I’m trying to render an house xRay scan animation on transparent alpha background,
When i’m rendering it, everything looks good in the render window but when i look at my frames file, all the frames are empty (full alpha).
I tryed to render single frame and save it manually but the issue is still the same.
I link you the screenshot of the setup.
EDIT : I saw a topic talking about PNG format not supporting emissive and transparency pixels. It suggest to render it in EXR format but the problem is still the same… Maybe the solution is near to this.
I don’t know where you saw that but that isn’t true, maybe they were talking about something else about .PNG’s.
Here is a .PNG with Emmisive and Alpha…
That’s very much true—specifically that PNG doesn’t support pixels that are emissive and transparent, I’m not sure that was made clear.
The PNG standard requires images to be stored unassociated (aka unpremultiplied, aka “straight,”) which means that any alpha-zero RGB values, or even any RGBA value where the R, G, or B exceed the A, can’t be transferred properly, since the unpremultiplication on export will kill the bright pixels (RGB > A means RGB / A > 1, which gets clamped at 1 since PNG is a display-referred format, and therefore won’t associate back to the same value), and the multiplication on import will kill the alpha-zero pixels (RGB x A = 0).
Your image right there is an example: all the glow has been killed, the image is only visible in the areas where alpha is present, and even there it feels weak & pale!
Is the shader on the object fully emissive and fully transparent? Like an Emission being added to a Transparent shader? Cause yes, that would result in that issue with PNGs. When you say it didn’t work with EXR either, were you viewing the rendered images in something like Blender, or just a regular system image viewer? Those often handle alpha improperly, and will show an alpha-zero image as blank, even if it contains data.
All that said, if your object really is entirely additive, you don’t need to bother with alpha at all—you’ll get the same result by rendering on black and using an Add blend mode in compositing!
