Basic image processing on a QImage

Hello forum people,

Does anyone know of an easy way to perform basic image processing algorithms on a QImage? I figured algorithms for modifying brightness and contrast where already implemented quite a few times in Qt, but I'm unable to find Qt functions or otherwise libraries that aren't a complete overkill for the task (e.g. using openCV and converting image formats back and forth).

So far, I've implemented the basic brightness / contrast / gamma filters myself, but moving on to implementing a simple blur (convolution with a Gaussian window) is too much...

Any suggestions?

Thanks!
Danny

Maybe you want to have a look at

http://doc.qt.nokia.com/4.6/qgraphicseffect.html

I didn't use it yet, though.

HIH

Johannes

Thanks for the quickly reply!

I'm kind of new in Qt, but according to my understanding this class doesn't exactly do what I want. I think it's used as a rendering effect on a QGraphicItem, when rendered on a QGraphicView. (Works on a painter, when there is a draw() event, etc.)

I really think I actually need something a lot more basic, just some trivial image processing code that works on the pixels of a QImage directly. Sounds like it must be implemented somewhere in Qt... no?

Thanks,
Danny

If you look into the implementation of QGraphicsEffect, you can see how it is implemented.

They use some QPixMapFilters, which sadly are declared private (qpixmapfilter_p.h).. Bu you can look into those files and see how it is done:

Blurring from qpixmapfilter.cpp:

Code:

---

static QImage blurred(const QImage& image, const QRect& rect, int radius, bool alphaOnly = false)
{
    int tab[] = { 14, 10, 8, 6, 5, 5, 4, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2 };
    int alpha = (radius < 1)  ? 16 : (radius > 17) ? 1 : tab[radius-1];
 
    QImage result = image.convertToFormat(QImage::Format_ARGB32_Premultiplied);
    int r1 = rect.top();
    int r2 = rect.bottom();
    int c1 = rect.left();
    int c2 = rect.right();
 
    int bpl = result.bytesPerLine();
    int rgba[4];
    unsigned char* p;
 
    int i1 = 0;
    int i2 = 3;
 
    if (alphaOnly)
        i1 = i2 = (QSysInfo::ByteOrder == QSysInfo::BigEndian ? 0 : 3);
 
    for (int col = c1; col <= c2; col++) {
        p = result.scanLine(r1) + col * 4;
        for (int i = i1; i <= i2; i++)
            rgba[i] = p[i] << 4;
 
        p += bpl;
        for (int j = r1; j < r2; j++, p += bpl)
            for (int i = i1; i <= i2; i++)
                p[i] = (rgba[i] += ((p[i] << 4) - rgba[i]) * alpha / 16) >> 4;
    }
 
    for (int row = r1; row <= r2; row++) {
        p = result.scanLine(row) + c1 * 4;
        for (int i = i1; i <= i2; i++)
            rgba[i] = p[i] << 4;
 
        p += 4;
        for (int j = c1; j < c2; j++, p += 4)
            for (int i = i1; i <= i2; i++)
                p[i] = (rgba[i] += ((p[i] << 4) - rgba[i]) * alpha / 16) >> 4;
    }
 
    for (int col = c1; col <= c2; col++) {
        p = result.scanLine(r2) + col * 4;
        for (int i = i1; i <= i2; i++)
            rgba[i] = p[i] << 4;
 
        p -= bpl;
        for (int j = r1; j < r2; j++, p -= bpl)
            for (int i = i1; i <= i2; i++)
                p[i] = (rgba[i] += ((p[i] << 4) - rgba[i]) * alpha / 16) >> 4;
    }
 
    for (int row = r1; row <= r2; row++) {
        p = result.scanLine(row) + c2 * 4;
        for (int i = i1; i <= i2; i++)
            rgba[i] = p[i] << 4;
 
        p -= 4;
        for (int j = c1; j < c2; j++, p -= 4)
            for (int i = i1; i <= i2; i++)
                p[i] = (rgba[i] += ((p[i] << 4) - rgba[i]) * alpha / 16) >> 4;
    }
 
    return result;
}

---

Good luck :-> !

Johannes

While not exactly what I originally wanted, your snippet was extremely useful!

So it seems like a basic (Q)image processing Qt library doesn't exist, right? That's too bad...

Thanks!
Danny

Just found a QtSolution for this: http://qt.nokia.com/products/appdev/...timagefilters/

HIH

Johannes

The OpenCV library may be what you're looking for ;)
I'm using it at the moment with Qt for a computer vision application :)

I've posted a contrast and a brightness filter on this forum .
you can check it out .

Can you share you contrast/brigthen filter ?
I would like to have look at it.

you can use fmt_filters filters. this filter are written in c++ but is compatible whit QImage. only check the examples.

homepage http://ksquirrel.sourceforge.net/subprojects.php

sorry by the double post..

please. someone of the staf f can delte this..