How to filter colors in runtime ? - iphone - iphone

Question

I have an image where each pixel has one of the three primary colors (RGBA).
And I have to change this image in run-time by changing each color channel by another (filter on run-time)
I have the .PVR and the corresponding glTexture2D, but how can I filter / change colors in run-time ?
I cannot use OpenGL ES 2.0
But I can use Cocos2D and OpenGL ES 1.x
:(

Answer 1

It's not trivial, but it could be useful to you:
// Convierte la imagen a blanco y negro
+ (UIImage *)convertImageToGrayScale:(UIImage *)i {
CGSize size = [i size];
int width = size.width;
int height = size.height;
// the pixels will be painted to this array
uint32_t *pixels = (uint32_t *) malloc(width * height * sizeof(uint32_t));
// clear the pixels so any transparency is preserved
memset(pixels, 0, width * height * sizeof(uint32_t));
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
// create a context with RGBA pixels
CGContextRef context = CGBitmapContextCreate(pixels, width, height, 8, width * sizeof(uint32_t), colorSpace,
kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast);
// paint the bitmap to our context which will fill in the pixels array
CGContextDrawImage(context, CGRectMake(0, 0, width, height), [i CGImage]);
for(int y = 0; y < height; y++) {
for(int x = 0; x < width; x++) {
uint8_t *rgbaPixel = (uint8_t *) &pixels[y * width + x];
// convert to grayscale using recommended method: http://en.wikipedia.org/wiki/Grayscale#Converting_color_to_grayscale
uint32_t gray = 0.3 * rgbaPixel[RED] + 0.59 * rgbaPixel[GREEN] + 0.11 * rgbaPixel[BLUE];
// set the pixels to gray
rgbaPixel[RED] = gray;
rgbaPixel[GREEN] = gray;
rgbaPixel[BLUE] = gray;
}
}
// create a new CGImageRef from our context with the modified pixels
CGImageRef image = CGBitmapContextCreateImage(context);
// we're done with the context, color space, and pixels
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
free(pixels);
// make a new UIImage to return
UIImage *resultUIImage = [UIImage imageWithCGImage:image];
// we're done with image now too
CGImageRelease(image);
return resultUIImage;
}
This converts the UIimage received into a gray scale image

Answer 2

This is the code I used to manipulate RGBA picture
-(UIImage*)convertGrayScaleImageRedImage:(CGImageRef)inImage{
CFDataRef m_DataRef = CGDataProviderCopyData(CGImageGetDataProvider(inImage));
UInt8 * m_PixelBuf = (UInt8 *) CFDataGetBytePtr(m_DataRef);
int length = CFDataGetLength(m_DataRef);
for (int i=0; i<length; i+=4){
int r = i;
int g = i+1;
int b = i+2;
//int a = i+3;//alpha
NSLog(#"r=%i, g=%i, b=%i",m_PixelBuf[r], m_PixelBuf[g], m_PixelBuf[b]);
m_PixelBuf[r] = 1;
m_PixelBuf[g] = 0;
m_PixelBuf[b] = 0;
//m_PixelBuf[a] = m_PixelBuf[a];//alpha
}
CGContextRef ctx = CGBitmapContextCreate(m_PixelBuf,
CGImageGetWidth(inImage),
CGImageGetHeight(inImage),
CGImageGetBitsPerComponent(inImage),
CGImageGetBytesPerRow(inImage),
CGImageGetColorSpace(inImage),
CGImageGetBitmapInfo(inImage)
);
CGImageRef imageRef = CGBitmapContextCreateImage(ctx);
CGContextRelease(ctx);
UIImage *redImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
return redImage;
}