Re: V4L2 Output Format

[Dave Milici <davemilici@xxxxxxxxxxxxx>]

It sounds like the video buffer is not being rendered into or filled in.

A zeroed buffer in YUV format will appear green in RGB space, since U  
and V = 0 indicate no red or blue color difference values.

This wikipedia article describes the relationship between YUV and RGB  
graphically and algebraically.

http://en.wikipedia.org/wiki/YUV


On Aug 6, 2010, at 3:49 PM, Vikram Ivatury wrote:

> Hi Dave,
>
> Thanks for the quick reply. I will go ahead and use the YUYV packed  
> format. When I used the VYUY format, my output image was all green -  
> any reasons you think this might happen?
>
> I am assuming that nothing is bring written to the image (all 0's in  
> YUV format) and then when it is converted to RGB that 0 is converted  
> to a green color value in RGB?
>
> Thanks,
> Vikram
>
> On Fri, Aug 6, 2010 at 11:17 AM, Dave Milici  
> <davemilici@xxxxxxxxxxxxx> wrote:
>
> On Aug 5, 2010, at 3:46 PM, Vikram Ivatury wrote:
>
> > I am using the .pixfmt = ATMEL_ISI_PIXFMT_CrYCbY and I am wondering  
> > what my
> > .capture_v4l2_fmt should be. Right now I have my .capture_v4l2_fmt =
> > V4L2_PIX_FMT_VYUY but I think it should be V4L2_PIX_FMT_YUYV? Is  
> > there a
> > difference?
>
> The difference is in the physical ordering of the Y vs U and V data  
> as to which byte comes first (lowest in memory). Some graphics  
> devices are able to offer the YUV packed formats with either  
> ordering which is why this would be exposed. YUYV ordering is the  
> most commonly used packed format.
>
> > I am looking at Table 3-4 in the Atmel ISI datasheet and there is  
> > nothing
> > listed under the V4L format for my specific ISI input of CrYCbY. I  
> > do not
> > want a wrong .capture_v4l2_fmt to lead to a color corruption in the  
> > preview
> > path. I am using a YUV to RGB conversion in my capture.c program.
>
> It will be obvious if you chose the wrong pixel format order. The  
> colors will be all wrong and super-saturated intensity (like really  
> bright orange).
>
>
>
> --
> University of Michigan, Aerospace Engineering
> Multi-Disciplinary Design - Space Systems Engineering
> M-Cubed Payload Team Lead
> Student Space Systems Fabrication Laboratory

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