Channels
Quoting Victor Domingos :
Is there a preference in GIMP, to make a channel appear as a
grayscale layer, instead of a red, green, or blue layer? Is
decomposing the image the only way to do this? I would laike to
compare two channels more easily, and the R/G/B color cast doesn't
seem to help...
There is not really such an option built-in to the GIMP. If your main
concern is just comparing the channels then you could create a layer
from them rather easily by dragging the component (R,G, or B) from its
position at top of the Channels dialog to the bottom, then dragging
the resulting new channel over to your image window. You can drag a
component directly to your image window, but realize that the
components displayed in the Channels dialog will then be based on new
layer; so in order to do this for the next channel, you would need to
hide the layer.
You might find a script I wrote a while back to be useful
(http://flashingtwelve.brickfilms.com/GIMP/Scripts/decompose.scm). It
decomposes a layer to its constituent components and uses those as
layermasks to red-, green-, and blue-filled layers. It doesn't handle
the alpha channel in the original layer (doing so would introduce some
inherent difficulties that are worse than having the limitation).
Once you have decomposed your layer using the script, you can edit the
layermasks of the respective channels -- viewing either the resulting
projection or using "Show layermask" to view the grayscale version of
the respective channel (I would recommend assigning a quickkey to the
Show Layermask function, as it is handy to switch between the two
views). To restore the original layer, just make only the four layers
(R, G, B, and black) visible, assure that none of them are showing its
layermask, and do a Merge Visible.
