On 28 Nov 2007, at 21:24, Chipp Walters wrote:

Or, you could probably do it really fast with an optimized imagedata
script where you average the values of each pixel and reapply. I would
think that would zip right along.

I managed to find a function from March last year from a discussion about making alphadata from images. Originally written by Wilhelm Sanke, with a few tweaks by me to make it universal for any image size.

Pass it the long ID of an image and it will return a one-channel image suitable for a mask.

On 13 Mar 2006, at 20:51, Ian Wood wrote:
function makeMask tMaskImg
  set the cursor to watch
  put width of tMaskImg into tW
  put height of tMaskImg into tH
  put the milliseconds into Start
  put the imageData of tMaskImg into iData
  put empty into tmaskdata
  put tW * 4 into re
  repeat with i = 0 to (tH - 1)
    repeat with j = 0 to (tW - 1)
      put  chartonum(char (i*re + (j*4+2)) of idata) into tC1
      put chartonum(char (i*re + (j*4+3)) of idata) into tC2
      put  chartonum(char (i*re + (j*4+4)) of idata) into tC3
      put the round of ((tc1 + tc2 + tc3)/3) into tM
      put numToChar(tM) after tMaskData
    end repeat
  end repeat
  return tMaskData
end makeMask

Add another tweak to put it back into RGB:

function makeMask tMaskImg
  set the cursor to watch
  put width of tMaskImg into tW
  put height of tMaskImg into tH
  put the milliseconds into Start
  put the imageData of tMaskImg into iData
  put empty into tmaskdata
  put tW * 4 into re
  repeat with i = 0 to (tH - 1)
    repeat with j = 0 to (tW - 1)
      put  chartonum(char (i*re + (j*4+2)) of idata) into tC1
      put chartonum(char (i*re + (j*4+3)) of idata) into tC2
      put  chartonum(char (i*re + (j*4+4)) of idata) into tC3
      put the round of ((tc1 + tc2 + tc3)/3) into tM
      put numToChar(tM) into tPix
      put tPix & tPix & tPix & tPix after tMaskData
    end repeat
  end repeat
  return tMaskData
end makeMask

And you can do something like:

put makeMask(long id of img 1) into tData
set the imagedata of img 1 to tData

to turn the specified image into greyscale. Takes about a second for a 640x480px image on a MBP 2GHz Core Duo, so not too speedy.

Ian
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