UIImageExtension.m

//
//  UIImageExtension.m
//
//  Licensed by ruralcoder.com under the
//  Creative Commons Attribution-ShareAlike 3.0 Unported License 

#import "UIImageExtension.h"

@implementation UIImage (Extension)

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


- (UIImage *) toThumbnail:(CGSize)size
{
	if (self.size.height <= size.height) return self; // no point wasting CPU. 
    // Height chosen as wished dimension 
    // due to cell height restrictions
	
	float scaleFactor = [DeviceUtils displayScale];
	
	CGSize thumbSize = CGSizeMake(size.width * scaleFactor, size.height * scaleFactor);
	
	UIGraphicsBeginImageContext(thumbSize);
	[self drawInRect:CGRectMake(0, 0, thumbSize.width, thumbSize.height)];
	
	UIImage *temp_image = UIGraphicsGetImageFromCurrentImageContext();
	
	UIGraphicsEndImageContext();
	
	UIImage *thumbnail = [UIImage imageWithCGImage:[temp_image CGImage]
                                             scale:scaleFactor 
                                       orientation:UIImageOrientationUp];
	
	if (thumbnail == nil)
		return self;
	
	return thumbnail;
	
}


- (UIImage *) toGrayscale 
{
    const int RED = 1;
    const int GREEN = 2;
    const int BLUE = 3;
    
    // Create image rectangle with current image width/height
    CGRect imageRect = CGRectMake(0, 0, self.size.width * self.scale, self.size.height * self.scale);
    
    int width = imageRect.size.width;
    int height = imageRect.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
                                                 scale:self.scale 
                                           orientation:UIImageOrientationUp];
    
    // we're done with image now too
    CGImageRelease(image);
    
    return resultUIImage;
}


@end