iOS Accelerate Framework vImage - Performance improvement?

Question

I\'ve been working with OpenCV and Apple\'s Accelerate framework and find the performance of Accelerate to be slow and Apple\'s documentation limited. Let\'s take for example:

Answer 1

Don't keep re-allocating vImage_Buffer if you can avoid it.

One thing that is critical to vImage accelerate performance is the reuse of vImage_Buffers. I can't say how many times I read in Apple's limited documentation hints to this effect, but I was definitely not listening.

In the aforementioned blur code example, I reworked the test app to setup the vImage_Buffer input and output buffers once per image rather than once for each call to boxBlur. I dropped <10ms per call which made a noticeable difference in response time.

This says that Accelerate needs time to warm-up before you start seeing performance improvements. The first call to this method took 34ms.

- (UIImage *)boxBlurWithSize:(int)boxSize
{
    vImage_Error error;
    error = vImageBoxConvolve_ARGB8888(&_inputImageBuffer,
                                       &_outputImageBuffer,
                                       NULL,
                                       0,
                                       0,
                                       boxSize,
                                       boxSize,
                                       NULL,
                                       kvImageEdgeExtend);
    if (error) {
        NSLog(@"vImage error %zd", error);
    }

    CGImageRef modifiedImageRef = vImageCreateCGImageFromBuffer(&_outputImageBuffer,
                                                                &_inputImageFormat,
                                                                NULL,
                                                                NULL,
                                                                kvImageNoFlags,
                                                                &error);

    UIImage *returnImage = [UIImage imageWithCGImage:modifiedImageRef];
    CGImageRelease(modifiedImageRef);

    return returnImage;
}