1 / 8

Human vision

Human vision. The image is formed on retina (sítnice) The light is focused on retina by lens (čočka) Retina contains two types of receptors: rods (tyčinky) for grey-scale vision in darkness (about 100 mil.) cones (čípky) for color vision (about 6,5 mil.)

ahmed-carson
Download Presentation

Human vision

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Human vision • The image is formed on retina (sítnice) • The light is focused on retina by lens (čočka) • Retina contains two types of receptors: • rods (tyčinky) for grey-scale vision in darkness (about 100 mil.) • cones (čípky) for color vision (about 6,5 mil.) • There are 3 types of cones for color vision (red, green, blue),the blue cones are substantially less sensitive than the other two • Each eye acquires 2D discrete color image • The final 3D image is formed from two 2D images (stereo vision)

  2. Camera vision Basic features of CCD cameras http://www.roperscientific.com/ccd/library_encyclopedia.shtml

  3. Quantum Efficiency (QE) • Example of the QE curve for two versions of a given camera

  4. Noise types (druhy šumu) • NR - Readout noise of the CCD (vyčítací šum) • NR [e-/pixel] = Nr = uncertainty in quantifying the electronic signal • Nr [e-/pixel] = readout noise specified by the producer • Depends on: • pre-amplifier design • post-amplifier electronics • CCD temperature (the lower, the lower the noise) • readout speed (the faster, the higher the noise) • ND – Dark current (Dark charge noise) (šum náboje ve tmě) • ND [e-/pixel] = SD1/2 = statistical fluctuations of SD • SD [e-/pixel] = Nd * time = dark charge signal • Nd [e-/pixel/sec] = dark charge specified by the producer • Depends on: CCD temperature (the lower, the lower the noise)

  5. Noise types (druhy šumu) • NP – Photon shot noise (fotonový šum) • NP [e-/pixel] = SP1/2 = statistical fluctuations of SP • SP [e-/pixel] = I * QE * time = measured signal • I [photons/pixel/sec] = photon flux (light intensity) • QE [e-/photon] = quantum efficiency specified by the producer • Depends on: only I, QE, time • NT – Total noise (celkový šum) • NT [e-/pixel] = (NR2 + ND2 + NP2)1/2 • Signal-to-noise ratio (SNR or S/N) • S/N = measured signal / total noise = SP / NT

  6. SNR Example • Example of different signal-to-noise ratio for given image

  7. Dynamic range (dynamický rozsah) • Dynamic range (camera) = number of bits in A/D converter • specified by the producer • 8 bit = 256 : 1 • 12 bit = 4096 : 1 • 16 bit = 65536 : 1

  8. Dynamic range (dynamický rozsah) • Dynamic range (real) = full well capacity / readout noise • specifies the real dynamic range • full well capacity depends on pixel size • readout noise depends on readout speed • high resolution (6.8 mm pixel size) & high speed (5 MHz): • 45 000 e- / 20 e- = 2 250 : 1  11,14 bit • high resolution (6.8 mm pixel size) & low speed (500 kHz): • 45 000 e- / 7 e- = 6 429 : 1  12,65 bit • low resolution (24 mm pixel size) & high speed (1 MHz): • 350 000 e- / 19 e- = 18 421 : 1  14,17 bit • low resolution (24 mm pixel size) & low speed (50 kHz): • 350 000 e- / 5 e- = 70 000 : 1  16,10 bit

More Related