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  1. Assuming that the adoption of adequate methods of test and selection of observers would bring the three-element methods under serious consideration for the selection of one as a standard method, it would appear that the additive three-color (red, green and blue mixture) method presents the most advantages. The single setting used to obtain a measurement calls for an exact match, both of brightness and color, which from the photometric standpoint is ideal. The measurement when obtained can be transformed into color sensation, or spectrum hue, brightness and purity values, if so desired, by comparatively simple steps. The spectrum hue, brightness and purity method as a method of measurement suffers under the serious disadvantage that one of the several settings necessary for a complete measurement is that of brightness with a large color difference, thus introducing a fertile field for wide discrepancies. The three-color subtractive method shares with the additive method the merit that the setting which yields the measurement is an exact match. It is, however, less simple, for the reason that the transmission, purity and hue of the absorbing "wedges" all change with depth. Unless the white light source which is modified by the absorbing wedges consists of spectrally narrow red, green and blue bands, the light transmitted by the three superposed wedges changes in intensity and purity at the same time. This necessitates the use of a neutral tint wedge or other device to complete the match, whereby the system becomes one of four elements instead of three. Furthermore, the reduction of the subtractive measurements to sensation, or hue, brightness and purity values is exceedingly difficult.
  2. An intermediate position is occupied by the polarization color scale as used in the Arons Chromoscope. Here the matter of reproducibility is well taken care of, being a question of angles of setting and thicknesses of quartz. The colors produced are spectrally different in character from the ones measured so that some difference of setting between different observers will occur, although this difference is much less than with the three color mixture method. The measurements when obtained are on scales having no obvious relation to wave-length or hue, and their reduction to a color sensation scale is a much lengthier process than the reduction of three color mixture measurements.
  3. "The Transformation of Color Mixture Equations from One System to Another." Journal Franklin Institute, Dec. 1915, p. 673.
  4. See Nutting, "A Method for Constructing the Natural Scale of Pure Color," Bull. Bureau of Standards, Vol. 6, No. 1.
  5. "The Addition of Luminosities of Different Color," Phil. Mag., Dec. 1912, p. 845.
  6. Ives and Brady, "An Apparatus for the Spectroscopic Synthesis of Color." Jnl. Franklin Institute, July 1914, p. 89.

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Assuming that the adoption of adequate methods of test and selection of observers would bring the three-element methods under serious consideration for the selection of one as a standard method, it would appear that the additive three-color (red, green and blue mixture) method presents the most advantages. The single setting used to obtain a measurement calls for an exact match, both of brightness and color, which from the photometric standpoint is ideal. The measurement when obtained can be transformed into color sensation, or spectrum hue, brightness and purity values, if so desired, by comparatively simple steps. The spectrum hue, brightness and purity method as a method of measurement suffers under the serious disadvantage that one of the several settings necessary for a complete measurement is that of brightness with a large color difference, thus introducing a fertile field for wide discrepancies. The three-color subtractive method shares with the additive method the merit that the setting which yields the measurement is an exact match. It is, however, less simple, for the reason that the transmission, purity and hue of the absorbing "wedges" all change with depth. Unless the white light source which is modified by the absorbing wedges consists of spectrally narrow red, green and blue bands, the light transmitted by the three superposed wedges changes in intensity and purity at the same time. This necessitates the use of a neutral tint wedge or other device to complete the match, whereby the system becomes one of four elements instead of three. Furthermore, the reduction of the subtractive measurements to sensation, or hue, brightness and purity values is exceedingly difficult.

An intermediate position is occupied by the polarization color scale as used in the Arons Chromoscope. Here the matter of reproducibility is well taken care of, being a question of angles of setting and thicknesses of quartz. The colors produced are spectrally different in character from the ones measured so that some difference of setting between different observers will occur, although this difference is much less than with the three color mixture method. The measurements when obtained are on scales having no obvious relation to wave-length or hue, and their reduction to a color sensation scale is a much lengthier process than the reduction of three color mixture measurements.

"The Transformation of Color Mixture Equations from One System to Another." Journal Franklin Institute, Dec. 1915, p. 673.

See Nutting, "A Method for Constructing the Natural Scale of Pure Color," Bull. Bureau of Standards, Vol. 6, No. 1.

"The Addition of Luminosities of Different Color," Phil. Mag., Dec. 1912, p. 845.

Ives and Brady, "An Apparatus for the Spectroscopic Synthesis of Color." Jnl. Franklin Institute, July 1914, p. 89.

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