Created
April 22, 2015 01:40
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| // | |
| // UIImage+Dithering.m | |
| // | |
| #import "UIImage+Dithering.h" | |
| typedef unsigned char PixelByte; | |
| @implementation UIImage (Dithering) | |
| - (UIImage *)ditheredImage | |
| { | |
| UIImage *source = self; | |
| CGImageRef imageRef = [source CGImage]; | |
| NSInteger width = CGImageGetWidth(imageRef); | |
| NSInteger height = CGImageGetHeight(imageRef); | |
| CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); | |
| PixelByte *rawData = malloc(height * width * 4); | |
| NSUInteger pixelBytesPerPixelByte = 4; | |
| NSUInteger pixelBytesPerRow = pixelBytesPerPixelByte * width; | |
| NSUInteger bitsPerComponent = 8; | |
| CGContextRef context = CGBitmapContextCreate(rawData, width, height, | |
| bitsPerComponent, pixelBytesPerRow, colorSpace, | |
| kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big); | |
| CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef); | |
| CGContextRelease(context); | |
| // Dithering Weights | |
| CGFloat w1 = 7.0 / 16.0; | |
| CGFloat w2 = 3.0 / 16.0; | |
| CGFloat w3 = 5.0 / 16.0; | |
| CGFloat w4 = 1.0 / 16.0; | |
| for (NSInteger y = 0; y < height; y++) | |
| { | |
| for (NSInteger x = 0; x < width; x++) | |
| { | |
| // Set color with 50% threshold | |
| CGFloat luminosity = [self getPixelByte:rawData x:x y:y]; | |
| NSInteger oldPixelByte = luminosity; | |
| NSInteger newPixelByte = (oldPixelByte < 128 ? 0 : 255); | |
| [self setPixelByte:rawData x:x y:y PixelByte:newPixelByte]; | |
| // Propagate errors to pixel bytes with error and weight | |
| NSInteger quant_error = oldPixelByte - newPixelByte; | |
| PixelByte PixelByte1 = [self getPixelByte:rawData x:x+1 y:y]; | |
| PixelByte PixelByte2 = [self getPixelByte:rawData x:x-1 y:y+1]; | |
| PixelByte PixelByte3 = [self getPixelByte:rawData x:x y:y+1]; | |
| PixelByte PixelByte4 = [self getPixelByte:rawData x:x+1 y:y+1]; | |
| [self setPixelByte:rawData x:x+1 y:y | |
| PixelByte:PixelByte1 + w1 * quant_error]; | |
| [self setPixelByte:rawData x:x-1 y:y+1 | |
| PixelByte:PixelByte2 + w2 * quant_error]; | |
| [self setPixelByte:rawData x:x y:y+1 | |
| PixelByte:PixelByte3 + w3 * quant_error]; | |
| [self setPixelByte:rawData x:x+1 y:y+1 | |
| PixelByte:PixelByte4 + w4 * quant_error]; | |
| } | |
| } | |
| context = CGBitmapContextCreate(rawData, | |
| CGImageGetWidth( imageRef ), | |
| CGImageGetHeight( imageRef ), | |
| 8, | |
| pixelBytesPerRow, | |
| colorSpace, | |
| (CGBitmapInfo)kCGImageAlphaPremultipliedLast); | |
| CGColorSpaceRelease(colorSpace); | |
| imageRef = CGBitmapContextCreateImage (context); | |
| UIImage *rawImage = [UIImage imageWithCGImage:imageRef]; | |
| CGImageRelease(imageRef); | |
| CGContextRelease(context); | |
| free(rawData); | |
| return rawImage; | |
| } | |
| #pragma mark - RawData accessor/setter utilities | |
| - (void)setPixelByte:(PixelByte *)rawData x:(NSInteger)x y:(NSInteger)y PixelByte:(NSInteger)color | |
| { | |
| NSInteger pixelByteIndex = (y * self.size.width + x) * 4; | |
| // Clamp color | |
| color = MIN(255, color); | |
| color = MAX(0, color); | |
| rawData[pixelByteIndex] = color; | |
| rawData[pixelByteIndex+1] = color; | |
| rawData[pixelByteIndex+2] = color; | |
| } | |
| - (PixelByte)getPixelByte:(PixelByte *)rawData x:(NSInteger)x y:(NSInteger)y | |
| { | |
| NSInteger pixelByteIndex = (y * self.size.width + x) * 4; | |
| CGFloat red = (rawData[pixelByteIndex] * 1.0) / 255.0; | |
| CGFloat green = (rawData[pixelByteIndex + 1] * 1.0) / 255.0; | |
| CGFloat blue = (rawData[pixelByteIndex + 2] * 1.0) / 255.0; | |
| CGFloat luminosity = 0.21*red + 0.72*green + 0.07*blue; | |
| return luminosity * 255; | |
| } | |
| @end |
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