UIImage+ImageEffects.m presented on WWDC 2013

UIImage+ImageEffects.h

/*
     File: UIImage+ImageEffects.h
 Abstract: This is a category of UIImage that adds methods to apply blur and tint effects to an image. This is the code you’ll want to look out to find out how to use vImage to efficiently calculate a blur.
  Version: 1.0
 
 Copyright (C) 2013 Apple Inc. All Rights Reserved.
 */

@import UIKit;

@interface UIImage (ImageEffects)

- (UIImage *)applyLightEffect;
- (UIImage *)applyExtraLightEffect;
- (UIImage *)applyDarkEffect;
- (UIImage *)applyTintEffectWithColor:(UIColor *)tintColor;

- (UIImage *)applyBlurWithRadius:(CGFloat)blurRadius tintColor:(UIColor *)tintColor saturationDeltaFactor:(CGFloat)saturationDeltaFactor maskImage:(UIImage *)maskImage;

@end

UIImage+ImageEffects.m

/*
     File: UIImage+ImageEffects.m
 Abstract: This is a category of UIImage that adds methods to apply blur and tint effects to an image. This is the code you’ll want to look out to find out how to use vImage to efficiently calculate a blur.
  Version: 1.0
 
 Copyright (C) 2013 Apple Inc. All Rights Reserved.
 */

#import "UIImage+ImageEffects.h"

@import Accelerate;
#import <float.h>


@implementation UIImage (ImageEffects)


- (UIImage *)applyLightEffect
{
    UIColor *tintColor = [UIColor colorWithWhite:1.0 alpha:0.3];
    return [self applyBlurWithRadius:30 tintColor:tintColor saturationDeltaFactor:1.8 maskImage:nil];
}


- (UIImage *)applyExtraLightEffect
{
    UIColor *tintColor = [UIColor colorWithWhite:0.97 alpha:0.82];
    return [self applyBlurWithRadius:20 tintColor:tintColor saturationDeltaFactor:1.8 maskImage:nil];
}


- (UIImage *)applyDarkEffect
{
    UIColor *tintColor = [UIColor colorWithWhite:0.11 alpha:0.73];
    return [self applyBlurWithRadius:20 tintColor:tintColor saturationDeltaFactor:1.8 maskImage:nil];
}


- (UIImage *)applyTintEffectWithColor:(UIColor *)tintColor
{
    const CGFloat EffectColorAlpha = 0.6;
    UIColor *effectColor = tintColor;
    int componentCount = CGColorGetNumberOfComponents(tintColor.CGColor);
    if (componentCount == 2) {
        CGFloat b;
        if ([tintColor getWhite:&b alpha:NULL]) {
            effectColor = [UIColor colorWithWhite:b alpha:EffectColorAlpha];
        }
    }
    else {
        CGFloat r, g, b;
        if ([tintColor getRed:&r green:&g blue:&b alpha:NULL]) {
            effectColor = [UIColor colorWithRed:r green:g blue:b alpha:EffectColorAlpha];
        }
    }
    return [self applyBlurWithRadius:10 tintColor:effectColor saturationDeltaFactor:-1.0 maskImage:nil];
}


- (UIImage *)applyBlurWithRadius:(CGFloat)blurRadius tintColor:(UIColor *)tintColor saturationDeltaFactor:(CGFloat)saturationDeltaFactor maskImage:(UIImage *)maskImage
{
    // Check pre-conditions.
    if (self.size.width < 1 || self.size.height < 1) {
        NSLog (@"*** error: invalid size: (%.2f x %.2f). Both dimensions must be >= 1: %@", self.size.width, self.size.height, self);
        return nil;
    }
    if (!self.CGImage) {
        NSLog (@"*** error: image must be backed by a CGImage: %@", self);
        return nil;
    }
    if (maskImage && !maskImage.CGImage) {
        NSLog (@"*** error: maskImage must be backed by a CGImage: %@", maskImage);
        return nil;
    }

    CGRect imageRect = { CGPointZero, self.size };
    UIImage *effectImage = self;
    
    BOOL hasBlur = blurRadius > __FLT_EPSILON__;
    BOOL hasSaturationChange = fabs(saturationDeltaFactor - 1.) > __FLT_EPSILON__;
    if (hasBlur || hasSaturationChange) {
        UIGraphicsBeginImageContextWithOptions(self.size, NO, [[UIScreen mainScreen] scale]);
        CGContextRef effectInContext = UIGraphicsGetCurrentContext();
        CGContextScaleCTM(effectInContext, 1.0, -1.0);
        CGContextTranslateCTM(effectInContext, 0, -self.size.height);
        CGContextDrawImage(effectInContext, imageRect, self.CGImage);

        vImage_Buffer effectInBuffer;
        effectInBuffer.data     = CGBitmapContextGetData(effectInContext);
        effectInBuffer.width    = CGBitmapContextGetWidth(effectInContext);
        effectInBuffer.height   = CGBitmapContextGetHeight(effectInContext);
        effectInBuffer.rowBytes = CGBitmapContextGetBytesPerRow(effectInContext);
    
        UIGraphicsBeginImageContextWithOptions(self.size, NO, [[UIScreen mainScreen] scale]);
        CGContextRef effectOutContext = UIGraphicsGetCurrentContext();
        vImage_Buffer effectOutBuffer;
        effectOutBuffer.data     = CGBitmapContextGetData(effectOutContext);
        effectOutBuffer.width    = CGBitmapContextGetWidth(effectOutContext);
        effectOutBuffer.height   = CGBitmapContextGetHeight(effectOutContext);
        effectOutBuffer.rowBytes = CGBitmapContextGetBytesPerRow(effectOutContext);

        if (hasBlur) {
            // A description of how to compute the box kernel width from the Gaussian
            // radius (aka standard deviation) appears in the SVG spec:
            // http://www.w3.org/TR/SVG/filters.html#feGaussianBlurElement
            // 
            // For larger values of 's' (s >= 2.0), an approximation can be used: Three
            // successive box-blurs build a piece-wise quadratic convolution kernel, which
            // approximates the Gaussian kernel to within roughly 3%.
            //
            // let d = floor(s * 3*sqrt(2*pi)/4 + 0.5)
            // 
            // ... if d is odd, use three box-blurs of size 'd', centered on the output pixel.
            // 
            CGFloat inputRadius = blurRadius * [[UIScreen mainScreen] scale];
            NSUInteger radius = floor(inputRadius * 3. * sqrt(2 * M_PI) / 4 + 0.5);
            if (radius % 2 != 1) {
                radius += 1; // force radius to be odd so that the three box-blur methodology works.
            }
            vImageBoxConvolve_ARGB8888(&effectInBuffer, &effectOutBuffer, NULL, 0, 0, radius, radius, 0, kvImageEdgeExtend);
            vImageBoxConvolve_ARGB8888(&effectOutBuffer, &effectInBuffer, NULL, 0, 0, radius, radius, 0, kvImageEdgeExtend);
            vImageBoxConvolve_ARGB8888(&effectInBuffer, &effectOutBuffer, NULL, 0, 0, radius, radius, 0, kvImageEdgeExtend);
        }
        BOOL effectImageBuffersAreSwapped = NO;
        if (hasSaturationChange) {
            CGFloat s = saturationDeltaFactor;
            CGFloat floatingPointSaturationMatrix[] = {
                0.0722 + 0.9278 * s,  0.0722 - 0.0722 * s,  0.0722 - 0.0722 * s,  0,
                0.7152 - 0.7152 * s,  0.7152 + 0.2848 * s,  0.7152 - 0.7152 * s,  0,
                0.2126 - 0.2126 * s,  0.2126 - 0.2126 * s,  0.2126 + 0.7873 * s,  0,
                                  0,                    0,                    0,  1,
            };
            const int32_t divisor = 256;
            NSUInteger matrixSize = sizeof(floatingPointSaturationMatrix)/sizeof(floatingPointSaturationMatrix[0]);
            int16_t saturationMatrix[matrixSize];
            for (NSUInteger i = 0; i < matrixSize; ++i) {
                saturationMatrix[i] = (int16_t)roundf(floatingPointSaturationMatrix[i] * divisor);
            }
            if (hasBlur) {
                vImageMatrixMultiply_ARGB8888(&effectOutBuffer, &effectInBuffer, saturationMatrix, divisor, NULL, NULL, kvImageNoFlags);
                effectImageBuffersAreSwapped = YES;
            }
            else {
                vImageMatrixMultiply_ARGB8888(&effectInBuffer, &effectOutBuffer, saturationMatrix, divisor, NULL, NULL, kvImageNoFlags);
            }
        }
        if (!effectImageBuffersAreSwapped)
            effectImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();

        if (effectImageBuffersAreSwapped)
            effectImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }

    // Set up output context.
    UIGraphicsBeginImageContextWithOptions(self.size, NO, [[UIScreen mainScreen] scale]);
    CGContextRef outputContext = UIGraphicsGetCurrentContext();
    CGContextScaleCTM(outputContext, 1.0, -1.0);
    CGContextTranslateCTM(outputContext, 0, -self.size.height);

    // Draw base image.
    CGContextDrawImage(outputContext, imageRect, self.CGImage);

    // Draw effect image.
    if (hasBlur) {
        CGContextSaveGState(outputContext);
        if (maskImage) {
            CGContextClipToMask(outputContext, imageRect, maskImage.CGImage);
        }
        CGContextDrawImage(outputContext, imageRect, effectImage.CGImage);
        CGContextRestoreGState(outputContext);
    }

    // Add in color tint.
    if (tintColor) {
        CGContextSaveGState(outputContext);
        CGContextSetFillColorWithColor(outputContext, tintColor.CGColor);
        CGContextFillRect(outputContext, imageRect);
        CGContextRestoreGState(outputContext);
    }

    // Output image is ready.
    UIImage *outputImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return outputImage;
}

@end