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Posted by brainflakes.org on 04/30/07 09:39
> I doubt that's the optimal solution. Function calls are relatively
> expensive in PHP. The difference in speed you observed between the
> different methods can probably be attributed to the number of calls
> made per element.
>
> Explain exactly what you're trying to do. There probably is a better
> approach.
I'm creating some custom image processing filters on 8bit greyscale
images
for($x=0; $x<$width; $x++){
for($y=0; $x<$height; $y++){
check value of pixels (0-255) in a 10x10 area around given pixel
calculate new value
plot value at x,y (0-255)
}
}
I figured the best way to do it would be to just "allocate" a memory
space of $width * $height bytes and copy the image into that, which I
guess is done by creating a string of that length. However even just
plotting to $string[$n++]=chr($val) (no co-ord calculations) is slower
then imagesetpixel() on an 8-bit image.
For some reason tho I can't actually render directly from the 8-bit
image (I use imagesetcolor() to set colours in a greyscale gradient
but imagepng complains there's the wrong number of colours) so I have
to copy the image in and out of a truecolour image anyway.
I have done some further optimisations on the actual processing code
and improved the speed about 10-fold, but if there's a faster way to
read/write 8bit data I'm still interested as every little helps when
you're doing batch processing. (tho I guess I should probably be doing
it in C or .net anyway ;)
Andrew
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