Hi, thank you for your reply.
It is directly related. In fact, I have explained how the "washed out look" occurs.
There are some misconceptions and misunderstanding:
• It is a wide spread misconception that ""better" file formats means an increase of disk space consumption". In fact, PNG is the least performant file format and can weight more than an OpenEXR file (depending on the OpenEXR chosen specifications).
That was not the main subject, though. Rather a "side note".
• In regard to Octane, as far as I have tested, I do not see any problem related to a PNG export with "alpha channel" enabled in the Kernel render settings. In both Octane Frame Buffer and in the compositing software I am using (Nuke, Fusion, etc). However, I exclusively use and work with Octane Standalone. I do not have a Cinema 4D license.
• That said, and do not hesitate to correct me if I am wrong, if I am not mistaken, there are two ways to view Octane's rasterized image output from two frame buffers:
> one being from Octane's "Live Viewer"/"Render Viewer",
> the other from the Cinema 4D's native/internal frame buffer.
If correct, did you ensure that the latter is not "treating" (processing, in any way) the input source from Octane's output? As I did mention, I am particularly referring to the the "double EOTF".
• Last but not least, omitting the fundamentals of "color management" in digital imagery is counter-productive and one doing so would be "shooting her-him-self in the foot", so to speak. I do understand that it is a deep rabbit hole that is very time consuming. Hence why I have tried to write one page that does cover the essentials, in the hope that it will help others (and is a work in progress page that I improve progressively).
Among the other messages, aoktar gave some pointers. Did you try his suggested steps?