corona sky

[aldola]

Hi, im loving the clouds but i think corona sky colors are not quite there yet, if often get a magenta cast and its difficult to get a nice blue sky.

im the only one thinking this?

[aldola]

an example

[aldola]

what im looking for

[Juraj]

That kind of Sky is only achievable by (in photography):

1) Polarizing filter - Not possible to simulate directly in 3D, closest is Visibility & Reflection override to adjusted version of Sky (negative exposure, gamma + saturation for example)
2) HDR merge
3) Post-production of Raw files - Selective HSL, lower luminance of blue/turquoise and higher saturation of blue/turquoise

Usually, a combination of above. Your photo example is even labeled "HDR" so it probably merged Sky luminance of at least two stops of light less if not more before adjusting saturation of it.

The Sky model that Corona now uses from Hosek is really very accurate. You can also lower the turbidity parameter to get clearer alpine blue sky, it simulates particles in the air.
But it's combination of many factors why architectural photos often features this heavily saturated deep blue look.

[romullus]

You can also increase altitude in Corona sky and it will give you more saturated blue sky.

[JGallagher]

You can also increase altitude in Corona sky and it will give you more saturated blue sky.

Yup, I accidentally set my altitude to 5000m rather than 500m and it looked like the photo shared.

[aldola]

Hi, i will try with altitude,


juraj you are right about that i took the photo by mixing 3 exposures and made some minor adjustments to it in capture one,

anyway the base photos looked similar to the final version, what i don't like about the corona sky is the magenta tint

i atached another photo with any adjustments, i taken with a 24 mm tilt shift lens, no polarizer filter, just the lens

[Juraj]

Have you ever opened .raw file and applied "linear" profile? It's bit harder to do in Lightroom or ACR (requires switching to much older profile and only then zero-ing attributes), but super easy with Capture One which you use (just select "linear" profile). It would show you the natural color without any tonemapping or post-processing.

It should not be any different if you use similar time of day, angle of looking at sky (not angle of sun), altitude and lower the turbidity.

White Balance between Corona and Cameras is bit tricky, as 6500K gets interpreted very differently by camera makers and raw editors. You might need to tweak this in Corona somewhat to your liking.

Then we're getting in color gamut which can also influence the tint and saturation perception quite a lot. Corona uses internally some generic WideGamut color space, but Corona Framebuffer and 3dsMax itself are not in any way color managed, so getting correct and accurate colors out of it as expected in comparison to well color-managed photo pipeline (mostly AdobeRGB on both sensor capture and raw editor interpretation) is complicated.

Attached is my 1 minute test. 1.7 Turbidity, 1000 meters altitude. sRGB color profile in my jpeg, no space transformation.

[Aram Avetisyan]

There is a simple workaround:
Set turbidity to the lowest (1.7), plug CoronaSky to ColorCorrection node (Max General one, not CoronaColorCorrect, for some reason Max map gave better results for me), set saturation to about 50.

Then post-process in VFB with saturation, contrast and filmic operators should give a pretty close result.

Of course, the ultimate control is in post-production with masks and color values.

[aldola]

thanks guys! nice example and info juraj, thank you very much

[lupaz]

I didn't read the other comments, but what I do to "color correct" the sky is to change the ground color.
It shouldn't be this way...But it works.
In fact, it works great when using volume effect, because the default haze color is too purple.

[Basshunter]

Have you ever opened .raw file and applied "linear" profile? It's bit harder to do in Lightroom or ACR (requires switching to much older profile and only then zero-ing attributes), but super easy with Capture One which you use (just select "linear" profile). It would show you the natural color without any tonemapping or post-processing.

It should not be any different if you use similar time of day, angle of looking at sky (not angle of sun), altitude and lower the turbidity.

White Balance between Corona and Cameras is bit tricky, as 6500K gets interpreted very differently by camera makers and raw editors. You might need to tweak this in Corona somewhat to your liking.

Then we're getting in color gamut which can also influence the tint and saturation perception quite a lot. Corona uses internally some generic WideGamut color space, but Corona Framebuffer and 3dsMax itself are not in any way color managed, so getting correct and accurate colors out of it as expected in comparison to well color-managed photo pipeline (mostly AdobeRGB on both sensor capture and raw editor interpretation) is complicated.

Hey Juraj. I'm still trying to understand your answer but there's a couple of things I still don't get. So hopefully you can help me out.

1) Are you saying that if we could see that last photo (the regular one, not the HDR) using a linear profile, the sky would look pale blue as in the renders? Cause I'm not sure about that to be honest.

2) If that's the case though, is it correct to say that the reason for those deep blues on the photo is just the tonemapping?

3) If tonemapping is the reason, does it mean that Corona ACES ouput has way less saturation/contrast than the tonemapping used on this photo? I say that because I can see that you had to add more contrast in order to reproduce those deep blues in corona. I think that one would expect that after the ACES output, renders are very close to photos (the ones straight from the camera) in terms of contrast, saturation, blacks ect. But this seems to not be the case. I still wonder what combination of operator could give me that.

This is a topic that has intrigued me for a while now since my clients always send me reference photos (straight jpg from their cameras) that always have deeper blues than my tonnepamed renders and for some reason I'm not able to achieve the same sky without having to tweak the color, which is not physically accurate in my opinion.

[Juraj]

No, I think I worded my first post wrongly. I was surprised myself how rich deep blue the Sky itself gets with low turbidity (both in 3D and reality :- ).
I have some architectural photography friends, professionals, and I know how much heavy processing they do to skies. Ultra-rich Blue has been post-production favourite style for long time. And before that, it was often created with polarising filter.

But as I've proven (mostly to myself) in my quick test, turbidity alone and reasonable altitude can create quite a lot of this look. Just not as extreme. So the end result is always a combination of the natural type of Sky reached under certain conditions (clear day and higher altitude) and processing (HDR, Contrast, Saturation,etc...).

I don't think ACES Output alone is close to what is currently common standard for photography post-production (much heavier contrast because we consume all content in digital media). I find the Corona's team version of ACES Output transform NOT to be very powerful, I think it's sort of midway, not weak, not strong. Definitely weaker than most contemporary processing done on cameras, and lot weaker than phones.

To be honest, default tonemapping/processing on current phones is like ACES, +6 Contrast, + 100 Vibrance :- ).
But this is super individual, my iPhone 14 Pro default is like +6 Contrast but -50 Saturation :- ). Very strange look at first, lot closer to ACES than my former Huawei.

But most camera jpeg profiles (straight out of camera) always had deeper contrast in blacks (deeper first half of S-Curve) and boosted contrast in blues (because it increases saturation of Skies, but not of human faces, so it still looks natural but also nice and punchy).

I actually thought of this lately because I found the same result in both photography and renderings I do across the past 10 years. My idea of ideal "contrast" has been moving up and up... maybe the social media is brainwashing me a bit. But then again, my famous architectural photography friend was printing books with +1000 Saturation Blue Sky already 15 years ago :- ).

[Basshunter]

To be honest, default tonemapping/processing on current phones is like ACES, +6 Contrast, + 100 Vibrance :- ).
But this is super individual, my iPhone 14 Pro default is like +6 Contrast but -50 Saturation :- ). Very strange look at first, lot closer to ACES than my former Huawei.

These numbers are inside Photoshop, right?

But most camera jpeg profiles (straight out of camera) always had deeper contrast in blacks (deeper first half of S-Curve) and boosted contrast in blues (because it increases saturation of Skies, but not of human faces, so it still looks natural but also nice and punchy).

What do you think is the best way to recreate this look via Corona tonemapping? I'm talking about the straight out of camera look with deep contrast in black and boosted contrast in skies.

[Juraj]

Outside of creating specific LUT file, I don't think it's possible. Corona framebuffer has lot of tools now, but it's still not Lightroom/AdobeCameraRaw. It doesn't even have vibrance which is much better than saturation (and Corona Saturation parameter is super strange to being with, I don't touch it at all).

The new ACES OT is pretty nice tonemapper, I already started using it for almost all my projects, but I still use lot of global adjustments in framebuffer, contrast or rather curve.

To be honest, I adjust the hell out of my Phone camera pictures as well :- ). I only shoot raw file with my iPhone 14 pro and use every single parameter even in the basic editor (which has like 3 HDR-like "brilliance/clarity/etc.." local adjustments, that is if I don't open it in Lightroom and do even heavier post-production.

I never liked the "straight out of the camera" jpeg look (not in my old Nikon D800, not in all my Sony Alpha generations, not in my Huawei, iPhones,etc..). I found it flat in camera as well. Don't really want to get back to the eternal discussion of tonemapping camera vs CGI :- ).

[Basshunter]

Yeah, some Corona processing controls behave really strange. I've talked about some of them in other threads. Hope the devs pay attention to that in the future.

On the other hand, I don't like the "straight out the camera look" either. At least not for the final image. But I think that having the ability to mimic that would help me in many ways. In fact, I think that having the ability to make the creation and post-processing of CG still images as close as possible to photography would bring a lot of benefits. But my English is not that good to enter in such a discussion. And at the end of the day, developers have the last stand on this. To make that possible they would have to start paying attention to simple requests like fixing the post processing tools inside Corona to behave like they do in photography software or give us the ability to save images in DNG for example to be edited easily later. I'd also love to have built-in presets that mimic some camera behavior like iPhone Camera.

I know lot of people prefer to work in a more "artistic" way, without having to constraint to real world rules when it comes to CGI. That's not my case. I'd like to have less guessing in my job. So for me having the possibility to replicate the real world and getting images that are as close as possible to what I'd get straight out of an iPhone or other camera would be wonderful. Then I could take that "photo" to LR or PS and for further editing and turn it into whatever I want. Anyway, I'm probably just rambling at this point.

[Juraj]

Well, I ask the devs for DNG 4 times per year at least :- ).

The ACES OT Tonemapper (not to be confused with full ACES color pipeline, which would not improve the realism in any way anyways) is very close to film/camera look as it gets.
It's perfect starting point. But it's also full tonemapper, so you cannot bring it to Lightroom or ACR and change exposure, highlights, shadows, etc..
And most framebuffer modifiers don't work correctly positioned before the ACES OT, but that's another longer discussion.

Honestly though, 95perc. of my "look"  these days is just ACES OT + Contrast/Curves + Some personal LUT for colors. Nothing secret or special in any way.

In fact, the screenshot in this thread is just ACES + Contrast. Looks good to me.

[aldola]

Don't you think that the aces ot is very contrasted? especially in the shadows, I would have liked a better explanation of their use from the corona renderer team

[Juraj]

Well it tries to emulate filmic response, and that was always S-curve with much deeper lower part. I don't find it very contrasty I can easily add 2 or 4 points of CoronaContrast until I like the result.
Ideally it could be countered with some shadow parameter but the final result is clamped and any modifier before ACES OT gets broken because it operates in linear space and it wasn't written to work like that. (I asked the devs about that many times, I never got any answer, the whole post-production stack just doesn't work well right now as it was designed at different stages and now it gets mixed.. and...that's long discussion, I gave up. Post-production is just not strong point of Corona Team, and I am happy we have what we have).

What use explanation would you want from the team? How it works internally? (Just filmic tonemapper). How it's meant to be used? (Just another alternative tonemapper).
I can completely replicate how it works with something like (HC=2, S-Curve and Saturation LUT that desaturates highlights). The ACES OT is bit more complicated, but I can replicate the look with 99perc. Which is why my new renders look exactly as my old renders :- )

[aldola]

yeah i worked with  10 hc and a contrast lut, somehow ACES OT looks a lot more contrasty, it is possible to add HC to ACES OT in the stack?

[Juraj]

Technically you can do any combination, it's just that most of the combinations aren't meant to work :- ). But you can also combine something to your liking.
Little bit of HC before ACES OT is effectively stronger highlights correction. But we're talking HC 1.01-1.5 +/-. Otherwise you flatten the whole whites.

[leviathan420]

and any modifier before ACES OT gets broken because it operates in linear space and it wasn't written to work like that.

sorry i get a bit confused with that whole stacking order thing ,by default acesot is at the bottom of the stack,so u mean it should always be at the top of the stack ?

[Aram Avetisyan]

and any modifier before ACES OT gets broken because it operates in linear space and it wasn't written to work like that.

sorry i get a bit confused with that whole stacking order thing ,by default acesot is at the bottom of the stack,so u mean it should always be at the top of the stack ?

Hi,

The operators are applied from top to bottom. It is generally a good idea to have ACES OT at the bottom of the stack, as after applying it (and some other oeprators) the image is not linear anymore (the real render values are clamped/compressed).

You can of course experiment and see what works for you.
The thing I would not recommend - having ACES OT at the upper part of the stack.

[leviathan420]

got it,thanks for replying