New JPEG encoder brightens/reduces contrast of YUV420 img

New JPEG encoder brightens/reduces contrast of YUV420 img

camkego's picture

Hello,

I am trying the new JPEG encoder in the 2013 release, and have noticed something odd.

When I encode YUV420 material, the JPEG image seems to have lower contrast and be brighter than the source material.

This seems like a colorspace issue, but I'm not sure if there is an option to change the behavior. [I don't want to re-color my raw source]

I am attaching a Big Buck Bunny (BBB) YUV420 raw, and the resulting JPEG output from sample_encoder.

It is tempting to point the fingers at my viewers, but the original BBB video my raw YV12 seem consistent, the raw was viewed using the '7yuv' tool.

I used the following command to go from raw to .jpg  :  sample_encode.exe jpeg -i bbbf.1080.yuv -o j.jpg -w 1920 -h 1080

Any help is appreciated.

I cannot seem to attach .yuv files, so here is Dropbox links:

https://www.dropbox.com/s/n6u9gqp3uj9fwxw/bbbf.1080.jpg

https://www.dropbox.com/s/1w7c7flt3hs5n7a/bbbf.1080.yuv

If desired, the original video is here: http://www.bigbuckbunny.org/index.php/download/

Frame #1000, about 39 seconds in was used.

Cameron

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Petter Larsson (Intel)'s picture

Hi Cameron.

Thanks for sharing your findings.

I can confirm that I do see the same increased brightness in the encoded JPEG image. We will explore if there is anything we can do to improve the color accuracy. I'll report back to this thread when I have more info to share.

Regards,
Petter 

Petter Larsson (Intel)'s picture

Hi again,

Further investigation was done on this subject. Our conclusion is that there are no issues with the MJPEG encoder as far as color correctness. We compared the results from encode by comparing output from reference decoder with original input.

I suspect that the reason for brightness difference is due interpretation by the YUV or JPEG display tools.

Regards,
Petter 

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