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# 4 - Color Mixing - PowerPoint PPT Presentation

4 - Color Mixing. S pectral P ower D istribution (SPD). Perfect absorber at all wavelengths = “Blackbody” (if T = 0 K). Blackbody with T = 3000 K. Units? W/(m 2 Hz steradian) W/(m 2 m ster) W/(m 2 m ster) W/(m 2 nm ster) etc. Color Perception & Color Mixing. Hue – the color

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### 4 - Color Mixing

Spectral Power Distribution (SPD)

Perfect absorber at all wavelengths = “Blackbody”

(if T = 0 K)

W/(m2 m ster)

W/(m2m ster)

W/(m2 nm ster)

etc.

• Hue– the color

• Saturation– how deep the color is. Higher saturation means less “whiteness”

• Brightness– the intensity of the light

What does the human eye see when mixing roughly “equal” amounts of Red, Yellow, Green, Cyan, Blue, and Magenta?

G + R = Y

B + R = M

B + G = C

B + G + R = W

(unequal amounts will produce other hues)

Any 3 colors that add up to make white light can be “primary” colors, but RGB seems to produce the widest range of other colors, so we usually refer to them as THE primary colors for additive mixing of light.

Example:

M + Y = (B + R) + (G + R) = (B + G + R) + R = W + R

originally contained red, orange, yellow, green, blue, indigo, and violet.

(colored lights)

Superposition

Partitive Mixing - close spatially

Visual Persistence - close temporally

(paints, filters, “what’s left?”)

Filter Types (or series of filters):

Kodak Wratten 44A Filter (or series of filters):

High transmission

We see this but not this

Spectral “Purity” (or series of filters):

• “Bandpass” -  (such as Full-Width-Half-Maximum)

• “Spectral Resolution” - R = /

• “Nonspectral” R ~ a few

• “Spectral” R ~ 10

• “Monochromatic” R > 100

Sun with“H” filter,  = 656.3 nm, R~10,000

Neutral Density Filters - These have “flat” transmission curves, or R << 1

Colored Pigments (Paints) (or series of filters):

Relies on combinations of additive and subtractive color mixing.

When layered, can depend in transmission, reflection, partitive color mixing, etc.