these blocks will contain a relatively large range of color. This is why it is called the least precise level in The Universal Color Language. On the other hand, it is the easiest level for the average person to understand, since the color names describing each block are only generic (basic) hue names (red, yellow, blue), and the neutrals (white, gray and black). Although this level is called the least precise, the boundaries of these blocks are specified just as accurately as those of the smaller blocks in the higher-numbered levels. The ten generic hue names and three neutrals and their abbreviations are listed in table 2 and circled in the round diagram in table 1. Thus, we can describe any color in this level of accuracy by using one of these generic hue names or white, gray or black. As an example, we could describe a certain carpet as a brown (Br) carpet. 6. Level 2

In level 2, the whole color solid is divided into 29 blocks; four of the level 1 blocks remain unchanged while 9 are divided into two or three parts. The 13 color names or designations used in level 1 are still applied to the appropriate 13 of the 29 blocks, while each of the 16 new blocks is assigned an intermediate hue name. These new intermediate hue names each fall between two of the generic hue names in level 1; they are listed in table 3. They are shown but not circled in the round diagram in table 1. In this level we can describe our brown carpet a little more accurately by calling it a yellowish brown (yBr) carpet.

7. Level 3

In level 3, the whole color solid is divided into 267 color-name blocks, as shown in the color-name charts in section 13 of the Color Names Dictionary. Each of the blocks in level 2 described by a generic or intermediate hue name is divided again. To each of these subblocks is assigned the generic or intermediate hue name of the original level 2 block and one or more appropriate modifiers describing its lightness and saturation. These modifiers are shown in figure 11 below and in figure 2 on page 3 of the Color Names Dictionary. The part of the color solid called gray is divided into three parts named light gray, medium gray and dark gray. This level constitutes the ISCC-NBS Method of Designating Colors, which uses the full set of 267 color-name blocks in the Color Names Dictionary. Now we can describe our yellowish brown carpet still more accurately as a light yellowish brown (1.yBr) carpet (color-name block or Centroid #76).

This level of accuracy of color designation is suited for a variety of scientific and industrial applications [2, 14, 21]. These designations have been used in descriptions of the colors of drugs and chemicals [1, 23, 45], in qualitative chemical analysis [27, 39], in dermatology [5], in photogrammetry [4], and in the descriptions of mica [13], building materials [24], soils [31] and flags [7, 21]. The ISCC-NBS color names, together with the Centroid Color Charts, are well suited for use in statistical studies of color trends in industrial usage, and in planning

lines of merchandise intended to have coordinated colors. In addition to these color names being used to designate the colors of manufactured items, chips of the Centroid Colors can also be used as the physical standards upon which the colors of these or other items can be based.

8. Level 4

Level 4 of our correlated series is exemplified by the Munsell Color System and its associated set of color standards, the Munsell Book of Color (see fig. 2). There are about 1500 color standards in the book which have been prepared with great care to illustrate visually equally-spaced scales (colors separated by visually equal steps) of hue, value and chroma. It is generally agreed that the perceived equality of the differences between adjacent samples in the book is good, but not perfect. The boundaries of the ISCC-NBS color-name blocks are specified in the Munsell system. The Munsell Book of Color can be used as a color-appearance system and lends itself to interpolation among and extrapolation beyond its colored samples. In this fourth level, other sufficiently detailed color-order systems can be used in place of the Munsell System. These other colororder systems include: Maerz and Paul (1st edition); Ridgway; Plochere; and the Color Harmony Manual (3rd edition). The number of divisions of the whole color solid in this level, 943 to 7056, refers to the number of colors in these color-order systems. A color-order system is a collection of color standards which samples the color solid systematically. Our light yellowish brown carpet can now be more accurately described by the Munsell notation 10YR 6/4, that is, 10YR designates the hue of the carpet and 6/4 designates its lightness and saturation respectively (for more details see pages 6 and 7, CND).

9. Level 5

Level 5 is illustrated by the visually interpolated Munsell notation. Since the spacing of the samples in the Munsell Book of Color is nearly uniform, it is possible through comparison of a color with the colored standards in the Munsell scales of hue, value and chroma to visually interpolate its Munsell notation. An experienced observer can interpolate reliably to a tenth of a value step, to a quarter of a chroma step, and to anywhere from one hue step at chroma/2 to as little as one-quarter of a hue step at chroma/10 and above. It is estimated that the maintenance of these accuracies is equivalent to the division of the whole color solid into about 100,000 small blocks. Since the color standards in the other color-order systems listed above are not arranged in visually equally spaced steps along clearly defined. scales, interpolation among contiguous standards can be carried out but not as conveniently nor as accurately as within the Munsell system. This is the level which is most used in visual matching and in color tolerance specifications. In this level, the color of our light yellowish brown carpet can now be very accurately specified as 91 YR 6.4/44. (see table 1, note**).