QImage color painting question

[sleam]

Hi, I got a QImage and I want to paint only the red color channel to screen with QPainter.
I want to paint the red color channel as grayscale, not as red. The blue and green channels should not be painted, I only want information from the red channel.

What is the best approach?

Thank you :)

[ZapB]

One simplistic way is to use iterate over the pixels of your QImage and create a new filtered QImage where each pixel has a value of (r, r, r) where r is the red channel of your original image. Then display your new image.

[ZapB]

If your image is going to be changing often then it might be better to do this in hardware by using OpenGL and a suitable fragment shader.

[sleam]

Thank you, yes, my image is updated 20 times a second, so I want to avoid heavy operations.

Is there no easy way around this? Do I really need to manipulate the image in such a way?

[ZapB]

For that kind of refresh rate I would definitely look at OpenGL so that the heavy lifting is done in hardware rather than software (assuming you have an accelerated OpenGL implementation).

[andre]

I agree: you'll have to turn to HW accelerated methods for this, and OpenGL would be the first candidate for that.

[sleam]

Okay, thank you :)