When adding a semitransparent effect in the Compositing in Blender, such as the Glare effect from the Filter group, the glares in transparent areas of the image are not saved when exporting the file as a PNG with transparency...
Video Transcript
When adding a semitransparent effect in the Compositing in Blender, such as the Glare effect from the Filter group, the glares in transparent areas of the image are not saved when exporting the file as a PNG with transparency.
I rendered the model you can see on screen on a transparent background by simply adding a Glare Filter node with the Threshold parameter set to 0.2.
As you can see, in the Compositing window, the glare is correctly shown, but it is not in the PNG file that I saved to disk.
Let's look at a node setup that allows us to save the semitransparent parts added with Compositing in post-production as well.
I'll show you the final node setup, so you can take a screenshot of this video and keep it. If you also want to know how it works, here's the explanation.
The Mix Add node allows us to create an Alpha transparency mask from the Alpha channel of the rendered image, without the Glare glow. We will add the Alpha mask from Glare, which, for some strange reason, is not saved to file.
When performing this operation, it's important to insert an RGB to BW node to convert the color of the Glare effect into a grayscale map, considering the colored parts of the image as opaque.
We also need to activate the Clamp checkbox in the Add node and use the information coming from the RGB to BW node as the second input image of the node.
The output of the Add node will be the correct opacity mask for this image.
We then need to apply this opacity mask to the image coming from the Glare node. To do this, add a Converter Set Alpha node to the setup.
As the last step, change the application mode of the Set Alpha node from Apply Mask to Replace, using the output coming from the Add node as the mask.
Now, by rendering and saving the image in a format that supports transparency, such as PNG in RGBA mode, you will find the semitransparent glares in the file on disk.