dubcats secret little hideout

[subpixelsk]

Hi dubcat

regarding calibrating hdris - is it neccesary to do even if I use separate light source (Corona Sun) for direct light? - for example noemotion hdris have no shadows from the sun

[aldola]

Hi, i use this 

https://3dcollective.es/producto/hdri-22pack-pro/


 i think the best quality on the market, no strange tint on the colors and the have very good dinamic range.

[dubcat]

regarding calibrating hdris - is it neccesary to do even if I use separate light source (Corona Sun) for direct light? - for example noemotion hdris have no shadows from the sun

Hey!

I would still adjust RGB Level to match Corona Sky values at least. Corona Sun will eat all the sky light from those low exposure HDRis.
And just to be sure, I would remove the low level sun. It will only get stronger if you adjust RGB Level.

If we combine Corona Sun and this NoEmotion HDRi without increasing the RGB Level, we won't even notice the HDRi.



If we do a quick sky calibration like this.




We can finally see the HDRi again.





------------------------------------------------------

I had a quick look at the free sample 3DCollective HDRi.

Looks like someone painted the sun with a large soft brush.
The sun value is 1079 times dimmer then Corona Sun.



Here is Corona Sun for size comparison

[Njen]

A general rule of thumb when processing HDRI's, or using something downloaded from the internet, it is important to know that at the equator, at 12pm noon, the sun is roughly 100,000 brighter than the average area of a large patch of sky. So as the sun gets lower in the horizon, the brightness of the sun decreases just a little because light has to travel through more atmosphere. And if there is any form of high level cirrus cloud, the brightness is decreased a tiny bit more too.

[aldola]

They are calibrated to use with the camera so 3DCollective_HDRi_022_1722_+8_4K the +8 means that you have to give +8 rgb  output amount to give the correct intensity, this one is a cloudy sky, the sunny ones have a +32 output value.

i dont know if they are correct but they give some nice shadows with the sun.

Adan martin  the creator is on the forum, so i think he can give a more correct explanation

[subpixelsk]

regarding calibrating hdris - is it neccesary to do even if I use separate light source (Corona Sun) for direct light? - for example noemotion hdris have no shadows from the sun

Hey!

I would still adjust RGB Level to match Corona Sky values at least. Corona Sun will eat all the sky light from those low exposure HDRis.
And just to be sure, I would remove the low level sun. It will only get stronger if you adjust RGB Level.

If we combine Corona Sun and this NoEmotion HDRi without increasing the RGB Level, we won't even notice the HDRi.



If we do a quick sky calibration like this.




We can finally see the HDRi again.





------------------------------------------------------

I had a quick look at the free sample 3DCollective HDRi.

Looks like someone painted the sun with a large soft brush.
The sun value is 1079 times dimmer then Corona Sun.



Here is Corona Sun for size comparison

Thanks for the reply. What values did you use for sun and sky ? default size and intensity for both? sun in realistic mode? Framebuffer rule of -5,24 exposure from PG skies calibration probably doesn´t apply here or am I wrong?

[dubcat]

Thanks for the reply. What values did you use for sun and sky ? default size and intensity for both? sun in realistic mode? Framebuffer rule of -5,24 exposure from PG skies calibration probably doesn´t apply here or am I wrong?

I left everything at default settings and just aligned the sun to the HDRi sun. This particular sun angle needed -5.285 EV for true albedo.
Corona Sky is a dynamic map that changes once you add a Corona Sun, and then it changes based on sun angle. I used Light Mix to isolate Corona Sky from the Sun.

[subpixelsk]

Thanks , one more question - how do you isolate sun from hdri? Output node creates a mask and then Corona mix map with black color where the sun is and sky map for the rest?

Or painting in photoshop?

[dubcat]

Thanks , one more question - how do you isolate sun from hdri? Output node creates a mask and then Corona mix map with black color where the sun is and sky map for the rest?

Or painting in photoshop?

Photoshop does not have 32bit floating point support, so if you open a HDRi in Photoshop and resave, it is basically ruined.

If you only have Photoshop, you can create a white mask where the sun is, and load it in 3dsMax as gamma 1.0
There are different methods you can split and add them together again, here is one example.



Affinity Photo has 32bit floating point support. So you can remove or isolate the sun inside the program.

[subpixelsk]

Are you using native 3ds max maps for a reason? would this work with Corona Mix and Corona Bitmap in the same way? when creating mask in photoshop, can I just add a new layer on the hdri and create mask? then is it correct to convert to 8bit and save as jpg? and then load into max with 1.0 gamma? In your last screenshot you showed that it is possible to avoid Corona Sun completely and use only masked sun to create direct light right? that 9999 rgb x 37 rgb is based on Corona Sun + Sky setup? matching 117 RGB value?

Also when using that hdri in real world scenario can I adjust exposure in framebuffer to my liking?

And how do you decide how large should the sun circle be? Do you include flares or only the sun disk?

Sorry for a lot of questions but I am trying to understand this to make it work correctly

[dubcat]

Hey!

Are you using native 3ds max maps for a reason? would this work with Corona Mix and Corona Bitmap in the same way?

You could use CoronaMix and disable "Perform mixing in sRGB space".
I usually drag and drop bitmaps into slate, and then run Corona Converter to convert them to Corona Bitmap.

when creating mask in photoshop, can I just add a new layer on the hdri and create mask? then is it correct to convert to 8bit and save as jpg? and then load into max with 1.0 gamma?

Yes to everything.

In your last screenshot you showed that it is possible to avoid Corona Sun completely and use only masked sun to create direct light right? that 9999 rgb x 37 rgb is based on Corona Sun + Sky setup? matching 117 RGB value?

Yes. I calibrated the HDRi sun to match isolated Corona Sun. Both will produce the exact same result.

Also when using that hdri in real world scenario can I adjust exposure in framebuffer to my liking?

True albedo matching is only necessary when we want to calibrate light and materials to real world values. When it's calibrated, you can use whatever you want to set  the mood.
If online stores could spend 1min extra when shooting HDRis, and just take a few pictures of a Color Checker or a 18% grey sphere. We could calibrate our HDRis to the actual capture.

And how do you decide how large should the sun circle be? Do you include flares or only the sun disk?

In this case I looked up at the NoEmotion sun. Moved a Corona Sun until it was in the middle of the NoEmotion sun, because the NoEmotion sun was huge.
Then I placed a standard camera at 0,0,0 facing south (south is the standard HDRi direction, the sun will show up in the center). Threw on a CoronaCameraMod, and enabled Projection type "Spherical". Then I changed the render resolution to match the HDRi and made a HDRi of Corona Sun. This is my mask.

When it comes to sun size, I guess it depends on what look you are going for. Sun size will not increase the light intensity of the sun, it will only make the shadows softer.
Most HDRi captures have a sun size of 2.

[Jpjapers]

Honestly, how do you know all this stuff?
Its fascinating to follow this thread. What is your background?

[sprayer]

Photoshop does not have 32bit floating point support, so if you open a HDRi in Photoshop and resave, it is basically ruined.

from adobe page

In Photoshop, the luminance values of an HDR image are stored using a floating-point numeric representation that’s 32 bits long (32‑bits-per-channel). The luminance values in an HDR image are directly related to the amount of light in a scene.

[dubcat]

What is your background?

Half Life 1 modder turned Archviz / BIM :)
My first introduction to 3dsMax was Autodesk Gmax, because Milkshape 3D was lacking a lot of features.

from adobe page

In Photoshop, the luminance values of an HDR image are stored using a floating-point numeric representation that’s 32 bits long (32‑bits-per-channel). The luminance values in an HDR image are directly related to the amount of light in a scene.

I've posted examples all over the forums for years, but I guess it's best I recap everything here.

I'm running the latest version.



#1
If you go back a few pages and download my ACES tonemapper script for Photoshop. You will notice that bright lights becomes black pixels. This is because Photoshop does not calculate negative values.
The script will split your render into two images and then divide those images together. Photoshop does not handle negative math well, and will return black pixels.

#2

Corona Sun



Corona Sun rendered as HDRi and re-saved in Photoshop as EXR.
Goodbye values.



Corona Sun rendered as HDRi and re-saved in Photoshop as HDR.
Better than EXR, still not what we expect.



#3

32bit floating point displacement.

Proper 32bit map rendered in Corona



Re-saved in Photoshop as EXR.
Since this map does not exceed 20 Photoshop Intensity, it will not clip.
Negative values work as intended also.



Re-saved in Photoshop as HDR.
Since this map does not exceed 20 Photoshop Intensity, it will not clip.
But since it's HDR, it will not have negative values.
It also has some weird ass shadow artifacts.



So if you use Photoshop you are left with these choices:

EXR: Clamped bright values and clamped negative values.
HDR: Somewhat proper bright values and no negative values.
Internal: Can't do negative math.

I bugged Adobe back in 2016 about this problem. They said they didn't understand what I meant about clipped values above +20 RGB, and asked me to take a print screen of the problem. (I had provided renders like the ones I posted here, but they wanted a print screen of the HDR image) That is when I gave up.

[sprayer]

I've made some test,
Indeed Photoshop save EXR and HDR in half point, but value is the same. Not sure about negative value, i've test corona sun.
About 20-Photoshop clipping it's just own maths inside Photoshop, but value is fine if you see in other software. For example if you look at corona VFB sun value it's has own value, if you copy VFB to 3ds max VFB it's will have another, so i've check max VFB for re-saved images from photoshop we can load them via 3ds max image viewer. Also i was check in Affinity Photo it's showing the same value as in max VFB and can save EXR in float point by the way.
Also i have check re-saved PSD in Affinity, PSD store also the same value as in max VFB, so the problem goes from Photoshop export module, but PS can work with float point and store all colors but only in PSD file format.  I find at adobe forums what people advice to use some plugins for saving full EXR, i was used EXR loader from arionFX by the way. Native PS EXR loader can't load layers from 3ds max EXR and it seams can't save too