Making a UIImageView grey - objective-c

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' ...

Answer 3

instead of a uiimageView, subclass a UIView, give it
#property (strong, nonatomic) UIImage *image;
with
#synthesize image = _image;
override the setter
-(void)setImage:(UIImage *)image{
_image = [self makeImageBW:image];
[self setNeedsDisplay];
}
- (UIImage *)makeImageBW:(UIImage *)source
{
CIImage *beginImage = source.CIImage;
CIImage *blackAndWhite = [CIFilter filterWithName:#"CIColorControls" keysAndValues:kCIInputImageKey, beginImage, #"inputBrightness", [NSNumber numberWithFloat:0.0], #"inputContrast", [NSNumber numberWithFloat:1.1], #"inputSaturation", [NSNumber numberWithFloat:0.0], nil].outputImage;
CIImage *output = [CIFilter filterWithName:#"CIExposureAdjust" keysAndValues:kCIInputImageKey, blackAndWhite, #"inputEV", [NSNumber numberWithFloat:0.7], nil].outputImage;
CIContext *context = [CIContext contextWithOptions:nil];
CGImageRef ref = [context createCGImage:output fromRect:output.extent];
UIImage *newImage = [UIImage imageWithCGImage:ref];
CGImageRelease(cgiimage);
return newImage;
}
-(void)drawRect:(CGRect)rect{
[_image drawInRect:rect];
}
somewhere else you can set the image with your NSURLRequest:
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0),^{
NSData *data = [NSURLConnection sendSynchronousRequest:(NSURLRequest *) returningResponse:nil error:nil];
if (data){
UIImage *image = [UIImage imageWithData:data];
if (image) dispatch_async(dispatch_get_main_queue(),^{
[view setImage:image];
});
}
});

Answer 4

This thread is a bit old but I came across it on my search. In this post I've pointed out 2 different methods in Swift to create a grayscale image that can be displayed in an imageView considering the alpha and scale of the image.
import CoreImage
extension UIImage
{
/// Applies grayscale with CIColorControls by settings saturation to 0.0.
/// - Parameter brightness: Default is 0.0.
/// - Parameter contrast: Default is 1.0.
/// - Returns: The grayscale image of self if available.
func grayscaleImage(brightness: Double = 0.0, contrast: Double = 1.0) -> UIImage?
{
if let ciImage = CoreImage.CIImage(image: self, options: nil)
{
let paramsColor: [String : AnyObject] = [ kCIInputBrightnessKey: NSNumber(double: brightness),
kCIInputContrastKey: NSNumber(double: contrast),
kCIInputSaturationKey: NSNumber(double: 0.0) ]
let grayscale = ciImage.imageByApplyingFilter("CIColorControls", withInputParameters: paramsColor)
let processedCGImage = CIContext().createCGImage(grayscale, fromRect: grayscale.extent)
return UIImage(CGImage: processedCGImage, scale: self.scale, orientation: self.imageOrientation)
}
return nil
}
/// Create a grayscale image with alpha channel. Is 5 times faster than grayscaleImage().
/// - Returns: The grayscale image of self if available.
func convertToGrayScale() -> UIImage?
{
// Create image rectangle with current image width/height * scale
let pixelSize = CGSize(width: self.size.width * self.scale, height: self.size.height * self.scale)
let imageRect = CGRect(origin: CGPointZero, size: pixelSize)
// Grayscale color space
if let colorSpace: CGColorSpaceRef = CGColorSpaceCreateDeviceGray()
{
// Create bitmap content with current image size and grayscale colorspace
let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.None.rawValue)
if let context: CGContextRef = CGBitmapContextCreate(nil, Int(pixelSize.width), Int(pixelSize.height), 8, 0, colorSpace, bitmapInfo.rawValue)
{
// Draw image into current context, with specified rectangle
// using previously defined context (with grayscale colorspace)
CGContextDrawImage(context, imageRect, self.CGImage)
// Create bitmap image info from pixel data in current context
if let imageRef: CGImageRef = CGBitmapContextCreateImage(context)
{
let bitmapInfoAlphaOnly = CGBitmapInfo(rawValue: CGImageAlphaInfo.Only.rawValue)
if let contextAlpha = CGBitmapContextCreate(nil, Int(pixelSize.width), Int(pixelSize.height), 8, 0, nil, bitmapInfoAlphaOnly.rawValue)
{
CGContextDrawImage(contextAlpha, imageRect, self.CGImage)
if let mask: CGImageRef = CGBitmapContextCreateImage(contextAlpha)
{
// Create a new UIImage object
if let newCGImage = CGImageCreateWithMask(imageRef, mask)
{
// Return the new grayscale image
return UIImage(CGImage: newCGImage, scale: self.scale, orientation: self.imageOrientation)
}
}
}
}
}
}
// A required variable was unexpected nil
return nil
}
}