Basic image processing on a QImage

[Danny]

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

[JohannesMunk]

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

[Danny]

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

[JohannesMunk]

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:

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;
}

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;
}

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Good luck :-> !

Johannes

[Danny]

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

[JohannesMunk]

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

HIH

Johannes

[dmginc]

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

[toutarrive]

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

[toutarrive]

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

[ecanela]

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

[ecanela]

sorry by the double post..

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