Computer Vision – Fundamentals of Human Vision Hanyang University Jong-Il Park

Division of Electrical and Computer Engineering, Hanyang University Introduction Understanding of Mechanism of Human Vision  To construct the measures of image fidelity & intelligibility  To design and evaluate image processing algorithms and imaging systems

Division of Electrical and Computer Engineering, Hanyang University Light ~ radiant energy which, by its action on the organs of visions, enables them to perform their function of sight  Spectral energy distribution of the light source L( ), = 350nm ~ 780nm  Light received from an object : reflectivity or transmissivity of the object Brightness (Perceived Luminance)

Division of Electrical and Computer Engineering, Hanyang University Human Eye visible range : 350 nm < wavelength < 780 nm photoreceptors of the retina  rods : about millions  cones : about 6.5 millions (Color Vision)  scotopic vision : rods (dark environment)  mesopic vision : rods + cones(middle range)  photopic vision : cones(bright environment) rods are more sensitive to light than the cones

Division of Electrical and Computer Engineering, Hanyang University Distribution of Photoreceptors

Division of Electrical and Computer Engineering, Hanyang University

Division of Electrical and Computer Engineering, Hanyang University The Human Visual System 홍채 각막 ( 안구의 ) 수양액 공막 ( 눈알의 ) 맥락막 Shape of lens, rather than the distance between lens and screen, is changed

Division of Electrical and Computer Engineering, Hanyang University The Human Visual System (cont.)

Division of Electrical and Computer Engineering, Hanyang University Luminance (or Intensity) : independent of luminance of the surrounding object  Luminosity Function (Relative Luminous Efficiency Function) Eye Physiology Light distribution Relative luminous efficiency function

Division of Electrical and Computer Engineering, Hanyang University Contrast  Brightness : dependent upon the surroundings Brightness

Division of Electrical and Computer Engineering, Hanyang University Brightness adaptation Dynamic range ~ 10 10

Division of Electrical and Computer Engineering, Hanyang University Intensity Discrimination Experiment

Division of Electrical and Computer Engineering, Hanyang University Weber’s Law

Division of Electrical and Computer Engineering, Hanyang University (100,101)(100,102)(100,105)(150,151)(150,153)(150,162)

Division of Electrical and Computer Engineering, Hanyang University cone rod

Division of Electrical and Computer Engineering, Hanyang University Brightness(cont.) Mach Bands

Division of Electrical and Computer Engineering, Hanyang University MTF of the Visual System Measurement of visual system in frequency domain MTF: Modulation Transfer function

Division of Electrical and Computer Engineering, Hanyang University Isopreference k: # of bits/pel  gray-level resolution N: # of pels  spatial resolution Preference depends on image!

Division of Electrical and Computer Engineering, Hanyang University Optical illusions

Division of Electrical and Computer Engineering, Hanyang University Moire pattern

Division of Electrical and Computer Engineering, Hanyang University Goal :  Image quality measurement  Performance evaluation of image processing techniques or systems Quantitative Criteria  Mean square criterion :  SNR(signal-to-noise ratio) :  PSNR(peak-to-peak SNR) : Image Fidelity Criteria

Division of Electrical and Computer Engineering, Hanyang University Image Fidelity Criteria (cont.) Subjective Criteria

Division of Electrical and Computer Engineering, Hanyang University Perception of Intermittent Light Perception depends on its frequency ( N cycles/sec)  small N : Flashes appear separated in time  increase N : unsteady flicker, unpleasant  increase N further : Continuous light perception Fusion frequency : Frequency at which an observer begins perceiving light flashes as continuous light Critical Fusion frequency (CFF) : about 50 ~ 60 Hz. Consider a light that flashes on for a brief duration N times/sec

Division of Electrical and Computer Engineering, Hanyang University Perception of Intermittent Light (cont.) Higher fusion frequency for larger size and larger intensity of the flickering object  very dim, small light : A few cycles/sec  very bright, large light : Over 100 cycles/sec Examples of intermittent light  fluorescent light : Over 100 times/sec  motion picture : 24 frames/sec with 1 frame shown twice  TV monitor : 30 frames/sec, 2fields/frame 60 fields/sec (NTSC system)

Division of Electrical and Computer Engineering, Hanyang University Empirical Observation Sharper images look better Same noise in uniform background region is more visible than noise in edge areas (spatial masking) Same noise in dark areas is more visible than noise in bright areas Same amount of artificial noise appears worse than natural looking noise

Division of Electrical and Computer Engineering, Hanyang University Colorimetry The perceptual attributes of color (HIS system)  Intensity : the amount of light, perceived luminance ex) distinction between dark grey and light grey  hue : the color as described by wave length ex) distinction between red and yellow  saturation : the amount of color that is present ex) distinction between red and pink the vividness of color Three primaries : Red, Green, Blue (RGB)

Division of Electrical and Computer Engineering, Hanyang University

Division of Electrical and Computer Engineering, Hanyang University Hue varies along the circumference Saturation varies along the radial distance Color representation

Division of Electrical and Computer Engineering, Hanyang University Eg. Color representation

Division of Electrical and Computer Engineering, Hanyang University Color absorption spectra

Division of Electrical and Computer Engineering, Hanyang University Color Vision Model Details to be covered later