Photorealism

Gran Turismo 4 image by MShades @ flickr

Perception

Color

Colors in the physical world can be any wavelength, or combination of wavelengths, of light

Color	Wavelength
Violet	420 nm
Blue	470 nm
Green	530 nm
Yellow	580 nm
Orange	620 nm
Red	700 nm

The Eye

Rods & cones absorb light, send signal to brain

Color Perception

Any visible wavelength is perceived the same as some combination of 3 basic colors
(roughly blue, green, and red)

RGB Color

RGB = Red , Green , Blue
Each component (R, G, or B), ranges from a minimum (no intensity) to a maximum (full intensity), typically 0.0 to 1.0.

Color on the Computer

glColor3f(1.0, 0.5, 0.0)

Computer numbers have a finite resolution - how many distinct values can be represented

24 bit color = 8 bits red + 8 bits green + 8 bits blue
(a.k.a. 8 bits per component)
8 bits = 256 possible values

32 bit color usually means 8 bits red + 8 bits green + 8 bits blue + 8 bits alpha
16 bit color can be 5 bits red + 6 bits green + 5 bits blue

RGB Photography

Prokudin-Gorskii, ca. 1910

RGB Photography

CMY Color

CMY = Cyan , Magenta , Yellow
    C = 1.0 - R
    M = 1.0 - G
    Y = 1.0 - B

CMYK = Cyan , Magenta , Yellow , Black

HSV Color

HSV = Hue , Saturation , Value

Color Gamuts

Luminance

The "brightness" of a color.

Formula, used in NTSC television standard, based on human perception:

    0.30 * R + 0.59 * G + 0.11 * B

Real-world Luminance

Background	Luminance
Moonless overcast night sky	0.00003 cd/m^2
Moonlit clear night sky	0.03
Twighlight sky	3
Overcast day sky	300
Day sky with sunlit clouds	30,000

Rods & cones adapt to average level of illumination

Rods most sensitive at low levels (scotopic vision)

Cones more sensitive at higher levels (photopic vision)

HDRI: High Dynamic Range Imaging - uses 16 or 32 bits per component

Visual Acuity

Resolution of the eye - approximately 0.5 arc-minute, at the center of vision

fovea: 1 - 2 degree area at center of retina with maximum density of cones

1280x1024, 17" monitor viewed from 2 feet : 1 pixel = ~ 1.4 arc-minutes

Signal from rods & cones is smoothed - lasts for several milliseconds after light hits rod/cone

Light flashing at > ~60 Hz appears to be continuous

Below the CFF, flashing is perceptible

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