UIImageEffects.m

/*
 File: UIImageEffects.m
 Abstract: This class contains 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: 1.1

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#import "UIImageEffects.h"

@import Accelerate;

@implementation UIImageEffects

#pragma mark -
#pragma mark - Effects

//| ----------------------------------------------------------------------------
+ (UIImage *)imageByApplyingLightEffectToImage:(UIImage*)inputImage
{
    UIColor *tintColor = [UIColor colorWithWhite:1.0 alpha:0.3];
    return [self imageByApplyingBlurToImage:inputImage withRadius:60 tintColor:tintColor saturationDeltaFactor:1.8 maskImage:nil];
}


//| ----------------------------------------------------------------------------
+ (UIImage *)imageByApplyingExtraLightEffectToImage:(UIImage*)inputImage
{
    UIColor *tintColor = [UIColor colorWithWhite:0.97 alpha:0.82];
    return [self imageByApplyingBlurToImage:inputImage withRadius:40 tintColor:tintColor saturationDeltaFactor:1.8 maskImage:nil];
}


//| ----------------------------------------------------------------------------
+ (UIImage *)imageByApplyingDarkEffectToImage:(UIImage*)inputImage
{
    UIColor *tintColor = [UIColor colorWithWhite:0.11 alpha:0.73];
    return [self imageByApplyingBlurToImage:inputImage withRadius:40 tintColor:tintColor saturationDeltaFactor:1.8 maskImage:nil];
}


//| ----------------------------------------------------------------------------
+ (UIImage *)imageByApplyingTintEffectWithColor:(UIColor *)tintColor toImage:(UIImage*)inputImage
{
    const CGFloat EffectColorAlpha = 0.6;
    UIColor *effectColor = tintColor;
    size_t 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 imageByApplyingBlurToImage:inputImage withRadius:20 tintColor:effectColor saturationDeltaFactor:-1.0 maskImage:nil];
}

#pragma mark -
#pragma mark - Implementation

//| ----------------------------------------------------------------------------
+ (UIImage*)imageByApplyingBlurToImage:(UIImage*)inputImage withRadius:(CGFloat)blurRadius tintColor:(UIColor *)tintColor saturationDeltaFactor:(CGFloat)saturationDeltaFactor maskImage:(UIImage *)maskImage
{
#define ENABLE_BLUR                     1
#define ENABLE_SATURATION_ADJUSTMENT    1
#define ENABLE_TINT                     1

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

    BOOL hasBlur = blurRadius > __FLT_EPSILON__;
    BOOL hasSaturationChange = fabs(saturationDeltaFactor - 1.) > __FLT_EPSILON__;

    CGImageRef inputCGImage = inputImage.CGImage;
    CGFloat inputImageScale = inputImage.scale;
    CGBitmapInfo inputImageBitmapInfo = CGImageGetBitmapInfo(inputCGImage);
    CGImageAlphaInfo inputImageAlphaInfo = (inputImageBitmapInfo & kCGBitmapAlphaInfoMask);

    CGSize outputImageSizeInPoints = inputImage.size;
    CGRect outputImageRectInPoints = { CGPointZero, outputImageSizeInPoints };

    // Set up output context.
    BOOL useOpaqueContext;
    if (inputImageAlphaInfo == kCGImageAlphaNone || inputImageAlphaInfo == kCGImageAlphaNoneSkipLast || inputImageAlphaInfo == kCGImageAlphaNoneSkipFirst)
        useOpaqueContext = YES;
    else
        useOpaqueContext = NO;
    UIGraphicsBeginImageContextWithOptions(outputImageRectInPoints.size, useOpaqueContext, inputImageScale);
    CGContextRef outputContext = UIGraphicsGetCurrentContext();
    CGContextScaleCTM(outputContext, 1.0, -1.0);
    CGContextTranslateCTM(outputContext, 0, -outputImageRectInPoints.size.height);

    if (hasBlur || hasSaturationChange)
    {
        vImage_Buffer effectInBuffer;
        vImage_Buffer scratchBuffer1;

        vImage_Buffer *inputBuffer;
        vImage_Buffer *outputBuffer;

        vImage_CGImageFormat format = {
            .bitsPerComponent = 8,
            .bitsPerPixel = 32,
            .colorSpace = NULL,
            // (kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little)
            // requests a BGRA buffer.
            .bitmapInfo = kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little,
            .version = 0,
            .decode = NULL,
            .renderingIntent = kCGRenderingIntentDefault
        };

        vImage_Error e = vImageBuffer_InitWithCGImage(&effectInBuffer, &format, NULL, inputImage.CGImage, kvImagePrintDiagnosticsToConsole);
        if (e != kvImageNoError)
        {
            NSLog(@"*** error: vImageBuffer_InitWithCGImage returned error code %zi for inputImage: %@", e, inputImage);
            UIGraphicsEndImageContext();
            return nil;
        }

        vImageBuffer_Init(&scratchBuffer1, effectInBuffer.height, effectInBuffer.width, format.bitsPerPixel, kvImageNoFlags);
        inputBuffer = &effectInBuffer;
        outputBuffer = &scratchBuffer1;

#if ENABLE_BLUR
        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 * inputImageScale;
            if (inputRadius - 2. < __FLT_EPSILON__)
                inputRadius = 2.;
            uint32_t radius = floor((inputRadius * 3. * sqrt(2 * M_PI) / 4 + 0.5) / 2);

            radius |= 1; // force radius to be odd so that the three box-blur methodology works.

            NSInteger tempBufferSize = vImageBoxConvolve_ARGB8888(inputBuffer, outputBuffer, NULL, 0, 0, radius, radius, NULL, kvImageGetTempBufferSize | kvImageEdgeExtend);
            void *tempBuffer = malloc(tempBufferSize);

            vImageBoxConvolve_ARGB8888(inputBuffer, outputBuffer, tempBuffer, 0, 0, radius, radius, NULL, kvImageEdgeExtend);
            vImageBoxConvolve_ARGB8888(outputBuffer, inputBuffer, tempBuffer, 0, 0, radius, radius, NULL, kvImageEdgeExtend);
            vImageBoxConvolve_ARGB8888(inputBuffer, outputBuffer, tempBuffer, 0, 0, radius, radius, NULL, kvImageEdgeExtend);

            free(tempBuffer);

            vImage_Buffer *temp = inputBuffer;
            inputBuffer = outputBuffer;
            outputBuffer = temp;
        }
#endif

#if ENABLE_SATURATION_ADJUSTMENT
        if (hasSaturationChange)
        {
            CGFloat s = saturationDeltaFactor;
            // These values appear in the W3C Filter Effects spec:
            // https://dvcs.w3.org/hg/FXTF/raw-file/default/filters/index.html#grayscaleEquivalent
            //
            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);
            }
            vImageMatrixMultiply_ARGB8888(inputBuffer, outputBuffer, saturationMatrix, divisor, NULL, NULL, kvImageNoFlags);

            vImage_Buffer *temp = inputBuffer;
            inputBuffer = outputBuffer;
            outputBuffer = temp;
        }
#endif

        CGImageRef effectCGImage;
        if ( (effectCGImage = vImageCreateCGImageFromBuffer(inputBuffer, &format, &cleanupBuffer, NULL, kvImageNoAllocate, NULL)) == NULL ) {
            effectCGImage = vImageCreateCGImageFromBuffer(inputBuffer, &format, NULL, NULL, kvImageNoFlags, NULL);
            free(inputBuffer->data);
        }
        if (maskImage) {
            // Only need to draw the base image if the effect image will be masked.
            CGContextDrawImage(outputContext, outputImageRectInPoints, inputCGImage);
        }

        // draw effect image
        CGContextSaveGState(outputContext);
        if (maskImage)
            CGContextClipToMask(outputContext, outputImageRectInPoints, maskImage.CGImage);
        CGContextDrawImage(outputContext, outputImageRectInPoints, effectCGImage);
        CGContextRestoreGState(outputContext);

        // Cleanup
        CGImageRelease(effectCGImage);
        free(outputBuffer->data);
    }
    else
    {
        // draw base image
        CGContextDrawImage(outputContext, outputImageRectInPoints, inputCGImage);
    }

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

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

    return outputImage;
#undef ENABLE_BLUR
#undef ENABLE_SATURATION_ADJUSTMENT
#undef ENABLE_TINT
}


//| ----------------------------------------------------------------------------
//  Helper function to handle deferred cleanup of a buffer.
//
void cleanupBuffer(void *userData, void *buf_data)
{ free(buf_data); }

@end