Qt - Verify if Image loaded is grayscale

Question

I have developed a small GUI in C++/Qt, I would like to know a fast way to test if image loaded is grayscale. In practise, when I load a grayscale image of gif format, I want it to be recognized as a grayscale image with depth()=8, and when I load a colored gif image, the depth of QImage would be 32.

Here's my open method :

void ImageViewer::open()
{
  int status_off = 0;
  fileName = QFileDialog::getOpenFileName(this, tr("Open File"), QDir::currentPath());

  if (!fileName.isEmpty()) {
    current_qimage = QImage(fileName);
    if (current_qimage.isNull()) {
      QMessageBox::information(this, tr("Image Viewer"),
          tr("Cannot load %1.").arg(fileName));
      return;
    }
    updateStatus(status_off);
    // Image is colored with depth=8
    if (current_qimage.depth()/8 != 4)
      {rgblum_status = 0;}
      else // Image is grayscale with depth=32
      {rgblum_status = 1;}

    loadImage();
  }
}

From my first test, it seems that current_qimage, in current_qimage = QImage(fileName); inherits firstly from the format (gif here) before the contents of the image. Therefore, QImage has in two cases a depth() equal to 32.

How to make the difference between these two gif images (one grayscale and the other colored) ?

score 3 · Accepted Answer · answered Feb 27 '13 at 21:46

3

The QImage class has a function that you can call to test if the image is grayscale or not: QImage::isGrayscale(). It works for both 8-bit color table indexed images and 32-bit images.

answered Feb 27 '13 at 21:46

Daniel Hedberg

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Qt - Verify if Image loaded is grayscale

1 Answers1