CSCE 441 Lecture 14
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Light and Color
Parts of the Eye
- Cornea
- Iris
- Lens
- Retina
- Rods (brightness only; most sensitive)
- Cones (147K / mm2 centered around fovea; but less in peripheral)
Image is focused on Fovea of retina
Current display systems maintain one focus plane
- Even for stereo (3D) displays
- Even if the image tries to simulate different focus planes
Intensity and Luminance
Intensity/Luminance How much light energy is carried by photos
Brightness is the interpretation of intensity
- Interpretation is logarithmic to actual intensity
- doubling luminance is a linear increase in perceived brightness
Display levels have discrete intensity levels.
Maximum intensity level of display device is 1.0
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \sum_{i=0}^n r^i \, I_i = 1.0}
Human eye can discern between Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle r = 1.01} difference in brightness levels.
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle n = -\log{(1.01 \, I_0)}}
Gamma Correction
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle I_{out} = k \, I_{in} \, \gamma}
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \gamma} and Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle k} are device-specific terms
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \gamma \in \left[ 2.0, 2.5 \right]} (usually 2.2)
Color space intensity is non-linear, so we have to convert to linear space and then convert back
Gamma meant to model CRTs only
LCDs have very different response curves that do not match the gamma curve
Dynamic Range
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \frac{1}{I_0}} is called dynamic range
ratio of maximum to minimum intensity (remember 1.0 is max)
varies by device
Contrast
Maxumum vs. minimum that can be displayed (in adjacent pixels) at the same time.
Limited Display Levels
Printing: either ink is there or not there (we can adjust the amount of ink, but not intensity)