Problem with Rendering an Alpha

Support Compositing and Post Processing
1

Good night,

I am having troubles finding a method to convert that black non illuminated texture into alpha…

I just want to keep the green glowing parts…

Any idea?


Thanks

2

screen.png1280×948 167 KB

Using only areas over a certain value as a factor

3

Can’t really understand what happened there :open_mouth:

But thanks =) it worked!

4

I’m breaking the color image (RGB) into other components - hue, saturation and value (HSV). Those are basically color (H), how much of it (S), and brightness (V). When we get rid of the color by setting the saturation to 0 (desaturate), all that is left is the value component. Glowing things usually have much higher value than everything else in the image so it should be suitable for this.

exclude_values.png1280×948 200 KB

After going to basic value I’m using color ramp node to exclude low values, which are the low value lines in the image, and I’m left with the glowing parts. That can then be used as a grayscale factor to mix the original or just set a new alpha to make also the black lines transparent.

Set alpha node sets straight alpha, meaning it sets the alpha channel (A in RGBA image) so the RGB values are still there but by using the alpha channel those values can be excluded. If needed, could also convert that to premultiplied which gets rid of the RGB values by multiplying the alpha channel value (which was set to 0) with each RGB channel value, resulting to 0, 0, 0, 0 RGBA for all transparent parts.