Black and White Photoshop effect on UIImage - ios

Question

Hello I'd like to create the following Black and White Photoshop effect on a UIImage
https://drive.google.com/file/d/0B5dHxpdDwpPec3dPTWdLVnNhZFk/view?usp=sharing
In which you can change the brightness of each of the six colors (reds yellows green cyans blues magentas)
I used this to make the image black and white but it doesn't allow me to change the specific colors
self.imageView.image = chosenImage;
CIImage *beginImage = [CIImage imageWithCGImage:chosenImage.CGImage];
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 cgiimage = [context createCGImage:output fromRect:output.extent];
UIImage *newImage = [UIImage imageWithCGImage:cgiimage];
self.imageView.image = newImage;
Thank You for your time

Answer 1

I think you can accomplish that effect with the following function:
- (UIImage *)grayScaleImageWith:(UIImage *)image blackPoint:(CGFloat)blackPoint whitePoint:(CGFloat)whitePoint andGamma:(CGFloat)gamma {
// Create image rectangle with current image width/height
CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height);
// Grayscale color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateCalibratedGray(whitePoint, blackPoint, gamma);
// 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;
}
Then call it filling the black and white values with the values selected on the UI:
CGFloat black[3] = { 0, 0, 0 }; // replace content with values from interface
CGFloat white[3] = { 100, 100, 100 }; // replace content with values from interface
[self grayScaleImageWith:image blackPoint:black whitePoint:white andGamma:1.8f];
I have not tested this code yet but I hope at least it points you in the right direction.