Incorrect result of image subtraction

Question

I wanted to subtract two images pixel by pixel to check how much they are similar. Images have the same size one is little darker and beside brightness they don\'t differ. B

Answer 1

You did not "subtract one pixel from the other" correctly. getRGB returns "an integer pixel in the default RGB color model (TYPE_INT_ARGB)". What you are seeing is an "overflow" from one byte into the next, and thus from one color into the next.

Suppose you have colors 804020 - 404120 -- this is 3FFF00; the difference in the G component, 1 gets output as FF.

The correct procedure is to split the return value from getRGB into separate red, green, and blue, subtract each one, make sure they fit into unsigned bytes again (I guess your Math.abs is okay) and then write out a reconstructed new RGB value.