G'MIC - GREYC's Magic for Image Computing: A Full-Featured Open-Source Framework for Image Processing
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A Full-Featured Open-Source Framework for Image Processing

Latest stable version: 3.6.3 (2025/10/13)

Reference
Table of Contents  ▸  List of Commands  ▸  Blending and Fading  ▸  sub_alpha◀  fade_z    |    animate  ▶

sub_alpha

Arguments:

  • [base_image],0<=_minimize_alpha<=1

Description:

Compute the 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.
The min_alpha argument is used to relax the alpha minimality constraint. When set to 1, alpha is constrained to be minimal. When set to 0, alpha is maximal (i.e. 255).

Default values:

minimize_alpha=1.

Example of use:

<a href="image.jpg" class="highslide" onclick="return hs.expand(this)">image.jpg</a> testimage2d {w},{h} +sub_alpha[0] [1] display_rgba

Command: <a href="image.jpg" class="highslide" onclick="return hs.expand(this)">image.jpg</a> testimage2d {w},{h} +sub_alpha[0] [1] display_rgba
Command: <a href="image.jpg" class="highslide" onclick="return hs.expand(this)">image.jpg</a> testimage2d {w},{h} +sub_alpha[0] [1] display_rgba
Command: <a href="image.jpg" class="highslide" onclick="return hs.expand(this)">image.jpg</a> testimage2d {w},{h} +sub_alpha[0] [1] display_rgba
G'MIC - GREYC's Magic for Image Computing: A Full-Featured Open-Source Framework for Image Processing

G'MIC is an open-source software distributed under the CeCILL free software licenses (LGPL-like and/or
GPL-compatible). Copyrights (C) Since July 2008, David Tschumperlé - GREYC UMR CNRS 6072, Image Team.