Changing colours of a bitmap/image?

[bgowland]

I'm working on something which reads in simple jpg images (example, a black arrow on a white square background). For skinning purposes (and user options) I'd like to be able to change individual colours so, for instance, if the user wants a white arrow on a black background they can do that.

Is there a way that I can read a jpg in as an Image then tell the image to substitute every occurence of a pixel that is colour X with colour Y?

I know I could just draw something as simple as an arrow programatically and set the colours at that stage, but the images are a little more complex than that.

Cheers,
Brian

[sub]

I dont know of any ready to use function, but if speed is not a primary concern you could always work your way through each pixel with Image.GetPixel(). A faster version of the same can be done with LockBits().

[Old Dog]

You might be better off using an image format that incorporates a color lookup table such as gif or 8-bit png. Simply change the entries in the table and you have changed the colors on the screen.

Also, you could change all the colors similarly, maintaining the color scheme.

[bgowland]

I dont know of any ready to use function, but if speed is not a primary concern you could always work your way through each pixel with Image.GetPixel(). A faster version of the same can be done with LockBits().

Thanks. I'll look at those - it might work as I wouldn't be looking at high-speed / dynamic changes - more like during the plugin initialization stage.

Cheers,
Brian

[bgowland]

You might be better off using an image format that incorporates a color lookup table such as gif or 8-bit png.

OK - I had something in the back of my mind about this sort of method. I'll try sub's suggestion and see if it's quick enough otherwise I'd need to convert the jpg files though (about 50 of them). I don't suppose you know of a command-line tool that I could pass a source jpg to and get it to output a gif or png do you?

Cheers,
Brian

[reven]

imagemagick

just google for it.

[Fatman_do]

imagemagick

just google for it.

Wow, that looks like a handy little program. I have needed to change image types before in batches but have never stumbled upon this.

Here is the link for the lazy:p
http://www.imagemagick.org/script/index.php

[bgowland]

reven - thanks for the suggestion - it looks useful.

Fatman_do - thanks for the link