Lights and Colour in VR. Cecília Sik Lányi University of Pannonia Veszprém

Transcription

1 Lights and Colour in VR Cecília Sik Lányi University of Pannonia Veszprém

2 Content First part Definitions (virtual reality, light ) Light types in VR Some examples of these lights Second part Colour temperature of the light Different light sources in VR Radiosity Some practical advice Third part Videos Conclusion 2

3 Motivation What motivated me to teach VR and multimedia? Not the fact that I have to spend sometimes 14 hours a day glued to my computer screen. The real motivation for me is for example when I get a message from a low-vision child s parent from somewhere around the world saying that this game what we developed is the child s favourite game. I have always been impressed by 3D artists who has taken the time and energy to ensure their images were truly photorealistic. Today we will deal with the most important basic knowledge about making lights in the VR. 3

4 Definition of Virtual Reality Virtual Environment (VE): A synthetic, spatial (usually 3D) world seen from a first-person s point of view. The view in a VE is under the real-time control of the user. Virtual Reality (VR) and Virtual World are more or less synonymous with VE. Multi-sensory VEs are closed-loop systems comprised of humans, computers, and the interfaces through which continuous streams of information flow. More specifically, VEs are distinguished from other simulator systems by their capacity to portray three-dimensional (3D) spatial information in a variety of modalities, their ability to exploit users natural input behaviour for human-computer interaction, and their potential to immerse the user in the virtual world. 4

5 What is light? We can read in the Bible: In the beginning God created the heaven and the earth. And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters. And God said, Let there be light: and there was light. And God saw the light, that it was good: and God divided the light from the darkness. (The First Book of Moses: Called Genesis, Chapter ) 5

6 Definition of the light Visible light is really a very small portion in a range of electromagnetic radiation. This radiation travels in waves of different wavelengths. The difference in wavelengths (the tops of each wave) is what makes the difference between blue, red, gamma rays, x-rays, radio waves etc. 6

7 White light White light is a combination of all colours in the visible spectrum. When we perceive an object as red for example, what really happens is that white light falls on a red surface, and all the wavelengths except those that give red light are absorbed by the material. Only the red portion of the spectrum is reflected back. We are going to discuss the colour of lights later, but first I would like to present you with some lighting basics and types of lights in a 3D professional modelling software, for example in Maya. 7

8 Lighting concepts The basic premise of good lighting is appropriate design.. Light gives objects or characters meaning in their surroundings. It also provides an appropriate and intentional atmosphere that will be logically interpreted by the viewer. The design potential of light is inherent in its physical characteristics. By controlling its intensity, colour, and direction, light becomes a key factor in creating a scene. Lighter and darker areas help to compose the frame and guide the eye towards certain objects and actions. 8

9 Choosing light types Once we have determined the direction and distribution of lights on a scene, we will also need to consider the type of light source. Light types: Directional lights Point lights Ambient lights Spot lights Area lights Volume lights 9

10 Directional Lights 10

11 Point Lights 11

12 Ambient Lights 12

13 Spot Lights 13

14 Area Lights 14

15 Volume Lights 15

16 Default Lights, Light intensity If there is no lights in a scene for example, Maya creates a Directional Light when the scene is rendered. This light is parented to the rendered camera and illuminates the scene regardless of where the camera is facing. Intensity can be defined as the actual or comparative brightness of light. Like most other render attributes, it can be modified either by using the slider or by mapping a texture to the channel. 16

17 Decay Rates No Decay: Light reaches everything. Linear: Light intensity decreases in direct proportion to distance (I=1/d) Quadratic: This is how light decays in real life (I=1/d*d) Cubic: Light decays faster than real life (I=1/d*d*d) 17

18 Bike examples together upper row: Directional-, Point-, Ambient-, lower row: Spot-, Are-, and Volume Light. 18

19 Lighting the models by upper row: Directional-, Point-, Ambient-, lower row: Spot-, Are-, and Volume Light. 19

20 Geometry primitives Default-, Directional-, Point-, Ambient-, Spot-, Area-, Volume Light. 20

21 Next topic: the colour of light Do we really know how wonderful light is? 21

22 The colour temperatures of light 22

23 Actual Light Colours and their 3D Equivalent 23

24 Always use the proper light coloration when creating photorealistic light! Every light source emits a different color so if you want to create realistic lighting you will need to use the appropriate light colour. In fact, you should avoid using white lights since they don t exist in reality. You would be surprised at how realistic your scene becomes when you use the correct light colour. 24

25 The impact of different light sources. It is easy to see how the light colour plays a major role in the credibility of the scene: different light sources produce different colours. 25

26 Creating Realities with Radiosity Radiosity is the indirect light that is distributed between objects. Most real-world objects reflect light, which means the light is bounced back and forth between the objects in the environment. This reflected light is responsible for most of the illumination in the environment. The actual light source illuminates only a specific point in the environment, whereas radiosity lights up the majority of the space. Reflected light is commonly referred to as indirect lighting, and is the most common form of lighting in reality: Natural light is primarily indirect lighting. 26

27 What happens to the light colour? The light that bounces off an object actually changes its colour. In fact, it assumes the colour of the object that is reflecting it. This effect is referred to as colour bleeding, which means the colour reflected between surfaces. This becomes an important factor to consider when lighting our scenes. If we don t accurately compensate for colour bleeding, our scenes will end up looking very artificial. 27

28 The effects of colour bleeding. The light that reflects off the walls has assumed its cream colour, which tends to neutralize a great deal of the colour tint that was created by the light source. We now have a very natural lighting scenario for all four light sources. 28

29 More colour bleeding 29

30 How do we add radiosity lighting to our images, scenes? The very professional 3D programs have radiosity lighting features. The mathematics for creating radiosity is very complex. Although, radiosity is a complex lighting formula, it can be simulated with success. Of course, the lighting won t be nearly as accurate as radiosity but it will certainly be significantly better than simply using direct lighting. In order to simulate radiosity we need to do two things: Add additional lights round the scene and give them colour bleeding. 30

31 The difference between direct and simulated radiosity. 31

32 Always remember to create colour bleeding with your radiosity lights! When light is bounced off an object it assumes the colour of the object. If you don t reflect this colour in your radiosity lights, you ll end up with a very artificial looking image and scene. 32

33 It is obvious that simulated radiosity is much better than the direct lighting but how exactly do we create it? Place several point lights around the scene to simulate the places where the light would bounce. It s very important that you use a point light and not a distant light or spotlight since we want the light to travel in all direction, which is what happens in reality. The placement of the light is determined by the light reflectivity of the object in the room. 33

34 Wire frame model of the rabbit sitting in the armchair. Proper placement of simulated radiosity point lights. The vertical placement of the radiosity lights 34

35 Always turn off specularity when simulating radiosity! Specular highlights can be created only by the light source, not by indirect lighting. Therefore, if you don t turn off the specularity for your indirect lights you ll end up with far too many specular highlights on your surfaces, making them appear very unnatural. 35

36 Diffusion and Radiosity When you start adding lights to a scene to simulate radiosity you run into the problem of surface colour saturation, which is where the surface actually shows too much of its own colour. Most surfaces in reality show only a small fraction of their own colour since they ray on the light around them to bring out their colour. When you have a surface with 100 percent diffusion, and you add radiosity lights, you end up showing more than 100 percent of the surface colour. 36

37 Never use 100 percent diffusion levels when simulating radiosity! You should never use 100 percent diffusion levels under any circumstances, but definitely not when simulating radiosity. Light acts as a colour amplifier, so if you use 100 percent diffusion levels your surface will end up with colour saturation, which is completely unnatural. Newer use 100 percent diffusion levels any circumstances. 37

38 What s the solution to surface colour saturation? Lower the diffusion of the surface to a point where the saturation no longer occurs. This may require some experimentation at first but in time you will be able to predict the diffusion levels you need to use. In the case of our phone image, the table should have a diffusion of around 70 percent, which is typical for most surfaces. 38

39 Using light gels Lighting gels is very helpful for creating complicated lighting effects in our images. A lighting gel gets its name from the film industry where they are used to changing the light colour and creating shadow maps. Lighting gels, also commonly referred to as shadow maps, are used to enhance our lights with colour filters and custom shadows. 39

40 Using lighting gels to create shadow effects 40

41 Using lighting gels to project stained glass images 41

42 Let us sum up what we have dealt with on a specific example. Here you can see real toy furniture on the table. It was modelled by my students last year in class, the subject was called Virtual Reality and it s application. 42

43 Two ill examples 43

44 Let us try with other simulated light sources! 44

45 2700 K (100 watt lamp) spot 2, 2700 K (100 watt lamp) spot 3, 4700 K (daylight flood lamp) area 1, 4700 K (daylight flood lamp) area 2 45

46 10000 K (light from clear blue sky) ambient 2, K (light from clear blue sky) ambient blue, 2200 K (incandescent lamp) directional 2, 6000 K (daylight fluorescent lamp) directional 2 46

47 This model was rendered by different light sources by Maxwell render engine 47

48 Videos (10-12 minutes) Toy furniture (living room and dining room) University street Castle in Veszprém Ags+ml h264_lan Demoreel-2005 Kitchen-multi. Lightingdemo mx_teaster 48

49 References Berndt C., Gheorghian P., Harrington J., Harris A., McGinnis C., (2004) Leraning Maya 6, Rendering, Alias Systems Birn J., (2000) Lighting & Rendering, New Riders Publishing Bowman, D.A., Kruijff, E., Laviola Jr., J.J., Poupyrev, I. (2004), 3D User Interfaces. Addison-Wesley Fleming B., (1998) 3D Photorealism Toolkit, John Wiley & Sons, Inc. Maxwll Render: Sik Lányi C., (2006) Virtual Reality in Healthcare, Intelligent Paradigms for Assistive and Preventive Healthcare, Ichalkaranje, A., et al. (Eds.), Springer-Verlag, pp Stanney, K.M. (2002), Handbook of virtual environments, ed. by: Stanney, K.M. editor, Handbook of Virtual Environments: Design, Implementation and Applications. Mahwah, N.J.: Lawrence Erlbaum Associates, Inc

50 Summary Today we covered some basic examples of how lights are used, and the light types for developing realistic virtual reality scenes. Until next time, I hope I will have the opportunity to share some practical advices too, so until next time, good luck, and remember: No detail is too small! And do not believe everything what you see! The films and VR scenes are always manipulated! 50

51 It is not manipulated! You can believe me! Cecília Sik Lányi University of Pannonia, Veszprém 51