Visual Media Processing II 2020 No.1 Fundamentals of Optics and Color Instructors: Yasuhiro Mukaigawa, Takuya Funatomi, Kenichiro Tanaka
Mini report • 3-digit unique ID has been sent to you. • If you haven’t gotten it, consult TA immediately. • Small questions are asked in the lecture. • Input your unique ID and answers to Google Forms. • Today’s mini -report: http://bit.ly/vmp2-2020-1 • Also, link has been sent by email. Visual Media Processing II (4098), 2020 Fall 2
What is Computer Vision? • Computer vision is a method that extracts visual information of real world from images. • It gives computers and robots the ability for visually recognizing real world. Real World Computer A red ball on the white table. It is soft . The picture was taken indoors . Observation target Observation Visual Media Processing II (4098), 2020 Fall
3D reconstruction • Photometric stereo (#7) 照度差ステレオ • Use multiple images taken with different lighting directions Visual Media Processing II (4098), 2020 Fall
3D reconstruction • Photometric stereo http://openaccess.thecvf.com/content_iccv_2015/papers/Gotardo_Photogeometric_Scene_Flow_ICCV_2015_paper.pdf Visual Media Processing II (4098), 2020 Fall
Photometric analysis 反射 陰 影 散乱 • Reflection, shade, shadow, scattering • Analysis by physics-based model Diffuse reflection Specular reflection Attached shadow Cast shadow Undefined Visual Media Processing II (4098), 2020 Fall
Photometric consistency • Rendered object match to environment? • Color • Shadow • Shade Etc. Strange rendering Photorealistic • Real environment should be measured. • Global lighting • Reflection model of sofa • Floor position Etc. [photo credit: Prof. Kiyokawa] Visual Media Processing II (4098), 2020 Fall 7
Computational photography • Breaking the limit of camera by computation. Real-time vein visualization Computational bokeh control after capture Visual Media Processing II (4098), 2020 Fall
Non-Line-of-Sight Imaging • Imaging around corner. • Sophisticated light reflection analysis. Scene Recovered Visible wall Light paths Obstacle NLOS scene RGB camera Visual Media Processing II (4098), 2020 Fall 9
Mini-report – Access Google Forms and answer questions. http://bit.ly/vmp2-2020-1 Visual Media Processing II (4098), 2020 Fall 10
Photometric analysis pipeline (#1, Today) Image processing / (#1, #2) image analysis (#3 - #8) in-camera Optics Sensor processing (#1, Today) (#2) Visual Media Processing II (4098), 2020 Fall 11
Ray, Wave, Particle • Ray Explainable region of Light Ray (Geometric optics) Wave (Wave optics) Photon (Quantum optics) • Wave • Particle (Photon) Visual Media Processing II (4098), 2020 Fall 12
Interaction between Light and Matter Specular reflection (Rayleigh) Scattering (Highlight) (Mie) Scattering (Blue sky) (Clouds) Shadow Interreflection (Indirect lighting) Fresnel reflection (Water reflection) Refraction Diffuse reflection (Transmission) Visual Media Processing II (4098), 2020 Fall 13
Reflection 反射 • Specular reflection • Diffuse reflection （拡散反射） （鏡面反射） 𝜄 𝑗 = 𝜄 𝑝 Perfectly smooth Microscopically rough • • Inherits incident light properties Contains material’s properties • Dichroic reflection model (Refer #5) • Specular (highlight) is light source color. • Diffuse reflection is material color. appearance specular diffuse Mixture of reflections Visual Media Processing II (4098), 2020 Fall 14
Refraction 屈折 • Snell’s law スネルの法則 • Refractive index 𝜃 : how slow compared to vacuum. 屈折率 sin 𝜄 𝑏 = 𝑤 𝑏 𝜄 𝑏 = 𝜃 𝑏𝑐 sin 𝜄 𝑐 𝑤 𝑐 • Fresnel transmission / reflection フレネル透過・反射 𝜄 𝑐 • Fresnel reflection is angular-dependent. reflection 100% transmission Reflection 0% No reflection 0 ° 90 ° • Dispersion 分散 Incident angle • Refractive index is wavelength-dependent. Refraction index wavelength Visual Media Processing II (4098), 2020 Fall 15
Mini-report http://bit.ly/vmp2-2020-1 Visual Media Processing II (4098), 2020 Fall 16
Polarization 偏光 • Linear polarization • Direction of oscillation is stable. 振動 • AoLP, DoLP • Polarization state can be observed by rotating polarizer. 偏光板 Angle of Linear Passed intensity of light Polarization (AoLP) = 𝜚 A Degree of Linear 𝜚 Polarization (DoLP) B = A / (A+B) Rotation angle of polarizer Visual Media Processing II (4098), 2020 Fall 17
Polarization Filters • Cut polarized reflection from water surface. • Fresnel reflection again. Normal photo • Fresnel reflection is polarized polarized Parallel component 100% Perpendicular component 0% 0 ° 90 ° With polarization filter Incident angle kenko-tokina.co.jp Visual Media Processing II (4098), 2020 Fall 18
Liquid Crystal and LCD 液晶 液晶ディスプレイ • Electrically rotate polarization angle. • White pixel • Black pixel Voltage Polarizers Groove Light By inducing voltage, polarized light Liquid crystal is not rotated and blocked by 2 nd polarizer. tdk.com Visual Media Processing II (4098), 2020 Fall 19
Circular Polarization 円偏光 • Polarization (oscillation direction) is rotating. Linear polarization Circular polarization watson.jp • Clockwise, anticlockwise 時計回り・反時計回り • Specular reflection changes the direction. CW Anti-CW 3D vision Sony.jp Visual Media Processing II (4098), 2020 Fall 20
Mini-report http://bit.ly/vmp2-2020-1 Visual Media Processing II (4098), 2020 Fall 21
Controlling light rays 22
Lens • Converting point light to parallel light and vice versa. A convex lens （凸レンズ） A concave lens （凹レンズ） • Gathering lights olympus-imaging.jp Visual Media Processing II (4098), 2020 Fall 23
Mirrors • Plane Ideal reflection Main reflection Fresnel Metal coating Everyday mirror Surface mirror Flat at nano-level 表面鏡 • Mathematically curved Paraboloid Ellipsoid Hyperboloid 放物面 双曲面 楕円面 Visual Media Processing II (4098), 2020 Fall 24
Filters and Coatings • ND Filters • Color filters Transmission Orange filter Blue filter ND filter Wavelength • Anti-reflection coatings 反射防止膜 • All filters and lens can have reflection. Destructive interference 弱めあう Visual Media Processing II (4098), 2020 Fall 25
Beamsplitters • Split into transmission and reflection. X % (100-X) % • Dichroic mirrors Half mirror (50%T-50%R) 2 色性 • Wavelength dependent beamsplitters reflection transmission transmission reflection Wavelength Wavelength Wavelength Visual Media Processing II (4098), 2020 Fall 26
Mini-report http://bit.ly/vmp2-2020-1 Visual Media Processing II (4098), 2020 Fall 27
Generating light rays • How to control light rays? • Projector as a ray generator Projected image Visual Media Processing II (4098), 2020 Fall 28
3LCD Projector • Separate 3 color channel and combine Projection lens 投影レンズ Dichroic prism to merge color channels LCD panel for each color Lenses for gathering light Dichroic mirrors to separate color channels White lamp Nitto-optical.co.jp Visual Media Processing II (4098), 2020 Fall 29
Time Division • Color is time divided Projection lens To screen Color wheel Light source • Quiz: How to identify time divided projectors? Visual Media Processing II (4098), 2020 Fall 30
Mini-report http://bit.ly/vmp2-2020-1 Visual Media Processing II (4098), 2020 Fall 31
What is Color? Photometric conversion from light to color.
Appearance of object • A sphere is placed on a table. • The camera position is fixed. • But there are many appearances. Visual Media Processing II (4098), 2020 Fall
Color Representations in Computer • Color names • red, orange, yellow, green, blue, or purple. • Numerical parameters • How many parameters are necessary to define colors? Visual Media Processing II (4098), 2020 Fall
Linear color spaces: RGB 色空間 • Invented for practical reasons. • Single wavelength primaries • R: 645.16nm • G: 526.32nm • B: 444.44nm • Represented as unit cube Visual Media Processing II (4098), 2020 Fall
Non-Linear color spaces: Hue, Saturation, and Value • Representing human intuitions about the topology of colors. • hues forms a circle from red through orange to yellow and then green, cyan, blue, purple, and then red again. • HSV color space • Hue （色相） , Saturation （彩度） , Value （明度） Visual Media Processing II (4098), 2020 Fall
CMYK color space • Mixture of color inks. • Cyan, Magenta, Yellow, and Black Visual Media Processing II (4098), 2020 Fall 37
Limitation of common color spaces • Most color spaces are subset of perceptible color region. Vivid colors tend to outside color space. Visual Media Processing II (4098), 2020 Fall 38
Mini-report http://bit.ly/vmp2-2020-1 Visual Media Processing II (4098), 2020 Fall 39
Three Aspects of Color (1) Spectral quantity (2) Recording using color filters (3) Human color perception Visual Media Processing II (4098), 2020 Fall
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