introduction to color ii adding and subtracting colors painting and printing …€¦ · ·...

•  Introduction to Color II –  Adding and Subtracting Colors –  Painting and Printing

http://www.colorado.edu/physics/phys1230

Physics 1230: Light and Color

FOUR PRIMARY COLOR GROUPS

http://www-cvrl.ucsd.edu/

Psychological colors consist of red, yellow, blue, green and the achromatic pair, black and white. This is the group we were taught as children. All colors can be described verbally as a mixture of these four psychological primaries.

Subtractive colors apply to print and pigment. In this case color exists because the pigment absorbs some light rays and reflects others. If we use red paint the pigment absorbs or subtracts all light rays other than red, which it reflects back to the eye. The subtractive primaries are magenta, yellow, cyan and black (CMYK). If you combine M, Y & C you get black.

Additive colors are created with light. You project a red light through a red screen or on a monitor or television. The additive primaries are red, green and blue (RGB). If you combine red, green and blue light you get white.

Artist’s primaries consist of red, yellow, and blue. From these primary colors the secondary colors orange, green and purple can be mixed from combinations of two primaries. The result when all three primaries are mixed is black

COLOR MIXING

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/primarycolors/colorseparation/index.html

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/filters/absorption/index.html

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/primarycolors/additiveprimaries/index.html

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/primarycolors/subtractiveprimaries/index.html

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/primarycolors/colorfilters/index.html

CONCEPT QUESTION

The additive primary colors are -

A.  cyan, magenta, and yellow

B.  red, green, and blue

C.  ROY G BIV

CONCEPT QUESTION

Color on your laptop screen is from -

A.  Addition of illumination

B.  Partitive mixing

C.  Time mixing

D.  Binocular mixing

METHODS OF ADDING COLORS

1. ADDITION OF ILLUMINATION: Examples are stage lighting and 3-color TV projection. Projected colors overlap.

2. PARTITIVE MIXING: Examples are TV screens, laptop screens, or tightly woven fabric. These are closely spaced dots of colors.

3. TIME MIXING: Examples are rotating color wheels and sequential illumination in LCD microdisplays.

4. BINOCULAR MIXING: Here a different color is sent to each eye, and the colors mix in the brain.

CONCEPT QUESTION

The spectral complement of magenta is -

A.  Blue and red

B.  Green

C.  White

CONCEPT QUESTION

Color mixing using paint obeys -

A.  Additive color mixing

B.  Subtractive color mixing

CONCEPT QUESTION

Mixing magenta and yellow paint will give a color of -

A.  White

B.  Red

C.  Green

CONCEPT QUESTION

Viewing the world through rose (magenta) colored glasses will make grass look -

A.  Magenta

B.  Black

C.  White

Let’s assume that the glasses transmit only magenta light.

CONCEPT QUESTION

Viewing blue cards through a cyan filter will make the cards look -

A.  Cyan

B.  Black

C.  Blue

D.  Red

CONCEPT QUESTION

Combining a green and yellow filter will transmit -

A.  Green and yellow

B.  Green

C.  Yellow

D.  Magenta

ADDING USING TRANSMISSION CURVES •  What happens if we combine a cyan filter and a green filter? What color is transmitted?

•  The combination passes green because - cyan filter + green filter = white - red + (- blue - red) = green In other words, what goes through two filters must be under the transmission curves of both.

400 500 600 700nm

100%

400 500 600 700nm

100%

400 500 600 700nm

100%

CONCEPT QUESTION

The intensity distribution curve shown here gives

A.  Yellow

B.  Unsaturated yellow

C.  Saturated yellow

D.  Saturated red

100%

CONCEPT QUESTION

The intensity distribution curve shown here gives

A.  Cyan

B.  Unsaturated green

C.  Unsaturated cyan

400 500 600 700nm

CONCEPT QUESTION ON PRINTING


To print a green apple, you will need the following ink -

A.  Green

B. CMYK

C. Yellow and cyan

D. Magenta and Yellow

COLOR PRINTING - COLOR PIXELS

The foundation of digital computing is the binary system. Based upon the number two, this system uses one or zero to control the on/off state. The simplest pixel has two choices: black or white. (A pixel with two choices is known as a one-bit image, or two raised to the power of one). Adding more bit information increases the number of color choices. The number of potential color choices for a pixel is called color bit depth. For example a four-bit pixel would have 16 color choices while an eight-bit pixel would have 256 color choices.

Color choices increase exponentially as the number of bits per pixel increases.

21 = 1 bit = 2 colors 26 = 6 bit = 64 colors 22 = 2 bit = 4 colors 27 = 7 bit = 128 colors 23 = 3 bit = 8 colors 28 = 8 bit = 256 colors 24 = 4 bit = 16 colors 216 = 16 bit = 32,768 colors

25 = 5 bit = 32 colors 224 = 24 bit = 16,777,216 colors

http://www.tu-harburg.de/rzt/tuinfo/periph/drucker/Color_Reproduktion/

“millions of colors”

no. of colors achievable depends on how much display memory you have

PIXELS IN ART

Seurat’s “Sunday in the Park” (1889)

PIXELS IN ART

Oleg Frolov’s “Saint Petersburg. Summer rain”

PIXELS IN ART • Salvadore Dali’s “Persistence of Memory”

PIXELS IN ART

• Salvadore Dali’s “Hallucinogenic Toreadore”

PIXELS IN ART

• Salvadore Dali’s “St. John on the Cross”

PIXELS IN ART

• Salvadore Dali’s “Gala Contemplating the Mediterranean Sea which at Twenty Meters becomes a Portrait of Abraham Lincoln” (1976)

COLOR PRINTING - CMYK


All color photographs, and other images that are painted or printed, are produced using just four colored inks or dyes: magenta, cyan, yellow (the subtractive primaries) and black (see Figure 1). Mixing inks or dyes having these colors in varying proportions can produce the colors necessary to reproduce just about any image or color. The three subtractive primaries could (in theory) be used alone, however the limitations of most dyes and pigments makes it necessary to add black to achieve true color tones. When an image is being prepared for printing in a book or magazine, it is first separated into the component subtractive primaries, either photographically or with a computer as illustrated above in Figure 1. Each separated component is made into a film that is used to prepare a printing plate for that color. The final image is created by sequentially printing each color plate, one on top of another, using the appropriate ink to form a composite that recreates the appearance of the original. Paint is also produced in a somewhat similar manner. Base pigments containing the subtractive primaries are mixed together to form the various colors used in final paint preparations.

Factors Affecting Color Printing Quality

Paper Paper affects the color reproduced by the CMYK printing process. Coated stocks will produce a wider range of colors than uncoated stocks because the rough surface scatters more, reducing the amount of light that comes back to the viewer.

Viewing Conditions Different light sources affect the colors that you see. For instance, a colored object viewed under fluorescent light will look radically different when viewed under incandescent light. Fluorescent light adds green to colors while incandescent light adds red. For this reason the printing industry developed a standard viewing condition known as the D50 (5000 Kelvin) light source in addition to a neutral gray background surround. This light source replicates daylight with equal parts of red, green, and blue.


Digital Values For Color The most common digital color system is a 24-bit color system. A 24-bit continuous tone system offers a choice of 16.7 million colors. A 24-bit RGB color allocates 8 bits to each color: red, green, and blue. CMYK color uses 32-bit color, with 8-bits allocated to each color. All color to be printed must be translated from RGB color to CMYK color.

COLOR PRINTING USING INKJETS

•  These printers use 4 inks - cyan, magenta, yellow and black, and are often called CMYK printers.

•  Some printers use inks that work so that light is reflected from white papers, passing through the ink which absorbs some of the light. (So to get good bright colors, the paper needs to be a good reflector of white light). Other printers use inks that are thick, and that reflect the colors instead of absorbing them.

•  Watercolors work like the ink in a color printer, but are usually thinner inks, so the light does pass through the colored layer and the paper has to be chosen carefully.

COLOR PRINTING - RESOLUTION Resolution is a way of describing images that are composed of pixels. An image appears to be continuous based upon its number of pixels and its resolution. In order for an image to be continuous, one must not be able to see the individual pixels that were used to create it. If resolution of an image is less than required by the output device, individual pixels will appear as jagged edges. A printed magazine image will look continuous from reading distance, but when viewed with a magnifying glass will show the individual dots within the halftone. Therefore, distance affects the continuous appearance of an image. Resolution of the output device is tied to the number of elements per inch it can address to produce a dot. As the elements per inch increase, more information is available to produce a better quality dot. The pixels in the example are shown as squares to represent the address grid. Pixels actually produced are usually round or oblong.


COLOR PRINTING - HALFTONES For the last 100 years, color printing has been based upon halftone screening. Halftone screening uses halftone cells (which are comprised of different sized dots) arranged in a grid pattern to create the illusion of light and dark areas. This conventional halftoning technique is referred to as amplitude modulation because the size or amplitude of a dot is changed or modulated to create different tonal values. The single dot within the halftone cell grows larger as the tone value becomes darker and smaller as the tone value becomes lighter. The center from one halftone cell to the next is always the same. The spacing of dot placement is controlled by the line screen which is referred to as lines per inch (lpi). The higher the line screen, the more continuous an image will appear. For example, halftone dots will be visible with a 60 line screen and invisible to the naked eye at a 150 line screen.


COLOR PRINTING - HALFTONES

Laser printers use a matrix of imaging elements to create the halftone dot. To determine the matrix, divide the dots per inch (dpi) of the laser printer by the intended line screen. For example, a 300-dpi printer combined with a 100 line screen would use a matrix of 3 x 3 image elements per halftone dot. The number of image elements per inch that a printer or imagesetter can produce is known as the device resolution. As the number of imaging elements per inch increases so does the quality of the halftone dot. The elements per inch combined with the line screen controls the number of gray levels that can be achieved with an output device. For example, a 1200 dpi laser printer using a 150 line screen would image 150 dots per inch and every inch would contain 64 imaging elements. Therefore each dot is created by a halftone cell that contains 8 x 8 imaging elements. An 8 x 8 cell contains a total of 64 on/off imaging elements. This 8 x 8 cell can potentially produce 64 levels of gray. So there is a tradeoff between grayscale and image resolution.


Development of Halftone printing

•  The same idea is used for color printing. Three examples of color halftoning with CMYK separations. From left to right: The cyan separation, the magenta separation, the yellow separation, the black separation, the combined halftone pattern and finally how the human eye would observe the combined halftone pattern from a sufficient distance. (from Wikipedia) The first printed photo using a halftone, December

2, 1873. Original idea by William Fox Talbot (1850s)

Lessons from Art – pointillism as a way of achieving additive mixing with paints?

Detail showing the contrasting dots of paint used in pointillism.

Seurat’s La Parade du Cirque (1889)

introduction to color ii adding and subtracting colors painting and printing …€¦ · ·...

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