On Mon, Jun 2, 2008 at 2:31 AM, Brendan Simons <brendansimons@...>
wrote:
> Hi all,
>
> Sorry for the basic level of this question. I'm absolutely new to GL
> programming. I'm trying to implement a very simple demosaicing
> algorithm on the graphics card (in order to render data from a really
> highres bayerfiltered ccd sensor to the screen in real time). I
> need to be able to do the following:
>
> 1) given a "raw" image, copy the data (a matrix of unsigned bytes) to
> video memory three times.
>
> 2) multiply each copy elementwise by a precomputed "mask" of 1s and
> 0s, so that the first copy records only the red values (all others
> become 0), the second green, and the last blue.
>
> 3) Interpolate the missing colour info. This step is different for
> green, and for red/blue, but it goes something like this: Copy a
> crop of the green matrix exactly one row and one column narrower on
> all sides. Now add (again elementwise) to that copy another crop of
> the green matrix, but this time shifted up one row. And again shifted
> down one row. And again shifted left on column. And one more shifted
> right one column. Divide the total (elementwise) by 4.
>
> 4) Copy the interpolated red, green and blue matrices to an opengl
> texture. Map the texture to a 2d square, and render the square to the
> screen (resizing / rotating / flipping as desired).
>
> I can figure out steps 1 and 4. Ideally steps 2 and 3 would be done
> in video memory, using opengl functions, but I can't find anything
> that would do elementwise multiplication, addition or cropping of
> matrices in the opengl stack. Can anyone point me in the right
> direction?
>
> Thanks,
> Brendan
> 
> Brendan Simons
>
>
If your going to be doing manipulations like that on the GPU I think you
will have to use shaders for that kind of customized computation.
Other than that you will have to do it on the CPU with arrays before sending
it to GPU...which is slower.
To send it three times you will need to make 3 different textures or send it
with glDrawPixels. You could also use FBOs to hold it in graphics memory
instead if you want.
For step 2 the Redbook will be able to help, there are colorMasks and
bitfields for excluding texture information which may be of help.
>
> 
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