I was developing a application that changes color image to gray image. However, some how the picture comes out wrong. I dont know what is wrong with the code. maybe the parameter that i put in is wrong please help. UIImage *c = [UIImage imageNamed:@"downRed.png"]; CGImageRef cRef = CGImageRetain(c.CGImage); NSData* pixelData = (NSData*) CGDataProviderCopyData(CGImageGetDataProvider(cRef)); size_t w = CGImageGetWidth(cRef); size_t h = CGImageGetHeight(cRef); unsigned char* pixelBytes = (unsigned char *)[pixelData bytes]; unsigned char* greyPixelData = (unsigned char*) malloc(w*h); for (int y = 0; y < h; y++) { for(int x = 0; x < w; x++){ int iter = 4*(w*y+x); int red = pixe lBytes[iter]; int green = pixelBytes[iter+1]; int blue = pixelBytes[iter+2]; greyPixelData[w*y+x] = (unsigned char)(red*0.3 + green*0.59+ blue*0.11); int value = greyPixelData[w*y+x]; } } CFDataRef imgData = CFDataCreate(NULL, greyPixelData, w*h); CGDataProviderRef imgDataProvider = CGDataProviderCreateWithCFData(imgData); size_t width = CGImageGetWidth(cRef); size_t height = CGImageGetHeight(cRef); size_t bitsPerComponent = 8; size_t bitsPerPixel = 8; size_t bytesPerRow = CGImageGetWidth(cRef); CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray(); CGBitmapInfo info = kCGImageAlphaNone; CGFloat *decode = NULL; BOOL shouldInteroplate = NO; CGColorRenderingIntent intent = kCGRenderingIntentDefault; CGDataProviderRelease(imgDataProvider); CGImageRef throughCGImage = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpace, info, imgDataProvider, decode, shouldInteroplate, intent); UIImage* newImage = [UIImage imageWithCGImage:throughCGImage]; CGImageRelease(throughCGImage); newImageView.image = newImage;