Converting QImage data from RGB to luminance

astodolski

Are there methods to convert RGB data (that which is passed to QImage constructor) to that of luminance (YUV) values?

SGaist

Hi,

AFAIK, QImage doesn't work in the YUV colorspace, however you could use a library like e.g. OpenCV for that

astodolski

[quote author="SGaist" date="1414483275"]Hi,

AFAIK, QImage doesn't work in the YUV colorspace, however you could use a library like e.g. OpenCV for that[/quote]

I could have used libVLC too. I posted here becuase I wanted to keep it within Qt only.

Thanks anyway. I thought it might have been possible.

However, perhaps taking the rgb data thats passed to QImage can be converted to luminance beforehand. Hopefully someone's done that already

SGaist

If it's just a question of color space conversion you should be able to do it yourself pixel by pixel.

astodolski

This is where I've gone with this:

@
void Worker::run()
{
QImage image;
marker markerFound;

const double rY = 0.299, gY = 0.587, bY = 0.114;

ProcessFrames();

if (bitCount == 32)
    image = QImage(imageAverage, imageWidth, imageHeight, QImage::Format_RGB32);

else
    image = QImage(imageAverage, imageWidth, imageHeight, QImage::Format_RGB888);

    QVector<marker>MarkerMap(0);

    for (int y = 0; y < imageHeight; ++y)
    {
        for (int x = 0; x < imageWidth; ++x)
        {
            int Sum = 0;
            int Y = 0;

            Y = (int)(imageAverage[(y * imageStride) + byteCount * x + 0] & 0xff) * rY +
                (int)(imageAverage[(y * imageStride) + byteCount * x + 1] & 0xff) * gY +
                (int)(imageAverage[(y * imageStride) + byteCount * x + 2] & 0xff) * bY;


            for (int c = 0; c < 3; ++c) //c = color i.e. RGB so 3 colors.
                Sum += imageAverage[(y * imageStride) + byteCount * x + c]; //We have a 3 color pixel value for testing.

            if (Sum <= thresholdValue)  // Map it or go check the next.
                continue;

            markerFound.x = x;          // Mapping it.
            markerFound.y = y;
            markerFound.intensity = Y;

            MarkerMap.append(markerFound);
        }
    }

}
@

SGaist

Thanks for sharing !