[FFmpeg-user] ffmpeg makes some sources darker

[Andy Furniss]

Andy Furniss wrote:
> Andy Furniss wrote:
>
>> Strange, unless there is something in the pngs that causes a
>> different viewer to produce different output.
>>
>> I looked again (display from ancient imagemagic) and can't see any
>> difference - psnr/ssim agree.
>>
>> The pngs are not the same md5sum wise
>>
>> md5sum frame1-yuv-709.png frame1-master.png
>> 1c086ed015ebe05aa1cfc66d9fe754a3  frame1-yuv-709.png
>> 91ab580b1db4361fcceadaffd24930bd  frame1-master.png
>
> The obvious difference between the pngs is master is bigger by 60 bytes
> and it has extra info in it, I can see with ffmpeg -i ... that SAR and
> DAR are shown - nothing about 709 but maybe that's in there as well?
>
> I tried making another png from yuv using out_color_matrix as well as
> in_color_matrix, but it produced the same file (md5sum) as just
> in_color_matrix.
>

I found the difference using identify from  ImageMagick - I don't know 
why display doesn't seem to show it for me but ...

identify -verbose frame1-yuv-709.png > idout-709
identify -verbose frame1-master.png > idout-master
diff idout-master idout-709
1c1
< Image: frame1-master.png
---
 > Image: frame1-yuv-709.png
5,6d4
<   Resolution: 1x1
<   Print size: 1920x1080
47c45
<   Gamma: 0.50994
---
 >   Gamma: 0.454545
65,68c63,64
<     date:create: 2016-01-04T21:52:55+00:00
<     date:modify: 2016-01-04T21:52:55+00:00
<     png:cHRM                 : chunk was found (see Chromaticity, above)
<     png:gAMA                 : gamma=0.45454544 (See Gamma, above)
---
 >     date:create: 2016-01-04T22:04:11+00:00
 >     date:modify: 2016-01-04T22:04:11+00:00
73c69
<     png:pHYs                 : x_res=1, y_res=1, units=0
---
 >     png:pHYs                 : x_res=0, y_res=1, units=0
76c72
<     filename: frame1-master.png
---
 >     filename: frame1-yuv-709.png
82,83c78,79
<   User time: 0.050u
<   Elapsed time: 0:01.060
---
 >   User time: 0.060u
 >   Elapsed time: 0:01.059