Course on Cartographic Techniques | Cartography Working Group | The Virtual Geography Department

 

Lesson 3: Color Mixing; Production & Printing of Color

This lesson covers color mixing and color specification by 5 different color modeling systems, plus introduces students to the difference between flat and process color printing. The lesson begins (Part I) with a review of the color dimensions of Hue, Value and Chroma. Part II covers color mixing, with a comparison of color specification of color between 5 systems: Munsell, CIE, RGB, Pantone, CMYK. For each system, students will learn the theoretical basis and its practical application to color mixing using the color dimensions. Part III compares and contrasts flat and process color printing methods for printing of cartographic products, and discusses which of the color specification systems is more suitable for which type of printing method. Exercise 3 requires students to create the same graded color series ( a single Hue, varying the Value and Chroma from light to dark) using color specification from each of the 5 color specification systems.
The San Diego Supercomputing Center (SDSC), 1991 module on Interactive Color has some useful sections on the CIE, Munsell and RGB Systems and on Color Separations for printing. Remember, their module will only work on a Macintosh. It is important to review the color dimensions at this point because they are an essential component to color specification within the color specification/color modelling systems to be discussed in this lesson. Here, they are very briefly reviewed with reference to additional diagrams on color mixing that combines variations on hue, value and chroma.

A. Hue

Hue is the term given to the various colors we perceive e.g., red, blue, green, red-purple, fushia, turquoise, etc.
Each hue has its own wavelength which will be demonstrated in the discussion of the CIE color modelling system. Each hue is given a name or identification code, depending on the color system used.
We can create millions of hues by combinations of primary Hues, together with alteration of Value and Chroma.

B. Value

Value refers to the lightness or darkness of a hue, or of an achromatic (gray only) or chromatic color. Value is higher when there is more lightness (no black added). Value is lower when black is added, making the hue appear darker. Value can be understood by looking at a gray scale that ranges from white or very light grey through to black. Note that the human eye can not easily distinguish more than 5-7 gray tones, and the differentiation is more difficult at the very light and very dard ends of the value scale. Value differences of 10 percent are not great enough for easy value or gray tone differentiation. Differences of 15 to 25% are more suited to easy gray tone differentiation. Value is also affected by background tone or shade.  Value is controlled with pigments by adding white to increase value, and lighten the hue, or by adding black to decrease value and darken the hue.

C. Chroma

Chroma, also known as the intensity, saturation, richness, or purity of a color, refers to the comparison of a hue to a neutral gray whereby the neutral gray is achromatic and a full hue (color) is fully saturated or pure and brilliant.
For any given hue, Chroma ranges from 0 percent (neutral gray) to 100% (maximum color saturation or Chroma). At the maximum level, the color appears pure and contains no gray. Chroma levels vary per hue, for example, the most intense yellow appears brighter than the most intense blue-green.
 

  •  II. Color Mixing and Color Specification Systems

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    Color specification systems enable us to specify color in a consistent fashion. If 2 people want a given map area to be red , each person will have a different mental image of what "red" should look like. But if there is an objective definition for that specific red, then that same red can always be recreated. Thus specification, or color model, systems are useful for designating consistent color in Cartography. Such systems were originally developed by color scientists in other disciplines for various uses including paint, dyes, architecture, dentistry, etc. The science of colorimetry is based on spectrophotometer measurements of reflected light from maps and other surfaces. In this lesson, the Munsell system is discussed first, followed by the most objective colorimetric system, CIE, then Pantone, RGB and Process Color or CMYK. There are many other systems; only these few will be discussed here.

    A. Munsell

    The Munsell system was developed by an artist named A. H. Munsell in 1905. His system is now used by government and industry for a variety of color specification purposes ranging from paints to colors of wiring. The Munsell system is useful in cartography because it is based on the color dimensions of hue, value and chroma. These color dimensions are formed into a color wheel or "solid". The color wheel has color plates (color slices), each with a different hue, and each plate contains a series of color chips of varied value and chroma for that given hue. Hue is represented as one of five main hues and 5 intermediate hues, totalling 10 Primary Hues: Red (R), Yellow-Red (YR), Yellow (Y), Yellow-Green (YG), Green (G), Green-Blue (GB), Blue (B), Blue-Purple (BP), Purple (P), and Purple-Red (PR). Note that the letters within parentheses are the color designations within the Munsell system, that is, to specify the color Red, the letter R is used. Within each hue there are 10 steps, e.g., for Red there is 1.0 R, 2.5 R, 5.0 R, 10.0 R, etc., thus there are 100 primary hues on a Munsell color wheel (10 hues * 10 steps = 100 hues) (See also Robinson, et. al., 1995, Color Figures 19.4 and 19.5, and figure 19.10, page 352, and Dent, 1996, Color Plate 1).

    Value is represented from top to bottom with the color chips becoming lighter or higher in value towards the top, and darker or lower in value towards the bottom. There are 10 value steps from 0 for white, to 10 for black (See also Robinson, et. al., 1995, Figure 19.11, page 353).

    Chroma increases outward from a neutral or achromatic core towards full saturation at the edge of each color plate. Chroma increases in steps of 2 from 0 for achromatic to 16 for full chroma, however, each hue reaches full saturation as different levels depending on the hue itself, and the value levels within each hue. For example, 5.0Yellow-red at value step 6 reaches full chroma at step 12, while 5.0 Blue at value step 6 reaches full chroma at step 6 (See also Dent, 1996, Color Plate 1).

    Color is designated in the Munsell system as follows: for 5.0 Blue 4/6, the first designation is for Hue and StepHue, then   Value/Chroma,  e.g.,  5.0 Blue  4/6  is for Blue at step 5.0, with value at step 4 and chroma at step 6. Value is always to the left of the slash and Chroma is to the right of the slash. All color chips within the Munsell color wheel are designated as such. These are illustrated in Robinson, et. al., 1995, Color Figure 19.5. and Dent, 1996, Color Plate 1.

    The Munsell system is less numerical and less objective than CIE but more user friendly in terms of selecting and specifying colors, therefore is more frequently used in practical cartography, especially as a standard from which to create color using the RGB and CMYK systems. Munsell colors do have their CIE equivalent, however, and can be specified within the CIE system which is explained next.

    B. CIE

    CIE stands for the Commission International de l'Eclairage which is french for the International Commission on Color. The system was obviously developed by color scientists in France.    (explanation with diagrams, and demo of colors within the system, and how to match CIE colors within the other systems listed below. CIE is an objective numerical system of color specification.  CIE includes 3 components:

    1. The Standard Illuminant - this refers to a light source, such as an incandescent lamp, the sun, overcast daylight or colored lighting.

    2. The Standard Observer - this is defined by the amounts of the additive primary colors of light needed to match solar light at each wavelength in the visible spectrum (red, green, blue). The standard observer can be plotted as spectral irradiance curves, designated x, y, z in the CIE Diagram.

    3. Chromaticity Coordinates - These are x and y coordinates corresponding to each hue in the CIE system. The coordinates are comprised of 3 components that correspond to the Color Dimensions (hue, value, chroma):

    a. Dominant Wavelength - The dominant wavelength corresponds to hue. The x,y location of a coordinate defines a specific hue in the CIE system.

    b. Purity - Purity is the physical CIE counterpart to Chroma, defined on a scale of 0 (achromatic, or the purity of the illumination source) to 100 (full purity of the spectral hue of the dominant wavelength).

    c. Luminosity - Luminosity is the lightness or darkness of a hue and corresponds to Value (Y Value). It is measured as the luminous reflectance of the color.

    These can be plotted on a chromaticity diagram as chromaticity coordinates, shown in Box 19.A, pg. 350, and fig. 19.9, pg. 350 (see also overhead)

    The CIE system has its limitations. The system applies to additive primary mixing of colors as light but not to the subtractive primary mixing of colors as pigment. When given two colors on the CIE diagram, their actual, numerical differences (dominant wavelength, purity and luminosity) will be different than their apparent visual differences (hue, value, chroma) as perceived by the human eye. It is difficult, therefore, to match color for mapping according to subjective human selection.

    Alternatives based on CIE:

    CIELAB - for subtractive primary color mixing, e.g., printing inks and computer printer/plotter output

    CIELUV - for emitted color on CRT monitors
     

    C. Pantone

    The Pantone Color Specification System involves the creation of individual colors by mixing a limited number of basic color printing inks in varied proportions according to specifications or color recipes. The basic Pantone colors are: Pantone Yellow, Pantone Warm Red, Pantone Rubine Red, Pantone Rhodamine Red,Pantone Purple, Pantone Reflex Blue, Pantone Process Blue and Pantone Green. Notice how each basic color is preceded by the word Pantone, to indicate that the color is part of the Pantone system. Pantone White and Pantone Black are used to vary the value of each Pantone hue, and the proportions of each basic color ink determine the chroma of each hue. Pantone colors come in coated (glossy) and uncoated (matte) for use on different paper types and for glossy vs matte results. Pantone also comes in the Process (Subtractive) Colors of Yellow, Magenta, Cyan and Black. Each process color is preceeded by the words "Pantone Process" e.g., Pantone Process Yellow. The basic colors are used for flat color printing, while the process colors are used for process color printing just as the CMYK system (see below for flat and process color printing, and CMYK color mixing).

    As noted above, Pantone colors are created by mixing the basic color inks in certain proportions. Pantone colors are cataloged in Pantone Formula Guides wherein every Pantone color is identified by a color chip, a color identification number (e.g., Pantone 360c), the "recipe" (proportions of the basic colors used to create the color) and the percentage that each component ink comprises within the total color. Pantone 360c (c for coated), for example, is comprised of  5 parts of Pantone Yellow (31.2 % of the total color ink used), 3 parts of Pantone Process Blue (18.8%) and 8 parts of Pantone White (50%). The user selects or specifies color by the color number and the printer uses the recipe to recreate the color to exact specification.
     

    D. RGB Color Model

    Color is not only created for printing on paper. We create color for electronic display on televisions, VCR's, projection screens, and computer monitors. The electronic creation and display of color makes use of the principle of color as light and involves color mixing of the additive primaries, where red, green, and blue light are mixed in varying intensities to create a multitude of colors. The intensity of light ranges from 0 (no light) to 256 (maximum light intensity). The light intensity controls the creation of hues of varied value and chroma. Red, green and blue can thus be combined in 256 possible intensities each for a maximum of 2563 or 16,777,216 possible color combinations. Where all three colors are displayed at 0, the result is black or the absence of light. When all three are combined at 256, the result is white, or maximum equal amounts of all three additive primaries as was demonstrated in the combination of additive colors of light in Lesson 1. Light gray can be created by adding equal, moderately high intensities of red, green and blue, while dark gray results from equal, moderately low intensities of all three colors. The subtractive primaries can be created by combining two of the three additive primaries at full intensity. Full Cyan is thus created by the combination of 256 Blue and 256 Green (and 0 Red). Full Magenta is formed by the combination of 256 Red and 256 Blue (and 0 Green), and Full Yellow is formed by the combination of 256 Red and 256 Green (and 0 Blue). And of course full Redis formed by 256 Red only, full Green by 256 Green only, and full Blue by 256 Blue only. Less intense versions of these colors are formed by combining lesser levels of the appropriate colors of light, e.g., a Medium Green might be formed by combining 256 Green and 125 Red. Other colors are formed by combining differing proportions of the additive primaries for example, Purple, at 256 Blue and 125 Red, and Orange at 256 Red and 125 Green. The concept is similar to the CMYK or process system of color mixing of the subtractive primaries as is explained in the next section.

    E. Color Chart Systems based on Process (or CMYK) Color Mixing

    The CMYK system of creating color involves mixing proportions of the process color inks, that is, certain percentages of cyan, magenta, yellow and black ink. These four process colors are often abbreviated as CMYK (where K stands for Black). The system is simple to understand and has great color mixing potential for cartographers in that a multitude of hues of varied value and chroma can be created using only 4 colors of ink. Experiment here with a java applet that allows you to mix varying proportions of cyan, magenta and yellow to create a range of different colors. To mix colors, select Color Printing,  use the arrows to alter the percentages of cyan, magenta and yellow, then drag the squares to overlap. The overlapping of the squares will result in a new color. While overlapped, try altering the percentages again and see how the color changes. Several existing colors can be selected from the lower pull down menu. Notice the percentages of cyan, magenta and yellow for each color. Note that this applet does not have black, thus many colors on a color chart cannot be reproduced here. The process, however, provides a good idea of how the subtractive primary colors are mixed to create other colors. (Java Applet created by Phillip Dukes of Bringham Young University, email: g-prd@physics1.byu.edu; and modified by Khoi Duong and Phuong-Mai Duong, computer science students at UNC-Charlotte)

    For printing in color from color maps and graphics, a full color image can  be separated into four photographic separations, one per process color, by using different color filters. Each color filter separates out or filters only one color image. A blue filter is used to separate the yellow image from a full color image, thus the yellow image will contain all portions of the full color image that contain any percentage of yellow. A red filter separates the cyan image, a green filter separates the magenta image (notice how the filters are the additive primary complimentary colors for each subtractive primary color), and a halftone screen separates the black image. Thus there are only four final images for printing. The proportion of ink that print each separation is controlled by the use of percentage dot screens in combination with the color filters. Such screens contain uniformly sized and spaced dots, and uniform open space between dots. These screens break a full color image into a series of dots that can be reproduced by a number of printing methods. The proportion of process color ink that is used to create colors is determined by the ratio of dots to open spaces, whereby the greater the percentage of dots to open space on the final combined color separation (e.g., a piece of film containing all areas that have some proportion of that ink color), the less ink that gets applied to the paper. Thus, if yellow is being printed using a screen that has 70% of the printing surface covered by dots, then the result will be 30% yellow, as only 30% of the open space is available for yellow to be printed. The 30% yellow image might be overprinted with 30% cyan to create a light green color. Of course a map will contain many areas with different percentage screens so that every map area will have its unique combination of CMYK according to the final printing colors. In other words, the yellow image, for example, will contain various percentage screens to represent the varied proportions of yellow ink that are required to create the all the colors on the final map. The screens must be placed at different angles as well in order to avoid what is termed a "moiree" effect wherein dots of the four process colors are visible and form patterns that are disturbing to the eye. Correct screen angling is required for smooth printing results. The following series of graphics illustrate the concepts of separate dot screens per color of printing ink, compositing of different color image screens, and screen angling (Note that more detail on these graphics can be found in the Interactive Color Module):

    Cyan Percentage Dot Screen
    Magenta Percentage Dot Screen
    Yellow Percentage Dot Screen
    Black Percentage Dot Screen
    Combined Cyan and Magenta Percentage Dot Screens
    Combined Cyan, Magenta and Yellow Percentage Dot Screens
    Composite of CMYK Percentage Dot Screens

    The four color images are then printed one after another onto the same map sheet. With each printing, the map colors begin to take shape as illustrated in the series of final composite "color separation images" listed below. The final illustration shows the composite of all 4 color separations to form a full process color printed picture. Notice that within each single color separation, there are lighter and darker areas of each ink (due to the different screens used to break up the image into dots for printing varied amounts of ink) which, when combined with the other 3 inks, also in varying proportions, creates a final color composite with many different hues of varying value and chroma. Notice also how different colors begin to be formed as selected separations are combined. The illustrations were taken from the Interactive Color Module where detailed explanations may be found and the user can interactively display selected color separations.

    Black Separation Image
    Cyan Separation Image
    Magenta Separation Image
    Yellow Separation Image
    Cyan and Magenta Combined
    Cyan, Magenta and Yellow Combined
    Full Color Composite Print

    Colors created by Process color, or CMYK color mixing are often compiled into Color Charts wherein each color contains a color chip and a description of the proportions of CMYK used to create the color. The color chart acts as a guide from which to select and specify colors for mapping. Color charts are often developed to provide a standardized set of colors which can be created by the process color method of printing. Each chart is different, however, in terms of the percentages of each process color ink used, and not every possible color can be represented on each chart. Thus only a selection of potential hues can be represented on any given chart, but with computer graphics software, experiments can be done to create hues that are not found on the chart. Individual mapping organizations may create their own color chart for internal use. In that way, any person can recreate any color found on the chart. If doing outside work, however, it will be useful to use a common color chart from which to specify and create color. An example of a section of a process color chart can be found in Robinson, et. al., 1995, Color Figure 20.2 where different percentages of magenta and yellow (in steps of 10%) are combined with 20% cyan (and 0% black) to form a variety of hues.

    The process color system is not as precise as CIE, in that the colors created will vary depending on a number of factors including ink quality, percentage screens used (e.g., smoother results occur from finer dot screens that contain more dots per inch), paper quality, printer used, computer monitor resolution, etc.

    III. Production & Printing of Color

    A. Mixing of Color for Printing

    When only a few copies of a map are required, a color printer can be used to make prints directly from the computer. This is very time consuming and costly, however, when many copies are required. When several hundred or thousand copies of a map are needed, the cartographer must turn to the printing press as a much more economical way to reproduce many good quality copies of a map. there are two methods for mixing color for the printing press: Flat Color and Process Color. Each is explained below.

    1. Flat Color

    The Flat Color process involves the mixing of solid color inks and running the paper through the press for as many colors of ink as are required. Pantone color inks are used in flat color printing where each color to appear on the map is created according to the colors' unique Pantone recipe. With flat color printing, a separate printing plate (separate color composite image) is prepared for each color of ink to appear on the map. This method enables the mixing of standardized ink hues for color specification, and is fine when only 2 or 3 inks (colors) are being used on the map, e.g., black, blue and red, but is not efficient with more than a few colors because the printing process becomes expensive (many printing plates, changes of ink cartridges and long press runs, thus labor, material and machine time) and hard on the paper when it runs through the press repeatedly for each application of ink.

    2. Process Color

    Process Color mixing involves the combination of varying percentages of the subtractive primary inks, that is cyan, magenta and yellow, plus black. Process Color mixing is designated at CMYK just like process color mixing. As was demonstrated above, a wide range of colors can be created by the combination of the subtractive primaries and black. With process color printing, 4 final combined images (negatives or positives) are created (depends on the plate making process) and from these, 4 printing plates, are made and sheets of paper are run through the press 4 times, one per ink. This method is much more economical when more than a few colors are being used on a map and many copies of the map are required (with just a few copies, a color printer can make prints directly from the computer without creating separate images). Refer also to the above section on process color mixing.

    There are several methods for creating the separation artwork for making process color printing plates. Two are described below:

    1. Create a color map and photograph it with lens filters that separate the image into 4 process color images (the images are in black and white with screened areas that determine the proportions of the appropriate process color ink to be printed onto the paper). Printing plates are made from these images.

    2. Create separate digital files for each process color ink using an image setter. The result is 4 negatives, one per process color ink, each with screened areas to determine the proportion of each ink to reach the page.  Printing plates are created from the negatives produced by each digital file.
     

    Graded Series:

    This concept is being introduced here for use in Exercise 3. More details on the application of graded series color to map symbolization will be covered in Lesson 4.

    Perceptual Grey Scale
    The human eye has limitations in its ability to differentiate value/chroma levels within gray tones or variations on one hue.
    The eye needs more percentage variation at the lower end of the scale in order to perceive difference and match colors with corresponding legend boxes.
    At the upper end, the eye can more easily differentiate close differences in percentages.

    e.g., 10, 25, 50, 75, 90 (or 100) are a good example of a 5 graded series where there is enough distinguishable difference between value/chroma levels of a given hue (or gray tones) for the eye to be able to easily differentiate the hues within the series.

    There are several types of graded series -- more in Lesson 4 [link].
      Assuming a single hue, 3 methods (applies to mixed hue plans too):

    1. Gradation by screening a solid ink e.g.,  10, 25, 50, 75% cyan

    2. Overprinting a solid ink with successive gradations of black ink, e.g., solid cyan with 10, 25, 50, 75% black overprinted

    3. Combination of the above, especially when more than 7 colors are to be included within the series.
    Note: black darkens the hues real fast (75% is too much -- it would appear nearly black at 50% cyan) and makes the hues dark and muddy looking rather than bright and attractive. Also, black dominates, especially when used in large sized areas on a map.
    For our exercise - use one hue, and #1 or 3 above. More on the other options next time.
     

    B. Process Color

    Create 4 final combined negatives or positives (depends on the plate making process) and from these, create 4 printing plates, one each for Y-M-C-K then run the paper thru the press 4 times, once per ink.
    The composites have varied percentage screens that let ink thru in screened amounts so that the result are varied mixtures of color.

    Show examples.
     
     

    IV. Graded Color Series
     

    Graded color series will be discussed in greater detail in Lesson 4: Color as a Map Symbol. It will be used in Exercise 3, however, for creating and matching a series of color in each of  3 color systems: Munsell, Pantone, and CMYK. The concept of a graded series is thus introduced here.

    The human eye has limitations in its ability to differentiate value/chroma levels within gray tones or variations on one hue.
    The eye needs a larger percentage variation at the upper end of the scale in order to perceive differences in hues and match colors on the map with corresponding legend boxes. At the lower end, the eye can more easily differentiate close differences in percentages, e.g., 10, 25, 50, 75, 100% Blue is a good example of a 5-step graded series where there is distinguishable difference between value/chroma levels of a single hue (or gray tones) for the eye to be able to easily differentiate the colors within the series.

    Assuming a single hue, 3 methods can be used to create a graded series (these methods apply to mixed hue plans too):

    1. Gradation by screening a solid ink e.g.,  10, 25, 50, 75, 100% Cyan

    2. Overprinting a solid ink with successive gradations of black ink, e.g., solid, or 100% Cyan with overprints of 0, 10, 25, 45, 60% black

    3. A combination of the above, especially when more than 7 colors are to be included within the series.
    Note: black darkens the hues very fast (60% is really too much, as the cyan would appear nearly black at 50% cyan) and makes hues look dark and muddy rather than bright and attractive. Also, black dominates, especially when used in large sized areas on a map. It is recommended, therefore, to start with low percentages of the hue, and only use black overprint for the top (darkest) one or two hues in the series.



    Exercise 3

    References

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    Created 5/26/98 by Laurie A. B. Garo. Last updated 6/4/99 by lg.
    The URL for this page is http://www.uncc.edu/lagaro/cwg/color/color_mixing.html