I know it's useful on audio, but, just out of interest, what are the
practical uses of doing an FFT on image data?
a|x
On 18 Sep 2009, at 09:41, Chris Wood wrote:
Good idea! The "butterflies" done by GLSLang, the stages by
JavaScript.
Maybe it's possible to do the reordering (bit-reversed addressing)
in a
filter, too.
The catch here is that you're stuck with core image if you want the
nice javascript features - it's similar to GLSL but lacking a lot of
the more advanced stuff that might be necessary. If not, it could work
out.
They also seem to need two output channels for each input, which
could be
more of an issue.
Uhm? Maybe you mean the real/imaginary parts? (Though, the input
has them,
too.)
Should be easy: we could abuse the color channels, since the
transform will
always be done separately for individual color components.
Yeah, the real/imaginary parts. The problem is that you do the
transform on each colour channel separately, so for rgb you need 6
channels (12 for the two buffers), which likely means 4 buffers in
practice.
Possible solution: convert the image from rgb to hsv - the V channel
contains most of the interesting data, so we can just process that and
save a lot of messing about with extra buffers plus 2/3 of the
processing (1 channel instead of 3).
And why not then abuse the color channels (we have 4!) for the
swap buffers,
too?
Yep. If we're going down the HSV route and just processing V, we can
use the R + G channels for the real + imaginary values. That leaves
two channels to spare so perhaps the H and S channels could sit there
if it won't harm performance.
Good ideas here, keep them coming :)
Chris
Jens
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