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+# Lecture 6
+
+## Continue on Light, eye/camera, and color
+
+### BRDF (Bidirectional Reflectance Distribution Function)
+
+$$
+\rho(\theta_i,\phi_i,\theta_o,\phi_o)
+$$
+
+#### Diffuse Reflection
+
+- Dull, matte surface like chalk or latex paint
+
+- Most often used in computer vision
+- Brightness _does_ depend on direction of illumination
+
+Diffuse reflection governed by Lambert's law: $I_d = k_d N\cdot L I_i$
+
+- $N$: surface normal
+- $L$: light direction
+- $I_i$: incident light intensity
+- $k_d$: albedo
+
+$$
+\rho(\theta_i,\phi_i,\theta_o,\phi_o)=k_d \cos\theta_i
+$$
+
+#### Photometric Stereo
+
+Suppose there are three light sources, $L_1, L_2, L_3$, and we have the following measurements:
+
+$$
+I_1 = k_d N\cdot L_1
+$$
+
+$$
+I_2 = k_d N\cdot L_2
+$$
+
+$$
+I_3 = k_d N\cdot L_3
+$$
+
+We can solve for $N$ by taking the dot product of $N$ and each light direction and then solving the system of equations.
+
+Will not do this in the lecture.
+
+#### Specular Reflection
+
+- Mirror-like surface
+
+$$
+I_e=\begin{cases}
+I_i & \text{if } V=R \\
+0 & \text{if } V\neq R
+\end{cases}
+$$
+
+- $V$: view direction
+- $R$: reflection direction
+- $\theta_i$: angle between the incident light and the surface normal
+
+Near-perfect mirror have a high light around $R$.
+
+common model:
+
+$$
+I_e=k_s (V\cdot R)^{n_s}I_i
+$$
+
+- $k_s$: specular reflection coefficient
+- $n_s$: shininess (imperfection of the surface)
+- $I_i$: incident light intensity
+
+#### Phong illumination model
+
+- Phong approximation of surface reflectance
+  - Assume reflectance is modeled by three compoents
+    - Diffuse reflection
+    - Specular reflection
+    - Ambient reflection
+
+$$
+I_e=k_a I_a + I_i \left[k_d (N\cdot L) + k_s (V\cdot R)^{n_s}\right]
+$$
+
+- $k_a$: ambient reflection coefficient
+- $I_a$: ambient light intensity
+- $k_d$: diffuse reflection coefficient
+- $k_s$: specular reflection coefficient
+- $n_s$: shininess
+- $I_i$: incident light intensity
+
+Many other models.
+
+#### Measuring BRDF
+
+Use Gonioreflectometer.
+
+- Device for measuring the reflectance of a surface as a function of the incident and reflected angles.
+- Can be used to measure the BRDF of a surface.
+
+BRDF dataset:
+
+- MERL dataset
+- CURET dataset
+
+### Camera/Eye
+
+#### DSLR Camera
+
+- Pinhole camera model
+- Lens
+- Aperture (the pinhole)
+- Sensor
+- ...
+
+#### Digital Camera block diagram
+
+![Digital Camera block diagram](https://static.notenextra.trance-0.com/images/CSE559A/DigitalCameraBlockDiagram.png)
+
+Scanning protocols:
+
+- Global shutter: all pixels are exposed at the same time
+- Interlaced: odd and even lines are exposed at different times
+- Rolling shutter: each line is exposed as it is read out
+