How to create a semi transparent shape?

asked 2014-06-28 10:34:05 -0600

Robby18

36 ●1 ●1 ●4

updated 2015-10-20 10:24:38 -0600

sturkmen

6772 ●3 ●48 ●79 https://github.com/stu...

Hi,

I would like to know, how to create a semi-transparent form like this: http://tellthattomycamera.wordpress.com/

I tried this:

rectangle (img, Point (100,100), Point (300,300), Scalar (0,125,125,0.4), CV_FILLED);

But does not work.

I know that the functions do not support alpha-transparency when the target image is 4-channel. But i use a 3-channel image (from webcam).

So why doesn't it work?

Thanks

answered 2014-06-29 22:27:55 -0600

Haris

3804 ●3 ●28 ●57

updated 2014-06-30 01:41:59 -0600

You can use addWeighted to create such an effect.

Like,

Load source image.
Create a black image with same type and channel as source.
Draw whatever you want on black image.
Use aaddWeighted, adjust alpha and beta(weight each array element) till you get the desired result.

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Thanks for the reply. I have just one last question, how do you use "alpha component" in the class Scalar? http://docs.opencv.org/modules/core/doc/drawing_functions.html

Robby18 ( 2014-06-30 07:49:57 -0600 )edit

According to a note in http://docs.opencv.org/3.2.0/d6/d6e/group__imgproc__draw.html, "The functions do not support alpha-transparency when the target image is 4-channel. In this case, the color[3] is simply copied to the repainted pixels. Thus, if you want to paint semi-transparent shapes, you can paint them in a separate buffer and then blend it with the main image."

efreet ( 2017-04-05 14:17:58 -0600 )edit

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