[FFmpeg-user] rgb8

[Roger Pack]

Can other apps use this dshow device?  If you plunk it into
graphstudionext does it work, what media format do you see on the
wires?
I guess the only question is "is it actually palletized"?
Based on the source it seems like we weren't sure...

On Sun, Jun 11, 2023 at 12:43 AM Michael Koch
<astroelectronic at t-online.de> wrote:
>
> Am 10.06.2023 um 11:48 schrieb Nicolas George:
> > Michael Koch (12023-06-10):
> >> Might it be possible that RGB8 in DirectShow is not the same as rgb8 in
> >> FFmpeg?
> > Duh.
> >
>
> There is a problem with a ASI178MM (monochrome) camera and its
> DirectShow driver. When I check the options with this command
>
> ffmpeg -list_options 1 -f dshow -i video="ASI178MM Camera (ZWO Design)"
>
> I get this output:
>
> [dshow @ 00000203f5b315c0]   pixel_format=rgb8  min s=3096x2080
> fps=1.0842e-12 max s=3096x2080 fps=30
> [dshow @ 00000203f5b315c0]   pixel_format=rgb8  min s=1280x960
> fps=1.0842e-12 max s=1280x960 fps=30
> [dshow @ 00000203f5b315c0]   pixel_format=rgb8  min s=1280x800
> fps=1.0842e-12 max s=1280x800 fps=30
> ...  (there are more sizes listed, all with the same pixel format rgb8)
>
> When FFmpeg gets a frame, it thinks the pixel format is rgb8 (as defined
> in FFmpeg: 2 bits red, 3 bits green, 3 bits blue). Of course that's
> wrong, because it's a monochrome camera and the data is 8-bit gray.
>
> My first idea was that it must be a bug in the DirectShow driver. The
> data is obviously correct 8-bit gray, but it's incorrectly labeled as
> "rgb8" instead of "gray".
>
> However when you look at the specifications of DirectShow
>
> https://learn.microsoft.com/en-us/windows/win32/directshow/uncompressed-rgb-video-subtypes
>
> you see that there exists no "gray" pixel format, and "RGB8" is a
> different pixel format described as "RGB, 8 bpp, palettized". It seems
> an uncompressed 8-bit gray frame must be encoded with "RGB8" pixel
> format, together with a palette which contains 256 levels of gray. With
> other words: It might be correct that the DirectShow driver reports
> "rgb8" pixel format.
>
> That's why I think that perhaps the issue is not in the DirectShow
> driver, but in FFmpeg.
>
> Michael
>
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