ios - xcode CVpixelBuffer 显示负值

Question

我正在使用 xcode，目前正在尝试使用以下代码从像素缓冲区中提取像素值。但是，当我打印出像素值时，它包含负值。有人遇到过这样的问题吗？

部分代码如下

- (void)captureOutput:(AVCaptureOutput*)captureOutput didOutputSampleBuffer:
(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection*)connection
{

CVImageBufferRef Buffer = CMSampleBufferGetImageBuffer(sampleBuffer);

CVPixelBufferLockBaseAddress(Buffer, 0);
uint8_t* BaseAddress = (uint8_t*)CVPixelBufferGetBaseAddressOfPlane(Buffer, 0);
size_t Width = CVPixelBufferGetWidth(Buffer);
size_t Height = CVPixelBufferGetHeight(Buffer);
if (BaseAddress)
{
    IplImage* Temporary = cvCreateImage(cvSize(Width, Height), IPL_DEPTH_8U, 4);

    Temporary->imageData = (char*)BaseAddress;
    for (int i = 0; i < Temporary->width * Temporary->height; ++i) {
        NSLog(@"Pixel value: %d",Temporary->imageData[i]);
        //where i try to print the pixels
    }
}

Answer 1

问题是 IplImage 的 imageData 是一个带符号的 char。因此，任何大于 127 的值都将显示为负数。

您可以简单地将它分配给一个 unsigned char，然后打印它，您将看到 0 到 255 之间的值，正如您可能预期的那样:

for (int i = 0; i < Temporary->width * Temporary->height; ++i) {
    unsigned char c = Temporary->imageData[i];
    NSLog(@"Pixel value: %u", c);
}

或者你可以用十六进制打印:

NSLog(@"Pixel value: %02x", c);