Reference

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sub_alpha

Arguments:

Description:

Compute the minimal alpha-channel difference (opposite of alpha blending) between the selected images

and the specified base image.
The alpha difference A-B is defined as the image having minimal opacity, such that alpha_blend(B,A-B) = A.

Default values:

opacity_gain=1.

Example of use:

$ gmic image.jpg testimage2d {w},{h} +sub_alpha[0] [1] display_rgba
Command: image.jpg testimage2d {w},{h} +sub_alpha[0] [1] display_rgba
Command: image.jpg testimage2d {w},{h} +sub_alpha[0] [1] display_rgba
Command: image.jpg testimage2d {w},{h} +sub_alpha[0] [1] display_rgba