Corona Sky Clouds - Massive Magenta Tint

[dj_buckley]

Trying to get my head around using the built in clouds and so far I'm not impressed.  They only seem to work if you leave the sky at defaults for everything.

As soon as you put the sky in a CC node it's game over.

I'll set the scene.  This is a sunny afternoon shot (2.30pm) in the Caribbean (or it's meant to be).  The sun is infront of the camera and off to the left (about 45 degrees)

Image 1 - this is the default Corona Sun and Sky with Clouds off.  It's way too pale (but there are plenty threads about that).

Image 2 - this is default Corona Sun and Sky with Clouds turned on.  Clouds look okay'ish.

Image 3 - this is default Corona Sun and Sky with Clouds off, plugged into a CoronaColourCorrect to boost the saturation of the sky a bit (0.25 Sat)

Image 4 - this is the same as Image 3, but with the Clouds on again.  The clouds are clearly pink.

The second column of images is the same as the first column but with PS Saturation set to 100.  This is to serve 2 purposes.  A).  It demonstrates just how pale the default CoronaSky is and B)  It demonstrates the very obvious magenta tint to the clouds.

Not only that but when turning on clouds the entire sky goes darker so the blues become a differnt colour.  Why is this?  It's almost as if enabling clouds gives the rest of the sky a grey wash.  My clouds amount is set to 0.25.

I appreciate I'm kinda looking towards the sun here so I'm not expecting an ultra saturated blue sky but even so, the default sun and sky looks so grey with a very subtle hint of blue.  I can deal with the colour though, it's the clouds that fully ruin everything.

Last note - there's another thread on here at the minute about banding in the sky.  This banding is evident in my screenshots too.

[Avi]

Hello,

Thank you for providing detailed information about your issues.

1. The magenta tint in the clouds is likely related to the turbidity value. You can try lowering the turbidity to decrease the amount of magenta in both the sky and clouds. Adjusting this parameter should help.

2. Regarding the slight shift in clouds' pink tint when using Corona Sky with Corona Color Correct, I'm not able to reproduce this issue on my end. In my testing, using Corona Sky with or without Corona Color Correct maintains consistent results. Please ensure that all settings are applied correctly, and if the issue persists, feel free to provide additional details or share specific settings for further investigation.

3. As for the shift in colors when turning on clouds and the overall darkening of the sky, I'll get back to you with more information from the devs.

4. Regarding the banding issue, it appears to be not related to Corona but possibly a 3ds Max-related issue. Try using the native 3ds Max sun and sky and check if the banding is still present. I'm also looking into this, as I've observed similar banding with the native sun and sky in 3ds Max.

If you have any more details or updates, feel free to share them

[dj_buckley]

Hi Avi

Maybe I'm missing something here but here goes ...

A).  Throughout your video from the start to the end, your clouds are clearly pink.  Even with your turbidity at 1.7, they're pink.

B).  Your ColourCorrect is set at default, so of course there will be no change, try bumping the saturation in your CC node to 0.25 as i explained in my initial steps.

C).  Test it without the saturation in the VFB at 1.  I only did this to exaggerrate the effects after my initial tests.

D).  I have ACES OT turned on in my tonemapping stack.

I'll send a scene over shortly.

[dj_buckley]

Here's the scene and the steps.

- Open File (note sun position in relation to camera etc etc)

- Start Interactive from Camera View

- All looks ok but the sky is very pale and not desirable - this is default settings (the only change is setting Cirrus Amount to 0)

- Change ColourCorrect saturation to 0.25 to get some blue back into the sky - YIKES where did that pink come from in the clouds.

- Change ColourCorrect saturation back to 0 to restore some normality

- Increase VFB saturation to 1 - YIKES that's where it's coming from, although they don't look like it at default settings the clouds are indeed carrying a pink hue which is clearly demonstrated when we increase the VFB saturation.

- Put VFB saturation back to 0

- Change ColourCorrect saturation to 0.25

- Reduce turbidity to 1.7 - nope still pink, this can be verified again by setting VFB saturation back to 1

- Increase altitude to 350m - eek, the clouds look slightly less pink but now the grounds gone pink, what's happening?

The point being, as soon as you plug the Corona Sky into a ColourCorrect to boost the blues, the clouds go all sorts of wrong because although they don't look pink with default settings, they are indeed carrying a pink tone which becomes really exaggerated with any saturation adjustments

[dj_buckley]

2. Regarding the slight shift in clouds' pink tint when using Corona Sky with Corona Color Correct, I'm not able to reproduce this issue on my end. In my testing, using Corona Sky with or without Corona Color Correct maintains consistent results. Please ensure that all settings are applied correctly, and if the issue persists, feel free to provide additional details or share specific settings for further investigation.

Not quite, the shift happens when you increase the ColourCorrect saturation to say 0.25,  this boosts the blues and brings that nice blue back, but it completely messes up the clouds.

[Avi]

Hi,

Thanks for the detailed explanation and the repro files. We are still investigating the issue.

Regarding the issue where Corona Sky gets a little darker and shifts color when we enable Corona Clouds, I was able to repro it and have logged it as a bug report in our system.

(Internal ID=1291174748)

[Avi]

Hi,

A quick update on this:

1. I have logged the magenta/pink tint on clouds issue as a bug report in our system to be further reviewed by our devs. Meanwhile, there is a workaround to use Color Correct OSL to selectively boost the bluish hue in the sky to get what you want. I am attaching a video showing how to use it. (Internal ID=1292055955)
2. There is a downside of using Color Correct OSL as it is crashing 3ds Max if you will try to color correct during IR. I have logged this as a bug report too in our system, but it should work fine in production rendering. I am aware that this is not the best workaround. (Internal ID=1292066486)
3. Furthermore, I have logged a feature request to provide a way to selectively color correct a hue range using Corona color correct map (Similar to Color Correct OSL). (Internal ID=1292062353)

We will let you know if there are any updates to this.

[dj_buckley]

3. Furthermore, I have logged a feature request to provide a way to selectively color correct a hue range using Corona color correct map (Similar to Color Correct OSL). (Internal ID=1292062353)

Thanks Avi - this would be ideal, not just for the Sky.

[alexyork]

Just to add that we've found the same pink issue with corona clouds.

[Avi]

Thanks, we will let you know if there are any updates on this.