122

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?

Improve this question
0

10 Answers 10

Reset to default
91

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:

green gradient

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

Adjust Hue in Colors -> Hue-Saturation

The result looks like this:

blue gradient

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

Improve this answer
2
  • 3
    Good answer. As an added note, if your button contains a border this will change it's color as well. To avoid this use the selection tool to only select the area you would like to recolor, then run Hue-Saturation.
    – Lee Harrison
    Feb 5, 2014 at 16:15
  • 3
    What if I want to change the image to a given RGB value?
    – Aaron Franke
    Dec 20, 2018 at 20:25
85

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

Source: How can I swap colors with GIMP?

Improve this answer
6
  • 2
    This also only seems capable of operating on a clicked region of contiguous pixes, not on all of the selected pixels. Like I commented above, this colorizes the pixel I invoke it on. The Select by Color has selected hundreds of pixels all over the image.
    – ProfK
    Mar 23, 2013 at 10:39
  • 3
    @ProfKaos It works fine for me. In case I have nothing selected, Color Exchange changes all the pixels in whole image.
    – MasterPJ
    Apr 17, 2013 at 10:40
  • 3
    I'm looking for a mathematical transformation. I'm converting #650000 to #590000, so I feel like I should be able to apply -060000 to every pixel, but I don't see any easy way...
    – isaaclw
    Jul 2, 2015 at 4:19
  • You can also use "Colors -> Map -> Gradient Map" to change gradients. Very useful
    – Javier Constanzo
    Jun 15, 2016 at 17:34
  • 2
    That's the answer. By adjusting the threshold, one can also handle the tones of the color (for example in case of anti-aliased character boundaries)
    – Csaba Toth
    Feb 3, 2017 at 22:23
26

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

Improve this answer
2
  • 3
    That only colorizes the pixel I invoke it on. The Select by Color has selected hundreds of pixels all over the image.
    – ProfK
    Mar 23, 2013 at 10:37
  • 1
    Does that keep the shading, resulting shades from dark blue to light blue?
    – Peter Mortensen
    Feb 19, 2014 at 10:34
9

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)

enter image description here

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

enter image description here

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

Using GIMP 2.8.6.

Improve this answer
3
  • 1
    Does that work with a shading, shades from dark blue to light blue?
    – Peter Mortensen
    Feb 19, 2014 at 10:25
  • 1
    Yes. If you zoom in the two samples I posted you will see the shades are properly changed.
    – Marco Lackovic
    Feb 19, 2014 at 11:16
  • This makes my image much darker than it should be. Is there a way that I can replace one color gradient with another color gradient?
    – Aaron Franke
    Dec 20, 2018 at 20:27
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.

Improve this answer
4
  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
Improve this answer
2

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.

Improve this answer
0
2

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.

Improve this answer
0

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.

Improve this answer
2
  • 5
    -1 That's not practical if there is a gradient, you'd have to change dozens of different colors.
    – sleske
    Mar 30, 2012 at 9:38
  • 1
    The two Gimp solutions given so far above aren't much better, so it looks like I'm stuck with it.
    – ProfK
    Mar 23, 2013 at 10:40
-3

Colors -> Components -> Channel Mixer

Improve this answer
1
  • 2
    There are already several good answers to this question. If you think something is missing, please write an answer at least matching quality of existing answers.
    – Máté Juhász
    Aug 28, 2020 at 16:35

You must log in to answer this question.