BabelColor
®
Color Measurement
and Analysis
MUNSELL COLOR SYSTEM
A perceptually uniform color space
Developed in the early 20 th century by the American artist Albert H. Munsell (1858-1918), this is the first widely accepted color order system. It is traditionally presented as a collection of color patches known as the Munsell Book of Color. First devised as a color description teaching aid, the Munsell Color System was expanded and quantitatively formalized in the 1940s. The analysis led to small adjustments in the samples color in order to improve the spacing uniformity between them. The results were published in 1943 (Ref. 1). The CIE coordinates of this “renotated” system, as it is referred to, are the starting points from which the colors of the Munsell patches are derived. The Munsell Color System is an international reference, defined in ASTM D1535 and other standards, that is used in many fields of work, from archaeology, when describing the colors of artifacts, to medical studies, when comparing the color of skin affections, to hobby activities such as accurately depicting the colors of scaled vintage airplanes. In this system, colors are identified with three parameters: Munsell Hue, Munsell Value and Munsell Chroma, or Munsell HVC for short; they are presented in the form “Hue Value/Chroma”. The Munsell Hues are separated in 10 hue ranges (please refer to the illustration above). Each hue range is identified by a major hue. The major hues are Red, Yellow, Green, Blue and Purple, as well as the five hues located between them and named by combining the names of the hues on each side. For example, the hue located between Yellow and Red is called Yellow-Red, instead or Orange; this naming convention minimizes the number of color names one has to deal with. Each hue range is further divided in 10 sub-zones defined by 11 radii labeled from zero to 10. The hue with a “10” prefix at the end of a zone corresponds to the hue with a “0” prefix of the next zone. For example, the 10Y hue is the same as 0GY; in practice the 10Y notation is the preferred one. The centers of each hue ranges are labeled 5R, 5YR, 5Y, 5GY, 5G, 5BG, 5B, 5PB, 5P, and 5RP. The color circle is, in effect, separated in 100 hue segments where each hue separation is perceptually uniform. A zero to 100 number can be used to describe the Munsell Hue but it is seldom seen; the zero is at 10RP (or 0R) and the numbers increase when going counter- clockwise, up to 100, also at 10RP. The Munsell Book of Color typically has samples with hues located at every 2.5 hue steps. For example: 10RP (i.e. 0R), 2.5R, 5R, 7.5R and 10R for the red hue range. Neutral colors are presented in the form “N 5/” with “N” written for the neutral hue, and no number for chroma since there is zero chroma. Fractional, i.e. higher precision, values are possible for each parameter, and “5.2R 4.8/17.5” is a valid Munsell notation. The Munsell Chroma, like the C* of the L*C*h representation, can be considered an approximate counterpart of perceived color saturation, while the Munsell Value is associated to the lightness (L*) of the color. It is important to understand that the color system was not designed so that unitary steps of hue, value and chroma corresponded to identical color differences. However, the perceived chroma and value increase uniformly for similar steps of their respective scales. For instance, the perceived difference between Chroma 4 and Chroma 6 samples (i.e. /4 and /6) should be the same as the one perceived between Chroma 6 and Chroma 8 samples. Please note that while the Munsell space uniformity is high, it is not perfect, and will not necessarily hold in all viewing conditions, in particular with different background shades; this is discussed further below. According to the ASTM D1535 standard, the estimated precision with which a color can be characterized by visual interpolation is 0.5 hue step, 0.1 value step, and 0.4 chroma step. Maximum Munsell Chroma This illustration presents the patches of the 5R hue page of the BabelColor Munsell Color System Catalog (not sold anymore), which is in the center of the Red hue range. We can see that the sample with the highest Munsell Chroma is “5R 5/18”. When presented in printed form, the maximum chroma for a given Munsell Value depends on three factors. The first factor is inherent to the Munsell system. Munsell Chroma coordinates have no preset upper bound and large chroma values eventually represent colors which are outside the range of human-visible colors. The second factor is that chroma is limited by the color gamut of the printing system, which is a combination of the tint (i.e. hue) and purity (i.e. saturation) of the inks as they appear once printed on the selected paper. While colors outside of a printer profile’s gamut can be printed, the produced colors are generally highly inaccurate; these colors should be identified and not printed. The third factor is a product design decision; in the BabelColor printed catalog, the chroma was limited at 18 (i.e. /18) for all pages. This was done to maximize the patch size while keeping the same patch size and patch layout for all pages. A few patches were thus removed, in the RP hues for instance, in order to more completely fill the pages of other hues. Munsell Color System uniformity Munsell layouts sometimes appear non uniform in the low-chroma/high-value region. This may be partly due to the background on which the patches are compared, but it is also inherent to the system. Even if improved by the “renotation” efforts of the 1940s (see Ref. 1), the Munsell system is not flawless. In fact, a committee, formed in 1947, worked for 30 years on a replacement color system called the Optical Society of America’s Uniform Color Scale (OSA-UCS) (Ref. 2). While they could achieve a system with better uniformity than the Munsell system, they concluded that: “…no regular rhombohedral lattice sampling of color space, with a fixed background, can exist; we will produce the best approximation to such a lattice for a neutral 6/ background that we can design…” In other words, the UCS system is more uniform, but only for one fixed background equivalent to Munsell N 6/. The OSA-UCS structure offers unique multidirectional navigation paths in color space; unfortunately, it was not widely adopted, maybe because of its non-intuitive color notation format. It is then not surprising to see that work was done during the same period to improve the Munsell system, also by imposing a background. This work resulted in the development of Munsell “re-renotation” tables (Ref. 3), published in 1967, where it is assumed that “…two colors forming the difference are viewed on a gray background whose Munsell value approximates the average of the values of the two colors.” However, we have not seen much use of these tables, and the “renotated” Munsell Color System published in 1943 remains a valid and trusted color reference. As for OSA-UCS, it remains useful whenever there is a need for a uniform color system, in color research for instance, or when designing multi-color targets. For those interested in the OSA-UCS system, you can import and export coordinates using this system and generate color lists restricted or not to particular OSA-UCS planes in PatchTool. Munsell Color System support in CT&A and PatchTool In CT&A, bidirectional conversions FROM and TO the Munsell notation can be performed in many ways • Munsell tools: A dedicated tool for bidirectional high precision conversion between Munsell and L*a*b*/RGB. • RGB vs RGB tool RGB to Munsell: Convert RGB data to high precision Munsell notation. • RGB vs RGB tool Color Deck: A digital catalogue of over 4000 Munsell patches, including those of the Munsell Book of Color. Used to convert samples presented in fixed uniformly distributed steps to XYZ/L*a*b*/RGB coordinates. • Convert TO Munsell Color Deck: Find the nearest Munsell (digital catalogue) sample for a given RGB input or for a sample from another Color Deck. PatchTool can export any color data list opened in the program to Munsell coordinates with high precision. Please consult the CT&A and PatchTool documentation on this Web site for more information. • Ref. 1: Final Report of the O.S.A. Subcommittee on the Spacing of the Munsell Colors, Sidney M. Newhall, Dorothy Nickerson, and Deane B. Judd, JOSA, Vol. 33, No. 7, July 1943, p385-418. • Ref. 2: o Uniform color scales, David L. MacAdam, JOSA, Vol. 64, No. 12, December 1974, p1691-1702 o OSA Uniform Color Scale Samples: A Unique Set, Dorothy Nickerson, COLOR research and applications, Vol. 6, No. 1, Spring 1981, p7-33 o On the Geometry of the OSA Uniform Color Scales Committee Space, Fred W. Billmeyer Jr., COLOR research and applications, Vol. 6, No. 1, Spring 1981, p34-37 • Ref. 3: One Set of Munsell Re-renotations, NATIONAL BUREAU OF STANDARDS REPORT #192693, Deane B. Judd and Dorothy Nickerson, December 26, 1967
BabelColor
®
MUNSELL COLOR SYSTEM
A perceptually uniform color space
Developed in the early 20 th century by the American artist Albert H. Munsell (1858-1918), this is the first widely accepted color order system. It is traditionally presented as a collection of color patches known as the Munsell Book of Color. First devised as a color description teaching aid, the Munsell Color System was expanded and quantitatively formalized in the 1940s. The analysis led to small adjustments in the samples color in order to improve the spacing uniformity between them. The results were published in 1943 (Ref. 1). The CIE coordinates of this “renotated” system, as it is referred to, are the starting points from which the colors of the Munsell patches are derived. The Munsell Color System is an international reference, defined in ASTM D1535 and other standards, that is used in many fields of work, from archaeology, when describing the colors of artifacts, to medical studies, when comparing the color of skin affections, to hobby activities such as accurately depicting the colors of scaled vintage airplanes. In this system, colors are identified with three parameters: Munsell Hue, Munsell Value and Munsell Chroma, or Munsell HVC for short; they are presented in the form “Hue Value/Chroma”. The Munsell Hues are separated in 10 hue ranges (please refer to the illustration above). Each hue range is identified by a major hue. The major hues are Red, Yellow, Green, Blue and Purple, as well as the five hues located between them and named by combining the names of the hues on each side. For example, the hue located between Yellow and Red is called Yellow-Red, instead or Orange; this naming convention minimizes the number of color names one has to deal with. Each hue range is further divided in 10 sub-zones defined by 11 radii labeled from zero to 10. The hue with a “10” prefix at the end of a zone corresponds to the hue with a “0” prefix of the next zone. For example, the 10Y hue is the same as 0GY; in practice the 10Y notation is the preferred one. The centers of each hue ranges are labeled 5R, 5YR, 5Y, 5GY, 5G, 5BG, 5B, 5PB, 5P, and 5RP. The color circle is, in effect, separated in 100 hue segments where each hue separation is perceptually uniform. A zero to 100 number can be used to describe the Munsell Hue but it is seldom seen; the zero is at 10RP (or 0R) and the numbers increase when going counter- clockwise, up to 100, also at 10RP. The Munsell Book of Color typically has samples with hues located at every 2.5 hue steps. For example: 10RP (i.e. 0R), 2.5R, 5R, 7.5R and 10R for the red hue range. Neutral colors are presented in the form “N 5/” with “N” written for the neutral hue, and no number for chroma since there is zero chroma. Fractional, i.e. higher precision, values are possible for each parameter, and “5.2R 4.8/17.5” is a valid Munsell notation. The Munsell Chroma, like the C* of the L*C*h representation, can be considered an approximate counterpart of perceived color saturation, while the Munsell Value is associated to the lightness (L*) of the color. It is important to understand that the color system was not designed so that unitary steps of hue, value and chroma corresponded to identical color differences. However, the perceived chroma and value increase uniformly for similar steps of their respective scales. For instance, the perceived difference between Chroma 4 and Chroma 6 samples (i.e. /4 and /6) should be the same as the one perceived between Chroma 6 and Chroma 8 samples. Please note that while the Munsell space uniformity is high, it is not perfect, and will not necessarily hold in all viewing conditions, in particular with different background shades; this is discussed further below. According to the ASTM D1535 standard, the estimated precision with which a color can be characterized by visual interpolation is 0.5 hue step, 0.1 value step, and 0.4 chroma step. Maximum Munsell Chroma This illustration presents the patches of the 5R hue page of the BabelColor Munsell Color System Catalog (not sold anymore), which is in the center of the Red hue range. We can see that the sample with the highest Munsell Chroma is “5R 5/18”. When presented in printed form, the maximum chroma for a given Munsell Value depends on three factors. The first factor is inherent to the Munsell system. Munsell Chroma coordinates have no preset upper bound and large chroma values eventually represent colors which are outside the range of human-visible colors. The second factor is that chroma is limited by the color gamut of the printing system, which is a combination of the tint (i.e. hue) and purity (i.e. saturation) of the inks as they appear once printed on the selected paper. While colors outside of a printer profile’s gamut can be printed, the produced colors are generally highly inaccurate; these colors should be identified and not printed. The third factor is a product design decision; in the BabelColor printed catalog, the chroma was limited at 18 (i.e. /18) for all pages. This was done to maximize the patch size while keeping the same patch size and patch layout for all pages. A few patches were thus removed, in the RP hues for instance, in order to more completely fill the pages of other hues. Munsell Color System uniformity Munsell layouts sometimes appear non uniform in the low-chroma/high-value region. This may be partly due to the background on which the patches are compared, but it is also inherent to the system. Even if improved by the “renotation” efforts of the 1940s (see Ref. 1), the Munsell system is not flawless. In fact, a committee, formed in 1947, worked for 30 years on a replacement color system called the Optical Society of America’s Uniform Color Scale (OSA-UCS) (Ref. 2). While they could achieve a system with better uniformity than the Munsell system, they concluded that: “…no regular rhombohedral lattice sampling of color space, with a fixed background, can exist; we will produce the best approximation to such a lattice for a neutral 6/ background that we can design…” In other words, the UCS system is more uniform, but only for one fixed background equivalent to Munsell N 6/. The OSA-UCS structure offers unique multidirectional navigation paths in color space; unfortunately, it was not widely adopted, maybe because of its non-intuitive color notation format. It is then not surprising to see that work was done during the same period to improve the Munsell system, also by imposing a background. This work resulted in the development of Munsell “re-renotation” tables (Ref. 3), published in 1967, where it is assumed that “…two colors forming the difference are viewed on a gray background whose Munsell value approximates the average of the values of the two colors.” However, we have not seen much use of these tables, and the “renotated” Munsell Color System published in 1943 remains a valid and trusted color reference. As for OSA-UCS, it remains useful whenever there is a need for a uniform color system, in color research for instance, or when designing multi-color targets. For those interested in the OSA-UCS system, you can import and export coordinates using this system and generate color lists restricted or not to particular OSA-UCS planes in PatchTool. Munsell Color System support in CT&A and PatchTool In CT&A, bidirectional conversions FROM and TO the Munsell notation can be performed in many ways • Munsell tools: A dedicated tool for bidirectional high precision conversion between Munsell and L*a*b*/RGB. • RGB vs RGB tool RGB to Munsell: Convert RGB data to high precision Munsell notation. • RGB vs RGB tool Color Deck: A digital catalogue of over 4000 Munsell patches, including those of the Munsell Book of Color. Used to convert samples presented in fixed uniformly distributed steps to XYZ/L*a*b*/RGB coordinates. • Convert TO Munsell Color Deck: Find the nearest Munsell (digital catalogue) sample for a given RGB input or for a sample from another Color Deck. PatchTool can export any color data list opened in the program to Munsell coordinates with high precision. Please consult the CT&A and PatchTool documentation on this Web site for more information. • Ref. 1: Final Report of the O.S.A. Subcommittee on the Spacing of the Munsell Colors, Sidney M. Newhall, Dorothy Nickerson, and Deane B. Judd, JOSA, Vol. 33, No. 7, July 1943, p385-418. • Ref. 2: o Uniform color scales, David L. MacAdam, JOSA, Vol. 64, No. 12, December 1974, p1691-1702 o OSA Uniform Color Scale Samples: A Unique Set, Dorothy Nickerson, COLOR research and applications, Vol. 6, No. 1, Spring 1981, p7-33 o On the Geometry of the OSA Uniform Color Scales Committee Space, Fred W. Billmeyer Jr., COLOR research and applications, Vol. 6, No. 1, Spring 1981, p34-37 • Ref. 3: One Set of Munsell Re-renotations, NATIONAL BUREAU OF STANDARDS REPORT #192693, Deane B. Judd and Dorothy Nickerson, December 26, 1967
