[FFmpeg-devel] YUV image conversion

[jelliott at rohan.sdsu.edu]

How can the user specify the format they want the image read into?  Can
you just specify PIX_FMT_GRAY in the command line?

> Hi,
>
> On Thu, Mar 3, 2011 at 7:52 PM,  <jelliott at rohan.sdsu.edu> wrote:
>> My problem is that when the U and V components are zero'd out, I obtain
>> a
>> green image when I am expecting a black and white image. ?On the other
>> end
>> of the spectrum, when I set the U and V components to 255, I obtain a
>> dark
>> magenta image. ?A black and white image can only be obtained if the U
>> and
>> V components are set to their midrange values of 217. ?I have attached
>> copies of sample images to illustrate this.
>>
>> I have found out, through emailing one of the authors of ffmpeg, that
>> the
>> U and V components have an offset of 128 in order to represent negative
>> values. ?I need to find out where in ffmpeg this offset is taking place.
>> I only want to stream the Y data without having to transmit values for
>> the
>> U and V data. ?I want to be able to set those values to 0 initially and
>> only transmit the Y data. ?If someone could point me in the right
>> direction as to how to do this or just point me to where the UV offset
>> is
>> coded, I would greatly appreciate it.
>
> Your solution is likely to transmit Y-data only and read it as
> PIX_FMT_GRAY (which is basically Y-only, like Y800) to
> PIX_FMT_YUV420P, that will do approximately the right thing.
>
> Ronald
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>