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copied!<p>This seems to work for me.</p> <pre><code>UIImage* modifyImage(UIImage* image) { size_t w = image.size.width; size_t h = image.size.height; CGFloat scale = image.scale; // Create the bitmap context UIGraphicsBeginImageContext(CGSizeMake(w*scale, h*scale)); CGContextRef context = UIGraphicsGetCurrentContext(); // NOTE you may have to setup a rotation here based on image.imageOrientation // but I didn't need to consider that for my images. CGContextScaleCTM(context, scale, scale); [image drawInRect:CGRectMake(0, 0, w, h)]; unsigned char* data = CGBitmapContextGetData (context); if (data != NULL) { size_t height = CGBitmapContextGetHeight(context); size_t width = CGBitmapContextGetWidth(context); size_t bytesPerRow = CGBitmapContextGetBytesPerRow(context); for (int y = 0; y < height; y++) { for (int x = 0; x < width; x++) { // Not sure why the color info is in BGRA format // Look at CGBitmapContextGetBitmapInfo(context) if this format isn't working for you int offset = y * bytesPerRow + x * 4; unsigned char* blue = &data[offset]; unsigned char* green = &data[offset+1]; unsigned char* red = &data[offset+2]; unsigned char* alpha = &data[offset+3]; int newRed = ...; // color calculation code here int newGreen = ...; int newBlue = ...; // Assuming you don't want to change the original alpha value. *red = (newRed * *alpha)/255; *green = (newGreen * *alpha)/255; *blue = (newBlue * *alpha)/255; } } } CGImageRef newImage = CGBitmapContextCreateImage(context); UIImage *done = [UIImage imageWithCGImage:newImage scale:image.scale orientation: image.imageOrientation]; CGImageRelease(newImage); UIGraphicsEndImageContext(); return done; } </code></pre>

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