link above, or email
ffmpeg-trac-requ...@ffmpeg.org with subject "unsubscribe".
