redshift object alpha render show up black

[clerk-relation]

Hi!
I've been having issues with png render. I have an object added redshift object tag(then select matte), with a dome light background it works perfectly. However, when there's no dome light background, just alpha, the object would should up as black in the render. I did check the alpha and add ao in AO setting. Can someone help please?

[Dr. Sassi]

Hi clerk-relation,

Since I write in a forum, I might overshare here:
I'm unclear what the AO (Ambient Occlusion) would add here. AO is a geometry fake when no Global Illumination is used—nothing to do with Alpha or Matte.
OR do you mean AOV (Arbitrary Output Variable), either way. The term Matte is perhaps used differently in Redshift than you would use it in Compositing, going by the file that you expect.
https://help.maxon.net/r3d/cinema/en-us/Default.htm#html/Matte+Options.html

For simple PNG and transparency, no AOV is needed. See the file below. Straight Alpha, with a separate Alpha file, to avoid the problems PNGs have with transparency, e.g., with Color Grading.
CV_2025_drs_25_RSap_01.c4d

This file uses just the simple PNG with "alpha" premultiplied, i.e., transparency, which should be used for web and similar uses.
CV_2025_drs_25_RSap_11.c4d

In AOV based Workflows, the Puzzle matte is used, using the RGB channels for three Materials IDs (Look into the Output Node) or Object IDs (RS Tag)
CV_2025_drs_25_RSap_21.c4d

Let me know what works for you.

Happy New Year.