Cambiar la imagen en color RGB a la imagen en escala de grises con el objetivo C

Question

Estaba desarrollando una aplicación que cambia la imagen en color a gris. Sin embargo, de alguna manera la imagen sale mal. No sé lo que está mal con el código. tal vez el parámetro que puse es incorrecto por favor ayuda.

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; 

Answer 1

Sólo tiene que utilizar esto:

- (UIImage *)convertImageToGrayScale:(UIImage *)image 
{ 
    // Create image rectangle with current image width/height 
    CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height); 

    // Grayscale color space 
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray(); 

    // Create bitmap content with current image size and grayscale colorspace 
    CGContextRef context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, colorSpace, kCGImageAlphaNone); 

    // Draw image into current context, with specified rectangle 
    // using previously defined context (with grayscale colorspace) 
    CGContextDrawImage(context, imageRect, [image CGImage]); 

    // Create bitmap image info from pixel data in current context 
    CGImageRef imageRef = CGBitmapContextCreateImage(context); 

    // Create a new UIImage object 
    UIImage *newImage = [UIImage imageWithCGImage:imageRef]; 

    // Release colorspace, context and bitmap information 
    CGColorSpaceRelease(colorSpace); 
    CGContextRelease(context); 
    CFRelease(imageRef); 

    // Return the new grayscale image 
    return newImage; 
} 

Answer 2

Si alguien quiere gris escala de las imágenes que contienen partes transparentes de la solución ofrecida por digipeople tendrá una máscara de negro alrededor de él. Use esto en su lugar para dejar el transparente tal como está.

- (UIImage *)imageToGreyImage:(UIImage *)image { 
    // Create image rectangle with current image width/height 
    CGFloat actualWidth = image.size.width; 
    CGFloat actualHeight = image.size.height; 

    CGRect imageRect = CGRectMake(0, 0, actualWidth, actualHeight); 
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray(); 

    CGContextRef context = CGBitmapContextCreate(nil, actualWidth, actualHeight, 8, 0, colorSpace, kCGImageAlphaNone); 
    CGContextDrawImage(context, imageRect, [image CGImage]); 

    CGImageRef grayImage = CGBitmapContextCreateImage(context); 
    CGColorSpaceRelease(colorSpace); 
    CGContextRelease(context); 

    context = CGBitmapContextCreate(nil, actualWidth, actualHeight, 8, 0, nil, kCGImageAlphaOnly); 
    CGContextDrawImage(context, imageRect, [image CGImage]); 
    CGImageRef mask = CGBitmapContextCreateImage(context); 
    CGContextRelease(context); 

    UIImage *grayScaleImage = [UIImage imageWithCGImage:CGImageCreateWithMask(grayImage, mask) scale:image.scale orientation:image.imageOrientation]; 
    CGImageRelease(grayImage); 
    CGImageRelease(mask); 

    // Return the new grayscale image 
    return grayScaleImage; 
} 

Answer 3

versión Swift, probado y funcionando al 100%:

func imageToGreyImage(image: UIImage) -> UIImage { 

    // Create image rectangle with current image width/height 
    var actualWidth = image.size.width; 
    var actualHeight = image.size.height; 

    var imageRect = CGRectMake(0, 0, actualWidth, actualHeight); 
    var colorSpace = CGColorSpaceCreateDeviceGray(); 

    var bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.None.rawValue) 

    var context = CGBitmapContextCreate(nil, Int(actualWidth), Int(actualHeight), 8, 0, colorSpace, bitmapInfo); 
    CGContextDrawImage(context, imageRect, image.CGImage); 

    var grayImage = CGBitmapContextCreateImage(context); 
    bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.Only.rawValue) 
    context = CGBitmapContextCreate(nil, Int(actualWidth), Int(actualHeight), 8, 0, nil, bitmapInfo); 
    CGContextDrawImage(context, imageRect, image.CGImage); 
    var mask = CGBitmapContextCreateImage(context); 

    var grayScaleImage = UIImage(CGImage: CGImageCreateWithMask(grayImage, mask), scale: image.scale, orientation: image.imageOrientation) 

    // Return the new grayscale image 
    return grayScaleImage!; 
} 

Y si quieres sin alfa acaba de borrar la línea siguiente:

bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.Only.rawValue)