Question

如何使用vImage从图像中“提取”一个频道？我现在的方法是：

vImage_Buffer redBuffer;
redBuffer.data = (void*)redImageData.bytes;
redBuffer.width = size.width;
redBuffer.height = size.height;
redBuffer.rowBytes = [redImageData length]/size.height;
vImage_Buffer redBuffer2;
redBuffer2.width = size.width;
redBuffer2.height = size.height;
redBuffer2.rowBytes = size.width;
vImageConvert_RGB888toPlanar8(&redBuffer, &redBuffer2, nil, nil, kvImageNoFlags);

redBuffer是一个工作图像，没有错误，但是vImageConvert给了我一个EXC_BAD_ACCESS，我尝试了很多选项，有些选项导致EXC_BAD_ACCESS，有些导致输出图像损坏。我做错了什么？

所以多亏Rob Keniger，我设法提取了频道，但是如果我尝试将它们与其他频道一起放回去，那么图像会被水平拉伸并且会有RGB条纹。他们为什么不正确地重新组合在一起？这是一个提取通道然后将它们重新组合在一起的示例：

    vImage_Buffer blueBuffer;
    blueBuffer.data = (void*)blueImageData.bytes;
    blueBuffer.width = size.width;
    blueBuffer.height = size.height;
    blueBuffer.rowBytes = [blueImageData length]/size.height;

    vImage_Buffer rBuffer;
    rBuffer.width = size.width;
    rBuffer.height = size.height;
    rBuffer.rowBytes = size.width;
    void *rPixelBuffer = malloc(size.width * size.height);
    if(rPixelBuffer == NULL)
    {
        NSLog(@"No pixelbuffer");
    }
    rBuffer.data = rPixelBuffer;

    vImage_Buffer gBuffer;
    gBuffer.width = size.width;
    gBuffer.height = size.height;
    gBuffer.rowBytes = size.width;
    void *gPixelBuffer = malloc(size.width * size.height);
    if(gPixelBuffer == NULL)
    {
        NSLog(@"No pixelbuffer");
    }
    gBuffer.data = gPixelBuffer;

    vImage_Buffer bBuffer;
    bBuffer.width = size.width;
    bBuffer.height = size.height;
    bBuffer.rowBytes = size.width;
    void *bPixelBuffer = malloc(size.width * size.height);
    if(bPixelBuffer == NULL)
    {
        NSLog(@"No pixelbuffer");
    }
    bBuffer.data = bPixelBuffer;

    vImageConvert_RGB888toPlanar8(&blueBuffer, &rBuffer, &gBuffer, &bBuffer, kvImageNoFlags);

    size_t destinationImageBytesLength = size.width*size.height*3;
    const void* destinationImageBytes = valloc(destinationImageBytesLength);
    NSData* destinationImageData = [[NSData alloc] initWithBytes:destinationImageBytes length:destinationImageBytesLength];
    vImage_Buffer destinationBuffer;
    destinationBuffer.data = (void*)destinationImageData.bytes;
    destinationBuffer.width = size.width;
    destinationBuffer.height = size.height;
    destinationBuffer.rowBytes = [destinationImageData length]/size.height;

    vImage_Error result = vImageConvert_Planar8toRGB888(&rBuffer, &gBuffer, &bBuffer, &destinationBuffer, 0);
    NSImage* image = nil;
    if(result == kvImageNoError)
    {
        //TODO: If you need color matching, use an appropriate colorspace here
        CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
        CGDataProviderRef dataProvider = CGDataProviderCreateWithCFData((__bridge CFDataRef)(destinationImageData));
        CGImageRef finalImageRef = CGImageCreate(size.width, size.height, 8, 24, destinationBuffer.rowBytes, colorSpace, kCGBitmapByteOrder32Big|kCGImageAlphaNone, dataProvider, NULL, NO, kCGRenderingIntentDefault);
        CGColorSpaceRelease(colorSpace);
        CGDataProviderRelease(dataProvider);
        image = [[NSImage alloc] initWithCGImage:finalImageRef size:NSMakeSize(size.width, size.height)];
        CGImageRelease(finalImageRef);
    }
    free((void*)destinationImageBytes);
    return image;

Answer 1

解决方案（或者，至少是一个解决方案的开头）：

.accept(MediaType.APPLICATION_JSON)

这对我有用，除了我开发的iOS相机应用程序的OpenCV版本;预览窗口在一侧显示一个白色条纹，每次OpenCV都不像我做的那样。我认为这不是你的问题，因为你的多重线条只有三行代码，所以值得一试。

Answer 2

您没有初始化redBuffer2输出缓冲区，因此您无法存储函数的输出。

//allocate a buffer for the output image and check it exists
void *pixelBuffer = malloc(size.width * size.height);
if(pixelBuffer == NULL)
{
    NSLog(@"No pixelbuffer"); 
    //handle this somehow
}

//assign the allocated buffer to the vImage buffer struct
redBuffer2.data = pixelBuffer;

Answer 3

vImageConvert_RGB888toPlanar8不接受vImage_Buffer结构的NULL指针。该函数标记为VIMAGE_NON_NULL（1,2,3,4），这应该会导致编译器抱怨此用法。

在OS X.10或iOS 8上添加了vImageExtractChannel_ARGB8888，但没有RGB888等效项。如果需要，您应该提交功能请求。 http://bugreporter.apple.com同时，你可以制作三个平面8输出缓冲区并抛出两个缓冲区。

vImageConvert提取一个通道

3 个答案: