Enable VFB EV spinner while in photographic exposure mode

[Fluss]

The title says it all, coming from that thread: https://forum.corona-renderer.com/index.php?topic=28968.msg168851

I am of opinion that Corona should go full way and allow EV modification even in full settings, so that is it absolutely identical to how digital cameras work. You set your settings (f-stop, shutter, iso..) and still have option to use EV as offset.
I'll make that a request when I'll remember.

[Juraj]

hah, I am idiot, I didn't think I could do it this simply :- ). I'll elaborate at least on the many benefits:

From realistic standpoint:

- It's easier to use EV offset than ISO,  even thought they are technically 100perc. identical in CGI. ISO being logarithmic, +2 from ISO200 is ISO800, how much is 2.5EV? Not the most straightforward if you need exact matching.
  EXIF reading of current photos does note if offset was used, so this is the fastest way to replicate exact backplate matching without any sort of translation mathematics.

- This is the very reason why this option exists even in full manual mode on digital cameras (while cameras will smartly decide whether to translate the offset into shutter speed or ISO depending on light, Corona would always be ISO, but that's ok).
   The reason is to quickly iterate and test, without changing (and potential forgetting) your manual settings. In studio photography, you want your manual settings leave untouched for consistency.

- Easy re-adjustment in post-production. +1 can be negated by -1 in post-production and achieve identical match, without affecting your manual settings used to match backplates or adjust exact motion blur and DOF.
  (again technically the same as recalculating ISO, but this is simple straightforward linear value, and not even photographers know how to properly translate ISO values. What is -0.5 EV in terms of ISO change? Not user-friendly for quick and straightfoward iteration).

From rendering standpoint:

- It enables you to quickly iterate in Framebuffer without affecting your exact camera settings. You don't need to select camera, or camera tab in settings.
  This is super useful esp. for Interactive rendering. There is no good reason why it needs to be as ONE or ANOTHER, as it's right now. It isn't even technically correct as EV offset is already part of EXIF standard and thus full part of manual settings.

- Easy re-adjustment in post-production. +1 can be negated by -1 in post-production and achieve identical match, without affecting your manual settings used to match backplates or adjust exact motion blur and DOF.

[cjwidd]

really well said, thank you^ +1

[maru]

Thanks for the idea, reported:
(Internal ID=500869394)

I just have one question:
Would it make more sense if:
- the EV setting in the VFB was connected with the EV setting in the Corona Camera (e.g. when using "Use simple EV" option)
or
- the EV setting in the VFB would be completely disconnected from any other render settings / camera settings - so it would be just like a post-processing effect applied on top of the final image? (like loading an image into an external app and changing EV)

[Fluss]

That's a tough one for me. It would make sense for the VFB to be Post-production only, ala Vray. But on the other hand, it's great to have control over rendering exposure straight from the VFB. Does it makes sense to implement a similar behavior as light mix -> a bake to scene/camera exposure button ?? So it remains a post-process spinner but still has the possibility to update rendering exposure

[Juraj]

Both 🙂 I'll write later how it could work.

[Nejc Kilar]

I also think its important to keep it in "both" ways. I'm sure Juraj will write up a better explanation that I would so I'm gonna yield to that :P