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@@ -1,4 +1,4 @@
-title: MAS 865.24 - computer vision and scanning
+title: MAS 865.24 - computer vision
description: A starter template for a Jeykll site using the Just the Docs theme!
theme: just-the-docs
color_scheme: light
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diff --git a/topics/01_cameras/index.md b/topics/01_cameras/index.md
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+++ b/topics/01_cameras/index.md
@@ -129,12 +129,17 @@ It is common to choose the $z$ axis to point **toward** the scene, and the $y$ a
## Technologies
+
+*source: https://www.automate.org/vision/blogs/ccd-vs-cmos-image-sensors-which-are-better*
+
We'll focus on the two main families of digital sensors: CCD and CMOS.
In both families, the actual light sensing is based on the electron-hole pair generation in MOS devices.
### CCD
+
+
In CCD sensors, the generated charges in the photodiodes are accumulated under a potential well, controlled by a voltage on the gate.
Charges can be moved to a neighboring pixel by performing a specific sequence on the gates. By shifting the charges all the way to the edge of the sensor, individual pixel values can be readout sequentially.
@@ -143,11 +148,40 @@ Advantage of CCD sensors include the simplicity of their design, and the large s
### CMOS
-## Bayer filter
+
+*source: Coath, Rebecca, et al. "Advanced pixel architectures for scientific image sensors." (2009).*
+
+## color
+
+The most common way of capturing color images with a digital sensor is a Bayer filter, interleaving color filters in front of pixels in this pattern:
+*source: https://en.wikipedia.org/wiki/Bayer_filter*
+
+For every red or blue pixel, there are two green ones. This is to mimic the human eye's increased sensitivity to green light.
+
+Without getting into the hellscape of color spaces, here is a standard formula to convert between RGB (red, green, blue) and YUV (luminance, chrominance) values:
+
+$$
+\begin{bmatrix}
+Y\\
+U\\
+V
+\end{bmatrix}
+=
+\begin{bmatrix}
+0.299 & 0.587 & 0.114\\
+-0.14713 & -0.28886 & 0.436\\
+0.615 & -0.51499 & -0.10001
+\end{bmatrix}
+\begin{bmatrix}
+R\\
+G\\
+B
+\end{bmatrix}
+$$
-<!-- source:https://en.wikipedia.org/wiki/Bayer_filter -->
+The luminance $Y$ can be thought of as a grayscale value. The coefficients in the matrix show that green values have twice the impact of red ones, and that blue values are the weakest.
# Lens
@@ -159,23 +193,34 @@ Advantage of CCD sensors include the simplicity of their design, and the large s
# Aperture
+An aperture gives control over the amount of light entering the lens. It's effectively equivalent to having a smaller lens diameter.
+
+*source: https://www.adorama.com/alc/camera-basics-aperture/*
+
+Aperture values are often expressed as f-numbers, defined as a ratio between the aperture diameter and the focal length of the lens:
-<!-- source:https://www.adorama.com/alc/camera-basics-aperture/ -->
+$$f_{\rm number} = \frac{d_{\rm aperture}}{f}$$
+
+This quantity is directly related to the light density reaching the sensor.
# Shutter
## Mechanical shutter
+*source: https://www.youtube.com/watch?v=CmjeCchGRQo*
-<!-- source:https://www.youtube.com/watch?v=CmjeCchGRQo -->
+
+*source: Hasselblad*
## Electronic shutter
# Photography basics
-## The 3 parameters
+## The three parameters
+
+Photography mainly comes down to setting three parameters on the camera:
- Aperture
- Shutter speed