Created
November 5, 2013 15:06
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Blur by Apple
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- (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, 1.0); | |
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, 1.0); | |
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, 1.0); | |
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; | |
} |
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