iOS Blur effects

UIImage+ImageEffects.h

//
//  UIImage(ImageEffects)
//  Megogo
//
//  Created by Philip Vasilchenko on 13.01.14.
//  Copyright (c) 2013 Megogo.net. All rights reserved.
//

#import <UIKit/UIKit.h>

@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

//
//  UIImage(ImageEffects)
//  Megogo
//
//  Created by Philip Vasilchenko on 13.01.14.
//  Copyright (c) 2013 Megogo.net. All rights reserved.
//

#import <Accelerate/Accelerate.h>
#import "UIImage+ImageEffects.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 = (NSUInteger) 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