QImage to QPixmap is too slow

[yoavmil]

A threaded pipe-line sounds right.
do this in 3 steps:
a) 1 thread reads data to qimage
b) 1 thread converts qimage to qpixmap
c) gui thread shows the qpixmap.

use signal/slots between threads

[kshegunov]

@betterorbest
That's a big image. Have you tried drawing the image directly, instead of converting it to a pixmap first? If that doesn't work have you tried drawing the image on a GL surface?

@yoavmil

b) 1 thread converts qimage to qpixmap

That ain't happening. QPixmap is not reentrant.

[A Former User]

@betterorbest said:

Now I have to first convert my image from the hardware data streams

The fastest way possible is to move the raw pixel data directly into an OpenGL Pixel Buffer Object and do all the transformations / rendering in the GPU.

[betterorbest]

@kshegunov
Thank you for your answer. I thought there may be some faster way without using opengl. But if this is the fact, I will finally try the opengGl. In other hand, drawing the image directly seems to be as slow as QPixmap::from(qImage).

[betterorbest]

@yoavmil
I tried your advice once. But the conversion from qImage to qPixmap is stiil the bottle neck. Thank you for your advice.

@Moderators
Thank you. I will try the openGl advice.

[Q139]

You could cut image to 2 or 4 or more parts , spread load between threads while processing and later reconstruct image to 1.

[kshegunov]

@betterorbest said:

Thank you for your answer. I thought there may be some faster way without using opengl.

Nope. OpenGL has facilities for such things, while the ordinary QPainter based approach doesn't. So I'd go with what @Wieland suggested.

[SGaist]

Hi,

Out of curiosity, what is the format of your images ?

[betterorbest]

@SGaist
The original data streams is raw data. I convert the raw data to color image with QImage::Format_RGB888.

[SGaist]

Are you only showing that image ?