[RESOLVED] EV vs. Corona EV

[Fluss]

Thx Maru saved, this could be useful.

[Jpjapers]

That spreadsheet is cool thanks Maru!
Juraj posted a thing a while back (which i think he referenced above) that i found pretty interesting and is now basically how i set up every scene because its so formulaic and works every time.

I also do not get the obsession with following F-Stops/Shutter for CGI work to set exposure. In physical realm, F-Stop and Shutter speed end up modulating exposure, but primarily affect depth of field and motion blur.
And those are almost always used creatively in photography.
Photographers in fact go to great lengths to decouple exposure from those effects, for example by using strong (up to 15 EV !!) ND filters so they can achieve strong motion blur independent of exposure.
Or inventing crazy techniques like 'Brenizer' stacking to achieve shallow depth of field in wide angle setup to get past the limitations of physical shutter size.

Remember, intensities of lights are mostly absolute, we only have one sun, but exposure is completely relative value, the less light penetrates the sensor, the higher you would compensate it.
There is no such thing as "F8, 1/16, ISO 100" for midday interior. Maybe it's cloudy day and the windows is 20cm2 and floor is black. There goes your setup.

Don't set your F-Stop, set your exposure, depth of field and motion blur. You can't set those effects unrealistically and the fact that you can achieve them independently, is amazing freedom of CGI, use it. Locking them in exact ratio might be helpful if you're integrating into exact filmed footage, but otherwise, you can liberate your approach.
ISO literally has no meaning in CGI if you aren't matching footage, it's the same as simple EV compensation. So might as well just stick with it, making life simpler with one less value and broadening creative potential as well as simplifying the whole setup.

Here is how I set my camera in CGI:

0) I start with some base lights, mostly it's Sun.
1) I set my exposure in "simple" EVs. I go up until the desired brightness is achieved. Simple.
2) I set depth of field until I achieve desired creative effect in my scene. It ends up being obviously realistic value: F8-F16 for various broad shots where I want just tiny natural blur at the end of my scene to soften the CGI look, and F4 for something like close-up vignette. But setting that value only affects Depth of Field.
3) If it's shot with motion blur (car trail, breezy tree) I set my motion blur with shutter.

Physically correct workflow can be creative and user-friendly. Not puzzle.

[cjwidd]

This is exactly the type of thinking I was trying to address in the 'Plz Halp' thread. The idea of artistic freedom implies an unconstrained question; if you are a beginner, you do not know what the reasonable limitations are and that can lead to confusion.

As an interpretation, it might follow like this:

Step 0: add sun / sky
Step 1: adjust to 'desired' brightness
...

At that instant the formula is derailed because, as a beginner, what (visually) constitutes desired brightness?

At the same time, an inversion of that logic (Step 2), "It ends up being obviously realistic value: F8-F16" points to a range of conceivable values that help to constrain the question.

I'm not trying to castigate the very helpful suggestions that were being put forward in the quoted example, but I am vaguely asserting that there is a (sort of) quantitative approach to implementing photorealism in CG. When we use subjective terms to describe photorealism, we lose track of the question.

Inb4: 'artistic freedom is what make great images' -> I'm not talking about artistic choices that make an image emotional or worthwhile. I'm talking about the qualities of an image that make it indistinguishable, or nearly indistinguishable, from a photograph.

[Jpjapers]

This is exactly the type of thinking I was trying to address in the 'Plz Halp' thread. The idea of artistic freedom implies an unconstrained question; if you are a beginner, you do not know what the reasonable limitations are and that can lead to confusion.

As an interpretation, it might follow like this:

Step 0: add sun / sky
Step 1: adjust to 'desired' brightness
...

At that instant the formula is derailed because, as a beginner, what (visually) constitutes desired brightness?

At the same time, an inversion of that logic (Step 2), "It ends up being obviously realistic value: F8-F16" points to a range of conceivable values that help to constrain the question.

I'm not trying to castigate the very helpful suggestions that were being put forward in the quoted example, but I am vaguely asserting that there is a (sort of) quantitative approach to implementing photorealism in CG. When we use subjective terms to describe photorealism, we lose track of the question.

Inb4: 'artistic freedom is what make great images' -> I'm not talking about artistic choices that make an image emotional or worthwhile. I'm talking about the qualities of an image that make it indistinguishable, or nearly indistinguishable, from a photograph.

Photorealism surely has to be subjective because its not measurable in itself. There isnt a metric for photorealism. But there are metrics for camera settings and physically based workflows that are 'known good' and produce consistent results. Outside of that, is where the sujective questions start like 'how bright should it be' or 'are my shadows too dark' etc. I think the best we can do is to build a physically plausible foundation in a scene and then do the art within those restrictions.

I don't think there is a way to talk about photorealism without it being subjective.

[cjwidd]

Probably not - at least not in some constructive or meaningful way. That being said, what Ludvik points out in the 'Time to ditch sRGB...' - about how it would be better if the viewport camera defaulted to photographic emulation - would probably help alleviate some of the confusion.

[zaar]

Oh, a post about the EV setting again! :D

I think I've asked about this before. I'm in the photopgraphic EV is the way to go boat. :D
Mainly because, even though you can't set it in your cameras (sony, canon or what ever), it's an established concept that already has an abbrevation. And EV is already used in other parts of 3dsMax! That's the main reason I think Corona is doing it wrongly. Just don't call it EV if it's not the same EV as in the exposure control and physical camera UI. Call it Exposure or "simple exposure"? And even if you can't set it on your IRL camera. It is still a concept that is used in educational material for photographic exposure. But I don't think anyone is really using a chart like the one half way down on this page (under the heading "Tabulated exposure values"):
https://en.wikipedia.org/wiki/Exposure_value

I have these values sort of half memorised and I use it when collegues ask me "is this camera setting ok?". If they are producing an office interior and I can check the EV on their camera and it's something like 15. I know they've set all their lights to atomic levels, and that we can't use that model as an xref if we do an exterior shot at dusk where everything else is correctly set up.
So I can tell them to adjust the lights to match a camera at EV 8-9 and it will look reasonable in other shots too.
Trying to talk about shutter, aperture and iso is out of the question. It's too complex for what many people are prepared to learn. So I personally find EV really practical as a rough guideline. It's not "how to get a correct exposure" it's more "am I the right ball park".
But maybe for a beginner who has no previous understanding of photographic concepts or terminology, the fact that EV 15 "makes your image darker" than EV 8 is really wierd? And in that way the way Corona EV works is really more intuitive.


A setting that allows you to switch between Corona EV and photographic would be nice. Or renaming Corona EV to something else that's not in conflict with an established abbrivation.

[cjwidd]

@Maru

Do the calculations that appear in the Photographic-to-CoronaEV.xlsx still apply to the new (v6) sun / sky (improved) system?

[maru]

@Maru

Do the calculations that appear in the Photographic-to-CoronaEV.xlsx still apply to the new (v6) sun / sky (improved) system?

Yes, they are unrelated to the environment/lighting.

[cjwidd]

Thank you!

[Juraj]

Step 1: adjust to 'desired' brightness
...
At that instant the formula is derailed because, as a beginner, what (visually) constitutes desired brightness?

Whatever you find visually attractive.

There is no such concept as photorealistic "brightness". It's something you decide based on "look" you are going for. Identical concept as in photography.
Dark---) Moody. Bright---) Clean, crisp, etc. Low-key, High-key look,.. these are creative concepts.

These are subjective values based on perception.

Yes there is histogram based approach in digital photography, or "Zones system" by Ansel Adams, but those are just guides for getting baseline.
There is no exposure at which something is realistic or not.