And yet another specular/bump/displacement related issue.

[sirio76]

Please refer to this post for the specular/bump issue:
https://forum.corona-renderer.com/index.php?topic=28841.0
And other similar report from other users:
https://forum.corona-renderer.com/index.php?topic=28892.0
https://forum.corona-renderer.com/index.php?topic=28382.0
Now I've discovered yet another bug related to the subject, this time involving displacement. That's what I get when switching from standard displacement to 2.5D mode, the specular lobes are inverted.
Please developers, you seriously need to look in to this and fix it ASAP, according to other report is the same on both Max and C4D version. There's really no point in developing cool new features when basic stuff like this doesn't work as it should:)
If needed I can provide the scene.

[TomG]

As a note, the "old" displacement, with autobump enabled, sometimes gave incorrect results. This does not happen with 2.5D displacement. This means that swapping to 2.5D displacement can give changes in how things look, but the 2.5D is correct and the old is incorrect. If autobump is not enabled, let us know. Thanks!

[sirio76]

Hi Tom,
I'm using V5 and I do not see any autobump option in my bump channel, I guess it was only present on older version. Anyway, standard displacement mode works better(beside this issue) and I prefer to use that instead of the 2.5D in order to get quality results. It is supposed to work properly or you already know it won't work well in standard mode?

[TomG]

Autobump isn't a channel setting, but an overall render setting, you can find it here (and it's enabled by default for some time now) - it's so much of a default that it isn't exposed in the regular UI, and is only in developmental/experimental stuff. It's not recommended to turn this off, and 2.5D displacement is recommended as the best solution, as it is more accurate than the old displacement method (and so may look different), as well as saving memory etc.

[TomG]

We'd only recommend not using 2.5D if it gives you artefacts in your scene (this can happen in situations with very long, very thin polys, which is something we are looking into). Hope this info helps!

[sirio76]

Thank's for the info Tom, I've never touched any settings in the software so I assume the autobump is set as default. Still in every situation the surfaces produced by standard displacement are better as far as quality is concern, you can clearly see faceted surface when using the 2.5D mode and I've seen this behavior in most of my shaders. 2.5D mode maybe good for large flat surface and for saving RAM but quality wise is not on par with the other method.
That unfortunately leaves me and other user with no options, 2.5D produce geometry artifacts and the standard mode produce shading artifacts because of the bump issue. By looking at my example can you guess if there is a solution? I mean a smooth mesh coupled with a proper shading.
Thank's a lot for your support;)

[sirio76]

Edit, I've just enabled the experimental staff and autobump is turned on as it should be.
While we are on the subject, I was looking at the bump sharpness option inside the experimental stuff, what is supposed to do?
Maybe playing with that will help with the bump look? I've always felt that something was wrong with the bump(beside the specular issues reported in the other topic), maybe because of the lack of a delta setting for the standard bitmap loaded in the bump channel, as a matter of fact if I use C4D procedural shaders where I can set the delta the bump look may improve a lot while with no such an option for the bitmap they just look sharper no matter of the intensity and doesn't give that "virtual extrusion" feeling. I've also reported this in the bug but was ignored for 7 months before being noted an now after over a year the's still no solution: https://forum.corona-renderer.com/index.php?topic=23049.msg140981#msg140981
Please notice that I really do not like to rant on forum(I'm not that kind of person;) ), I'me really sorry for this long bug report but I'm trying to get in to Corona for over a year for my commercial works and I still feel is not production proved for my needs(here an example of a small/medium interior: https://www.c4dzone.com/it/forum/viewtopic.php?f=12&t=33639 ), you can easily imagine that I need a very robust software for my works and I hope Corona will get there eventually.