claude bouaziz-viallet (claude.bouaziz-viallet@betula-electronique.com) wrote:

I am a beginner with Gimp (and mailing-lists in fact !).

I am trying to modify a RGB picture and obtain the following :

- black becomes #993300, - all the other colors take a shade lighter till... - white is changed to something approaching #efdfd7 !

I am fairly certain that you are working on an image with an indexed color palette. Change the mode of the image to RGB to avoid effects like this.

Bye,
Simon

claude bouaziz-viallet (claude.bouaziz-viallet@betula-electronique.com) wrote:

I must beg you pardon for misleading you with my English syntax ! in fact I WANT to obtain the following changes :

- black becomes #993300,
- all the other colors take a shade lighter till... - white is changed to something approaching #efdfd7 !

Oh, sorry for jumping on the perceived FAQ... :-)

For what you *really* want to do you can use the curves tool (Layers->Colors->Curves). When the curves dialog pops up you can select the three RGB-Channels individually. Then in each channel you can drag the control points to get the desired color. In your example this would be:

Red channel: Control points at 0, 153 (=#99) and 255, 239 (=#ef). Green channel: 0, 51 and 255, 223 Blue channel: 0, 0 and 255, 215

This modifies each channel independantly and might result in some unexpected colors, you need to look if this is what you expect.

As an alternative you can select #993300 and #efdfd7 as foreground/background colors and select Filters->Colors->Map->Gradient Map. Select the "FG->BG" Gradient and apply the filter. This however maps the colors of the gradient to the image according to the gray value of the pixels, so this is perfect for grayscale images, but might lose wanted information for color images.

Hope this helps.

Bye, Simon

On Sun, Jan 23, 2005 at 07:54:36PM +0100, claude bouaziz-viallet wrote:

Thank you for your VERY quick answer Simon. I am impressed !

I must beg you pardon for misleading you with my English syntax ! in fact I WANT to obtain the following changes :

- black becomes #993300,
- all the other colors take a shade lighter till... - white is changed to something approaching #efdfd7 !

i would approach this in a different order. and you should note that my ability to work with color is self taught (mostly) and there is only that which i have needed to fill my needs. which means that others might have better suggestions/methods to obtain this effect that you want.

you can easily lighten all of the colors by using the Levels Tool and moving the center triangle located just below the histogram display.

changing black and white to other values -- there are several different ways this can be accomplished, i am going to suggest only two ways and i am not sure that either will work for you.

Filters -->Colors -->Color To Alpha. with the lightened image, run this filter on black and put the new color in a layer underneath.

or Index the image via Image -->Mode -->Index and change the black to the new color via the Dialogs -->Indexed Palette dialog. then change the image back to rgb Image -->Mode -->RGB

both should work the same with the white as well.

these are just two ways. there are several color tools and filters that might do what you want better. best to play with them yourself and keep an eye out for better suggestions from this list.

the more i understand colors, the more i understand how little i know about them.

carol