C Function to create a blurred CGimageRef (supply an image and a blur radius). Uses vImage Accelerate Framework for Mac OS X/iOS 5+ and is VERY fast.

vImageFastBlur.c

// Assumes ARGB8888
CGImageRef CGImageCreateBlurredImage(CGImageRef inImage, NSUInteger blurRadius)
{
    if (!inImage) { return NULL; }

    uint32_t radius = (blurRadius % 2) ? (uint32_t)blurRadius : (uint32_t)++blurRadius;
    vImage_Error error;
    vImage_CGImageFormat imageFormat = {(uint32_t)CGImageGetBitsPerComponent(inImage), (uint32_t)CGImageGetBitsPerPixel(inImage), CGImageGetColorSpace(inImage), CGImageGetBitmapInfo(inImage), 0, NULL, kCGRenderingIntentDefault};
    
    vImage_Buffer source;
    error = vImageBuffer_InitWithCGImage(&source, &imageFormat, NULL, inImage, kvImageNoFlags);
    
    vImage_Buffer destination;
    error = vImageBuffer_Init(&destination, CGImageGetHeight(inImage), CGImageGetWidth(inImage), (uint32_t)CGImageGetBitsPerPixel(inImage), kvImageNoFlags);
    
    error = vImageTentConvolve_ARGB8888(&source, &destination, NULL, 0, 0, radius, radius, NULL, kvImageEdgeExtend);
    
    if (error) {
        free(source.data);
        free(destination.data);
        return NULL;
    }
    CGImageRef outImage = vImageCreateCGImageFromBuffer(&destination, &imageFormat, NULL, NULL, kvImageNoFlags, &error);
    free(source.data);
    free(destination.data);
    return outImage;
}