iphone: How can I remove the red colors from an image? (RGB colors)

Question

Let's say I have an UIImageView, and I wanna show only blue and green colore from it, (RGB colors). Like in Photoshop, I can choose what colors to show, red, blue, and green, so in the image to delete the red color.

So how can I do it? I really new in Objective-c and all :)

Answer 1

There are many ways to do this. If you have access to the image bitmap data, you can just set the red channel to zero on all the pixels. You might need to draw the image into a CGBitmapContext, get the pointer to the bitmap data, and then create a new CGImage that gets turned into a UIImage.

Or you can create a UIView subclass with a custom drawRect: method which first draws the image normally, and then draws a color set to RGB (0, 1, 1) with the blend mode (set by CGContextSetBlendMode) to kCGBlendModeMultiply.