Making a UIImageView grey

Question

I'm setting UImageViews within table cells using setImageWithUrl from the AFNetworking library, but I need the images to be greyscale... is there any way I can do this. I've tried a few UIImage greyscale converters, but I guess they don't work because I'm setting something that hasn't downloaded yet.

Answer 1

Try this method:

- (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;
}

I found it here: http://mobiledevelopertips.com/graphics/convert-an-image-uiimage-to-grayscale.html

Answer 2

I took the code from @Jesse Gumpo's example, above, but here it is as an interface.

@implementation UIImage ( Greyscale )

- (UIImage *)greyscaleImage
{
    CIImage * beginImage = [ self CIImage ] ;
    CIImage * evAdjustedCIImage = nil ;
    {
        CIFilter * filter = [ CIFilter filterWithName:@"CIColorControls" 
                                        keysAndValues:kCIInputImageKey, beginImage
                                            , @"inputBrightness", @0.0
                                            , @"inputContrast", @1.1
                                            , @"inputSaturation", @0.0
                                            , nil ] ;
        evAdjustedCIImage = [ filter outputImage ] ;
    }

    CIImage * resultCIImage = nil ;
    {
        CIFilter * filter = [ CIFilter filterWithName:@"CIExposureAdjust" 
                                        keysAndValues:kCIInputImageKey, evAdjustedCIImage
                                            , @"inputEV", @0.7
                                            , nil ] ;
        resultCIImage = [ filter outputImage ] ;
    }

    CIContext * context = [ CIContext contextWithOptions:nil ] ;
    CGImageRef resultCGImage = [ context createCGImage:resultCIImage 
                                              fromRect:resultCIImage.extent ] ;
    UIImage * result = [ UIImage imageWithCGImage:resultCGImage ] ;
    CGImageRelease( resultCGImage ) ;

    return result;
}

@end

Now you can just do this:

UIImage * downloadedImage = ... get from AFNetwork results ... ;
downloadedImage = [ downloadedImage greyscaleImage ] ;

... use 'downloadedImage' ...