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I'm looking for terms, search keywords, or filter names related to how to do the following:

Let's say you have a photo of a meadow. You also have separate color palette (ex: https://coolors.co/fe5d26-f2c078-faedca-c1dbb3-7ebc89 ) and what you are looking to do is to slightly modify the photo so that it fits the color palette more. In other words, you want all the greens to lean more towards the green in your color palette (in hue, saturation, etc), all the oranges lean towards the orange in your palette, etc.

What is that called? Is there a mechanism in Gimp, for example, that does something like this? I've been trying to google it but to google something you need to know the keywords/terms for this type of thing.

I've tried Map > Color Exchange in Gimp but the RGB thresholds confuse me. Whatever I put in for the threshold, it either doesn't change anything in the image or changes areas it's not supposed to. Is there a plugin in Gimp or a website or whatever that does something like this (semi-)automatically, given an image and a color palette?

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    This question is somewhat related. But it's a bit glitchy. Not sure I understand exactly what you are after here. You could also look into something like Indexed Color which reduces the pixel colors in an image to a limited palette. More of a low res, pixel art look.
    – Wolff
    Jul 4 '21 at 1:06
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What's it called? Colour matching, colour mapping, etc.

Anyway. Here's one fairly simple method. This is a subtle technique, which doesn't completely destroy an image. It will still look like a photograph, just with the colours tweaked.

  1. Take an image of your colour palette (a screenshot), open it in GIMP and do Image > Mode > Indexed Color. Set the number of colours to 5. Open the Palettes dockable dialog. You should be able to find the indexed colour palette for the current document. Take a note of its name. Leave this document open.

enter image description here

  1. Do File > Open, and open an image you want to recolour

  2. Change the image mode to to Indexed colour as before, but this time choose a custom palette, click on the palette icon and select the palette you made previously, choose dithering: Floyd-Steinberg (reduced color bleeding). This will create a somewhat extreme recoloured image, but don't worry, the next steps will fix it.

  3. Select all (Ctrl+A), and copy (Ctrl+C) that recoloured image. Then undo the changes (Ctrl+Z) so you are back to the original photograph

  4. Do Edit > Paste as > New Layer, then set the layer blending mode to "LCh Color"

Here's an example toggling the original image layer, and LCh Color layer

enter image description here

enter image description here

Note: If there are areas of colour you didn't want to change, such as the blue sky, you could use a layer mask on the LCh colour layer to apply the colour change selectively. If the overall effect is too strong, you could also reduce the opacity of the LCh colour layer.

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