I am using ImageMagick-6.8.8-Q16 on a Windows 8 PC. I'm trying to use it to overlay one image, "overlay.jpg", on top of a "background.jpg". Both JPGs are the same size. I tried the following 3 commands, with these results:
convert background.jpg overlay.jpg -compose darken -composite bg-ov-darken.jpg
convert background.jpg overlay.jpg -compose multiply -composite bg-ov-multiply.jpg
convert background.jpg overlay.jpg -compose add -composite bg-ov-add.jpg
The first two options, "darken" and "multiply", give me the expected result. However, "add" gives me a bright blue in just one section of the image's overlap (the outputs are, top-bot, "darken", "multiply", and "add").
This is not what I was expecting... is it right? Or is this a bug? I have attached the two input JPGs.