Fast way to show QImage

  • Hello everyone, I have a sequence of images that I need to show with frequency 50 fps. All images in format QImage::Format_Indexed8.

    1. My first approach was to convert image to pixmap (in separate thread) and than set it to QLabel(in main thread), it works but in pretty inefficient way. Image on a Qlabel was lagging.
    2. I also tried with QGraphicsView and QGraphicsScene. Result was almoustly the same as in first approach. Image was also lagging.
    3. Another approach was through QVideoFrame( example), it also works with all other images formats except QImage::Format_Indexed8, so I need to convert it to QImage::Format_RGB32 and than set to QAbstractVideoSurface that also was not so efficient.

    Now I have doubts that in all approaches Qt somewhere in background convert image from QImage::Format_Indexed8 to some QImage::Format to draw it on QWidget, please correct me if I am wrong. I will be glad to any suggestions or help about this topic.

  • Ok, I figured it out. As I assumed, it always convert from QImage::Format_Indexed8 to some other format, cause in documentation written:
    Drawing into a QImage with QImage::Format_Indexed8 is not supported.
    Thus instead of using QImage::Format_Indexed8, I need to use QImage::Format_Grayscale8. So the best way to show image, it is with reiplementing QPaintevent with or without using OpenGl.

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