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Hi everybody
I just tested these HDRI's: http://www.viz-people.com/index.php?pag ... t&Itemid=1
Since I remembered that in Maxwell since 2.0 you should be able to get a crisp shadow with an HDRI.

I tested #3 from the catalog (http://www.viz-people.com/images/VizPeo ... atalog.pdf) which gives a really nice light in their example:

but the result I get is this:

almost no shadows and no color in the lights ... and a very dull ambience

What is wrong? Why do they look so different than in other engines? Am I doing something wrong? Do I have to tweak the HDRI manually?

Thanks for help.
cheers, kami

I don't know that I can solve your problem necessarily but here are some of my thoughts.

1. To me the whole 'you can get crisp shadows from hdri's in v2.x' was a bit of a bait and switch. It's not untrue, but what they failed to mention is that no commercial HDRI's seem to be of a high enough quality to actually do this (none that I've tried anyhow). So I think it requires some tweaking which either means opening it up in Photoshop and brightening the sun or perhaps combining the commercial HDRI with an HDRI created from a Maxwell Sky (which are of sufficient quality to create sharp shadows). Hopefully someday we'll get some sort of cloud generator which will solve this issue.

2. It looks like your clouds are huge compared to the commercial image. Perhaps there's something wrong wiith the scaling? Or perhaps it's just another section of the sky we're seeing which is more overcast.

3. I suspect you're getting a similar warm color cast as what's in the commercial image but it's harder to tell since your materials aren't white.

4. Personally, i've taken to using HDRI's for all my channels except illumination where I use physical sky for it's sharp shadows. I've spent hours tweaking HDRI's to get sharp shadows and it just hasn't seemed worth it.

-Brodie

hi brodie

thanks for your answer.
it made my try around a little bit with photoshop and I came to an solution which is quite usable:
Use an exposure-correction and increase the contrast with gamma. In my case, setting gamma from 1.0 to 0.6 showed nice results. No need to only make the sun stronger. I also decreased the saturation by 30% because it was a bit too saturated for my feeling.

Here is the original HDRI:


This is the one with 0.6 gamma and -30 saturation

I think this comes pretty to close to what I'd suspect.

And the last one, which is blurre and with 0.6 gamma (saturation 100%)


(all channels use the same value)
Hopefully this method works also fine with other HDRI's, maybe with another gamma value ...

cheers, kami

Very interesting. I'll have to give that a shot. I think it would work quite well if you saved out the gamma adjusted one and used it for the Illumination channel and the standard one for the rest of the channels.

Thanks again,

-Brodie

hi kami,

i can tell that sharp shadows are possible with maxwell ... see here

in this case i had troubles with other emitters stealing the processing power away from the hdr. (long thread not started by me!)

concerning good hdrs, i am very pleased with the results i get from the hyperfocal hdri.. and they work straight without changing the gamma.
It is a while i have been through these things so i won't write much more before i get it wrong, but here are a few links explaining what needs to be done with hdri if they render in a strange way.

http://www.hyperfocaldesign.com/industr ... rces-links

Problem with photo-made HDRI images (eg. those from vizpeople store) is that they don't contain *sun* because it's hard to take picture of sun with normal camera. To see the sun in reality you need to compensate exposure to about -15EV -18EV, to see "sun" in those images you need to take it down about -3EV -5EV, that makes difference, because 12EV is really a lot. I'm pretty sure renders from vizpeople contain additional "sun" lightsource (like vray sun) or they are gamma corrected. So only images without visible sun (cloudy etc.) will correctly light scene. Not to mention optics bloom and flare...

Easiest solution for us is to add sun in photoshop on HDRI but then there will be no transparent shadows behind glass from sun (from maxwell sun they are present) and maxwell sun renders faster.
So how to add maxwell sun to scene with HDRI? But add it in the way it is visible to camera and reflections so there is simulens and reflective materials look correct. If somebody has idea please share

polynurb wrote:So how to add maxwell sun to scene with HDRI?

My procedure maybe is not the cleanest one, but it works for me. I use C4D but I guess any package can do the same, first I make a emitter simulating the sun, just a square targeting the center of the scene with the lat and long that I want, then I put a empty object (null object) in the middle of the scene targeting the emitter that works as a sun and I put a camera in that position so the sun is straight in front of me, now is when I put the hdr that I want and move it until the hdr sun goes in the same place than the emitter sun that I created and that´s it.

BTW check cgskies they have good quality and even the small free samples create hard shadows.

Cheers
JC

Firstly, some HDRI do look dull and have been saved with shifted gamma, which needs adjustment.

After that, painting/boosting the sun in PS works well, but I also prefer an emitter most of the time - easier control.

Brodie, your making a mistake from a technical perspective, if you put completely different inputs into illumination and ref/refract you have broken the engine, however you can put a blurred version into illum to speed up rendering, but with softer shadows ofcourse.

Just wanted to make that clear for others.

@jc4d:
What power of that emitter do you set?

A bright one, and boost further with multi-light, I dont know if their is an optimum level in relation to other emitters. I dont think it matters once your in a sensible range.

For sun emitters, I keep them as close as is believable, maybe 1-2000 meters, depends on scale. I also use a flat plane - with a 32 bit softened circle alpha, but a low poly disc is ok, just not quite as nice reflections.

I was looking for power number to type in to be very close to original sun to match other light etc but most probably it will be really big

Hi Alex, as I said before maybe my setup is wrong but works for me , the distance from the center of the scene to the sun emitter is 50000cm the emitter size is 100cm X 100cm and the power is watts 80000000, efficacy 683 and color temp set to 5500.

Here is an screenshot were the axis represent the sun object and then adjust the hdr texture to match with the position of the sun.


Cheers
JC

PS,
Lately I have noticed so much blue tint when HDR is used, I don´t know if is because the famous HDR quality.

Also you should put your sun emitters target point (usually 0,0,0) at the same place as the maxwell scene object (also probably at 0,0,0). That way the hdri is centred to the same point as the sun emitter, aaannnddd it also means you can use maxwells sun preview indicator (scale it up a bit) as a visual guide for lining up the emitter sun... to a specific time of day.

Thank you both, I was thinking about making sphere with hole and map with HDRI and keep Maxwell sun and sky on but making emitter and centering it is easier. All in all most important is what it will look like not the camera exposure.

hoping that one day NL gives us a manual sun to play with our hdri like most the other render engine