If we take the help of the corresponding command image
:
$ gmic h image
image (+):
[sprite],_x[%|~],_y[%|~],_z[%|~],_c[%|~],_opacity,_[opacity_mask],_max_opacity_mask
Draw specified sprite on selected images.
(equivalent to shortcut command 'j').
If one of the x,y,z or c argument ends with a '~', its value is expected to be
a centering ratio (in [0,1]) rather than a position.
Usual centering ratio are { 0:left-justified | 0.5:centered | 1:right-justified }.
Default values: 'x=y=z=c=0', 'opacity=1', 'opacity_mask=(undefined)' and 'max_opacity_mask=1'.
I would rather change them to opacity_mask
and max_opacity_mask
.