Pastel, blown out pixels with HDRI skies

[danio]

Hello all - I recently bought some HDRI skies for an online source. I really like them and they are very high quality, but in some scenes I notice that I get burnt out pixels. They appear as cyan, blue, red things like that. They show up mostly in reflections or shiny materials.

I have tried Linear, Reinhard with a low burn value, stuff like that. I've tried clamp output + sub-pixel mapping, etc. None of that fixes it, it just slightly changes it for the better (or worse). The only thing that works is raising the gamma above 1.0 for the HDRI maps which makes the image dim and unsharp shadows. My preferred setup has actually been to be around .8 gamma for sharp shadows but in the problem scenes that is just REALLY bad. I'm of course loading with VRay HDRI map.

If I lower the exposure to where the burnt out reflection of the sun is no longer a problem, the rest of the image is too dark.

Any advice on how to handle this? It's driving me nuts and I have some images due in a few days and would love to resolve it. Thank you!

Dan

[urbanite]

I had something similar but rotating hdr few degrees in vrayhdri material slot helped.

Best,
Tomek

[windowlicker]

I have found blown out pixels in some of the HDRIs we have. I fixed it by simply retouching the problem-pixels in Photoshop.

[peterguthrie]

Not mine I hope? If so let me know and I'll fix them.

[danio]

Hi Peter - Yeah I bought a bunch of yours recently to help with my school projects. I seriously doubt it's a flaw with your HDRI though. I suspect it's more my settings. At the same time I've been poking at them for some time and can't find any major culprits. Rotating does help but then its a constant game of not catching the sun reflection at that one angle. The two that I've been working with on this are 1123 and 1846.

By raising my gamma to 1.25-1.75 depending things can be ok.

[joconnell]

Just curious if you're using linear workflow or not? Cyan and red definitely sound like burnt out, oversaturated colours - are you using a 2.2 workflow?

[jacksc02]

Danio - if you keep the gamma at 1 do you get the same errors?

[danio]

Chris: Yes, even a stock setting of 1.0 still gives weird colors in sky, reflection, etc.

joconnell: My goal is LWF, it's quite possible I have goofed somehow though! In my Max Gamma LUT settings it reads:

Gamma: 2.2
Input: 2.2
Output: 1.0

in my VRay tab under render settings I have:
Linear Multiply
Dark: 1.0
Bright: 1.0
Gamma: 2.2
No sub pixel
No clamp
Yes Affect BGround
No Don't Affect colors
No Linear workflow

I've also tried rendering out @ 32bit with my VRay gamma @ 1.0 and I get the same issues.

Most of the problems seem to go away if I do a mat override though! Even the blown out sky! Reinhard fixes it a bit but not totally and I don't love the more saturated nature (.15). I also haven't run into this as much in other scenes. In fact I just finished up a whole big grad studio project using PGSky 0743 for all the images interior and exterior and had no blow outs anywhere. I'm starting to wonder if its a rogue material somewhere.

[danio]

Oops, nevermind that: the mat override does NOT fix the blown out sky. And I think the reason it helps is just because my override material is not glossy at all.

[danio]

Well this is very odd, but I just opened a scene I trusted, merged in my trouble scene, and the whole 'sky color shift' thing is gone. I wish I knew what the issue was but I can't track down any settings that would seem to relate...? I checked gamma\lut, render settings, hdri settings, everything. I've been using VRay for a long time and this is just totally weird.

The scene is also much brighter now and less saturated. Very weird.

[chriserskine]

have you tried clamping the output?

[danio]

Enabling clamp @ 1.0 in Vray settings helped but didn't solve it.

I currently have 'Force Color Clamping' checked in VFB. If I uncheck it makes the problem come back even in the new file.

Going back to the old file I notice that the same icon (Force Color Clamping) is actually referred to as 'View Clamped Color.' This seems like a pretty significant difference...why would VFB icons change from one file to the next?

[peterguthrie]

Are you sure this isn't just a case of overbright reflections? with my skies this is just something to be expected as the dynamic range is very high. There isn't really a quick solution apart from "sampling the shit out of them" as Thorsten said in this thread: http://www.chaosgroup.com/forums/vbu...well-above-1-0

Maybe you could post an image to show the problem?

[danio]

Ok, so here is my near final product from the NEW file that seems to be working well:

http://dl.dropbox.com/u/34053128/5_West_Far.jpg

Here is the bad file showing that I don't have a 'force color clamping' button in my VFB. The button here is 'Show clamped colors' You can see the crazy colors:

http://dl.dropbox.com/u/34053128/Bad.jpg

Here is the good file (with the old file merged in without its settings) showing I have a different button in my VFB that's just called 'force clamped colors'...this is with all the same color mapping settings as far as I can tell:

http://dl.dropbox.com/u/34053128/Good.jpg

I've run into aliasing and firefly problems before (especially with interiors) and sometimes i'll clamp\sub-pixel map but this seems way different?

EDIT: cleared up typo regarding button names.

[trixian]

You have turned off forced clamping in the VFB (or actually set it to view clamped colours). it will then colour code all values over 1. Turn it back on (button second from the bottom left).

Bah....never mind. Didn't notice you were aware of this in one of your posts.

Ok.....re-reading the thread, It is evident you misunderstand what you are seeing. The button in the VFB is a dual button. That is 4 states. On\off view clamped colours, and on\off force colour clamping. Why this is set up like it is I do not know. Probably someone being too clever when designing UI elements. Most importantly, VFB tweaks are saved with the max file, which is quite handy actually.