[osg-users] Image::readPixels and color matrix

[Robert Osfield]

HI Glenn,

ColorMatrix is only used in fragment program (a fixed function
pipeline at that) so doesn't affect glReadPixels, rather than
rendering itself.  ColorMatrix is supported on all hardware/drivers
either so it may well not even work on your hardware.  These days
using a fragment shader to do the conversion would be the better
approach.#

W.r.t reading to a 422 format... this conversion may well be done on
the CPU.  I don't think that this format is support into osg::Image
anyway though...

W.r.t setReadPixelsColorMatrix(), well consider this is not related
OpenGL state or function is inappropriate.

Robert.

On 7/20/07, Glenn Waldron <gwaldron at gmail.com> wrote:
> Robert et al.,
>
> I am using an FBO to render to a texture. I've attached an osg::Image so it
> will read back the image each frame via glReadPixels.
>
> I ultimately require the image to be in YUV422 format, not RGB. Now from
> what I've read, I can actually do the conversion on the card by first
> applying a color matrix (glColorMatrix) to convert RGB to YUV, then calling
> glReadPixels() with GL_422_EXT. This would be great since it would reduce
> the number of readback pixels by 50% (since YUV422 stores 2 pixels in each
> 32 bit word).
>
> SO, my question is: is there a way using OSG to apply that color matrix so
> that osg::Image::readPixels will use it? If not, would you entertain the
> idea of setting a "setReadPixelsColorMatrix()" or some such method to
> osg::Image?
>
> Thanks in advance. -gw
>
> --
> Glenn Waldron : Pelican Mapping : http://pelicanmapping.com : 703-652-4791
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