QT4 How to blur QPixmap image?

Question

QT4 How to blur QPixmap image?

I am looking for something like one of the following:

Blur(pixmap); 
painter.Blur(); 
painter.Blur(rect);

What is the best way to do this?

Answer 1

1st) declare an external QT procedure:

QT_BEGIN_NAMESPACE
  extern Q_WIDGETS_EXPORT void qt_blurImage( QPainter *p, QImage &blurImage, qreal radius, bool quality, bool alphaOnly, int transposed = 0 );
QT_END_NAMESPACE

2nd) Use:

  extern QImage srcImg;//source image
  QPixmap pxDst( srcImg.size() );//blurred destination
  pxDst.fill( Qt::transparent );
  {
    QPainter painter( &pxDst );
    qt_blurImage( &painter, srcImg, 2, true, false );//blur radius: 2px
  }

Answer 2

Method 1a: capture the raw bits and do it yourself. You must be familiar with bitmaps and blur algorithms to implement blur. If you need such accuracy, this is the way to go.

QImage image = pixmap.toImage();
if (image.format() != QImage::Format_RGB32)
     image = image.convertToFormat(QImage::Format_RGB32);
uchar* bits = image.bits();
int rowBytes = image.bytesPerLine();
DoMyOwnBlurAlgorithm(bits, image.width(), image.height(), rowBytes);
return QPixmap::fromImage(image);

Method 1b: Who Needs Raw Bits? Instead, you can use image.pixel (x, y) and image.setPixel (x, y, color). It will not be as fast as 1a, but it should be a little easier to understand and code.

QImage image = pixmap.toImage();
QImage output(image.width(), image.height(), image.format());
for (int y=0; y<image.height(); ++y)
   for (int x=0; x<image.width(); ++x)
      output.setPixel(getBlurredColor(image, x, y));
return output;

2: QGraphicsBlurEffect . :

QPixmap BlurAPixmap(const QPixmap& inPixmap)
{
    QLabel* label = new QLabel();
    label->setPixmap(inPixmap);
    label->setGraphicsEffect(new QGraphicsBlurEffect());
    QPixmap output(inPixmap.width(), inPixmap.height());
    QPainter painter(&output);
    label->render(&painter);
    return output;
}

. , , . 2 .

Answer 3

:

#include <QtGui/QApplication>
#include <QImage>
#include <QPixmap>
#include <QLabel>

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;
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QLabel label;
    QImage image("image.png");
    image =  blurred(image,image.rect(),10,false);
    label.setPixmap(QPixmap::fromImage(image));
    label.show();

    return a.exec();
}

Answer 4

. Qt 5.3, QGraphicsEffect QImage ( ).

QImage applyEffectToImage(QImage src, QGraphicsEffect *effect, int extent = 0)
{
    if(src.isNull()) return QImage();   //No need to do anything else!
    if(!effect) return src;             //No need to do anything else!
    QGraphicsScene scene;
    QGraphicsPixmapItem item;
    item.setPixmap(QPixmap::fromImage(src));
    item.setGraphicsEffect(effect);
    scene.addItem(&item);
    QImage res(src.size()+QSize(extent*2, extent*2), QImage::Format_ARGB32);
    res.fill(Qt::transparent);
    QPainter ptr(&res);
    scene.render(&ptr, QRectF(), QRectF( -extent, -extent, src.width()+extent*2, src.height()+extent*2 ) );
    return res;
}

, , :

QGraphicsBlurEffect *blur = new QGraphicsBlurEffect;
blur->setBlurRadius(8);
QImage source("://img1.png");
QImage result = applyEffectToImage(source, blur);
result.save("final.png");

, , . :

QGraphicsDropShadowEffect *e = new QGraphicsDropShadowEffect;
e->setColor(QColor(40,40,40,245));
e->setOffset(0,10);
e->setBlurRadius(50);
QImage p("://img3.png");
QImage res = applyEffectToImage(p, e, 40);

And pay attention to the degree parameter, it adds the extentnumber of pixels to all sides of the original image, especially useful for shadows and blur, so as not to be cropped.

Answer 5

A Gaussian blur is an easy way to create a blur effect.

Edit: And so, I came across Qt QGraphicsBlurEffect . Introduced in Qt 4.6, it seems to do exactly what you want.