How to set opacity of a QImage

[timain]

Hello,
I'd like to know what is the best way to set an opacity of a QImage.

I know there is setOpacity(int) function defined in QPixmap class but I work with QImage..

Thank you.

[SGaist]

Hi,

AFAIK, you would need to use an ARGB format. Then it depends on what you are currently doing with that QImage, painting ?

[andre]

You can also apply the opacity at the time of painting, if that's what you are doing.

[timain]

Thanks for your reply ,

In fact, I have a slider "Opacity" and I want to modify opacity of a QImage and see directly the result.

[andre]

How do you show the image in the first place? What widget are you using to display it?

[timain]

I have a QLabel with a QImage (base image ) and I want to drag others QImage on this( anomaly image like triangle, circle, square, etc). During dropEvent, I copy all pixels of the anomaly image on the base image into the rectangle where it is dropped. So I save a finally image which is the baseImage containing the anomaly.

Currently I can set opacity of the default image pasted on the base image, I can see it directly, this is my function.
@void AjoutDefaut::opacity(QImage& image)
{
m_method = 9;
showSliders();
if ( m_A>255 || m_A<0 )
{
m_A=50;
}
QPixmap transparent(image.size());
transparent.fill(Qt::transparent);
QPainter p;

p.begin(&transparent);
p.setCompositionMode(QPainter::CompositionMode_Source);
p.drawPixmap(0, 0, QPixmap::fromImage(image));
p.setCompositionMode(QPainter::CompositionMode_DestinationIn);
p.fillRect(transparent.rect(), QColor(0, 0, 0, m_A));
p.end();
image = transparent.toImage();
loadImage(image);
//m_currentAnomaly = image;
repaint();

}@

I have the result that I want. ( transparency setted )
And, this is my function which save now the image after setting the anomaly opacity:
@
QImage DragWidgetCible::insertAnomaly( QImage base )
{
QImage result = QImage();
result = base.copy(0, 0, base.width(), base.height());
result.convertToFormat(QImage::Format_ARGB32);
for(int elem=0; elem<m_anomalyContainer.size(); elem++)
{
m_anomalyContainer[elem].getAnomaly().convertToFormat(QImage::Format_ARGB32);
binariseAnomaly(m_anomalyContainer[elem].getAnomaly(), 1);
int width = m_anomalyContainer[elem].getAnomaly().width();
int height = m_anomalyContainer[elem].getAnomaly().height();
QPoint p(m_anomalyContainer[elem].getAnomalyPos());

 for(int i=p.x(),k=0; i<p.x()+width, k<width; i++,k++)
 {
   for(int j=p.y(), l=0; j<p.y()+height, l<height; j++, l++)
   {
      QRgb x = m_anomalyContainer[elem].getAnomaly().pixel(k, l);
      qDebug() << qGray(x);
      if(!m_opacityUpdated)
      {
          if (qAlpha(x) != 0 && (qGray(x) != 255))
          {
                result.setPixel(i, j, x);
          }
      }
      else (// we are in this case because  m_opacityUpdated = true )
      {
          result.setPixel(i, j, x);
          m_opacityUpdated = false;
      }
    }
 }

}
return result;
}@

BUT, when I see the final saved image, I have another kind of opacity: a dark image, and when the opacity is setted to 0, the anomaly is black.

[ipanera]

This works for me. I hope helps

@QImage image;
image.load(":/images/ok.png");
//If the image doesn't have set the alpha chanel
image = image.convertToFormat(QImage::Format_ARGB32);
//...

QImage image2;
image2 = setOpacity(image, 0.5);
//...

QImage setOpacity(QImage& image, qreal opacity)
{
QImage newImg(image.size(), QImage::Format_ARGB32);
newImg.fill(Qt::transparent);

QPainter painter(&newImg);
painter.setOpacity(opacity);
painter.drawImage(QRect(0, 0, image.width(), image.height()), image);

return newImg;

}@