Convert from RGB to BGR w/o OpenCV for ofVideoGrabber frame

@rudycazabon wrote:

Greetings everyone -

I need to use ofVideoGrabber as opposed to OpenCV to VideoCapture. In previous code I wrote I used Mat::data to pull the actual pixel of the frame as a uchar* … and reading through the ofVideoGrabber::getPixels() call I see that it too returns a unsigned char*.

However, when it comes time to convert the incoming from ofVideoGrabber from RGB to BGR format I get a failure. The code I am using is as follows:

void ConvertBGR(
const size_t imageWidth,
const size_t imageHeight,
const std::vector<uint8_t*>& srcs,
float* dst,
const std::vector& mean,
const std::vector& scale)
{
const size_t channels = 3;
const size_t channelSize = imageWidth * imageHeight;
const size_t imageSize = channelSize * channels;

float* rBuffer = &dst[channelSize * 0];
float* gBuffer = &dst[channelSize * 1];
float* bBuffer = &dst[channelSize * 2];

const size_t rOff = 2;
const size_t gOff = 1;
const size_t bOff = 0;

size_t idx = 0;

// swap the bytes
for (size_t mb = 0; mb < srcs.size(); mb++) {
const uint8_t* srcBuffer = srcs[mb];

  idx = imageSize * mb;

  for (size_t h = 0; h < imageHeight; h++) {
  	size_t srcIdx = h * imageWidth * channels;

  	for (size_t w = 0; w < imageWidth; w++, idx++, srcIdx += channels) {
  		rBuffer[idx] = ((float)srcBuffer[srcIdx + rOff] - mean[0]) / scale[0];
  		gBuffer[idx] = ((float)srcBuffer[srcIdx + gOff] - mean[1]) / scale[1];
  		bBuffer[idx] = ((float)srcBuffer[srcIdx + bOff] - mean[2]) / scale[2];
  	}
  }

}
}

My call to this function using ofVideoGrabber is as follows:

ofVideoGrabber grabber;

< grabber initialization code >
<success!!>

ConvertBGR(inputWidth, inputHeight, { grabber.getPixels() }, inputPtr, mean, scale);

The call to this same function using OpenCV is successful. The call to this function from ofVideoGrabber.getPixels() fails rBuffer, gBuffer and bbuffer for access violations/memory not accessible.

Any and all comments and insights from the community would be greatly appreciated.

Regards,
RudyC

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