在iOS 8的加速框架中如何使用vImage缩放图像?

I am trying to resize a CMSampleBufferRef as quickly as possible on an iOS 8 device for use in image processing. From what I have found online, the way to do this seems to be by using the vImage API in the Accelerate framework. However, I haven't done much with the Accelerate framework and I can't quite figure out how to do this. Here is what I have so far to scale an image to 200x200:

我正在尝试在ios8设备上尽可能快地调整一个CMSampleBufferRef，以便在图像处理中使用。从我在网上找到的东西来看，这似乎是通过在加速框架中使用vImage API来实现的。但是，我并没有对加速框架做过多的工作，我也不知道该怎么做。下面是我到目前为止对200x200的图像进行缩放的方法:

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
    CVImageBufferRef cvimgRef = CMSampleBufferGetImageBuffer(sampleBuffer);
    CVPixelBufferLockBaseAddress(cvimgRef,0);
    void *imageData = CVPixelBufferGetBaseAddress(cvimgRef);
    NSInteger width = CVPixelBufferGetWidth(cvimgRef);
    NSInteger height = CVPixelBufferGetHeight(cvimgRef);

    unsigned char *newData= // NOT SURE WHAT THIS SHOULD BE...
    vImage_Buffer  inBuff = { imageData, height, width, 4*width };
    vImage_Buffer  outBuff = { newData, 200, 200, 4*200 };

    // NOT SURE IF THIS IS THE CORRECT METHOD... video output settings for kCVPixelBufferPixelFormatTypeKey is set to kCVPixelFormatType_32BGRA
    // This seems wrong since the image scale is ARGB, not BGRA.
    vImageScale_ARGB8888(inBuffer, outBuffer, NULL, kvImageNoFlags);
    CVPixelBufferUnlockBaseAddress(cvimgRef,0);
}

Where outBuffer is the result. After that, I am also not sure how to convert the outBuffer back to a CVImageBufferRef for further image processing. Any suggestions would be appreciated!

输出缓冲区就是结果。在此之后，我也不确定如何将outBuffer转换为CVImageBufferRef来进行进一步的图像处理。如有任何建议将不胜感激!

3 个解决方案

#1

vImageScale returns just a buffer data, and pay attention that buffers need to be freed.
I don't know if there is a faster way just using that out buffer but I would convert the buffer into a CGImage. Something like that taken from here so take it as a reference

vImageScale只返回一个缓冲区数据，并注意缓冲区需要被释放。我不知道是否有更快的方法来使用这个缓冲区，但我会将缓冲区转换成CGImage。像这样的东西从这里开始，所以把它作为参考。

vImage_CGImageFormat format = {
        .bitsPerComponent = 8,
        .bitsPerPixel = 32,
        .colorSpace = NULL,
        .bitmapInfo = (CGBitmapInfo)kCGImageAlphaFirst,
        .version = 0,
        .decode = NULL,
        .renderingIntent = kCGRenderingIntentDefault,
    };
ret = kvImageNoError;
    CGImageRef destRef = vImageCreateCGImageFromBuffer(&dstBuffer, &format, NULL, NULL, kvImageNoFlags, &ret)

Later I will convert it into a CVPixelBuffer.

稍后我将把它转换成CVPixelBuffer。

- (CVPixelBufferRef) pixelBufferFromCGImage: (CGImageRef) image
{
    NSDictionary *options = @{
                              (NSString*)kCVPixelBufferCGImageCompatibilityKey : @YES,
                              (NSString*)kCVPixelBufferCGBitmapContextCompatibilityKey : @YES,
                              };

CVPixelBufferRef pxbuffer = NULL;
CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, CGImageGetWidth(image),
                    CGImageGetHeight(image), kCVPixelFormatType_32ARGB, (__bridge CFDictionaryRef) options,
                    &pxbuffer);
if (status!=kCVReturnSuccess) {
    DLog(@"Operation failed");
}
NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);

CVPixelBufferLockBaseAddress(pxbuffer, 0);
void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);

CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(pxdata, CGImageGetWidth(image),
                                             CGImageGetHeight(image), 8, 4*CGImageGetWidth(image), rgbColorSpace,
                                             kCGImageAlphaNoneSkipFirst);
NSParameterAssert(context);

CGContextConcatCTM(context, CGAffineTransformMakeRotation(0));

CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image),
                                       CGImageGetHeight(image)), image);
CGColorSpaceRelease(rgbColorSpace);
CGContextRelease(context);

CVPixelBufferUnlockBaseAddress(pxbuffer, 0);
return pxbuffer;
}

I'm pretty sure that is possible to avoid the conversion into a CGImage and start using the buffer, but I never tried.

我很确定，可以避免转换成CGImage并开始使用缓冲区，但我从未尝试过。

#2

You have to use a resampling filter in conjunction with any vImage operations that alter image geometry: page 32, vImage Programming Guide.

你必须使用一个再采样过滤器和任何改变图像几何的维法师操作:第32页，vImage编程指南。

#3

- (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 );

// PROCESS vIMAGE HERE

/ /流程vIMAGE这里

    err = vImageBuffer_CopyToCVPixelBuffer(&outbuffer, &cgformat, pixelBuffer, vformat, bgColor, kvImageNoFlags);

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

CVPixelBufferUnlockBaseAddress( pixelBuffer, 0 );

return (CVPixelBufferRef)CFRetain( pixelBuffer );

}

}