Re: What is the GraphicsMagick equivalent of ImageMagick's +opaque?

On Sat, 19 Jan 2019, [email protected] wrote:

> Extracting a specific color (red) from an indexed BMP in ImageMagick goes like this:
>
> $ convert input.bmp +opaque "#FF0000" red.png
>
> Trying it with GraphicsMagick fails as it appears to not support +opaque, only -opaque.

Depending on if it meets your needs, you can use the -channel option:

   gm convert input.bmp -channel Red red.png

It is also possible to use the -operator and -recolor options to deal 
with image channels.

This version assigns a zero value to the Green and Blue channels so 
you get a red channel which still looks red (rather than a grayscale 
image):

   gm convert input.bmp -operator Green Assign 0 -operator Blue Assign 0 red.png

Use of the -recolor command is left as an exercise but the 
documentation provides useful examples. :-)

> How does one do the equivalent with GraphicsMagick? Perhaps there is a cheatsheet for migrating from ImageMagick to GraphicsMagick?

The GraphicsMagick options documentation (also the manual page) is 
useful since it is pretty accurate and well maintained.

I am not sure of a cheat-sheet.

Bob
-- 
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
Public Key,     http://www.simplesystems.org/users/bfriesen/public-key.txt