Desaturating an image?

[donquibeats]

Hello

In my PyQt5 program, I have a colour (RGB) QImage and I'm being asked for the option to desaturate it, to create a black-and-white version of the image for printing.

So my question is, where to start? A bunch of Googling hasn't revealed a clear answer. Is there an image processing library that already has this covered? Or do I need to start making my own function that steps through the pixel data?

Thanks for any pointers

[jsulm]

@donquibeats See https://stackoverflow.com/questions/27949569/convert-a-qimage-to-grayscale

QImage image = ...;
image.convertToFormat(QImage::Format_Grayscale8);

[donquibeats]

Thanks very much, not sure how I didn't find that in my searching.

In the meantime it turned out to be quite easy to code it myself, and I ended up knocking up a function which could vary the saturation, rather than just making it greyscale. Here's the code below in case anyone finds it useful.

img is a QImage and v is a float. v=0 will give black and white, v=0.5 will halve the colour saturation. v=2 will double the saturation, but I haven't added any min() or max() in the example so that would need to be added if v>1.

    for x in range(0, img.width()):
        for y in range(0, img.height()):
            c = img.pixel(x, y)
            r1, g1, b1 = qRed(c), qGreen(c), qBlue(c)
            grey = (r1 + g1 + b1) / 3
            r2 = grey + (v * (r1 - grey))
            g2 = grey + (v * (g1 - grey))
            b2 = grey + (v * (b1 - grey))
            img.setPixel(x, y, qRgb(int(r2), int(g2), int(b2)))