sci 200 physical science lecture 9 color mixing
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SCI 200 Physical Science Lecture 9 Color Mixing. Rob Daniell July 28, 2011. Color Mixing. Gilbert & Haeberli: Physics in the Arts Chapter 7 Additive color mixing Chapter 8 Subtractive color mixing Supplementary materials: - PowerPoint PPT PresentationTRANSCRIPT
SCI 200 Physical Science Lecture 9
Color Mixing
Rob DaniellJuly 28, 2011
SCI200 - Lecture 10 2revised 2011.07.27
Color MixingGilbert & Haeberli: Physics in the Arts
Chapter 7 Additive color mixingChapter 8 Subtractive color mixing
Supplementary materials:Malacara, Daniel: Color Vision and
Colorimetry: Theory and Applications,SPIE Press, Bellingham, 2001
Wikipedia articles on Hue, sRGB, & ITU Recommendation 709 (Rec. 709)
SCI200 - Lecture 10 3revised 2011.07.27
Color MixingTrichromacy allows fairly strong hue
discriminationNevertheless:
The same hue can be produced by different spectral distributions
Response of cones to any particular spectral distribution of light is complex
Is there a (relatively) simple way to describe or specify a particular hue?
SCI200 - Lecture 10 4revised 2011.07.27
Spectral Response of Cones
Two laser pointers (left) at 532 nm and 633 nm give the same hue as a single laser pointer (right) at 570 nm Note that the authors seem to ignore the 2 pulses in the
Type II cone produced by the 633 nm light Gilbert & Haeberli, Physics in the Arts, pp. 86-87.
SCI200 - Lecture 10 5revised 2011.07.27
Idealized Color Wavelength Ranges
Gilbert & Haeberli, Physics in the Arts, p. 83.
400-500 nm 500-600 nm 600-700 nm
SCI200 - Lecture 10 6revised 2011.07.27
Color Mixing
Additive mixingTwo light sources
Combined by adding the intensity at each wavelength
Subtractive mixingFilters, paints, dyes
Combined effect is produced by subtracting colors
Also depends on the light source
SCI200 - Lecture 10 7revised 2011.07.27
Additive Color Mixing (a), (b), & (c): three non-
monochromatic light sources
(d), (e), & (f): three two-color mixtures, each producing a third color
(g): spectral yellow (h): unsaturated yellow
produced by combining spectral green and spectral red
(i): the three non-spectral light sources mixed to produce white
SCI200 - Lecture 10 8revised 2011.07.27
Additive Color Mixing (a): spectral blue + spectral
yellow = white Complementary colors
(b): broad band white Mixture of many colors
metamers: Two different intensity distributions that appear the same to your eye
SCI200 - Lecture 10 9revised 2011.07.27
Additive Color Mixing
•Additive color rules:• R + G + B = W• R + G = Y• G + B = C• R + B = M
• Complementary colors:• R + C = W• G + M = W• B + Y = W
• Can 3 colors be combined to produce any other color?
C = Cyan, M = Magenta, Y = Yellow
W = White
SCI200 - Lecture 10 10revised 2011.07.27
Additive Color Mixing
• Red, Green, & Blue can be combined to produce most colors, but some saturated colors cannot be reproduced.• Red, Green, & Blue can be
combined to produce more colors than any other choice of primary colors
C = Cyan, M = Magenta, Y = Yellow
W = White
SCI200 - Lecture 10 11revised 2011.07.27
Additive Color Mixing
CIE Color Matching experiments in 1922 Illuminated region subtended a visual angle of 2°
Only the viewer’s fovea is illuminated Matching field produced by 700 nm, 546.1 nm, 435.8 nm
Three spectral lines in mercury vapor
SCI200 - Lecture 10 12revised 2011.07.27
Additive Color Mixing
Hue, Saturation, and Luminance of the reference field were to be matched as closely as possible.
For some wavelengths (in fact, nearly all wavelengths) of the monochromatic source, a perfect match was impossible. Except by adding one of the red, green, or blue matching colors to the
reference field.
SCI200 - Lecture 10 13revised 2011.07.27
Additive Color Mixing• Suppose you attempt to match
spectral cyan (490 nm) using• spectral red (650 nm)• spectral green (530 nm)• spectral blue (460 nm)
• Spectral cyan produces• I: 1 pulse• II: 7 pulses• III: 2.5 pulses
• spectral blue + spectral green produce• I: 2 + 0 = 2 1• II: 2.5 + 16.5 = 19 9.5• III: 1 + 9 = 10 5
SCI200 - Lecture 10 14revised 2011.07.27
Additive Color Mixing• Spectral cyan:
• I: 1 pulse• II: 7 pulses• III: 2.5 pulses
• 50% blue + 36% green:• I: 1 + 0 = 1• II: 1 + 6 = 7• III: 0.5 + 3 = 3.5
• Spectral cyan + 33% red:• I: 1 + 0 = 1• II: 7 + 0 = 7• III: 2.5 + 1 = 3.5
• 50% blue + 36% green matches spectral cyan + 33% red
SCI200 - Lecture 10 15revised 2011.07.27
Additive Color Mixing• 50% blue + 36% green
matches spectral cyan + 33% red• But spectral cyan + spectral
red yields white:• So spectral cyan + 33% red is
the same as 67% cyan + 33% white
• That is, unsaturated cyan
SCI200 - Lecture 10 16revised 2011.07.27
Additive Color Mixing
• Above: Spectral cyan on left; unsaturated cyan on the right• 50% blue + 36% green matches spectral cyan + 33% red• But spectral cyan + spectral red yields white:
• So spectral cyan + 33% red is the same as 67% cyan + 33% white• That is, unsaturated cyan
SCI200 - Lecture 10 17revised 2011.07.27
Additive Color Mixing
• Combine 460 nm (blue), 530 nm (green), and 650 nm (red)• To match the wavelength on the horizontal axis• Negative fractions mean you must ‘unsaturate’ the color you are trying to
match• Standard observer: Based on data from 1931
SCI200 - Lecture 10 18revised 2011.07.27
Additive Color Mixing
• Previous figure redrawn so that complementary spectral colors lie opposite each other.• Saturated colors lie along the
outside• Mixtures of two colors are
proportional to the distance between them• along the line joining them
• A line from one spectral color through the white point ends at the complementary color• White point depends on the
precise standard used• The hue of the color at F is found
by extending a line from white through F to the edge
SCI200 - Lecture 10 19revised 2011.07.27
Additive Color Mixing
• International Commission for Illumination (CIE)• Did not want to use ‘negative
colors’ to match saturated colors• Defined ‘imaginary colors’ [X], [Y],
and [Z]• Not physical colors, but related
• Defined ‘color matching functions’ x, y, and z• Relative amounts of [X], [Y], and
[Z] needed to match a given spectral color (wavelength)
• Results in “tristimulus” values x, y, and z
• z = 1 - x - y • x and y together are called the
‘chromaticity’ of a color
SCI200 - Lecture 10 20revised 2011.07.27
Additive Color Mixing
• CIE Chromaticity Diagram:• Horseshoe shaped curve
represents saturated monochromatic colors• 380 nm - 700 nm
• ‘purples’ (mixtures of blue and red) lie along bottom edge• z = 1 - x - y• Interior of horseshoe
represents unsaturated colors
SCI200 - Lecture 10 21revised 2011.07.27
Additive Color Mixing
• CIE Chromaticity Diagram:• Specify a color by three
values• Chromaticity (x and y)• Lightness (or
Brightness)• No representation is
perfect• None can reproduce
the precise color sensitivity of the human eye
• Individual differences
SCI200 - Lecture 10 22revised 2011.07.27
Additive Color Mixing
• RGB example:• 3 standard wavelengths:
• 700 nm (red)• 546.1 nm (green)• 435.8 nm (blue)
• These three colors can only reproduce colors in the interior of the triangle
SCI200 - Lecture 10 23revised 2011.07.27
Additive Color Mixing
•CIE chromaticity diagram:• Three “primary” colors
can only produce the colors inside the triangle - the “gamut” of the color set.• This triangle
corresponds to the three colors used in a typical color monitor.
SCI200 - Lecture 10 24revised 2011.07.27
Additive Color Mixing
•Monochromatic complementary pairs• 700 nm -- 494 nm• 600 nm -- 490 nm• 571 nm -- 380 nm• No complementary pairs
between 494 nm & 571 nm
SCI200 - Lecture 10 25revised 2011.07.27
Additive Color Mixing
• Color Triangle (Fig. 7.4) from textbook• Doesn’t cover gamut of the
human eye• Does not conform to the
sRGB standard used for color televisions and computer monitors
• Does come close to maximizing the gamut of representable colors
SCI200 - Lecture 10 26revised 2011.07.27
Additive Color Mixing
• Color Triangle inside a chromaticity diagram (Fig. 7.15)• It appears that the text uses
• Red = 700 nm• Green = 530 nm• Blue = 440 nm
• Does not conform to the “sRGB” standard for color television and computer monitors
SCI200 - Lecture 10 27revised 2011.07.27
Additive Color Mixing
• sRGB standard• Based on 1931 CIE
chromaticity• Red: x = 0.64, y = 0.33• Green: x = 0.30, y = 0.60• Blue: x = 0.15, y = 0.06• White point:
• x = 0.3127, y = 0.3290
From the diagram, the dominant wavelengths are
Red: 611 nm Green: 549 nm Blue: 464 nm
From Wikipedia
http://en.wikipedia.org/wiki/Rec._709
SCI200 - Lecture 10 28revised 2011.07.27
Additive Color Mixing
• AdobeRGB standard• Based on 1931 CIE
chromaticity• Red: x = 0.64, y = 0.33• Green: x = 0.21, y = 0.71• Blue: x = 0.15, y = 0.06• White point:
• x = 0.3127, y = 0.3290
From the diagram, the dominant wavelengths are
Red: 611 nm Green: 535 nm Blue: 464 nm
Green point is main difference with sRGB
From Wikipedia
http://en.wikipedia.org/wiki/Rec._709
SCI200 - Lecture 10 29revised 2011.07.27
Additive Color Mixing
• Complementary Colors to the “line of purples” appear to range from c491 nm to c579 nm
SCI200 - Lecture 10 30revised 2011.07.27
Additive Color Mixing• correspondence
between wavelength and hue (angle):– complicated
SCI200 - Lecture 10 31revised 2011.07.27
Additive Color Mixing• correspondence
between RGB and hue (angle):
SCI200 - Lecture 10 32revised 2011.07.27
Additive Color Mixing
• LEDs approximate monochromatic red, green and blue:• Red = 645 nm• Green = 510 nm• Blue = 465 nm
SCI200 - Lecture 10 33revised 2011.07.27
Additive Color Mixing
• LEDs approximate monochromatic red, green and blue:• Red = 645 nm• Green = 510 nm• Blue = 465 nm
SCI200 - Lecture 10 34revised 2011.07.27
Additive Color Mixing Methods
Methods and TechniquesSimple addition
Two or more light sourcesStage lights
Partitive mixingSeparate sources close to each other
Television screens & CRT displaysLCD displays
Rapid successionUses persistence of vision
SCI200 - Lecture 10 35revised 2011.07.27
Subtractive Color Mixing
•Subtractive color combination:• Filters that absorb or block
light of certain colors• Ink or pigments that reflect
only certain colors and absorb the others
• Primary Subtractive Colors:• Cyan, Magenta, Yellow• Supplemented by Black in
“four color printing”C = Cyan, M = Magenta, Y = Yellow
SCI200 - Lecture 10 36revised 2011.07.27
Subtractive Color Mixing: Idealized Filters
Idealized Red Filter Idealized Green Filter Idealized Blue Filter
SCI200 - Lecture 10 37revised 2011.07.27
Subtractive Color Mixing: Idealized Filters
Idealized Red Filter + Idealized Green Filter = “black” (no transmission)
SCI200 - Lecture 10 38revised 2011.07.27
Subtractive Color Mixing: Idealized Filters
Idealized Cyan Filter (blocks Red)
Idealized Magenta Filter (blocks Green)
Idealized Yellow Filter (blocks Blue)
SCI200 - Lecture 10 39revised 2011.07.27
Subtractive Color Mixing: Idealized Filters
Idealized Cyan Filter + Idealized Magenta Filter = Blue filter
SCI200 - Lecture 10 40revised 2011.07.27
Subtractive Color Mixing: Block Diagrams
Subtractive Primaries:• C = B + G = W - R
• M = B + R = W - G
• Y = G + R = W - B
-G
-R
-B
SCI200 - Lecture 10 41revised 2011.07.27
Subtractive Color Mixing: Block Diagrams
Basic Subtractive Rules:• C + M = B
• C + Y = G
• M + Y = R
• C + M + Y = Bk (Black)
-R -G
-R -B
-G -B
-R -G -B
SCI200 - Lecture 10 42revised 2011.07.27
Subtractive Color Mixing
Dyes & Pigments:• Chemicals that absorb and/or reflect selective parts
of the visible spectrum• Ideal dyes & pigments follow the same rules as
ideal filters (i.e., subtractive color mixtures)• Real filters, dyes, and pigments often behave in
complicated and (almost) unpredictable ways.
SCI200 - Lecture 10 43revised 2011.07.27
Subtractive Color Mixing
Real filters, dyes & pigments:• Usually smooth “corners”• Sometimes complicated
structure• Rarely achieve trans-
missions and reflectances of 100%
SCI200 - Lecture 10 44revised 2011.07.27
Subtractive Color Mixing
Real filters, dyes & pigments:• Can produce unexpected results
The transmission of two or more filters in series is the product of the transmissions of each individual filter.
For example: one filter with 70% transmission combined with another filter with 50% transmission produces a combined transmission of 35%
1 filter
2 identical filters
10 identical filters
SCI200 - Lecture 10 45revised 2011.07.27
Subtractive Color Mixing
Real filters, dyes & pigments:• Can produce unexpected results
Combining filters or dyes with different transmittance functions can result in startling color shifts.
blue dye
yellow dye
one-to-one mixture
SCI200 - Lecture 10 46revised 2011.07.27
Subtractive Color Mixing
With subtractive colors the perceived color depends on the light source
cool white flourescent bulb
reflectance of a magenta object
resulting intensity distribution, the product of (a) and (b).
SCI200 - Lecture 10 47revised 2011.07.27
Subtractive Color Mixing
With subtractive colors the perceived color depends on the light source (example 2)
a gray object
a brown object
In sunlight, the two objects at right have very different colors. Under an incandescent bulb, which emits much less blue light, the objects have very similar colors.
SCI200 - Lecture 10 48revised 2011.07.27
Subtractive Color Mixing
Different light sources have different intensity distributions:
Incandescent light bulb
Deluxe Warm White Fluorescent bulb
High Pressure Sodium Lamp
SCI200 - Lecture 10 49revised 2011.07.27
Subtractive Color Mixing
Gamut of subtractive primaries:
Gamut of color TV or computer monitor:
Gamut of color slides:
SCI200 - Lecture 10 50revised 2011.07.27
Subtractive Color Mixing
Printing inks: color is due to a combination of reflection and transmission:
SCI200 - Lecture 10 51revised 2011.07.27
Homework Discussion
• Translation between Textbook color triangle and 8 bit RGB
• Hue, especially “purples”
SCI200 - Lecture 10 52revised 2011.07.27
Homework DiscussionTranslation between Textbook color
triangle and 8 bit RGB8 bit RGB is the color representation
system used on most computer monitors and other LCD graphic displays
1 byte = 8 bits: 0101100112 = 17910
Smallest number = 010 Largest number = 28 – 1 = 255
Each pixel is represented by 3 bytes1 each for red (R), green (G), and blue (B)
SCI200 - Lecture 10 53revised 2011.07.27
Homework Discussion• Translation between color
triangle and 8 bit RGB• r, g are “given”• b = 1 – r – g • Example: The point
indicated • r = 0.55,• g = 0.2,• b = 1 - 0.55 - 0.2 = 0.25
• Problem: Find the equivalent RGB representation
SCI200 - Lecture 10 54revised 2011.07.27
Homework Discussion• Translation between color
triangle and 8 bit RGB• Point:
• r = 0.55,• g = 0.2,• b = 1 - 0.55 - 0.2 = 0.25
• 1st Step:• Identify brightest component• r = 0.55 R = 255
• 2nd Step: Calculate the other two components:• G = (g/r) × 255• = (0.2/0.55) × 255 = 93 • B = (b/r) × 255• = (0.25/0.55) x 255 = 116
8 bit representation:R = 255G = 93B = 116
SCI200 - Lecture 10 55revised 2011.07.27
Homework Discussion• Translation between color
triangle and 8 bit RGB• Practice Problem #1:• Locate this point on your
color triangle• r = 0.15,• g = 0.25,• b = 1 – r – g = ___________
• 1st Step:• Identify brightest component
• 2nd Step: • Calculate the other two
components:
8 bit representation:R = ____G = ____B = ____
SCI200 - Lecture 10 56revised 2011.07.27
Homework Discussion• Translation between color
triangle and 8 bit RGB• Practice Problem #2:• Determinre r, g, b from the
indicated point:• r = _______,• g = _______,• b = 1 – r – g = ___________
• 1st Step:• Identify brightest component
• 2nd Step: • Calculate the other two
components:
8 bit representation:R = ____G = ____B = ____
SCI200 - Lecture 10 57revised 2011.07.27
Homework Discussion• Hue• Color: r = 0.35, g = 0.55• b = 0.1
• Dominant wavelength = 575 nm
• RGB:• R = 162• G = 255• B = 46• G > R > B
SCI200 - Lecture 10 58revised 2011.07.27
Homework Discussion• Hue• Color: r = 0.35, g =
0.55, b = 0.1• RGB:
• R = 162• G = 255• B = 46
• Lab:• L = luminance• a = red vs. green• b = blue vs. yellow
SCI200 - Lecture 10 59revised 2011.07.27
Homework Discussion• Hue• Color: r = 0.40,
g = 0.15, b = 0.45
• Dominant wavelength = c545 nm
SCI200 - Lecture 10 60revised 2011.07.27
Homework Assignment
• Read Chapters 7 & 8• Homework Packet 10
– Due August 4• Lab on Thursday, July 28 (today)
– Color Addition
SCI200 - Lecture 10 61revised 2011.07.27
Upcoming Labs• Lab 7: Color Addition
– July 28• Lab 8: Color Subtraction
– August 4• Reminder: Last Exam
– August 11