Photoreal ~ what makes it?

Started by cyphyr, March 06, 2013, 06:49:35 pm

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gregtee

Oh, a good point that Chris brought up is the use of gray balls and calibration images.  Professionals use these all the time to determine if their scenes are properly balanced.  We employ the use of calibration scene setups that consist of Macbeth charts, spheres with 18% gray values added to them so that we know right off the bat if our lighting is even in the ballpark or not.  Key to fill ratios are easy to set when you're looking at uniform shading values. 

Another technique is to just put an 18% gray value on everything in your scene and then light it.  This is more a technique used in stand alone renderers to help with lighting but it can be useful in TG because these surfaces render very quickly and are good proxies for how a camera views the world from a luminance perspective.  You can quickly "sketch out" your lighting angles and find problems that might otherwise get hidden in shaders and textures.  Once you're happy with the overall look of the lighting, again what I consider the most important aspect of the image, you can start layering in the textures and shaders.  If problems start to pop up at that point you now know where to troubleshoot as you've already determined that your base lighting is correct. 

-Greg
Supervisor, Computer Graphics
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Oshyan

Great info guys, this is shaping to be a very, very useful thread. :)

- Oshyan

chris_x422

Hey Greg,

No problem, I'm currently at Iloura in Melbourne, lighting on the great gatsby.
Still learning from some great lighting artists :) as I usually work as a generalist.

Back on topic, I'd just like to add that there is so much information on the net regarding lighting that's worth researching, and its pays dividends to try a few new techniques to expand your knowledge of lighting.

Here's a good one that also references someone you all know, Ansel Adams.
http://www.scratchapixel.com/lessons/3d-advanced-lessons/things-to-know-about-the-cg-lighting-pipeline/0-18-stop-and-exposure-explained/

Chris



gregtee

Chris's link is great example of the linear workflow.  A lot of work has gone into facilitating this approach at the various effects facilities around the world and is pretty much standard practice everywhere.  Artists, and especially lighters routinely speak in the same terms that DPs and photographers do these days with regards to lighting.  It's not at all uncommon to hear someone say "make that two stops brighter", or use the gray ball to calibrate your light intensities to match what was shot on set. 

Terragen pretty much has already built it's world internally to take this all into account, but it's still a good idea to understand this stuff if you're striving for photorealism because at the end of the day we're trying to make our images look like photographs (assuming that's your goal of course) so it's handy to understand why photographs come out the way they do. 
Supervisor, Computer Graphics
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cyphyr

March 09, 2013, 05:20:28 am #79 Last Edit: March 09, 2013, 05:56:52 am by cyphyr
As I said a lot to take in but one thing occurs to me right away. The techniques you have both described, Macbeth Charts and various grey/reflective balls in particular are for matching virtually created environments (and elements of those environments) to a real world image or film stock. Will this even work in an entirely virtual environment? If I drop a Macbeth Chart into my Terragen render what do I have to compare it to? I *think* I should be able to simply compare the luminance and colour values from the rendered image to the source Macbeth chart and adjust exposure accordingly.
Hmm much to ponder ...
cheers
Richard

ps: Uncanny Valley would be a GREAT title for a contest :)
www.richardfraser.co.uk
https://www.facebook.com/RichardFraserVFX/
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gregtee

Yes, if you took a Macbeth Chart and dropped it into your TG scene it should be useful as a calibration tool see what your exposure is, but when doing all CG environments it's all relative.  The chart will tell you however if your TG assets and lighting are calibrated properly in relation to real world lighting or if you were cross pollinating TG renders with renders from other programs that went through the same calibration process to combined in a compositing program. 
Supervisor, Computer Graphics
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TheBadger

Macbeth Chart & grey/reflective balls

Dose someone have a link to a good resource on reading about these things; what they are, how to use them, both in relation to compositing film and CG, as well as using them in a complete CG environment.

I have seen both many times in threads on line, but never with much discussion of them.

The so called Macbeth Chart sounds like it comes out of photography ("middle grey"), so Im interested in seeing how to use it in CG.
It has been eaten.

cyphyr

Check the link Chris posted a few posts up, it's a whole series of articals, pretty technical but understandable in the most part.
Richard
www.richardfraser.co.uk
https://www.facebook.com/RichardFraserVFX/
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Ryzen 9 3900X @3.79Ghz, 64Gb (TG4 benchmark 6:20)
i7 5930K @3.5Ghz, 32Gb (TG4 benchmark 13.44)

gregtee

A lot of this stuff is mostly useful when you're trying to marry CG rendered stuff into live action plate photography, but that's not say all CG stuff won't benefit from it. 

When we go out on set we bring all this stuff along because it helps us when we get back to the facility later with the calibration process.  The Integration Department uses this stuff to make sure HDR latlongs are properly graded, and having the gray balls and Macbeth charts in the latlongs allows them to make sure the exposure is right and the grades are neutral. 

Once that's done and we know that the on set HDRs are properly color corrected we take them into our CG environments knowing that IF we use these images on dome lights with their intensities set to 1 that it'll be the correct luminance value to start lighting our 18% gray valued CG models and environments.  At that point it's just a matter of apply the shaders to the assets, which have already themselves  most likely been developed in a calibrated "look development" scene that contains a latlong attached to a dome light with the same settings as our CG scene light.  The assumption is that if the asset created in the look development scene was made from the same baseline lighting intensities that you can just plug them into any new CG scene and it'll work, assuming of course you new CG scene lights have also been through the same calibration process.  This save a ton of time and allows easy re-use of assets from previous shows without having to redo a lot of work.

Terragen already pretty much enforces this workflow because everyone is developing their scenes and assets with the same lighting model and shaders, so if someone does a good job building and texturing a tree for example and uploads it to the forum it'll be pretty much guaranteed to work in any other TG scene out there unless someone has really done something whacky with their lights or sun settings. 

Supervisor, Computer Graphics
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gregsandor

So we're really back to "that art thing" as one of my studio managers used to call it.  Terragen's lighting and atmosphere model is pretty good to begin with so when it comes down to it making a good picture is a matter of having a good subject photographed in a visually interesting way.  Composition makes or breaks it.

Thejazzshadow

I haven't read through this disucsiion fully so I apologize if someone already said this. From my own experience, another way for a picture to look real is if no one suspects it to be fake. If I make a picture of a planet or of some scene where the viewer knows a camera could never be, then people know it is CGI and tend to notice where it is different unless of course the artist did an extremely excellent job. However, if I made a Terragen picture of say my back yard or of some other place that is real, people would not expect it to be fake and would more in likely believe it even if it had the same flaws as the picture of the planet. Of course, these "flaws" are more in likely picked out by CG artists such as those on this forum. Again this is just from my experience.

efflux

March 23, 2013, 10:28:26 pm #86 Last Edit: March 23, 2013, 10:34:17 pm by efflux
Quote from: gregsandor on March 09, 2013, 11:19:41 pm
So we're really back to "that art thing" as one of my studio managers used to call it.  Terragen's lighting and atmosphere model is pretty good to begin with so when it comes down to it making a good picture is a matter of having a good subject photographed in a visually interesting way.  Composition makes or breaks it.


I haven't read through all this thread except I saw gregsandor's post. I don't think art has anything to do with making something photoreal. Art will make it interesting to look at though. You can be very skillful at making the picture look real but putting art into it is a different matter. Some TG2 images have a lot of art about them but aren't realistic looking. Maybe they just have a good mood. It's when you get both these things right that you get a really great render.

I think you need detail. Real landscapes usually have a huge amount of detail. You need sense of scales i.e lots of different scales of things we know about. For example, If it looks like sand we know what size that is. I think the scale thing lets down a lot of TG2 images that otherwise would be convincingly realistic. Lighting is important but TG2 pretty much handles that without too much tweaking. Atmosphere is also quite important. How thick mist is etc. Then make it look like a photo. How a lens reacts to light, exposure, how photographers frequently post process photographs, those sorts of things. People are used to looking at photography.