Just FYI, Core Image is normally dealt with n the Quartz list rather
than here, but not to worry.
On 22 May 2008, at 22:36, Jordan Woehr wrote:
Does this mean that it is not possible to write a bilateral filter
which does the computations on the GPU?
Filters of variable kernel size are tricky (to say the least).
Apple's blur filter seems to generate different GPU programs depending
on the radius parameter, but it does run on the GPU. It might also be
multi-pass. You can see that varying the radius of the blur is quite
low performance compared to changing the image it's blurring.
If your filter has a fixed kernel size (that isn't too big), then it
can normally be coded. The key problem is the the kernel language has
no conditional branching, so loops of variable length aren't allowed.
Fixed length
You may have more luck coding for OpenGL rather than CoreImage, and
using GLSL. Unfortunately Apple decided to remove the parts of GLSL
that the hardware of the time didn't support when they created the
CIKernel language. Now that hardware is more capable CI is stuck with
those limitations.
That said, getting a OpenGL solution running will probably need you to
be familiar with Pixel Buffer Objects (PBOs), Frame Buffer Objects
(FBOs) and devising some way of putting your 4D data into textures
(which you'd have to do for CoreImage anyway).
Another advantage of going the OpenGL route is that you've be able to
use 3D textures, rather than just 2D images that you'll be working
with in CoreImage. At least that's only one dimension off.
Is there source code available for
this filter and if so where is it? I have had no luck finding it so
far.
You won't find it, it's in a framework that isn't open-source.
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