Controlling Render Exposure

[mabulsoud]

Hello,

I'm trying to render at a target exposure. I used to be able to do that before the new tone mapping by using the photographic exposure for the camera. The reason is in my previous tests from years ago that used to significantly reduce render times (maybe that changed?) Is this something we're still able to do with the new tone mapping?

You can see in the attached image the original linear value is way too bright. We always correct that with tone mapping so it's not so much a question about how to get the right look but trying to improve performance.

Thank you.

[Avi]

Hello,

Yes, you can still control the exposure using the new tone mapping system. In order to do this, you need to add the Photographic Exposure operator to your Tone Mapping stack. This operator allows you to adjust the exposure settings, such as ISO, shutter speed, and f-stop, similarly to how you would control exposure in a real camera.

You can go through this article for more info: https://support.chaos.com/hc/en-us/articles/4528299288721-How-to-use-photographic-exposure-controls-in-Corona-for-3ds-Max-

[mabulsoud]

Hi Avi,

I have been using photographic exposure but it doesn't control the exposure the image is "rendered" at (the linear RGB) like it used to. Only the tone mapped values change. Is there a way to change the actual linear RGB value to bring it closer in range to the final tone mapped image?

Thanks,

[maru]

I am not sure if I understand your request correctly, but if so, then I think you can achieve what you want using the following setup of operators:
the photographic exposure takes the exposure from the camera and uses that as the "base" (what the rendering is initiated with)
then the simple exposure decides about the additional exposure adjustment

What I understand is that you would like to take advantage of the fact that Corona considers the "initial" exposure for determining what GI should look like. This leads to the following effect:
https://support.chaos.com/hc/en-us/articles/4528530828689-Exposure-changes-when-I-start-rendering-

If you want to get faster rendering / less noise at the cost of some bias, instead of using that "trick" I would recommend adjusting the max sample intensity value in Render Setup > Performance. Lowering this value will make GI darker and the scene will generally render faster. The default value is 20 and values around 10-5 should still give you some visible GI. Lower values will make GI almost invisible. The value of 0 removes any sample clamping so your GI will be brighter and you will get fireflies. :)

[mabulsoud]

Hi Maru,

Thanks for the response. I've tested photographic exposure with IR and it didn't pick it up as "initial exposure". Everything was rendering the same as with simple exposure. I will try with a full rendering and see if that changes.

Best,

Marwan

[mabulsoud]

Hello,

I've tested doing a rendering with photographic exposure (not IR) and the non tone mapped values are still in the high 20s. This is different behavior from previous versions (Corona 7 I think?) Is there a way to get this back with messing with the GI? There's also a lot of interiors that are open and visible on these exterior views so I'd rather not make those unnecessarily darker.

Thanks,