This procedure fills the steganographic subchannel of the colormap with random noise thus overwriting any potential visual information in the subchannel.
The steganographic subchannel of the colormap is overwritten.
Here is the example image (horses.jpg, JPG, 2400x1600):
> (define image (colormap-readjpg "horses.jpg")) image > (subchannel-noise! image) ok > (define subchannel (subchannel-get image)) subchannel > subchannel #<bitmap orow:-1 ocol:-1 xres:-1 yres:-1 w:2400 h:1600> > (bitmap-writepng subchannel "horses-subchannel3.png") ok >
The subchannel as written to the PNG file horses-subchannel3.png displays as follows (now containing just random noise):