Pinhole camera

• CCD or CMOS


  common term for internal sensor in a camera
• A pinhole camera is a simple camera with a tiny aperture that projects an inverted image
• Spectrum


  The spectrum refers to the range of different wavelengths present in light, human eye can perceive 380 (violet) to 750 (red) nanometers
• Electromagnetic Spectrum (Raging martians invaded Venus using x-ray guns)

  A) Radio

  B) Martians

  C) Infrared

  D) Visible

  E) Ultraviolet

  F) X-ray

  G) Gamma

  
• CCD (Charge-Couple Device)

  A) Visible light

  B) IR blocking filter

  C) Color Filter controlling light to the sensor

  D) Colorblind sensor transforming light into electricity

  
• How is color image formed ?

  • 8x8 Color CCD in Bayer pattern
  • 8 bits for each Red, Green and Blue
  • demosaicing: value of a color is usually the average of the neighboring colors
• Some camera manufacturers provide software development kits (SDKs) that allow reading the raw sensor data directly from the camera
• Raw data is the unprocessed output from the individual red, green, and blue color-filtered pixels on the image sensor
• Raw vs JPEG

  A) JPEG file

  B) RAW file

  
• Raw data can provide higher color bit depth (more tonal levels) per color channel than typical 8-bit (256 levels) JPEG/TIFF images
• Pipeline of digital cameras

  A) Camera body

  B) Sensor (CCD, CMOS)

  C) Gain (ISO)

  D) analog to digital

  E) Raw

  F) Demosauc

  G) JPEG

  
• Coded exposure cameras independently vary the exposure times across different groups of pixels on the sensor to capture additional visual information beyond a single exposure
• Spectral imaging refers to capturing image data across multiple wavelengths or bands of the electromagnetic spectrum, beyond just the visible range captured by typical color cameras
• Besides traditional imaging, there's varying exposure and spectral imaging
• RGBE (Red, Green, Blue, Emerald more like Cyan) filter is an alternative color filter used by some Sony cameras
• Real cameras are modeled using extrinsic and intrinsic parameters
• Extrinsic parameters define the position and orientation of the camera in 3D world coordinates (rotation R and translation t matrices)
• Intrinsic parameters define the optical properties of the camera lens and sensor (focal lengths, principal point, skew)
• Rolling shutter problem

  images are distorted by motion, shutter speed supresses this effect
• CMOS vs CCD

  A) Rolling shutter

  B) Global shutter

  
• The pinhole camera model is often used, which creates a 2D perspective from 3D world points using the intrinsic and extrinsic parameters of the camera
• Rotation matrix is 3x3 because it represents the axes of orientation of camera relative to the world
• Camera model

  A) 2D image coordinates

  B) Intrinsic properties

  C) focal point in x

  D) focal point in y

  E) x of principal point

  F) y of principal point

  G) Extrinsic properties

  H) Rotation of camera in world

  I) Translation vector between Origin and camera

  J) 3D world coordinates

  
• Perspective projection transforms 3D points into 2D points on an image plane.
• Camera model in general form

  $x =$$K [R|t] X_{3D}$, where K is intrinsic matrix, R|t is extrinsic matrix, and X3D is world coordinate matrix
• Parallel projection

  Treats all light rays as parallel, objects of different sizes appear the same size
• Weak-perspective projection

  Simplified version assuming distant objects, keeping parallel lines parallel
• Vanishing point


  one or multiple points, where parallel lines in the 3D world seem to converge; distant objects, closer to the vanishing point seems smaller
• Types of projection

  A) Perspective

  B) Orthographic