View Full Version : Making a usable PCX: Indexing and Setting Transparant Colors with GIMP

Feb 07, 2011, 06:12 AM
You can start off in RGB mode, make all your changes to the picture with all the special features you want to add.

Once you are finished with your picture, then you have to go to indexed mode to get it down to 256 colors and then you have to make the last two colors the tranparant colors.


You are using GIMP:

1) Pull down Image> Mode > Indexed
I'm using version 2.4.6, so if you have another version the pull downs and views may be a bit different.

2) Save as *******.pcx
This will generate a Color Map (palette) that is 256 colors (should be 0-255).

(After saving the pcx you may have to open it again if you see less than 256 colors (this is rare), this would only happen if the picture was mostly all the same color or if you previously saved it in GIMP format (*.xcf), opening the pcx again will guarantee a 256 color palette.)

Below is a picture of a sample color map showing the postion of the green and pink that are used in most pcx's for the 2 transparant colors.
I circled the pink in position 255, (color index=255) (value=ff00ff).
Note: On the newer versions of GIMP the Colourmap can be found: Windows> Dockable Dialogues>Colourmap

3) Copy the image first, to be pasted shortly (select all, copy, don't paste yet).

4) Click on the color map, the last 2 colors (254 and 255) are the transparant colors, usually green (00ff00) and pink (ff00ff) are used.

Note: If green and pink are already used elsewhere in the colour map, then make note of what the values are for position 254 and 255 and change those other positions to those noted values so you retain all the colors that were in the palette. (Basically you are swapping the colors between the positions)

Change the values of 254 and 255 to 00ff00 and ff00ff respectively.

Double click on the palette color (on the color map) you want to modify and this window will come up.

Pink = 255, 0, 255 = 00ff00

Use the slide bars to change the RGB settings for each color you want to change in the palette.

5) Paste the copied image, and all the colors should be there with the transparant colors in place.

6) Save as *******.pcx


Feb 08, 2011, 09:53 PM
Note: On the newer versions of GIMP the Colourmap can be found: Windows> Dockable Dialogues>Colourmap

Thank you! I've been using GIMP 2.4.7 for years now for the little PCX work that I do, simply because I know where the color map is in that version from Kyriakos's tutorial (, and my previous Googling attempts to find out where it was in GIMP 2.6 didn't help, so I eventually decided to just keep using 2.4.7 forever, even though 2.6 felt noticeably faster. I'd actually thought about spending the time to figure it out and PM-ing Kyriakos to see about updating the tutorial once I did, but it never seemed easier than sticking with the old version.

I'm curious why you're using the older version though. Does it coexist with the rest of your system better than 2.6?

Feb 09, 2011, 05:56 AM
Never had a problem with 2.4.6 and it is nice that the colourmap is always on the main GIMP window since I mostly use it for PCX's.

Jul 17, 2011, 03:39 PM

Jul 17, 2011, 04:05 PM

I don't think you read my process very well.

There is no magenta or neon green to take out before it is indexed.

I don't add those transparant colors until the very end and that would be just before I paste the saved picture.

Jul 17, 2011, 04:20 PM
There is no need to have more than one layer in this process.

I didn't want to confuse anybody, but what I usually do is start in RGB mode and then posterize down to 256 colors.

Then copy the image to be pasted at the end.

Then go to index mode and add the transparant colors, then paste the copied image.

Jul 17, 2011, 05:38 PM
I didn't mean to distress you, Zozo. I've re-read your tutorial, & still don't see where you remove the magneta before you index the file, which I think helps immensely. Still, this is your thread, & I have no business imposing my opinion of that on you. I've edited my post to remove the offending material. Sorry I intruded.