Auto threshold value of monochrome conversion

[M. Bashir]

Hi All,

It's easy to convert any image to monochrome format by using QImage::convertToFormat like this:

pImage.convertToFormat(QImage::Format_Mono, Qt::MonoOnly|Qt::ThresholdDither|Qt::AvoidDither);

pImage.convertToFormat(QImage::Format_Mono, Qt::MonoOnly|Qt::ThresholdDither|Qt::AvoidDither);

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but convertToFormat always guessing that the value of conversion's threshold is 255 where in some cases we need to use another threshold's value. I checked out GIMP and I noticed that it uses an automatic method for guessing threshold's value (see the example below) so I'm wondering:

How I can convert images to monochrome format by using auto threshold's value just like GIMP conversion method?

Original


QImage conversion


Automatic GIMP conversion

P.S

I've wrote a stupid function for converting images to monochrome by using a specified threshold's value as following but I need to know how I can automatically specify threshold's value:

QImage getThresholdBW(QImage pImage, int threshold)
{
    QImage result = pImage;
    result.fill(255);
    for(int x=0; x<pImage.width(); x++)
        for(int y=0; y<pImage.height(); y++)
            result.setPixel(x, y, qGray(pImage.pixel(x, y))>threshold?qRgb(255, 255, 255):qRgb(0, 0, 0));
 
    return result;
}

QImage getThresholdBW(QImage pImage, int threshold)
{
    QImage result = pImage;
    result.fill(255);
    for(int x=0; x<pImage.width(); x++)
        for(int y=0; y<pImage.height(); y++)
            result.setPixel(x, y, qGray(pImage.pixel(x, y))>threshold?qRgb(255, 255, 255):qRgb(0, 0, 0));

    return result;
}

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