3.1 Image

Resizing image

• if we throw away even rows and columns -> losing informations

Camera image as a function

• f(x,y) : position to light
• cameras cannot measure continuous space

Sub-sampling camera

• aliasing; dropping the rest of the rows and columns
  • CMOS sensor have this problem

Signal to Noise Ratio (SNR)

• low light -> high SNR
• we should collect as much light as we can
  • bigger sensors, larger fill factor
  • minimize off time, long exposures (slower shutter speed)

3.2 Image sensors

CMOS

• (+) random access to pixels
• (+) cheaper
• (-) lower fill factor

CCD

• (+) larger fill factor
• (-) harder to read out image
• (-) more expensive

Rolling shutter

• Camera sensors work like a scanner.
• Reading values from each sensor cannot happen simultaneously.
• Fast moving object will create an image different from our sight

3.3 Image sampling

Aliasing

Nyquist rate

• is a minimum sampling rate to avoid aliasing

  • = two samples per cycle

Fourier transform

• decomposes any signal into components
• we can figure out max frequency in components
• to avoid aliasing, samplint rate >= 2 * max frequency

Low pass filtering (optical)

• allows the low frequencies to pass

3.4 Image scaling

Image as array of pixels

• F[x,y] : pixels
• f(x,y) : a continuous function

3.5 Filtering

• Mean filtering
  • mean value from nearby 8 & 1 itself

Up-resizing

3.6 Aliasing

3.7 Format

• Compression ways
  • Lossless compression
  • Lossy compression
• Formats
  • JPEG
  • GIF
  • PNG