Re: How preserve existing alpha with -separate?

>My input is a 32bpp TGA saved from Photoshop CS3, and I need IM to
>invert the blue channel, then swap the blue and green channels, then
>output a 32bpp TGA again.
>
>It all works fine, except I can't get IM to preserve the pre-existing
>alpha channel data, instead it fills the alpha channel with white.
>
>convert in.tga -type TrueColorMatte -channel blue -negate +channel
>-separate -channel all -swap 1,2 -combine out.tga


try

convert in.tga -channel rgba -alpha on -separate \
\( -clone 2 -negate \) -swap 2,4 -delete 4 -swap 1,2 -combine out.tga


(seemed to work for me on the logo image where white was made 
transparent and saved to png)