Homework #12 Cameras and Lights in Maya Due Thursday, November 29 th 20 points (10 points if late)

Transcription

1 Upcoming Deadlines Have clicker ready Homework #12 Cameras and Lights in Maya Due Thursday, November 29 th 20 points (10 points if late) Homework #13 Creating Stereoscopic 3D Images Due Thursday, December 6 th 20 points (10 points if late) For full schedule, visit course website:

2 Homework #12 For this assignment you are given a photograph of a real object and you will try to match the camera and the lighting. Each person will have a choice of four photos; for the assignment match any one of these photos (for extra credit, do more than one). To find the photographs assigned to you, go to the assignment description in the course website.

3 Photo

4 Homework #12 The Maya model for this "widget" object has been created for you and may be downloaded from course website (see the assignment description). Open the object in Maya, create a floor for it to sit on, position the camera, add some lights, and adjust everything until your rendered Maya image looks as closely as possible to the photograph. Try to match any colors, for the object and the lights, as well as the details of the shadows (e.g., penumbra angles, ambient light, drop-off).

5 Maya Render

6 Homework #12 To finish, move the position of your camera to view the scene from another direction (suggest that you turn the camera roughly 45 degrees to either side). Render #1 Render #2

7 Homework #12 Finally, upload the photo you chose to use and the two Maya rendered images into a posting entitled "Recreating Cameras and Lights in Maya." Note that this is a new assignment this year so there are no examples from previous semesters; contact me if you have any questions. Due by 8am on Thursday, November 29 th 20 points (10 points if late)

8 Homework #12 Non-Maya Alternative: One of the four photographs is a pair of soup cans. Recreate the camera and lighting in that photograph as accurately as possible then take your own photos of the scene. Finish by taking a second photograph with the camera at about 45 degrees to either side of its original position. Upload both of your photographs as well as the photograph that you're matching. Note that it will not be easy to duplicate the lighting conditions using common house lamps; only do this alternative if you find it absolutely impossible to work with Maya.

9 Survey Question From which of these assignments did you learn the most: A) Term papers B) Homeworks using Tracker C) Stop-motion animation homeworks D) Homeworks using Maya E) Reverse video reference

10 Review Question Which path does light ray take after entering the water? A) Path A D B) Path B C) Path C A B C D) Path D

11 Law of Refraction C) Path C Angle is smaller in the denser material. The light ray bends but does not cross the normal (line perpendicular to the surface)

12 Review Question What looks like a pool of water in this photo is actually a mirage image of the sky created due to the desert heat. Mirages are produced by: A) Refraction B) Reflection C) Scattering D) Miracles E) Myopia

13 Mirages A) Refraction Mirages are caused by the refraction of air because hot air has lower optical density than cold air. Cool Air Hot Air

14 Review Question Natural lighting underwater is primarily from overhead because sunlight cannot enter the water at more than about a 45 degree angle. A) True or B) False?

15 Total Internal Reflection A) True. For the same reason you can only see the sky from underwater when looking up at more than about a 45 degree angle. Mirror See sky

16 Optics & Lighting Part IV: Scattering

17 Elements of Optics Reflection & Surfaces Lights & Shadows Refraction Scattering Color & Vision

18 DW Consulting Example Disco lights for Intel commercial

19 Basic Scattering Some sunlight is scattered, making the fog visible.

20 Scattering Out & Scattering In To this viewer, the fog has scattered out some of the light so the sun isn t as bright To this viewer, the fog has scattered in some light so the fog is visible.

21 Scattering vs. Absorption Scattering is a deflection of the light. Absorption is an elimination of light. 100% 40% 50% 10% For example, if 40% of the light is scattered and 10% is absorbed then 50% directly reaches viewer.

22 Extinction Extinction defined as absorption plus scattering. 40% 100% 50% 40% scattered 10% absorbed 10% 100% 10% 50% 40% 10% scattered 40% absorbed Extinction is 50% in both cases.

23 Demo: Scattering vs. Absorption Beakers filled with water placed on overhead projector. Beaker has drop of white ink, the other has a drop of black ink. What is seen on the screen??

24 Demo: Scattering vs. Absorption Glass dishes filled with water placed on overhead projector. One dish has drop of milk, the other has a drop of black ink. Projected image has two dark spots. Black ink absorbs light. White ink scatters light.

25 Particle Sizes & Scattering Tiny Particles (Rayleigh Scattering) Large Particles (Reflection/ Refraction) Air Cloud Birds Small Particles (Mie Scattering)

26 Particle Sizes & Color Rayleigh Scattering Tiny Particles Scatter blue light the most, red the least; white light scattered with a hue shift to blue. Gas fumes Fine smoke Air molecules Particles smaller than wavelength of visible light.

27 Rayleigh Scattering by Color For tiny particles (under 400 nm) scattering is strongest for blue light and weakest for red light. Scattering Strength Blue light: 440 nm Green light: 550 nm Red light: 660 nm Particle Size nm 400 nm

28 Tyndall Scattering Tyndall scattering is very similar to Rayleigh scattering since both are the scattering of light (especially blue light) by very small particles. Blue iris Opalescent glass

29 Demo: Aerogel Opalescence Aerogel is ultralight, hard foam made from SuperGlue. Scattering makes aerogel look blue while the transmitted light is yellow. Flashlight shines white light on a piece of aerogel

30 Particle Sizes & Color Mie Scattering Small Particles Scattering of hues varies with particle size, usually averaging out to white. White paint Milk Clouds Particles comparable to wavelength of visible light.

31 Mie Scattering by Color Blue light: 440 nm Green light: 550 nm Red light: 660 nm For small particles Mie scattering strength varies greatly with the particle size. Since particles tend to be a mix of sizes, all hues are scattered equally resulting in white. Scattering Strength Particle Size 400 nm 800 nm 1200 nm

32 Particle Sizes & Color Large Particles Reflect light off the surface or, if transparent, refract and transmit light. Confetti Sand Rain Particles much larger than the wavelength of visible light.

33 Suspended Particles A dust storm is seen from the reflection off the suspended dust particles rather than true scattering. Mie scattering by water droplets in clouds. Reflection from suspended particles.

34 Volumetric Lighting Volumetric lighting is used to create the volume of scattered light, usually due to Mie scattering in dust or fog.

35 Scattering & Angle Direction of light scattering is not random. Backward Forward Less light More light

36 Mie Scattering & Angle Mie scattering is strongest in the forward and weakest backward directions. Fog

37 Mie Forward Scattering Sun Sun is behind the fog in this photo Fog Mie scattering from drier fog Drier Vent Camera

38 Mie Backward Scattering Sun is behind the camera in this photo Fog Drier Vent Mie scattering from drier fog Sun Camera

39 Sun Rays Mie scattering by fog mist Intensity of sun rays varies with the angle between sun and viewer. Notice that the light on the ground is bright even though the ray s intensity appears to taper off along the sun ray. To camera To camera

40 Rayleigh Scattering & Angle Rayleigh scattering is strongest in the forward and backward directions. It is weakest to the sides (90 degrees). Gas fumes

41 Brightness of the Sky The darkest part of the sky tends to be about 90 degrees from the direction of the sun. Rayleigh scattering by air molecules

42 Single vs. Multiple Scattering Light rays may scatter multiple times, if the scattering medium is dense. Light Fog Heavy Fog

43 Demo: Scattering in a Fish Tank Single versus multiple scattering is nicely shown by shining a flashlight into an aquarium filled with clean water then adding more and more milk.

44 Single Scattering in a Fish Tank Single scattering produces a narrow beam of light. Flashlight Mie scattering by very dilute water/milk mix.

45 Single Scattering in a Fish Tank Intensity differences due to scattering angle (i.e., near the light we have more forward scattering). Flashlight To camera To camera

46 Multiple Scattering in a Fish Tank Multiple scattering produces a diffuse beam of light. Flashlight Hue shift from white (near flashlight) to orange-red on the opposite side.

47 Scattering in a Fish Tank With single scattering only particles in the direct beam are scattering the light. To camera With multiple scattering particles outside the beam are illuminated by light scattered from out of the beam. To camera

48 Optical Thickness Total scattering depends on optical thickness. 100% 20% 80% 100% 40% 60% Demo: Beaker on projector; fill with milky water

49 Shadows & Multiple Scattering With multiple scattering the side opposite from the light can be in shadow. Shadows

50 Atmospheric Perspective Objects in the distance have a bluish, unsaturated color due to combination of Rayleigh, Tyndall, and Mie scattering.

51 Atmospheric Perspective Far away mountains can have a bluish ting due to blue light scattered in by Rayleigh scattering Weak scattering but big optical depth

52 Atmospheric Perspective Example

53 Fog and Smog Atmospheric perspective can remove all contrast for distant objects, turning them into silhouettes. Notice clock face

54 Perspective of Color Not only did Leonardo da Vinci make good use of what he called Perspective of Color but he also correctly predicted that this is why the sky is blue. The Virgin and Child with Saint Anne, 1510 The Virgin of the Rocks, 1482 La Gioconda,

55 Underwater Perspective Water is transparent but absorbs red light about x100 more than blue light. Objects in distance are bluish but saturated. Significant reflection by suspended particles. Particles are easily mixed in water due to buoyancy.

56 Sunrise & Sunset At sunrise and sunset the rays from the sun pass through a thick layer of atmosphere so Rayleigh scattering removes much of the blue light.

57 Quiz Question Which statement is correct? A) The photo on the moon has a dark sky because it is night time. B) The shadows of the rocks on the moon appear very dark because the photo is underexposed. C) The shadows of the rocks on the Earth are not very dark because they are illuminated by the sky. D) On the moon the Sun is always directly overhead. Moon Earth

58 Quiz Question Which statement is correct? A) The photo on the moon has a dark sky because it is night time. B) The shadows of the rocks on the moon appear very dark because the photo is underexposed. C) The shadows of the rocks on the Earth are not very dark because they are illuminated by the sky. D) On the moon the Sun is always directly overhead. Moon Earth

59 The Sky is a Light Source On Earth the sky is an important light source during the day. Mostly creates a bluish ambient light but with variations due to time of day and weather. Rouen Cathedral Series, Claude Monet

60 Next Lecture Seeing Color Homework #12 Recreating Cameras and Lights in Maya Due Tuesday, May 8 th (Next Tuesday) Please turn off and return the clickers!