Replace (swap) colour in Bitmap

Jay S

I have googled loads, and all I can find is changing the whole bitmap to a new colour.

The basis of it is that I want to swap all the Red in an image (RGB: 231,9,9. Hex E70909)
to lets say Fushia, or another RGB colour.

I can't seem to work out how to specifically swapp just a single colour for another.

The image is only 80x80px so I don't think GetPixel (which supposedly is slow) would impact it that much. That is, if GetPixel is the correct thing to use.

4 Replies

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Vulpes13y ago
He's written it as 'extension method' - notice the 'this' in front of the Bitmap parameter, bmp.

So, as long as you include the BitmapExt static class in your project, you can call it like this:

b.ChangeColour(0,128,0,0,0,0);

where 'b' is a Bitmap variable.

Alternatively, you can call it 'statically' like this:

BitmapExt.ChangeColour(b,0,128,0,0,0,0);
Jay S13y ago
Kinda got it to work...thanks anyway.
Jay S13y ago
I've seen that suggestion and cannot for the life of me get it to work.

When he calls it:

bmp.ChangeColour(0,128,0,0,0,0);

This doesn't work as "ChangeColour" isn't and extension of Bitmap...

Guess i will keep googling.
Vulpes13y ago
Image manipulation is not really my thing but there's a method in this SO thread (posted by Sayse) which purports to change a particular color in a bitmap to another color. As you'll see, this uses LockBits rather than SetPixel and so should be reasonably efficient:

http://stackoverflow.com/questions/16346212/can-you-change-one-colour-to-another-in-an-bitmap-image