IM on OS X: Use mask to split an image

[antonv]

I would like to take an image, apply a checkerboard pattern to it so that the result is two images one having the even squares of the original image + transparency and the other having the odd squares of the original image + transparency.

[snibgo]

Make the chequerboard in black and white. Then ...

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convert infile ( chequerboard -negate ) -compose CopyOpacity -composite outfile

... will make one output file. For the other, leave off "-negate".

[antonv]

Thank you!

For posterity... this is how you can make a checkerboard:

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convert -size 640x480 pattern:checkerboard -auto-level +level 0,100% checkerboard.gif

[fmw42]

convert -size 640x480 pattern:checkerboard -auto-level +level 0,100% checkerboard.gif

There should be no need for +level 0,100%, which is a no-op (does nothing) in this case. It would only be needed if you want to change the checkerboard to something of less contrast if you use values other than 0 and 100%