Using Merge Multiply to make things transparent

Hello, I’m trying to create an effect that fades away after a few frames. It took me quite a while of searching for a way to make things transparent but I just decided to use a Merge (Multiply) node with a solid that turns from white to black.

It’s all okay working with it until I had to render the image. The rendered images are just blank .png’s. I tried using different formats, rendering it as an .mp4, still blank.

I then tried to change the input of the writer node to a node before any merge node, and it rendered fine. I changed it back, then changed the merge node into Over, and it rendered fine as well.

This is my first day of using Natron. Thanks!

can you test with 2.3.16 beta2?
alternatively, you can set tou input premult of the writer node to opaque

Where may I get the beta?

Also,
Will an opaque input premult remove transparency from the output? The thing i’m doing requires transparency, thanks!

If you still can’t achieve what you want, make a sample project using “draw” nodes like colorwheel, checkerboard, radial, instead of image inputs, and attach it here

Sounds like you don’t have alpha channels set up properly. In the viewer if you hit R, G, or B you will see those channels represented in black and white. For example if a pixel has a high red value it will be white, if it has no red it will be black.

The same applies to the alpha channel (hit the A key in the viewer) which denotes transparency (or more accurately geometric occlusion). Right now your multiply merge operation is only performing operations in the RGB channels and you don’t have an alpha channel applied, therefore nothing will be rendered out.

This article should give answers to most of your problems.