Change one colour to another?

Question

In GIMP, I have a green button GIF image: it shades from dark green to light green, against a transparent background. I would like to change it to blue, and keep the shading, so it shades from dark blue to light blue.

How can I do this?

Answer 1

If you load a GIF image, you likely have a paletted image. Make sure to change it to RGB first with: Image → Mode → RGB. Changing colors (including resize operations) won't work very well with palettes because Gimp limits its selection of colors to the colors defined in the palette.

I suggest rotating Hue in Colors → Hue-Saturation.

Given an initial image like this:

You change Hue first by clicking on Master and then dragging the Hue slider and then adjust Brightness and Constrast to your liking.

The result looks like this:

You can easily make it colder or warmer, darker or lighter, more or less saturated.

Answer 2

If you are using GIMP 2.8.2, you can simple use Colors -> Map -> Color Exchange.

Source: How can I swap colors with GIMP?

Answer 3

You're looking for menu Colors, and especially the function Colorize.

Answer 4

To change a color to another specific color to I suggest to use Colorify.

Suppose we want to change the blue color (#05adee) of the superuser logo into a green color near to #05ad27.

1. Colors → Color to Alpha: choose the secondary color which will be made transparent (white in our example)

2. Colors → Colorify → Custom color: choose the destination color and add about 10-40 to the Value (of the HSV)

3. Set the secondary color as background color (white in our example)
4. Image → Flatten Image

Using GIMP 2.8.6.

Answer 5

The first successful method I found to do the same sort of thing was to use ImageMagick, but with a different operator than the earlier-suggested --separate/-swap.

The different operator is either -recolor or -color-matrix, depending on ImageMagick version.

Specifically, because I knew a "master color" of the original image (green, in your case and mine) and I knew the "master color" in the desired result image (blue, in your case, orange in mine), I gave ImageMagick' -recolor/-color-matrix option a transformation matrix with values that reflected the differences in each of the RGB channels.

For example, in my case, the fully green color was R:141 G:198 B:63 and I wanted it changed to R:231 G:159 B:70. The rest of the colors wanted to be changed equivalently.

So that means I wanted new pixels' R value to be 231/141ths of the current red value. Green values to be 159/198th of the current values. And blue values to be 63/70ths of the current values.

So:

convert input.png -recolor      "1.638297872 0 0    0 0.803030303 0   0 0 1.111111111" output.png

or

convert input.png -color-matrix "1.638297872 0 0    0 0.803030303 0   0 0 1.111111111" output.png

or

This seemed to work in a flash after fruitlessly spending a lot of time wrestling with Gimp/plugins and paint.net/plugins.

Answer 6

1. Change your foreground color to your desired color. (for example blue in your case)
2. Change Background to white or something
3. Open gradient tool and set FG to BG or FG to transparent.
4. Select area or Color using 'Select by Color'
5. Colors -> Map -> Gradient Map

Answer 7

If you update the HUE with an existing image color the hue will be initiated with those levels... Need first to make a white #fff background. I did

Colors -> Colorize and set the HUE lightness to 100... this will remove any color from your image.

Then You can use Colors -> Colorify and apply the color You want.

Answer 8

I don't know how to do it in GIMP, but ImageMagick has functions to separate and combine color channels. See this page.

I was able to convert a green GIF file to blue with this command:

convert input.gif -separate -swap 1,2 -combine output.gif

I guess that 1 and 2 refer to green and blue channels, 0 is red.

Answer 9

On simple small graphics, I zoom in a lot and then change the colors myself using the brush.

Just change the brush size to 1 pixel.