Does anyone have example code for vImage processing on iOS?

Question

I have read through every bit of documentation out there that I can find, but cannot get a simple vImage call to work. I just need a real example. Documentation is very sparse.

Answer 1

If you're processing video in real-time, and your input is processed in a pixel buffer, here's how to copy that buffer into a vImage, at which point you can call whatever commands you like:

- (CVPixelBufferRef)copyRenderedPixelBuffer:(CVPixelBufferRef)pixelBuffer
{ 
    CVPixelBufferLockBaseAddress( pixelBuffer, 0 );

    // vImage processing
    vImage_Error err;
    vImage_Buffer buffer;
    buffer.data = (unsigned char *)CVPixelBufferGetBaseAddress( pixelBuffer );
    buffer.rowBytes = CVPixelBufferGetBytesPerRow( pixelBuffer );
    buffer.width = CVPixelBufferGetWidth( pixelBuffer );
    buffer.height = CVPixelBufferGetHeight( pixelBuffer );
    vImageCVImageFormatRef vformat = vImageCVImageFormat_CreateWithCVPixelBuffer( pixelBuffer );
    vImage_CGImageFormat cgformat = {
        .bitsPerComponent = 8,
        .bitsPerPixel = 32,
        .bitmapInfo = kCGBitmapByteOrderDefault,
        .colorSpace = NULL,    //sRGB
    };
    const CGFloat bgColor[3] = {0.0, 0.0, 0.0};
    vImageBuffer_InitWithCVPixelBuffer(&buffer, &cgformat, pixelBuffer, vformat, bgColor, kvImageNoAllocate);

    vImage_Buffer outbuffer;
    void *tempBuffer;
    tempBuffer = malloc(CVPixelBufferGetBytesPerRow( pixelBuffer ) * CVPixelBufferGetHeight( pixelBuffer ));
    outbuffer.data = tempBuffer;
    outbuffer.rowBytes = CVPixelBufferGetBytesPerRow( pixelBuffer );
    outbuffer.width = CVPixelBufferGetWidth( pixelBuffer );
    outbuffer.height = CVPixelBufferGetHeight( pixelBuffer );

    err = vImageEqualization_ARGB8888(&buffer, &outbuffer, kvImageNoFlags);

    if(err != -1)
        err = vImageContrastStretch_ARGB8888(&buffer, &outbuffer, kvImageNoFlags);

    if(err != -1)
        err = vImageBuffer_CopyToCVPixelBuffer(&outbuffer, &cgformat, pixelBuffer, vformat, bgColor, kvImageNoFlags);

    if(err != -1)
        free(tempBuffer);

    CVPixelBufferUnlockBaseAddress( pixelBuffer, 0 );

    return (CVPixelBufferRef)CFRetain( pixelBuffer );
}

Answer 2

Updating Ole Bermann's answer: the Accelerate framework was added in iOS 5.0.

Answer 3

An even more advanced example, with optimization of the equalization and stretching functions (ignore commented out code, although you can use it—it works, too:

- (CVPixelBufferRef)copyRenderedPixelBuffer:(CVPixelBufferRef)pixelBuffer {

CVPixelBufferLockBaseAddress( pixelBuffer, 0 );

unsigned char *base = (unsigned char *)CVPixelBufferGetBaseAddress( pixelBuffer );
size_t width = CVPixelBufferGetWidth( pixelBuffer );
size_t height = CVPixelBufferGetHeight( pixelBuffer );
size_t stride = CVPixelBufferGetBytesPerRow( pixelBuffer );

vImage_Buffer _img = {
    .data = base,
    .height = height,
    .width = width,
    .rowBytes = stride
};

vImage_Error err;
vImage_Buffer _dstA, _dstR, _dstG, _dstB;

err = vImageBuffer_Init( &_dstA, height, width, 8 * sizeof( uint8_t ), kvImageNoFlags);
if (err != kvImageNoError)
    NSLog(@"vImageBuffer_Init (alpha) error: %ld", err);

err = vImageBuffer_Init( &_dstR, height, width, 8 * sizeof( uint8_t ), kvImageNoFlags);
if (err != kvImageNoError)
    NSLog(@"vImageBuffer_Init (red) error: %ld", err);

err = vImageBuffer_Init( &_dstG, height, width, 8 * sizeof( uint8_t ), kvImageNoFlags);
if (err != kvImageNoError)
    NSLog(@"vImageBuffer_Init (green) error: %ld", err);

err = vImageBuffer_Init( &_dstB, height, width, 8 * sizeof( uint8_t ), kvImageNoFlags);
if (err != kvImageNoError)
    NSLog(@"vImageBuffer_Init (blue) error: %ld", err);

err = vImageConvert_ARGB8888toPlanar8(&_img, &_dstA, &_dstR, &_dstG, &_dstB, kvImageNoFlags);
if (err != kvImageNoError)
    NSLog(@"vImageConvert_ARGB8888toPlanar8 error: %ld", err);

err = vImageEqualization_Planar8(&_dstR, &_dstR, kvImageNoFlags);
if (err != kvImageNoError)
    NSLog(@"vImageEqualization_Planar8 (red) error: %ld", err);

err = vImageEqualization_Planar8(&_dstG, &_dstG, kvImageNoFlags);
if (err != kvImageNoError)
    NSLog(@"vImageEqualization_Planar8 (green) error: %ld", err);

err = vImageEqualization_Planar8(&_dstB, &_dstB, kvImageNoFlags);
if (err != kvImageNoError)
    NSLog(@"vImageEqualization_Planar8 (blue) error: %ld", err);

err = vImageConvert_Planar8toARGB8888(&_dstA, &_dstR, &_dstG, &_dstB, &_img, kvImageNoFlags);
if (err != kvImageNoError)
    NSLog(@"vImageConvert_Planar8toARGB8888 error: %ld", err);

err = vImageContrastStretch_ARGB8888( &_img, &_img, kvImageNoError );
if (err != kvImageNoError)
    NSLog(@"vImageContrastStretch_ARGB8888 error: %ld", err);

err = vImagePermuteChannels_ARGB8888(&_img, &_img, map, kvImageNoFlags);
if (err != kvImageNoError)
    NSLog(@"vImagePermuteChannels_ARGB8888 error: %ld", err);

free(_dstA.data);
free(_dstR.data);
free(_dstG.data);
free(_dstB.data);

CVPixelBufferUnlockBaseAddress( pixelBuffer, 0 );

return (CVPixelBufferRef)CFRetain( pixelBuffer );

}

Answer 4

Documentation does not exist because the vImage libraries are not available on iOS.

vImage is available on iOS since 5.0. The documentation is here.