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Select an image layer from an image cube at layer layer_number or specify from the top, bottom or middle layer of the cube.
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An image is generated by combing RGB from three images. R from first, G from second and B from third.
alpha value r g b [delta number]
Set transparency to images. r, g and b are integers range 1-255, representing intensity of red, green and blue of the color(s) that are to be transparent. E.g. ima alpha value 255 255 255 will set 100% white to be transparent. The delta number argument is for setting transparency to fit a range of rgb colors at a distance (D) away from the given rgb values. If number is set to 10, then
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