Let’s get technical with light and pixels
This post is going to be quite dry and lacking of pictures, I hope you will forgive me because this stuff is actually quite interesting. I have learned all of this through mindless perusing of sites, and blogs. Below is basically a summation of some of the teachings of Master Zap. And of course everything is generalized
When you talk about lights and units, you can break them (generally) into two categories. Radiometry and Photometry. Radiometry is what you measure. It is actual radiation and its base unit is the Watt. Photometry is what you see, it is the perceived brightness, and its base unit is the lumen. The relationship of these two is based on the relationship on the sensitivity of the human eyes. This is called the “Photopic Response Curve” For any spectra of light, it can be expressed as a number called “luminous efficacy” (lm/W)
As you can see from the graph, we see green the most–>exactly 555 nm of wavelength. So it will have a very high luminous value. Whereas over in the far left area of the violet where there is exactly the same amount of watts we will have a 0 photometric value to us.
Computer graphics is technically radiometric units, photometric units can be more useful.
. photometric radiometric
Luminous power = lm (W)
Luminous Intensity = lm/sr = cd (W/sr) cd=candela
Luminance = lm/sr/m^2 =cd/m^2 (W/sr/m^2)
Illuminance = lm/m^2 (W/m^2)
sr = steradian
radian=2d angle where the arc length of a circle is equal to the radius
circle =2pi radians
steradian
3d angle where the area on a sphere is equal to the square of the radius
A sphere covers 4pi steradians
luminous power = the amount of light leaving the entire light in every direction at once.
luminous intensity = the amount of light leaving the entire light in a particular direction.
luminance = the amount of light leaving a particular point on a light and goes in a particular point. Our everyday perception of brightness is luminance.
illuminance = the amount of light arriving at a particular point on a surface, but coming from every direction. A sum of all the luminances in all directions seen from a point.
Now you can begin to see how this is all related to the CG world and rendering. But what about pixels?
PIXELS:
A camera is a luminance measuring device.
Pixels can be many different things. They can be the actual brightness of something. R,G,B are proportional to spectral radiances. Weighted value is proportional to luminance. The range of this is 0 – whatever. You can have as much as you want. We cram these into low dynamic ranges and call it black to white. That is just the limit of the file type, not of reality. It can be how much something reflects (0-1 range) such as texture images.
Most computer graphics displays have a display of 8 bits of red, green, and blue. 0 is black, 255 is white and 127 LOOKS like middle gray, but even though 127 is half of 255, it is not half the brightness. The human eye is a funny thing. We perceive light in a non-linear way.
This is a perceptually linear ramp:
This is a linear ramp:
If you measure the values of luminance, you will see that the perceptually linear ramp is not right. If you really made the same change for each step, you would see a curve like the bottom image. We perceive huge jumps in the dark area and small jumps in the light area.
If we try and encode an image using the linear values it will look horrible, whereas if we encoded it using the perceptually linear values, it will look correct. This is exactly what the computer monitor does. The pixel response of the monitor is not linear. 127 is not half as bright as 254. This, of course, is called gamma. A computer’s gamma is typically 2.2.
All this means that your 8 bit images have gamma encoded into them so they will display correctly on your monitor.
When you work in an 8 bit format your gradients between colors become muddled and ugly.
All this creates disastrous results when rendering. This is why, when working realistically, you need to work in a linear method. There are tons of “how to’s” out there, I have even provided links in a previous post on this blog.
If you work nonlinearly lots of bad things happen. You get unrealistic fall offs, you get blown out effects when using physical lights, you also get artifacts around highlights. There is a weak propagation of Indirect Light, and you get unrealistically strong reflections. There is also a huge problem with motion blur, it looks dark and smudgy and highlights will not streak properly.
Swatches?
For you Maya USERS in the house!
Ever create a material preset that looked awesome and you want to save it, but you want that cool little thumbnail so you can find what it looks like again? Well I found out how :-)
I learned a neat little trick today that is quick enough I could share with all of you. Here is a quick tutorial on how to create those thumbnail images associated with your materials that you create.
Step One: Open the scene where you want your material to be rendered on the object you want rendered that has some good lighting.
Step Two: Open your hypershade and navigate to the library where your newly created shaders are. (I strongly suggest having one because things like to break when you start moving your shaders to new homes).
(Create new tab, navigate to the directory). MM drag the .ma material file into your scene and apply it to your object.
Step Three: Render (I suggest a 400X400 image, but it doesn’t really matter)
Step Four: In the render window where your new image is now sitting, click on view>grab swatch to hypsershade/visor.
Step Five. You will now be asked to draw a marquee selection around the area that you want to have as a thumnail.
Step Six: Once this is selected make sure you have your hypershade open and you can see your .ma material file in your library(The one that is sitting in your library not the one that is in your scene) . Middle mouse your selection onto this icon. It will replace that default icon with your new beautiful render of your material!
That’s it!
TheBeals has a job!
Finally, 6 months after graduamatation, I have a job. Err well technically a paid internship. Which sounds pretty decent, until you realize it is with Adidas then it’s more like :) –> :O. So crazy, I am so terribly excited. I start the 19th at their Headquarters in Portland. Best part? I get a little key card with my photo on it!-ok well maybe not the best part, but it’s still pretty sweet. Their campus is HUGE and so amazing. I highly suggest googling and even google map it (adidas headquarters, portland, or). So amazing.
As a result of this I’ve been brushing up on my skills because I am sure that the first they ask me to do will be the one thing I haven’t done in a long time. Here is a little comp. test that I worked on today. I wanted to make sure I still knew my way around After Effects. Either way, I did none of the 3D work, just composited it :-)
Ipod_test_Comp
Hrmm wonder how I can just insert the video straight here.
Also with this new adventure in my life I am also learning some new moves from fxPHD.com. Mainly more lighting/rendering theory taught by Master Zap. I’m taking another two lighting classes-maya and Renderman. Lasts 10 weeks or so. So it will be a fantastical 3 weeks-At the end of which I should have some pretty awesome new material to post and some more knowledge up in my noggin that I can share with all ya’ll!
Fire Test
I’ve never really dealt with particles, but I have to say once you get on the right road, it’s pretty fun. The black outlines at the base of the flames are an outline of the logo that will go in it. I am getting some weird build up right above the letter though. hrmm…
My Procedure for matching the lighting and materials of a photograph
I was asked what my approach is to matching the lighting and materials in a photograph. If you have had to deal with this, you know it is fairly tricky. However, I believe if you follow these steps it will make things much easier and much quicker to do correctly.
1A.) In this write-up I am going to assume you don’t have any specific data from the shoot. e.g: light data, camera data, hdr probe etc…
1B.) Research. This can happen after the modeling bit or before-it doesn’t matter too much. Recently, I have had to match a photograph of a wine bottle. For my wine setup, I had to no idea how photographers setup their lights to light glass. It’s such a tricky thing to light. In fact you don’t even light glass-crazy right? You create reflections. I did not know this when I started and learned about it through my research. If you do a bit of research before, it will shave off hours of experimenting. You will learn little tricks and hints and see how they setup up their lights. That way when you see a reflection or highlight you understand how and about where that is coming from. Another good bit of knowledge is “family of angles.” This topic tells you based on the object from the camera, where a reflection will show up. Google is your friend with this area. Also know what you are ligthing. For example, you light glass and metal in completely different ways. Metal depends on reflections toward the camera, and glass depends on reflections on the sides. :)
1C.) Modeling. No matter the subject that you are trying to emulate, you have to try and model it as close to the photograph as possible, especially if it is highly reflective or refractive. Why? Well say you have the model pretty close to the photograph, but not exactly. The reason this will throw you off is because every surface point on your model that is different than from the photograph you will get a different light play than what is on the photograph, even if your lights are in the exact place in your scene as they are in the photograph. So you will not get the same highlights/reflections/refractions that the photograph is getting which will lead you to have to do hacks to make it “look” about the same. Which, in the end, will only cost you time and energy.
2.) Initial setup. As well with modeling, this part is key. First create a camera, never ever, ever, ever use the perspective camera to do these renderings. My favorite, and probably the easiest and quickest, method is to load the image as a background image and move the camera so your object is in the same place as the object in the photograph. Don’t forget to mess with the camera’s focal length to match the camera that was used. A more exact way is to measure out the vanishing points of the photograph, find those angles and recreate them in your 3D app. Key your camera or add a bookmark so you don’t lose your place.
3.)The real step one. Once you get your camera setup, setup your initial materials and a couple of lights just you can work w/ your mats. The mats don’t need to be exact. For this all I am saying to do is if your object is highly reflective, create a highly reflective material, if it has blurred reflections create something w/ blurred reflections, if it is glass create a quick glass with the appropriate colors of course. This way we can dial in where the lights are based on reflections and highlights.
Because we are trying to match real world materials, use physically correct materials, I believe every renderer has something like this in it now. DO NOT use a blinn or a phong unless you absolutely have to. If you do, make sure you get your falloffs correct. For mental ray stick with the Mia_Material (Arch&Design for you Max users). It even has nifty presets for metal and glass which is perfect for this step.
4.)Camera. Since we are dealing with the real world that means that everything has to be “physically correct” this includes the camera. This one I always go back and forth messing with. Sometimes I setup my lights first and then do this and other times I setup the camera first. I think it just depends on what you are doing and your taste. In this case I applied a photographic lens shader with just a basic light setup first.
5.) Lighting. I have found that messing with highlights and reflections first and doing the fill last is the best way to work. The highlights and reflections are the most obvious and so the easiest to nail first and then the fill will fall into place.
Make note of where the light sources are in the photograph. Generally real world photography deals with a minimum of 3 lights, sometimes 2. This is the point where you need to decide if you are going to try and match the lighting exactly as they did or if you are going to do some tricks that will give the same look, with less render time. An example of this is often in lighting, the photographer will shine a light at a bounce card which will bounce the light back at the object which creates really diffuse lighting and often a nice highlight. If you do this in 3D your render times are gonna skyrocket really quickly. An easier way is to use an area light w/ soft shadows and have it visible with maybe a reflect card BEHIND it. Gives about the same result w/ 1/4 the rendering time.
Also, I notice a lot of people have all their render settings turned up to max when testing. Don’t do this, it is unneeded. Turn down your aliasing to -2 and 0 instead of 0 and 2 and turn down the amount of reflections and refractions you have. If you are doing glass make sure they are high enough so you won’t get black in your refractions/reflections. These settings will lower your render time by half at least. Also if you are using fg or gi, lower these settings even if you get a little bit of blotchiness. Stop making life harder for yourself!
IF ipr will work for you in this part I would highly suggest using it. Create the light shape you need. If you are just getting a reflection then you can leave the intensity at 1 w/ no falloff, and ipr your scene and now move that light and manip it so you can get that same shape and size on your object. Once you get this in place hide the light and do the same for every reflection. Once this is done then unhide them all and go to the next step.
6.) Lighting Cont. Along with your mats and your camera, your lights need to be physically accurate as well. You have a couple choices in this area. You can apply a physical light to the light/photon emitter of a POINT LIGHT and then an .ies profile to that to emulate a specific light. WARNING: Maya has issues with this. Max is muuch much better if you want to go down this road. These profiles only seem to play nicely with point lights.
Another option, and my favorite, is to load a blackbody or a cie_d into the color attribute of your light. This way you can control the kelvin temperature and intensity realistically. Don’t forget to have a quadratic falloff and shadows enabled.
NOTE: The white point of your camera will affect the look of the color of your temp on your light.
Once you get the reflection properties down, hide these lights, and work on the highlights. You only want to work with one light at a time to make sure you know what is doing what. Once you get these dialed in, then unhide the lights and see how they work with each other and adjust accordingly. Once you get the highlights and reflections down then go ahead and apply the fill. You can hide the other lights and dial this in or you can do so with the other lights in the scene, since you are just adjusting the fill and if fg in on the fill will need the other lights.
7.) Finally finesse the materials, add textures, crank the samples. During this mode, cranking the anti-aliasing and refl/refr properties will be a good idea.
Job Possibility?
I am in the running for a possible paid internship with an extremely notable company right here in Portland! I won’t say who it is with, but I will say I am very excited. This would be such an amazing opportunity for me and I know I would be able to make a big impact in this company. I would be doing everything that I love to do. And the best part? I get paid to do what I love! I love my industry.
Since this interview process has begun, I have noticed how far a nice and pleasant H.R. person is. I’ve had my dealings with a few H.R since my graduation and while every one is “nice,” it gets to be easy to tell who is faking and who isn’t. I bring this up because I am just blown away by the H.R at this company. She is so incredibly nice and is completely organized and has always gotten back to me very quickly. She is always willing to help out where she can and make everything a little more pleasant which makes me want to put in 110 percent. What’s even better? She has the same name as my car! A little nerdy, but hey we all have our quirks.
Once I got the initial interview, I wanted to basically prove to myself that I can do everything they would need me to do. Think an art test, but not quite. I think the meaning is pretty obvious so I won’t go into that. I hope I can post this, I’m never quite sure how these things work, if it is ok to post something that has a company name on it. If it’s not-SORRY I’ll take it down!
Maya and Mental Ray were used, naturally. Can you figure out the company yet?
What I’ve learned from a girl named Pirate Chick….
So this Pirate Project was by far the most intensive and time consuming project that I’ve done to date. In fact no freelance, school, or personal project even comes close, but it just looks like a normal project. There’s nothing really intricate about it. There is no insane detail or crazy long render times (ignoring the first test renders of hair of course), I didn’t need to use proxy objects or instances. I had no use for referencing, so why did this project take so long to finish? It wasn’t for lack of time put in, I worked on it most days. In fact I have lost track of the amount of hours put in this project… it is far above 300… so why don’t have I have much to show for it. Well actually I do. It may not be in the artwork-let me explain.
This project started out as a portfolio piece… something that will turn heads, hopefully something that would get me a job. This being my purpose for it, I tore through it in the beginning. Going as quick as I could, spending all day on it. I was getting good reviews, nothing horrible and then I got one critique that made me put things on the backburner for a couple days.
The critique was something along the lines of “This is really great work, but I think you are missing the point. You are creating this to show, you need to create this to learn.” I took this to heart and realized he was right. This project needs to be about personal growth and bettering my abilities through learning. So I slowed down.
I went back to old problem areas and fixed them, I re routed much of my topology, creating a cleaner edge flow, even though it wasn’t completely necessary. I broke down the materials that I was using and figured out what made them tick. This part was fairly easy. I only used two different type of materials-exluding the hair. The Mia material (or for those Max user the Arch and Design material) and the sss material, both created-or at least in part-by Master Zap.
The sss shader was by far the harder of the two to understand, especially with the version I was using. I was using the “newer” version which had A&D reflections built in, so they would produce realistic reflections. I realized with the sss material that the radii and the depth didn’t matter soo much-these values could be within the ballpark and be ok. What mattered most was the overall scale and spec along with your maps. You need spot on diffuse and epidermal maps to pull off a realistic skin shader. This gets pretty tricky because there’s an endless amount of mixing and matching and everyone has their own way.
The mia material was pretty straight forward glossy=glossy, samples=samples diffuse=diffuse etc… The trickier part was the BRDF curve. Small small changes to any number gives you far different results. This is pretty lame because this is the most important part of the shader to get it right.
Tip for getting good metal: Use the IOR fresnal (pronounced FRE-NAL, it’s named after some french dude)and set it to a super high value of something around 30 (air is 1)
The mia material is amazing, it can be used for just about everything, from satin, to cloth, to leather, to wood, to conrete, to metal, to glass-whatever. It is a physically accurate model which means you can’t make it behave incorrectly!! OR maybe you just have to try reallly reallly hard.
I also learned that what makes a character feel like a character isn’t the realistic materials or the fancy lighting, it’s the character of the character. It’s the pose, it’s the glint in the yea, it’s the curve of the lip that says “I know something you don’t.” THIS is the hardest part to nail in the character. I wasn’t able to hit this nail. I got close and had a couple glancing blows, but I never managed to nail it.
But this is what learning is. You keep practicing till you get it right. You don’t have to get everything right in one go, it’s a process. From here on out I know that I am a much better modeler, lighter, and texture artist, and I know exactly what I need to work on… everything. haha-that’s what being an artist is all about isn’t it? You’re never done, you’re never fully satisfied with an art piece, there is always something more to be done, to be learnt. It’s a process.
The fun is in learning, exploring, creating, and imagining. It’s about building up your texture and reference libraries and then bragging to all your friends that you need to by another TB hdd because the one you just bought 6 months ago is full due to texture collection, reference gathering, and tutorial videos. It’s about sitting at home with your dual monitor setup, sitting a nice comfortable chair, watching house/big bang theory/scrubs/lost/mythbusters/futurama/ or listening to music, and losing yourself in your work. It’s about wondering why it’s getting lighter outside instead of darker and then realizing it’s because the sun is rising and you really DO need to go to sleep because you have a final exam in 5 hours. It’s about wanting to create and learn new things and new ideas. It’s about learning that even though this is all you want to do, you really do have to go out to the bar with your friends every once in a while and catch up and have a good time. And finally, it’s about realizing it was never about the money, or working at Pixar or for some top secret govt. program (Even though I would never turn it down and would brag to high heaven if that ever happens… hire me-I’m young and cheap =D), it’s about doing what you love, it’s for the sake of the game. You do it so one day some little kid will look up to you like you’ve done to the industry giants your whole life.
So to conclude this episode, you shouldn’t create art to show, you should create it for yourself-to learn-and for others in hopes that it will effect them the same way it did you.
Final Pirate
So I ended up using: Maya, 3Ds Max, Mental Ray, Renderman, Wings 3D, Headus, Zbrush, Bodypaint, Photoshop.
Maya was used for just about all the modeling. Wings was used for some
of the simpler things such as the sword and belt, mainly so I can get
practice using a different modeling program. There was no way I was
going to use Max for modeling, I don’t understand how anyone can model
productively in that program. Maya was also used for my first lighting
setup and all of my material tweaking. I couldn’t get the sss shader
to look how I wanted, I kept getting overly dark shadows, so I
switched to Max which solved that problem even though I used the same
type of lights and distances. It’s a pain to move things from one 3d
app to another, but at least MR. stayed the same =). Since I was still
using MR, I was able to transfer over all material attributes w/o any
problem. The final render was done in Max
Zbrush was obviously for sculpting. Headus was for unwrapping,
Photoshop for texture creation and color adjustments, bodypaint was
for additional painting work and for seam painting.
At first I tried Hair in Maya and it just didnt work which helped me
make up my mind if I wanted to move to Max because I heard Max has a
pretty good fur/hair system (if anyone has been around me, they know
my vast hatred for Max, but desperate times call for desperate
measures). I then tried hair and fur and could pretty decent results
fairly quickly, but render times were absurd (8hours w/ raytracing, 10
minutes w/o-which is still a while just to tweak). I knew Renderman is
really good with hair and I had a copy of Renderman on an old hdd. So
I plugged in that hdd and spent a couple days learning how to do maya
hair again. Turned on RM set up the same lighting setup with a couple
tweaks, turned on deep shadows, cranked a couple settings and voila
beautiful renders at around 2 minutes a pop. This is one of the
reasons I had difficulty with getting nice contact shadows between the
hair and the body. 2 different 3d programs and 2 different rendering
programs, not pleasant.
Linear Workflow – Learn it!
So I was going to write an article on linear workflow because no one is doing it! (aside from every film house :-)) But I figured that this topic has been talked to death so I am just going to give you some links that are easily found on google, but this is mainly for people that don’t even know what a linear workflow is. And maybe because I’m feeling a bit lazy and wanting to finish my pirate character:
Pre-reading:
http://mymentalray.com/wiki/index.php/Gamma
Reading:
http://www.djx.com.au/blog/2008/09/13/linear-workflow-and-gamma/
http://3dlight.blogspot.com/2008/09/linear-workflow-for-maya-mental-ray.html
http://www.teamten.com/lawrence/graphics/gamma/
Forum Thread:
http://forums.cgsociety.org/showthread.php?f=2&t=610790
Heres a quote for the famous Master Zap:
If you render on a “standard” computer monitor (i.e. an sRGB monitor which has a practical gamma of 2.2 on average) with no regard to gamma anywhere in your workflow (i.e. pretending the monitor has gamma=1, like unfortunately most software defaults to), then when you think you are making something twice as bright, you are actually making it almost 5 times as bright.
This makes even the most trivial math turn out completely wrong. Basically, your renders come out as if 2 + 2 = 10
This is why highlights blow out unrealistically, why reflections look wrong, why you can’t seem to be able to use physically correct lights with a quadratic falloff, and why you have to save everything in comp with a bunch of horrendous dirty tricks like “screening” your speculars back on (Yuk!).