Image color remapping in C#

Question

I have 22 colors which I want to use to draw any image with just these 22 colors.

Image image = GetImageFromURL(""); // returns an image object
Bitmap bitmap = new Bitmap(image);

String[] colors = {
    "#FFFFFF", // white
    "#C1C1C1", // light grey
    "#EF130B", // red
    "#FF7100", // orange
    "#FFE400", // yellow
    "#00CC00", // light green
    "#00B2FF", // cyan
    "#231FD3", // blue
    "#A300BA", // purple
    "#D37CAA", // pink
    "#A0522D", // light brown
    "#000000", // black
    "#4C4C4C", // dark grey
    "#740B07", // dark red
    "#C23800", // dark orange
    "#E8A200", // dark yellow
    "#005510", // dark green
    "#00569E", // dark cyan
    "#0E0865", // dark blue
    "#550069", // dark purple
    "#A75574", // dark pink
    "#63300D", // dark brown
};

How would I do this best? I currently have no idea how to translate billions of colors to just these 22 colors...

I would appreciate any help, thanks in advance.

Try finding closes match in your pallet with the color you want to convert to? Maybe calculate score based on all three different RGB. — Karolis Kajenas, Feb 24 '18 at 22:25
About what @Karolis said, you can use vector math to find the distance from the pixel color to the palette colors and use the nearest one. — Gusman, Feb 24 '18 at 22:31
One approach is to convert the image into 8-bits image using some image processing library or a third party tool https://nl.mathworks.com/help/matlab/ref/rgb2ind.html that would limit the number of available colors to 256. Then find the closest match. — Anton Sizikov, Feb 24 '18 at 22:32
https://stackoverflow.com/questions/21856184/the-best-way-to-reduce-quantity-of-colors-in-bitmap-palette — Anton Sizikov, Feb 24 '18 at 22:34
@AntonSizikov That one is about choosing a palette. This case already _has_ a palette. — Nyerguds, Mar 01 '18 at 22:29
Why are your colours _strings_, though? [Convert them](https://stackoverflow.com/a/2109938/395685) to an array of `Color` objects. — Nyerguds, Mar 01 '18 at 22:40
You should add more details. How is the application going to interact with the user? — alansiqueira27, Mar 01 '18 at 22:55
We already have this question: https://stackoverflow.com/questions/34557480/quantization-reduction-of-colors-of-image — Hans Passant, Mar 01 '18 at 23:32
@HansPassant quantization is _creating_ a palette. That isn't applicable here; the palette is already available. (Also, that particular question uses `GetPixel` and `SetPixel`, and so does the answer. Ew.) — Nyerguds, Mar 01 '18 at 23:48

score 0 · Answer 1 · answered Mar 01 '18 at 22:37

The closest colour match for each pixel can be found using Pythagorean distance in 3D colour space. I explained the full process here, including how to apply this change to an image in an efficient way:

How to convert a colored image to a image that has only two predefined colors?

This question was about a 2-colour palette, but as long as an 8-bit-per-pixel image is used as result, the process is exactly the same for any palette.

Image color remapping in C#

1 Answers1