[FFmpeg-user] How chrRangeToJpeg_c() works?

[Andrew Randrianasulu]

пн, 9 сент. 2024 г., 23:04 Andrew Randrianasulu <randrianasulu at gmail.com>:

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> пн, 9 сент. 2024 г., 18:06 Andrew Randrianasulu <randrianasulu at gmail.com>:
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>> Looking at libswscale/swscale.c (due to
>> https://trac.ffmpeg.org/ticket/11182#comment:5) I do not understand
>> how it works :)
>>
>> why shits to 11 and to 12 ?
>>
>> // FIXME all pal and rgb srcFormats could do this conversion as well
>> // FIXME all scalers more complex than bilinear could do half of this
>> transform
>> static void chrRangeToJpeg_c(int16_t *dstU, int16_t *dstV, int width)
>> {
>>     int i;
>>     for (i = 0; i < width; i++) {
>>         dstU[i] = (FFMIN(dstU[i], 30775) * 4663 - 9289992) >> 12; // -264
>>         dstV[i] = (FFMIN(dstV[i], 30775) * 4663 - 9289992) >> 12; // -264
>>     }
>> }
>>
>> static void chrRangeFromJpeg_c(int16_t *dstU, int16_t *dstV, int width)
>> {
>>     int i;
>>     for (i = 0; i < width; i++) {
>>         dstU[i] = (dstU[i] * 1799 + 4081085) >> 11; // 1469
>>         dstV[i] = (dstV[i] * 1799 + 4081085) >> 11; // 1469
>>     }
>> }
>>
>> ===
>> can anyone knowledgeable  write/add some more comments in code ? please :)
>>
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> it seems that same code (under slightly different name) was living in
> swscale_template.c since at least 2009 ...
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> https://git.ffmpeg.org/gitweb/ffmpeg.git/blobdiff/c1977fbbd7d1e7825010e301fa236e910b760aab..bae76dc3eb6e5cd07f5881092d375ddc0270f693:/libswscale/swscale_template.c
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and it was commited in 2008:

https://git.ffmpeg.org/gitweb/ffmpeg.git/commit/6bc0c7928a386d5cf99c198ec1b795aff6bf7656

Fix jpeg yuv.

author Michael Niedermayer <michaelni at gmx.at>
Mon, 8 Sep 2008 15:36:38 +0300 (12:36 +0000)
committer Michael Niedermayer <michaelni at gmx.at>
Mon, 8 Sep 2008 15:36:38 +0300 (12:36 +0000)
commit 6bc0c7928a386d5cf99c198ec1b795aff6bf7656
tree a90c126c5d92e65bfe4ad9dac24473eaae8464ed tree
parent f7b1d72f45c97f3fc57632a0a23d01cee51c4a4e commit | diff

Fix jpeg yuv.
Fixes issue504.

Originally committed as revision 27547 to svn://
svn.mplayerhq.hu/mplayer/trunk/libswscale

hm, but this does not make it less opaque for me ;)

I guess it was working for all those years .. mostly?


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