Fake Shadows / Negative Light

[yp]

Vray, 3Ds Max 2013

 

Hej,

 

there are some topic about this floating around but I couldn't find the right one- if there is any..

 

I light a scene with a hdri in a dome which mostly lacks more defined shadows. Increasing the gamma improves (strengthens) shadows but not enough yet. So linking a vray sun or in this case a standard direct light to the dome works good, but to get more shadows the direct light intensity needs to be increased which brightens up the whole scene..

 

Actually I'd like to have control over the shadows of the direct light only and controlling the brightness of the correctly set hdri and values of the camera.

 

So I after thinking and googleing I followed the tips which are around- setting a standard light to black light color, setting shadow color to pure white and using negative values for intensity.

 

Actually it doesn't work with VrayShadows- at least I couln't get it to.

 

Unticking transparent shadows gives the ability to change shadow color, but I can't achieve black shadows... see attachments.

 

white: setup as should be (with ray traced shadow) - result similar to any grey value but brighter in relation

 

white with ticked transparent shadows: setup as should be (with ray traced shadow) - no shadows

 

pink: colored shadows work- negative multiplier has no effect, only dense multiplier.

 

black: no shadows

 

grey value: increases negative shadows..

 

 

Edited June 5, 2014 by yp

[yp]

Hm...

 

seems like the multiplier has no effect in this case, only defines if the value is below 0.

 

Changing the "dense" value to a negative value inverts the white shadows- which works at first sight, but somethings wrong with the shadow, it's way too dark in the corners next to the windows..

 

Edited June 5, 2014 by yp

[Francisco Penaloza]

Interesting research, but predictable results.

if you want to only use HDRI you need to use good image sources. Yes you can adjust gamma on the HDRI to accentuate the light intensity but this create other problems , the right way is starting with good HDR images, the one's IMO that are the best are the ones from Hyper Focal Design, when you use his images for first time you'll realize how bad are all the other dome lights

If you want to keep using your images, you can use a Spot light to create or accentuate your hard shadows, but you need to push back your HDRI gamma to default or close to default and adjust your spot light intensity until you get a good shadow. if not you'll create strange color casts or lights spills.

[yp]

Yeah, predictable for sure if you think a little about it.

Like interverting (positive / negative) values results in inverted effect like inverted shadows, inverted colors etc.

 

Actually I still would like to get it to work, maybe there is no way to do it with standard lights and vray..

 

Ill have a look a Hyper Focals site- just saw their new timelapse hdri's today. Maybe time to think about animations one day

 

Changing the hdri gamma to some value around 7,5 or higher give a little more sharper shadows but doesn't affect the color too much. Different when lowering it more

 

Normally I use a standard light as seen in the pics above and it's alright- but brightens up the scene too much and takes away some of the naturalism of purely hdri light scenes (IMO), see pic.

Besides that eg. painting a exposure spot into hdri to sharpen shadows is a VERY good thing too (eyedropping exposure value and painting it)

 

Using elements to control shadows in post is another thing too.

[RyderSK]

Since you want absolute control over shadows in Max, then HDRi approach isn't right from beginning, since you have to modify your HDRi in Photoshop(or alternatively HDR Studio) to have complete control over dynamic range without inducing in gamma change craziness.

 

I would just use HDRi for reflection purely and adjust everything else using VraySun/Sky.

 

HDRi doesn't have any nicer/different light than analytical lights, it's the single package that makes it attractive, but since you want control, then that's out.

[yp]

Yeah, thanks for that insight.

 

That's more or less what I do, using vraysun / direct light.

 

Guess you're right that I want it all in one but still want control

This setup seems better probably.

 

I just assumed when a suitable camera system took HDRIs of a daytime when every object around has nice shadows it should be just perfect when you use it in a scene- but maybe that's wrong :)

[RyderSK]

No, that assumption is correct, but it needs to account HDRi's "quality" itself, as mentioned by Francisco. What is the problem often, is not enough dynamic range is contained within the daylight ones. For example, +4/-4 //8EV stops is enough for overcast one, because you really only want the reflection from the dynamic range, but for midday strong sun you might need as high as 16+ (although I've seen even higher than that).

 

[there is an "article" about it here, heh, it's an advertisment for Hyperfocal skies though ;- ) but still, it conveys the message http://www.cgarchitect.com/2013/12/effects-of-hdr-vs-mdr-on-image-based-lighting ]

 

Some authors state the dynamic range, some don't. MOST are not really that good. And those which are good technically, are often not interesting artistically. It's problematic circle :- ) Basically, even today, the HDRi for Archviz are....just kind trashy imho, compared to the ubiquitous quality of those done by MOOFE for automobile industry (but again, the price is 20 euros vs 200 for non-commerical up to like 10k min. for campaign use, as those are right managed).

 

I have them all, like ALL of them. Peter Guthrie, CG-Source, Dutch skies (very famous in VFX industry),etc... but am I really satisfied with any..not really. I use like 4-5 continually, which I modify heavily in Photoshop for every project (contrast, intensity of direct/in-direct light, hue, shadow penumbra is tied to size of direct 'hot-spot',etc..), but I still didn't ruled out good old Sun/Sky combo when valid :- ).

[yp]

Yeah, thanks, interesting article! Didn't expect that much difference in quality..

 

Ill get my hands on a civetta one of these days (well, actually in August) to play around a little too :)

28 f-stops and 100 mpixels full spherical seem exciting, hope the weather is nice for a trip..!!

 

If I get out some results I'll hand some over