Draw lines with transparency x( serveral lines with difference transparency on a color image (not using addWeighted that is slow I have 500 lines) on Color image

[lucasjinreal]

I know there is a addWeighted method. But what I need is draw many lines, every line with different transparency.

Which means, can not using N mask to draw then addWeighted, that too slow speed.

To draw a line on BGR format image:

line(img_a, p1, p2, c, 2, CV_AA);

It does not add alpha even c is Scalar with alphas.

I convert image from BGR to BGRA with 4 channels, but the line still full with color rather than with transparency.

Any body could help me out with simply what I need?

serveral lines with difference transparency on a color image (not using addWeighted that is slow I have 500 lines).

[kallaballa]

@lucasjinreal check this out: #20780 (comment)

[SmileLars]

@lucasjinreal check this out: #20780 (comment)

Hi :)
Can you please explain/show how to efficiently draw a line with alpha onto a mat image?
I have tried many things, like creating a bounding box around line than blending whats inside box. But it is still too slow. Compared to other drawing metodes outside opencv. Even do it 3x the speed, blending 1000 lines takes a while. Something that should have taken just some seconds.

I didn't understand how to implement what you linked to. :/ I had appreciated if you could show/explain to me how it is done :)