Aşağıdaki şekilde gri tonlama içine bir görüntü dönüştürmek için çalışıyorum:

#define bytesPerPixel 4
#define bitsPerComponent 8

-(unsigned char*) getBytesForImage: (UIImage*)pImage
{
    CGImageRef image = [pImage CGImage];
    NSUInteger width = CGImageGetWidth(image);
    NSUInteger height = CGImageGetHeight(image);

    NSUInteger bytesPerRow = bytesPerPixel * width;

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    unsigned char *rawData = malloc(height * width * 4);
    CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
    CGColorSpaceRelease(colorSpace);

    CGContextDrawImage(context, CGRectMake(0, 0, width, height), image);
    CGContextRelease(context);

    return rawData;
}

-(UIImage*) processImage: (UIImage*)pImage
{   
    DebugLog(@"processing image");
    unsigned char *rawData = [self getBytesForImage: pImage];

    NSUInteger width = pImage.size.width;
    NSUInteger height = pImage.size.height;

    DebugLog(@"width: %d", width);
    DebugLog(@"height: %d", height);

    NSUInteger bytesPerRow = bytesPerPixel * width;

    for (int xCoordinate = 0; xCoordinate < width; xCoordinate  )
    {
    	for (int yCoordinate = 0; yCoordinate < height; yCoordinate  )
    	{
    		int byteIndex = (bytesPerRow * yCoordinate)   xCoordinate * bytesPerPixel;

    		//Getting original colors
    		float red = ( rawData[byteIndex] / 255.f );
    		float green = ( rawData[byteIndex   1] / 255.f );
    		float blue = ( rawData[byteIndex   2] / 255.f );

    		//Processing pixel data
    		float averageColor = (red   green   blue) / 3.0f;

    		red = averageColor;
    		green = averageColor;
    		blue = averageColor;

    		//Assigning new color components
    		rawData[byteIndex] = (unsigned char) red * 255;
    		rawData[byteIndex   1] = (unsigned char) green * 255;
    		rawData[byteIndex   2] = (unsigned char) blue * 255;


    	}
    }

    NSData* newPixelData = [NSData dataWithBytes: rawData length: height * width * 4];
    UIImage* newImage = [UIImage imageWithData: newPixelData];

    free(rawData);

    DebugLog(@"image processed");

    return newImage;

}

Bu yüzden bir görüntü dönüştürmek istediğimde sadece processİmage çağrı:

imageToDisplay.image = [self processImage: image];

Ama imageToDisplay görüntü gelmiyor. Sorun ne olabilir?

Teşekkürler.

Alfa kanalı korunmuş bir sürüm gerekli kodu Dutchie432 tarafından yayınlanan değiştirdim bu yüzden:

@implementation UIImage (grayscale)

typedef enum {
    ALPHA = 0,
    BLUE = 1,
    GREEN = 2,
    RED = 3
} PIXELS;

- (UIImage *)convertToGrayscale {
    CGSize size = [self 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), [self 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;
}

@end