Bill, this is phenomenal. I added the progress bar BECAUSE it was
taking so long.
Your code is much faster. I tried adding the revision below to you
stack, but I keep botching something and it is recognizing 0 changes.
Once you are happy with it, I think it would be great to see it in
Revolution Online. Until then, could you post your final?
Thanks
Bert
On Jun 29, 2009, at 2:30 PM, Bill Marriott wrote:
Bernd,
Thanks for the pointer... I believe I've corrected the error. Here's
the key
part of the loop with friendly variable names and comments:
-- starting with the whole image, check a range of pixels for
differences
-- keep slicing the range in half until we find a block of
unchanged
pixels
repeat while char currPixel+1 to currPixel+rangeToCheck of
ImageA <> \
char currPixel+1 to currPixel+rangeToCheck of ImageB
-- aha, the range we're testing has changes
if rangeToCheck >= 8 then
-- eight bytes is at least two pixels... it's still too
big;
slice it in half
put rangeToCheck div 4 div 2 * 4 into rangeToCheck
else
-- we're down to a single changed pixel now
-- record which pixel has changed (offset within the
imageData)
put 1 into bytesChanged[currPixel+1]
-- move to the next pixel; assume that changed pixels are
near
each other
add 4 to currPixel
end if
end repeat
-- we found one or more unchanged pixels; skip this section of
data
add rangeToCheck to currPixel
-- and update the range to encompass the remainder of the image
put dataLength - currPixel into rangeToCheck
end repeat
My routine will be optimal the fewer changes there are in the image,
and the
less distributed (more localized) those changes are. It took about
680 ms on
my 2.66 GHz Core i7 Vista system, so I took the progress bar out. :)
Can
anyone improve on it?
"BNig" <[email protected]> wrote in message
news:[email protected]...
I like the ideas to speed up the analysis of differences among 2
images.
My
impression is that your approach with div 2 is leading to erroneous
resutls
because by dividing by 2 you break the 4 byte blocks of imagedata.
150 div
2
= 75, 75 div 2 = 37, 37 div 2 = 18. You get the idea. You eventually
compare
blocks of 4 that belong to 2 pixels. That can be alright but not in
all
[...]
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