Question

我正在尝试在iOS 8设备上尽快调整CMSampleBufferRef的大小以用于图像处理。根据我在网上找到的，这样做的方法似乎是使用Accelerate框架中的vImage API。但是，我没有对Accelerate框架做太多工作，我也无法弄清楚如何做到这一点。这是我到目前为止将图像缩放到200x200：

- (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);
}

结果是outBuffer。之后，我也不确定如何将outBuffer转换回CVImageBufferRef以进行进一步的图像处理。任何建议将不胜感激！

Answer 1

vImageScale只返回缓冲区数据，并注意需要释放缓冲区我不知道是否有更快的方法只使用该输出缓冲区，但我会将缓冲区转换为CGImage。类似于here的内容所以将其作为参考文献

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)

稍后我会将其转换为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;
}

我非常确定可以避免转换为CGImage并开始使用缓冲区，但我从未尝试过。

Answer 2

您必须将重采样过滤器与任何改变图像几何的vImage操作结合使用：第32页，vImage编程指南。

Answer 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 );

//在这里处理vIMAGE

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

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

CVPixelBufferUnlockBaseAddress( pixelBuffer, 0 );

return (CVPixelBufferRef)CFRetain( pixelBuffer );

}

如何在iOS 8的Accelerate框架中使用vImage缩放图像？

3 个答案: