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MJPEG colour space issues

This is a long standing bug but now that there are colour space options to change, it is easily noted:

If you use BT.601 or BT.701 with some cameras, the black levels get clipped when below a certain level. The previous bug for this was WIRE-15741 but it is now clearly visible as to what is going on.

Older videos of the problem:
https://www.youtube.com/watch?v=SkWWIZhAUNE
https://www.youtube.com/watch?v=3YMovagvio8
https://youtu.be/1ULRSXbA0K0
https://www.youtube.com/watch?v=ka3WrNQ71x8
https://www.youtube.com/watch?v=Glr6K3LsSMI
 

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    • PaulMEngineering
    • Software Engineer, Telestream
    • PaulM
    • 2 yrs ago
    • Reported - view

    Matthew Potter

     

    Thank you for verifying the fix but you still seem to think it is a bug. I will try to explain.

    In previous versions (on Windows), Wirecast would only offer 601 or 709 transfer matrices for JPEG sources.  JPEG uses its own transfer matrix (and dynamic range) for YCbCr data.  You now have the option to use that transfer matrix in order to get the correct colors.  In fact, that is now the default option for JPEG sources.  Choosing 709 for a 601 source will make the colors bad. Choosing 601 for a 709 source will make the colors bad. Likewise, choosing 601 or 709 for a JPEG source will make the colors bad.

    The the Colorspace option allows you to override Wirecast's default choice of transfer matrix for any YCbCr source that does not indicate which one should be used (which is case for almost all DirectShow video sources).  The defaults are 601 for any source less than 720 lines tall, 709 for any source 720 lines or taller, and (as of 13.1) JPEG for any Motion JPEG source.

    When the Colorspace option is disabled, it's because we're able to programmatically determine which transfer matrix to use.  The option changes to Dynamic Range when the source is RGB because, obviously, there's no need for a transfer matrix.

    With all that said, I would guess that now users should not need to touch either Colorspace or Dynamic Range most of the time.

    Thank you for your previous bug reports with regard to color rendering of Motion JPEG sources.  It did call our attention to the problem.  With the new JPEG decoder, we both improved our color rendering and improved performance/efficiency which is particularly evident with 4K UVC sources.

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    • Matthew Potter
    • Creative Technologist & Problem
    • Matthew_Potter
    • 2 yrs ago
    • Reported - view

    PaulM Thank you for the explanation. Clearly the later version (now with the ability to update and change the colour space) are better. It Is worth noting that the previous bugs reported for this issue were to due with the improper selection and had been an issue. The fact that it can be changed now is an improvement though.

    Hopefully this post (and video) can help somebody resolve a concern if it happens to them as it had me at one point during a live production.

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  • 2 yrs agoLast active
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