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Commit d3871d64 authored by Quentin Bolsee's avatar Quentin Bolsee
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camera section

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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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topics/01_cameras/img/ccd.png

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topics/01_cameras/img/cmos_pixels.png

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topics/01_cameras/img/sensor.jpg

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......@@ -129,12 +129,17 @@ It is common to choose the $z$ axis to point **toward** the scene, and the $y$ a
## Technologies
![](img/sensor.jpg)
*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
![](img/ccd.png)
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
![](img/cmos_pixels.png)
*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:
![](img/bayer.png)
*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.
![](img/aperture.png)
*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
![](img/shutter.gif)
*source: https://www.youtube.com/watch?v=CmjeCchGRQo*
<!-- source:https://www.youtube.com/watch?v=CmjeCchGRQo -->
![](img/leaf_shutter.png)
*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
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