1

Additive Color Process

• shine color spotlights on a white screen

• color TV or computer monitor

• the way the eye sees colors

Primary Colors for Additive Color

• blue

• green

• red

Additive Color

RED GREEN

BLUE

0.6 - 0.7µm

0.5 - 0.6µm

0.4 - 0.5µm

Yellow0.5-0.7

µm

Cyan0.4-0.6

µm

Magenta0.4-0.5 and0.6-0.7 µm

White0.4-0.7

µm

Example: Color spotlights shining on a white screen (Text, Plate 2)

R

G

B

C

M

Y

Primary ComplementADDITIVE COLORS:

G+B

R+B

R+G

Primary + Complement = WHITE

2

Subtractive Color Process

• light shining through filters

• 3 dye layers of processed color film act as “filters”

Primary Colors for Subtractive Color

• yellow

• magenta

• cyan

Subtractive Color

Green

BlueRed

Black

Example: Color filters in front of a white light (Text, Plate 2)

YELLOW CYAN

MAGENTA

Absorbs blue;Transmits green and red

Absorbs green;Transmits blue

and red

Absorbs red;Transmits blue

and green

R

G

B

C

M

Y

Primary ComplementSUBTRACTIVE COLORS:

Primary + Complement = BLACK

3

Question: What component(s) of white light will pass through both a yellow and a magenta filter?

Yellow filterMagenta filter

B G R

Red

(Abs. blue, Trans. green & red)(Abs. green, Trans. blue & red)

Question: What component(s) of white light will pass through both a green and a red filter?

Green filterRed filter

B G R(Abs. blue & red, Trans. green)(Abs. blue & green, Trans. red)

All three colors will be absorbed(the result will appear black)

Question: Cyan light is incident on a yellow object. What color(s) is(are) reflected?

B G

Yellow object(absorbs blue,

reflects green & red)

cyanGreen

Note: the yellow object would also reflect red,but there is no red in the source light.

4

0.4 0.5 0.6 0.7wavelength (µm)

0.4 0.5 0.6 0.7wavelength (µm)

Normal Color FilmSpectral Region:

Sensitivity:Resulting Color:

Near IRNo---

RedX

Red

GreenX

Green

BlueX

Blue

Color IR FilmSpectral Region:

Sensitivity:Resulting Color:

Near IRX

Red

RedX

Green**

GreenX

Blue

BlueNo*---

* Use blue blocking filter (Wratten #12 or #15).** Actually most reds photograph yellow because the infrared-sensitive layer has some sensitivity to red as well as near infrared (red + green = yellow).

Color vs. Color-IR Film Response

5

6

7

8

9

10

11

Landsat-7 ETM+ image: Wausau, Wisconsin – 27 July 1999

Bands #2 (0.52-0.6 µm), #3 (0.63-0.69 µm), and #4 (0.76-0.90 µm)

Band #8 (0.5-0.9 µm)

12

• Differentiation of general land cover types • Vegetation discrimination

tree species, wetland species, crops

• Delineation of turbid vs. non-turbid waters (pollutants)• Floating vs. submerged aquatic vegetation• Soil moisture variability• Stressed vs. non-stressed vegetation• Interpreters tend to respond to red color variations• High contrast film• Good haze penetration (due to blue blocking filter)

Color Infrared Film:Advantages

• Proper exposure more critical (high contrast film)• Storage and handling very critical (processing)• Little to no detail in shadows• Difficult to interpret without simultaneously acquired normal color film• Normally does not give pre-visual detection of plant stress• Does not sense heat (except for molten lava, etc.)• Just because two objects look different, their infrared reflectance need not be different. Changes could be in visible, IR, or both

Color Infrared Film:Disadvantages (or cautions)