US3560758A

US3560758A - Color identification system taking into account the color and reflecting of the base material

Info

Publication number: US3560758A
Application number: US696409A
Authority: US
Inventors: Melvin E Swanberg
Original assignee: Conductron Corp
Current assignee: Conductron Corp
Priority date: 1968-01-08
Filing date: 1968-01-08
Publication date: 1971-02-02
Anticipated expiration: 1988-02-02

Abstract

The color identification system takes the color and the reflectivity of the base material of a printed or drawn colored document into account as it identifies the pigments which define the various differently colored areas of that document, and thus is a relative color identification system; and that color identification system can accurately identify the pigments which define the various differently-colored areas on that document by classification of each color, which is detected, as being within a range of colors, which includes all colors that can be expected to result from one pigment.

Description

o H Unite States Patent nu 3,560,758

[72] Inventor Melvin E. Swanberg 2,774,276 12/1956 Glasser etal. 250/226X Claremont, Calif. 3,060,790 10/ 1962 Ward 250/226X [21] Appl. No. 696,409 3,069,971 12/1962 Simmon et a1. 250/226X [22] Filed Jan. 8, 1968 3,120,782 2/1964 Goddard et al. 250/226X [45] Patented Feb. 2, 1971 3,127,517 3/1964 Kestenbaum.. 250/220 [73] Assignee Conductron Corporation 3,133,201 5/1964 Rock 250/226 St. Charles, Mo. 3,255,305 6/1966 Chatten 328/1 15 a corporation of Delawar 3,003,388 10/ 1961 Hunter et a1 250/226X OTHER REFERENCES Hambleton: International Dyer & Textile Printer; Jan. 20, 1967 pp 102- 105 [54] COLOR IDENTIFICATION SYSTEM TAKING INTO ACCOUNT THE COLOR AND REFLECTING OF Pnmary Examiner-Walter Stolweln THE BASE T RIA Attorney-Kingsland, Rogers, Ezell, Eilers and Robbins 34 Claims, 57 Drawing Figs.

[52] US. Cl 250/226, ABSTRACT; The color identification ystem takes the color 250/7195 35 6/ 176 and the reflectivity of the base material of a printed or drawn ll?- eolgred document into account as it identifies the pigments Fleld of Search define the various differently colored areas of that 174, 177, 186, 191, 193, 250/226, document, and thus is a relative color identification system; 209, 225 and that color identification system can accurately identify the pigments which define the various differently-colored areas on [56] References cued that document by classification of each color, which is de- UNITED STATES PATENTS tected, as being within a range of colors, which includes all 2,669,902 2/1954 Barnes 350/ l 4 colors that can be expected to result from one pigment.

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o I Z 3 Y J 6 7 COLOR IDENTIFICATION SYSTEM TAKING INTO ACCOUNT THE COLOR AND REFLECTING OF THE BASE MATERIAL Electro-optics systems have been devised which will scan a printed document, convert the printed data thereon to electrical signals, and transmit and/or record those electrical signals for the purpose of storage, computer manipulation. and/or reproduction of the data encoded on the printed document. Some such scanning systems have been provided with the capabilities of converting various colors on the printed document to electrical signals which could be reconverted to reproduce those colors; and those systems were intended to sense, convert, transmit, and reconvert those colors with a high degree of faithful reproduction. The colors of the colored areas on a document, such as a map, are intended to convey to the observer the fact that a particular area or line concerns a single particular parameter such as terrain contours, roads, rivers, and such; and the colors used are usually easily discriminated as being visually different, and they are chosen to avoid confusion of the parameters represented by each different color. The colors of the colored areas on a document, such as a map which is printed or drawn in color, are not homogeneous in nature; and, instead, those colors consist of incompletely pigmented areas of the paper, cloth or other base material of that document plus small volumes of pigment in the interstices of that base material. Even if the colors of the small volumes of pigment in the interstices of the base material of a given colored area on a document were ofa homogeneous nature, the incompletely pigmented fibers of that base material would keep the overall color of that colored area from being homogeneous. In addition, a document, such as a map which is printed or drawn in color, may be edited by additions in colors which only approximate in appearance the original colors used on that document; and, in such cases, it is the intent to use the similar-appearing colors to convey the same meaning conveyed by the original colors. In addition, a document such as a map which is printed or drawn in color, may be edited by erasers, and this means that small traces of pigment remain, or are smudged, into the surrounding area; and, in such cases, it would be desirable to remove those small traces of pigment by returning the pigmented area to the original color of the base material. As a result of the variations described above, the absolute colors which appear on a document, such as a map, can vary over a large range of colors although a given range of colors is intended to convey a single specific type of information. The unintended color variations appearing on the document can be considered a noise factor which is normally ignored by the visual observer. To provide an electro-optic scanning system which will perform the function of parameter identification through the use of color identification, it is desirable to identify the pigment used to print a specific color rather than to identify the absolute color resulting from that pigment. The standard color identification systems which are absolute color identification systems cannot be conveniently used to identify the pigments which define the various differently-colored areas on a printed or drawn document.

Light from a light source is passed through a filter, is passed through a light modulator, and is then passed through an optical element to form a spot of red light on the surface of a printed or drawn document, such as a map, which has differently-colored areas thereon. Light from a second light source is passed through a second filter, is passed through a second light modulator, and is then passed through a second optical element to form a spot of green light which is coincident with the spot of red light; and light from a third light source is passed through a third filter, is passed through a third light modulator, and is then passed through a third optical element to form a spot of blue light which is coincident with the spots of red and green light. The light modulators modulate the intensities of the light of the spots of red, green and blue light with a sine wave and with a phase displacement of 120 between the sine wave intensity modulation of the light of the spots of red, green and blue light; and hence, although the combined spot of light will be essentially white, the red component of that spot of light will be dominant at a given instant, l20 later the blue component will be dominant, and after that the green component will be dominant. Relative movement will be provided between the combined spot of light and the colored document to provide a scanning of the differently-colored areas on that document. During the scanning of those differently-colored areas, each scanned area will reflect light toward a lens system; and the differentlycolored areas on that document will reflect light which varies in lightness, saturation and hue. That lens system will tend to image the reflected light as a spot of light on an aperture plate which has a single aperture; but an optical element which is intermediate that lens system and that aperture plate will cause two spots of light, rather than just one spot of light, to appear on that aperture plate. In addition, that optical element will orthogonally polarize the light which forms those two spots of light. The centers of those two spots of light will be displaced so individually-different portions of those two spots of light will pass through the single aperture in the aperture plate and will pass to a second optical element as a single cone of orthogonally-polarized light. That second optical element will divide that single cone of orthogonally-polarized light to form two displaced cones of light; and it will direct those displaced cones of light onto spaced-apart light-sensitive elements which will supply signals to an electronic circuit. The second optical element will additionally polarize the light, which forms the two displaced cones of light, so one of the light-sensitive elements will see only one of the individually-different portions of the two spots of light formed by the first optical element and so the other of those light-sensitive elements will see only the other of those individually-ditferent portions of those two spots of light.

The signals which the light-sensitive elements will supply to the electronic circuit will contain lightness, saturation and hue information; and that electronic circuit will analyze that information to determine the color and reflectivity of the base material of printed or drawn colored documents, and will also analyze that information to identify the pigments in the differently-colored areas on those documents. Specifically, that electronic circuit will analyze the information from the lightsensitive elements to determine the color and reflectivity of the base material of printed or drawn colored documents, and will control the intensities of two of the light sources to keep the average value of light reflected from that base material constant. That electronic circuit also will analyze the information from the light-sensitive elements to determine the angleswhich shall be referred to herein as longitude angleswhich represent the differences between the true values of the base material and of the pigments in the differently-colored areas on the document; and, in addition, that electronic circuit will combine the lightness and saturation information to develop vectors which represent the color contrasts between the base material of that document and the pigments in the differentlycolored areas on that document, and it will determine the angleswhich shall be referred to herein as the latitude anglessubtended by those vectors and vectors representing the differences between the lightness values of those pigments and the average lightness value of the base material of that document. Those latitude angles, those color contrast vectors, and those longitude angles will positively and accurately identify the pigments which define the various, differently-colored areas on the document-despite variations in the colors and reflectivities of different portions of the base material of that document, and despite variations in the pressures used during the printing of different portions of that document.

The optical element, which causes the two spots of light to appear on the aperture plate, is oriented relative to the direction of scanning of the document so the individually-different portions of those two spots of light, which pass through the aperture of that aperture plate, will correspond to areas on that document which are displaced transversely of that direction of scanning. The resulting, effective, transverse displacement of those areas on that document is important, because it permits the simultaneous sensing of the hue angle, color contrast, and latitude angle of each of those areas. That simultaneous sensing enables the color identification system of the present invention to provide a high degree of resolution of those boundaries of the colored areas on a printed or drawn colored document which are parallel, or are only slightly inclined, to the direction of scanning. The scanning action itself enables that color identification system to provide a high degree of resolution of those boundaries of the colored areas on the document which are normal, or are sharply inclined, to the direction of scanning; and hence that color identification system is able to provide a high degree of resolution of all of the boundaries of the colored areas on a printed or drawn colored document.

This invention relates to improvements in Control Systems. More particularly, this invention relates to improvements in color identification systems.

It is, therefore, an object of the present invention to provide an improved color identification system.

Color identification systems usually are based upon the concept that each pigment has a definite position within a color solid, and that the position of each pigment can be identified by a hue angle, a saturation vector, and a lightness vector. Where the color of a material is homogeneous in nature-as in the case of an aqueous solution of a dye-an absolute color identification system can be used to accurately identify the pigment which provides the color for that material. However, the colors of colored areas on a printed or drawn colored document, such as a map, are not homogeneous in nature;

and, instead, consist of incompletely-pigmented fibers of the paper, cloth or other base material of that document plus small volumes of pigment in the interstices of base material. In addition, the amount of pigment in the partially-pigmented fibers of the base material of the document will vary with variations in the ink-absorbing capability of that base material and with variations in the pressures used in printing or drawing of that document. Moreover, in a typical scanning system, a single scan line will be wide enough to sense the immediately adjacent portions of two different colored areas, and thus will provide values which are the averages of the hue values, lightness values, and saturation values of the two areas rather than the hue values, lightness values, and saturation values of either of those two areas. All of this means that the colored areas on a printed or drawn colored document do not provide a consistent absolute color value, and hence color identification systems which are based upon absolute color values are incapable of conveniently identifying the pigments used in 'printing or drawing. It would be desirable to provide a color identification system which could classify the colors appearing in the differently-colored areas of colored documents into groups of color ranges because such a color classification system would make it possible to automatically and accurately identify the pigments used in printing or drawing the differently-colored areas of the colored documents. The present invention provides such a color identification system; and that color identification system takes into account the color and reflectivity of the base material of each printed or drawn colored document and variations of pigmentation of the colored areas of the material, and thus is able to accurately identify the pigments used in preparing that document. It is, therefore, an object of the present invention to provide a color identification system which takes into account the color and reflectivity of the base material of a printed or drawn colored document.

The color identification system provided by the present invention identifies each pigment, used in printing or drawing a colored document, by its position within a color solid; but the position of any given pigment is not defined by the usual absolute values of hue, saturation and lightness. Instead, the position of any given pigment within the color solid is defined by an angle-referred to herein as the longitude anglewhich represents the diflerence between the hue values of that pigment and of the base material of the colored document and by an angle-referred to herein as the latitude angle-which is subtended by the lightness-difierence vectors and a color contrast vector which is a function of vectors representing the difference between the lightness values and the saturation values of that base material and of that pigment. By taking into account the hue value, the lightness value, and the saturation value of the base material of the colored document, the color identification system provided by the present invention is able to accurately identify the pigments in the differently-colored areas on that document. It is, therefore, an object of the present invention to provide a color identification system which defines the position of a pigment, used in preparing a colored document, within a color solid by an angle which represents the difference between the hue values of the pigment and of the base material of the document on which that pigment is printed or drawn and by an angle which is subtended by the lightness-difference vectors and a color contrast vector which is a function of vectors representing the difference between the lightness values and the saturation values of that base material and of that pigment. It is a further object of this invention to use the color contrast vector as the criterion for detecting the presence of printed or drawn areas.

The base material of a printed or drawn colored document such as a map, usually has a substantially uniform hue value, a substantially uniform saturation value, and a substantially uniform lightness value; whereas the hue values, saturation values, and lightness values of the pigments in adjacent differently-colored areas on that document can vary widely. The color identification system provided by the present invention utilizes that fact to distinguish between the hue values, saturation values, and lightness values of the pigments of the differently-colored areas on that document; and it does so by scanning those differently-colored areas with phase-modulated light to enable light-sensitive elements to develop modulated electric signals. Those electric signals will haveDC components which correspond to the hue values, saturation values, and lightness values of the base material of the colored document, and they will have AC components which correspond to the hue values, saturation values, and lightness values of the pigments in the differently-colored areas on that document. The AC components of those electric signals can be readily separated from the DC components of those electric signals; and hence the color identification system provided by the present invention can readily distinguish between the hue values, saturation values, and lightness values of the base material of a printed or drawn colored document and the hue values, saturation values, and lightness values of the pigments the differently-colored areas on that document. It is, therefore, an object of the present invention to provide a color identification system that scans the difierently-colored areas on a printed or drawn colored document with phase-modulated light to enable light-sensitive elements to develop modulated electric signals which have DC components corresponding to the hue values, saturation values, and lightness values of the base material of that document and AC components corresponding to the hue values, saturation values, and lightness values of the pigments of the differently-colored areas on that document.

In sensing the differently-colored areas on a printed or drawn colored document, it is important to precisely determine the locations of the boundaries of those differentlycolored areas. Where relative movement is provided between a printed or drawn colored document and a spot of light that is used to scan the differently-colored areas on that document, and where the boundaries of the differently-colored areas are normal or are sharply inclined to the direction of scan, the time-varying signals resulting from a single scanning spot moving from one colored area into a differently-colored area can be used to determine the location of the boundary between those differently-colored areas. However, where a typical scanning system is used, and where the boundaries of the differently-colored areas are parallel or are only slightly inclined to the direction of scan. the single scanning spot will move parallel along a boundary or move slowly from one colored area into a differently-colored area and the resulting constant signal or slowly-varying signal will not help to determine the position of the boundaries of that colored area. Moreover. in a typical scanning system. a single scan line will be wide enough to sense the immediately-adjacent portions of two differentlycolored areas, and thus to provide values which are the averages of the he values, lightness values, and saturation values of the two areas rather than the hue values, lightness values, and saturation values of either of those two areas. To enable a typical scanning system to determine the locations of boundaries which parallel or are only slightly inclined to the direction of scan, that scanning system would have to scan a line across a colored area on a document, would have to remember" one or more of the values obtained during that scan, would have to scan a further line which did not cross that colored area, and then would have to compare the resulting one or more values with the remembered value or values. However, the cost of providing a scanning system with memory circuits is high; and, when those circuits drift, that scanning system can not accurately locate boundaries which parallel or are only slightly inclined to the direction of scan. Consequently, it would be desirable to provide a color identification system which could simultaneously scan two areas that were displaced transversely of the direction of scan and that could develop two separate signals corresponding to those two areas. The present invention provides such a color identification system; and it is, therefore, an object of the present invention to provide a color identification system which can simultaneously sense two areas that are displaced transversely of the direction of scan and which can develop two separate signals corresponding to those two areas.

The color identification system provided by the present invention simultaneously senses two areas that are displaced tranversely of the direction of scan by causing light, reflected from an illuminated spot on the surface of a printed or drawn colored document, to pass to an optical element which forms two spots of orthogonally-polarized light on an aperture plate adjacent the single aperture in that plate. Those two spots correspond to the spot of light on the printed or drawn colored document, but they have the centers thereof displaced so the portion of one of those spots which passes through that single aperture will correspond to one part of the spot of light on the colored document and so the portion of the other of those spots which passes through that single aperture will correspond to a further part of the spot of light on the colored document. A second optical element receives the light which passes through the aperture in the aperture plate; and it further polarizes that light and directs part of that light onto one light-sensitive element while directing the rest of that light onto a second light-sensitive element. The further polarization of the light will coact with the initial light polarization, provided by the first optical element, to enable the one light-sensitive element to see only the light reflected from the one part of the spot of light on the colored document and to enable the second light-sensitive element to see" only the light reflected from the further part of the spot of light on the colored document. The one light-sensitive element thus will be able to develop a signal which corresponds to the light values reflected by just the one part of the spot of light on the colored document and the second light-sensitive element will be able to develop a signal which corresponds to the light values reflected by just the further part of the spot of light on the colored document. The first optical element is so oriented relative to the direction of scan that the two parts of thespot of light on the printed or drawn colored document are displaced transversely of that direction of scan. As a result, the

color identification system provided by the present invention can simultaneously sense two areas on a printed or drawn colored document which are displaced transversely of the direction of scan and can develop separate signals corresponding to those two areas. It is, therefore, an object of the present invention to provide a color identification system which has an optical element that *sees" a spot of light on a printed or drawn colored document and that forms two transversely-displaced spots of orthogonally-polarized light on an aperture plate adjacent the single aperture in that plate, and has a second optical element which further polarizes the light passing through that aperture and enables one light-sensitive element to see just the light corresponding to one part of the spot of light on the colored document and enables a second light-sensitive element to see just the light corresponding to a further part of that spot of light.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description a preferred embodiment of the present invention is shown and described but it is to be understood that the drawing and accompanying description are for the purposes of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing:

FIG. 1 is a perspective view of a color solid, and it shows the location of a given pigment within that color solid;

FIG. 2 is a perspective view of a color identification unit which is intended to scan a document that has been printed or drawn in color and to develop electric signals corresponding to the differently-colored areas on that document;

FIG. 3 is a diagrammatic, perspective showing of the optical elements of the color identification unit shown in FIG. 2;

FIG. 4 is a block diagram of one preferred circuit for the color identification unit shown in FIG. 2:;

FIG. 5 is a partially-sectioned, diagrammatic showing, in plan, of the manner in which a spot of light, that is reflected from a printed or drawn document, is caused to form two displaced spots of light on an aperture plate;

FIG. 6 is a diagrammatic showing, in elevation, of the two displaced spots formed on the aperture plate shown in FIGS. 3 and 5;

FIG. 7 is a showing of the waveforms of the modulated light used to form a spot of light at the surface of the printed or drawn document shown by FIGS. 2 and 3;

FIG. 8 is a block diagram which shows the components and connections of the Sensors," Gain Control Circuits, Power Supply, and Signal Conditioning and Filtering" blocks of FIG. 4;

FIG. 9 is a block diagram which shows the components and connections of the Hue Balance Control" block of FIG. 4;

FIG. 10 is a block diagram which shows the components and connections of the Color Contrast and Latitude Computer" block of FIG. 4;

FIG. 11 is a block diagram which shows the components and connections of the Hue Reference Generator block of FIG. 4;

FIG. 12 is a block diagram which shows the components and connections of the Hue Comparator block of FIG. 4;

FIG. 13 is a block diagram which shows the components and connections of the Latitude Comparator block of FIG.

FIG. 14 is a block diagram which shows the components and connections of the Digital Code Generator block of FIG. 4;

FIG. 15 is a block diagram showing the components and connections of the Line Sensing block of FIG. 4;

FIG. 16 is a showing of the lower Hue Position Control" block of FIG. 1 ll;

FIG. 17 is a showing of the upper Hue Position Control block of FIG. 11;

FIG. 18 is a showing of the components and connections of the Phase Control Circuit" block of FIG. 11;

FIG. 19A is a showing of the components and connections of the upper Gate Generator, Coincidence Circuits, Integrators," Comparator Reference Selector, Amplitude Comparators, Validity Comparators" and AND Gates blocks of FIG. 12;

FIG. 19B is a showing of the components and connections of the lower Gate Generator," Coincidence Circuits," lntegrators," Comparator Reference Selector," Amplitude Comparators,- Validity Comparators" and AND Gates" blocks of FIG. 12;

FIG. 20 shows one form of integrator that could be used in the Integrators blocks of FIG. 12;

FIG. 21 is a showing of the components and connections of the NOR Gate" block and of the two AND Gates" blocks of FIG. 14;

FIG. 22 shows the three, phase-displaced, square waves which are developed by the Phase Control Block" that is shown in FIG. 11 and that has the components and connections thereof shown in FIG. 18;

FIG. 23 shows the waveforms developed by the light sensors in response to light reflected from the white base material of a document;

FIG. 24 shows the waveform developed by the light sensors in response to light reflected from a colored area which absorbs all of the blue light and none of the red or green light directed onto it, and also shows the component parts of that waveform;

FIG. 25 is a perspective view of a vector diagram showing the lightness vector, the saturation vector, the contrast vector, the latitude angle, and the longitude angle of the color corresponding to the waveform of FIG. 24;

FIG. 26 shows the waveform developed by the light sensors in response to light reflected from an orange-colored area on a document, and also shows the component parts of that waveform;

FIG. 27 shows the waveform developed by the light sensors in response to light reflected from an area on a document which is white throughout one-half thereof and which is orange throughout the other half thereof, and also shows the component parts of that waveform;

FIG. 28 shows the signal developed by a light sensor as that light sensor sees a scanning spot of light cross an orange colored line on a document;

FIG. 29 is a polar-coordinate graph showing the longitude angles of seven representative pigments, showing seven angle slots incorporating those longitude angles, and showing three further angle slots;

FIG. 30 shows waveforms corresponding to the ten angle slots shown in FIG. 29;

FIG. 31 is a further polar-coordinate graph showing the longitude angles of three additional representative pigments, showing three angle slots incorporating those longitude angles, and showing two further angle slots;

FIG. 32 shows waveforms corresponding to the five angle slots shown in FIG. 31;

FIG. 33 shows an array of actual and simulated areas on a document adjacent a line on that document, and the actual areas of that array are shown by solid lines whereas the simulated areas of that array are shown by dashed lines;

FIG. 34 shows by solid and dashed lines, respectively, the waveforms developed as the line of FIG. 33 passes through the actual and simulated areas on FIG. 33;

FIG. 35 shows a waveform which represents the signals at the outputs of two of the sum amplifiers and at the output of one of the OR gates of FIG. 15;

FIG. 36 shows a waveform which represents the signals at the outputs of two of the other OR gates of FIG. 15;

FIG. 37 shows a waveform which represents the signals at the outputs of the other two sum amplifiers and at the output of the remaining OR gate of FIG. 15;

FIG. 38 shows the waveforms at the active outputs of the two gate generators and at the output of the AND gate of FIG. 15;

FIG. 39 shows the array of actual and simulated areas adjacent a further line on the document of FIG. 33;

- -FIG. 40 shows by solid and dashed lines, respectively, the waveforms developed as the line of FIG. 39 passes through the actual and simulated areas on FIG. 33;

FIG. 41 shows by a solid line a waveform which represents the signal at the output of one of the OR gates of FIG. 15;

FIG. 42 shows waveforms which represent the signals at the outputs of two of the other OR gates of FIG. 15;

FIG. 43 shows a waveform which represents the signals at the outputs of the other two sum amplifiers and at the output of the remaining OR gate of FIG. 15;

FIG. 44 shows the waveforms at the active outputs of the two gate generators and atthe output of the AND gate of FIG. 15;

FIG. 45 shows the array of actual and simulated areas adjacent a further line on the document of FIG. 33;

FIG. 46 shows by solid and dashed lines, respectively, the waveforms developed as the line of FIG. 45 passes through the actual and simulated areas of FIG. 33;

FIG. 47 shows by a solid line a waveform which represents the signal at the output of one of the OR gates of FIG. 15;

FIG. 48 shows waveforms which represent the signals at the outputs of two of the other OR gates of FIG. 15;

FIG. 49 shows waveforms which represent the signals at the outputs of the sum amplifiers and at the output of the remaining OR gate of FIG. 15;

FIG. 50 shows the waveforms at the active outputs of the two gate generators and at the output of the AND gate of FIG. 15;

FIG. 51 shows the array of actual and simulated areas adjacent a colored area on the document of FIG. 33;

FIG. 52 shows by solid and dashed lines, respectively, the waveforms developed as the area of FIG. 51 passes through the actual and simulated areas on FIG. 33;

FIG. 53 shows a waveform which represents the signal at the output of one of the OR gates of FIG. 15;

FIG. 54 shows a waveform which represents the signals at the outputs of two of the other OR gates of FIG. 15;

FIG. 55 shows a waveform which represents the signals at the output of the other two sum amplifiers and at the output of the remaining OR gate of FIG. 15; and

FIG. 56 shows the waveforms at the active outputs of the two gate generators and at the output of the AND gate of FIG. 15.

COMPONENTS OF COLOR IDENTIFICATION UNIT Referring to the drawing in detail, the numeral 20 generally denotes a color solid which has a diagonal 22 that is the locus of all achromatic light; and the upper end of that diagonal represents white while the lower end of that diagonal represents black. The numeral 30 denotes the position, within the color solid 20, of a given pigment; and the absolute values of the lightness, hue and saturation of that pigment determine that position. Specifically, the absolute lightness value of that pigment determines the distance 36 from the lower end of the diagonal 22 to a plane which is normal to that diagonal and which passes through the position 30. The absolute hue value of that pigment determines the angle 32 in that plane; and the absolute saturation value of that pigment determines the length of the vector 34 in that plane.

The use of absolute lightness values, absolute saturation values, and absolute hue values to identify pigments is standard in the art of colorimetry; but, while such absolute values can be used to accurately identify pigmentssuch as aqueous solutions of dyes-which are homogenous in nature, such absolute values can not be used to accurately identify a pigment which is printed or drawn on a colored document, such as a map. Specifically, the colored areas on a printed or drawn colored document are not areas wherein the pigments are homogeneous in nature, because those colored areas consist of incompletely-pigmented fibers of the paper, cloth or other base material of that document plus small volumes of pigment in the interstices of that base material; and hence any identification, of a pigment in a colored area on a printed or drawn document, which was based upon absolute values of lightness, saturation and hue could not accurately identify that pigment because of the lightness, saturation, and hue values of the incompletely-pigmented fibers of that base material. If normal printing or drawing pressures were used to apply a deep red pigment to an area of a white material which had only a very limited ability to absorb that pigment, or if very light printing or drawing pressures were used to apply that pigment to an area of a white material which had an average ability to absorb that pigment, those areas would appear to be pink in color; and an identification based upon absolute values of lightness, saturation and hue would indicateincorrectly--that the pigment was pink. The extent to which an identification based upon absolute values of lightness, saturation and hue will be in error can vary with the viscosity of the pigment, the physical softness of that pigment, the humidity at the time the document is prepared, the temperature at the time the document is prepared, the printing or drawing pressure used, the length of time the printing or drawing pressure is maintained, the ability of the base material of the map to absorb the pigment, and the lightness, saturation and hue values of that base material; and, in many cases, those errors can be gross in nature. Moreover, in a typical scanning system, a single scan line will be wide enough to sense the immediately adjacent portions of two differently-colored areas and thereby provide values which are the averages of the hue values, lightness values, and saturation values of the two areas rather than the hue values, lightness values, and saturation values of either of those two areas. Thus, as a scanning spot crosses from a white base material area into a colored area, which for purposes of illustration is deep red, the color which is sensed will vary from white through pink and red to deep red. Hence, the incompletelypigmented fibers of the base material and the location of the scanning spot at the edge of the colored area will produce a mixture of the saturation values and the lightness values of the pigment and base material. The values of lightness, saturation, and hue of such a mixture will be average values which are dependent upon the percentage of unpigmented base material and pigmented base material which fall within the area of the scanning spot, as well as the degree of pigmentation of fibers; and those average values could be almost anywhere between the lightness, saturation, and hue values of the pigment. However, and importantly, every identification of a colored area on a printed or drawn document which is based upon absolute values of lightness, saturation and hue, will be inaccurate.

The color identification system of the present invention makes it possible to accurately identify the pigments used in printing or drawing the colored areas on a document by taking into account the effects which the incompletely-pigmented fibers of the base material of that document have upon the apparent colors of those colored areas and the effects of the scanning spot sensing immediately-adjacent portions of base material and pigmented area. Specifically, instead of merely sensing a lightness value which corresponds to the overall lightness of a colored area on a printed or drawn document, the present invention senses the lightness value of the base material of that document and then subtracts that value of lightness from all values of lightness which appear on the document, thereby developing a lightness value which accurately represents the difference between the lightness values of that base material and of the colored areas of the document. Uncolored areas will result in a lightness difference value of zero. Similarly, instead of merely sensing a saturation and hue value which corresponds to the overall hue of a colored area on a printed or drawn document, the present invention senses the saturation and hue of the base material of that document and then subtracts those values of saturation and hue from all sensed values of saturation and hue, thereby developing a saturation and hue value which accurately represents the difference between the saturation and hue values of that base material and of the colored areas on the document. Uncolored areas will result in a saturation difference value of zero, which represents an absence of hue. The color identification system of the present invention simplifies the subtracting of the lightness, saturation and hue values of the base material of a document by directing varying intensities of red, blue, and green light onto that document so an essentially constant intensity of achromatic light is detected as being reflected from the base material of that document. Because the light detected as being reflected from that base material will be achromatic and constant in intensity, any values of hue and saturation or any changes of intensity in the light reflected from the printed or drawn colored document will be a measure of the hues and saturations and lightness of the colored areas on that document relative to any hue and saturation and lightness values of that base material.

In the color solid 20 of PK]. 1, the numeral 35 denotes the position which represents the controlled color reflected from the base material of a printed or drawn document; and the numeral 37 denotes a lightness value which corresponds to the lightness of that base material. The numeral 36 denotes a lightness vector which represents the lightness value of a pigment used in printing or drawing a colored area on that document. By subtracting the value of the lightness vector 36 from the lightness value 37, the lightness value 40 which represents the lightness difference value of that pigment can be obtained. The vector denoted by the numeral 37 is the locus of all colors which have a saturation value of zero, and hence the vector 34 will represent the difference between the saturation value of the base material and of the pigment represented by the position 30. The angle 32 which is subtended by the saturation vector 34, with respect to a reference vector 31, will represent the differences between the hue values of the base material and of the pigment represented by the position 30. A vector 38 which is drawn between the position 35 and the position 30 represents the contrast between the base material of the document and the pigment used to print or draw a colored area on that document; and the tangent of the angle 42 subtended by the vector 38 and the vector 40 represents the ratio between the saturation vector 34 and the lightness difference vector 40. In determining the pigment used in printing or drawing a colored area on a document, the color identification system provided by the present invention senses the angle 32 and the angle 42. The incompletely-pigmented fibers of the base material and the location of the scanning spot at the edge of a colored area will produce a proportional change in the

vectors

40, 34, and 38; but the angles 32 and 42 will remain unchanged. The color identification system provided by the present invention senses the angles 32 and 42, thereby providing the identification of pigments independent of uncontrolled variables. The value of the contrast vector 38 also is sensed, and it is used for the purpose of detecting and determining the position of the boundaries of colored areas.

Referring particularly to FIG. 2, the numeral 50 generally denotes the cabinet of one preferred embodiment of color identification unit that is made in accordance with the principles and teachings of the present invention. That cabinet has self-aligning, preloaded ball bearing assemblies, not shown, adjacent the opposite ends thereof; and a lightweight metal drum 52 is mounted on a precision axle which is journaled in those ball bearing assemblies. That drum has an accuratelymachined outer surface; and that outer surface can receive a document 53 which has been printed or drawn in color. That document can be held in intimate engagement with the outer surface of that drum by a flexible sheet of tough, transparent material, such as Mylar, which has one end thereof secured to that drum and which can have the free end thereof readily secured to or separated from that drum. The cabinet 50 also has an electric gear motor, not shown, which rotates the drum 52 at a predetermined speed; and an optical shaft encoder, not shown, which generates drum-rotation position data will be coupled to the drum 52. An adjustable servo-type mounting, not shown, will permit easy and accurate zeroing" of that encoder relative to that drum. That encoder will preferably generate a 16-bit word for digital determination of circumferentially-spaced points on the document 53; and a count of the number of revolutions of the drum 52 will determine the spacing between axially-spaced points on that document.

The numeral 54 denotes a precision-ground guide rod which is mounted on the cabinet 50 so it is precisely parallel to the axis of rotation of the rotatable drum 52; and the numeral 56 denotes a second precision-ground guide rod which is mounted on that cabinet so it is precisely parallel to that axis of rotation. As indicated by FIG. 2, the

guide rods

54 and 56 are spaced apart a short distance in the horizontal direction. A ball lead screw 58 is rotatably supported by ball bearing assemblies, not shown, which are adjacent the opposite ends of the cabinet 50; and that lead screw is precisely parallel to the axis of rotation of the rotatable drum 52 and to the

guide rods

54 and 56. A precision gear train, not shown, is connected between the rotatable drum 52 and that lead screw to provide a positive and definite relationship between the rotation of that lead screw and the rotation of that rotatable drum. The numeral 60 generally denotes a scanner which has a base plate 62 that is equipped with accurately-mounted linear ball bearing assemblies, not shown. Those linear ball bearing assemblies will coact with the

guide rods

54 and 56 to permit that scanner to move easily in a direction parallel to the axis of rotation of the rotatable drum 52 while effectively preventing all movement of that scanner transversely of that axis of rotation. The scanner 60 is equipped with a lead nut, not shown, which can be moved into engagement with the lead screw 58 to enable that lead screw to drive that scanner along the lengths of the

guide rods

54 and 56. That lead nut can, however, be moved out of engagement with the lead screw 58 to permit the scanner 60 to be moved freely along the lengths of those guide rods. A flexible cable 61 contains flexible conductors which are connected to the electrical components mounted within the scanner 60, and that flexible cable will extend and retract as needed to permit unimpeded movement of that scanner along the lengths of the guide rods 54 and S6. The flexible conductors will extend to the electronic equipment that will be stored behind panels or doors at the front of the lower portion of that cabinet.

The cabinet 50 has a cover 63 which is shown as being transparent and which overlies and encloses the upper portion of the rotatable drum 52. That cover can be raised upwardly and moved out of register with that rotatable drum to facilitate the securement of the document 53 to, and to facilitate the separation of that document from, that rotatable drum. An elongated guard 65, which is shown as being transparent, is provided adjacent the bottom of the rotatable drum 52; and that guard will underlie and protect the bottom of that rotatable drum. The cover 63 and the guard 65 will be spaced apart sufficiently to enable the scanner 60 to directly confront the document 53.

As shown particularly by FIG. 3, the scanner 60 has three

light sources

64, 66 and 68 therein; and those light sources will preferably be quartz-iodide-type incandescent lamps or zirconium arc lamps. The quartz-iodide-type incandescent lamps are desirable because they are small in size, because they have high color temperatures, and because they provide positionally-stable sources of light. Zirconium arc lamps are desirable because they are highly efficient, consume relatively low amounts of power, and provide point sources of light; but such lamps tend to experience objectionable instability with regard to the intensities and positions of those point sources of light. Each of the light sources should have a power rating of 200 or more watts.

Absorption-

type filters

70, 72 and 74 are disposed, respectively, in the paths of light issuing from the

light sources

64, 66 and 68; and one of those filters will essentially permit only red light to pass through it, another of those filters will essentially permit only blue light to pass through it, and the last of those filters will essentially permit only green light to pass through it. To protect the

filters

70, 72 and 74 from overheating, an interference type filter, not shown, will be disposed between the

light sources

64, 66 and 68 and those filters to remove energy having wavelengths longer than 700 millimicrons.

The numeral 76 generally denotes a light modulator housing which is mounted within the scanner 60; and that housing has an opening 78 in register with the light passing through the filter 70, has an opening 80 in register with the light passing through the filter 72, and has an opening 82 in register with the light passing through the filter 74. That light modulator housing has three light modulators therein; and those light modulators are in register, respectively, with the

apertures

78, 80, and 82 in that light modulator housing. Those light modulators can be opto-mechanical or opto-electrical in nature; and polarizing elements plus liquid devices such as Kerr cells, mechanical devices such as rotatable pattem-bearing discs, polarizing elements plus crystal devices such as pockel cells can be used as the light modulators in the light modulator housing 76.

The numeral 84 generally denotes an optical element which will receive the light that successively passes through the filter 70 and the aperture 78, and that optical element will form a spot of colored light on the document 53. The numeral 86 generally denotes an optical element which will receive the light that successively passes through the filter 72 and the aperture 80, and that optical element will form a spot of colored light which is congruent with the spot of colored light formed by the optical element 84; and the numeral 88 generally denotes an optical element which will receive the light that successively passes through the filter 74 and the aperture 82, and that optical element will form a spot of colored light which is congruent with the spot of colored light formed by the optical element 84 and with the spot of colored light formed by the optical element 86. The resulting spot of light is denoted by the numeral 90; and, while it will have red, blue and green components, it will be an essentially white spot of light.

The spot 90 of light illuminates the area being scanned and should be as small as alignment problems permit, in order to provide a high degree of light flux density. In the said one preferred embodiment of color identification unit, the diameter of the spot 90 is between five one-hundredths and twotenths of an inch.

Although the

optical elements

84, 86, and 88 have been shown as lenses which image the red, green, and blue light paths to a common point on the document 53, a preferred optical system would use a dichroic mirror to combine those light paths. Where the

light sources

64, 66 and 68 are quartziodide-type incandescent lamps, the

optical elements

84, 86 and 88 will preferably project demagnified images of the filaments of those light sources onto the document 53 to form the colored spots of light which combine together to form the spot 90 of light.

The light modulator in register with the aperture 78 will modulate the intensity of the light passing through that aperture; and, similarly, the light modulators in register, respectively, with the apertures and 82 will modulate the intensities of the light passing through those apertures. Those light modulators will phase-displace the light of the red, green and blue spots of light, which combine together to form the spot of light. The frequency of modulation, provided by the three modulators within the light modulator housing 76, must be higher than any frequency which will be developed by the relative movement between the spot 90 of light and any data printed or drawn on the document 53; and the higher the frequency of modulation of those modulators the higher the rate at which the document 53 can be scanned. The frequency of modulation of the light modulators should be as high as practical-being in the range from 100,000 cycles per second to the practical upper limit of the light modulators used and the bandwidth of the signal-processing circuits. in one preferred embodiment of color identification unit provided by the present invention, the light modulators in the modulator housing 76 will modulate the light from the

light sources

64, 66 and 68 at a frequency of 200 kilocycles per second. Also, those light modulators will develop modulated waveforms which are sine waves.

The document 53 will reflect part of the light which is used to form the spot 90 of light; and a lens system 92 will tend to image that reflected light on an aperture plate 96 which has a single aperture 98 therein. The image formed on the aperture plate 96 will be an approximately 10 times magnified image of

Claims

1. The method of identifying a pigment used in preparing a document that comprises: determining the hue of said pigment relative to the hue of the base material of said document; determining the position of said pigment with respect to the black end of the locus of achromatic light of a color solid relative to the position of said base material of said document with respect to said black end of said locus of achromatic light of said color solid; determining the saturation of said pigment relative to the saturation of said base material of said document; and using the relative hue, the relative position along said achromatic locus, and the relative saturation of said pigment to identify said pigment.

2. The method of identifying a pigment as claimed in claim 1 wherein said document is scanned by a spot of light composed of a plurality of chromatically-different spots of light.

3. The method of identifying a pigment as claimed in claim 1 wherein said document is scanned by a spot of light composed of a plurality of chromatically-different spots of light and wherein the intensities of said chromatically-different spots of light are modulated.

4. The method of identifying a pigment used in preparing a document that comprises: determining the hue of said pigment relative to the hue of the base material of said document; determining the position of said pigment with respect to the black end of the locus of achromatic light of a color solid relative to the position of said base material of said document with respect to said black end of said locus of achromatic light of said color solid; determining the saturation of said pigment relative to the saturation of said base material of said document; using the relative hue, the relative position along said achromatic locus, and the relative saturation of said pigment to identify said pigment; scanning said document by a spot of light composed of a plurality of chromatically-different spots of light; and setting the intensities of said chromatically-different spots of light to cause the light received from said base material to be essentially white.

5. The method of identifying a pigment used in preparing a document that comprises: determining the hue of said pigment relative to the hue of the base material of said document; determining the position of said pigment with respect to the black end of the locus of achromatic light of a color solid relative to the position of said base material of said document with respect to said black end of said locus of achromatic light of said color solid; determining the saturation of said pigment relative to the saturation of said base material of said document; using the relative hue, the relative posItion along said achromatic locus, and the relative saturation of said pigment to identify said pigment; scanning said document by a spot of light composed of a plurality of chromatically-different spots of light; setting the intensities of said chromatically-different spots of light to cause the light received from said base material to develop a DC signal as long as said received light is essentially white light and to create a ripple on said DC signal whenever said received light is not essentially white; and said ripple being used to adjust the intensity of at least one of said chromatically-different spots of light.

6. The method of identifying a pigment used in preparing a document that comprises: determining the longitude angle of said pigment within a color solid; determining a value corresponding to the position of said pigment with respect to the black end of the locus of achromatic light of said color solid; determining a value corresponding to the contrast of said pigment; using the first said value and said second value to obtain a third value corresponding to the cosine of the latitude angle of said pigment within said color solid; and using said longitude angle and said cosine of said latitude angle to identify said pigment.

7. The method of identifying a pigment as claimed in claim 6 wherein the first said value is the square of said position of said pigment along said achromatic locus, wherein said second value is the square of the contrast of said pigment, and wherein said third value is the square of said cosine of said latitude angle.

8. A color identification unit that comprises: a light source that can direct light onto a document; a light sensor that can receive light from said document; said light sensor developing an essentially DC signal in response to light received from the base material of said document and developing an essentially AC signal in response to light received from a colored area on said document, said essentially AC signal developed by said light sensor including information on the position of the pigment used in preparing said colored area with respect to the black end of the locus of achromatic light of a color solid; a first circuit that responds to signals developed by said light sensor to provide a signal which is a measure of the latitude angle of said pigment within said color solid; and a second circuit that responds to signals developed by said light sensor to provide a signal which is a measure of the hue of said pigment.

9. A color identification unit as claimed in claim 8 wherein said first circuit has a subcircuit which determines a value corresponding to said position of said pigment along said achromatic locus, wherein said first circuit has a second subcircuit which determines a second value corresponding to the contrast of said pigment, and wherein said first circuit has a third subcircuit which combines the first said and said second values to develop said signal which is a measure of said latitude angle.

10. A color identification unit that comprises: a light source that can direct light onto a document; a light sensor that can receive light from said document; said light sensor developing an essentially DC signal in response to light received from the base material of said document and developing an essentially AC signal in response to light received from a colored area on said document, said essentially AC signal developed by said light sensor including information on the position of the pigment used in preparing said colored area with respect to the black end of the locus of achromatic light of a color solid; a first circuit that responds to signals developed by said light sensor to provide a signal which is a measure of the latitude angle of said pigment within said color solid; said first circuit having a subcircuit which includes a squaring circuit and a low frequency filter that coact to provide a value corresponding to said position of said pigment along said achromatic locus; said first circuit having a second subcircuit which includes said squaring circuit and a delay circuit and a rejection filter that coact to provide a second value corresponding to the contrast of said pigment; and said first circuit having a third subcircuit which combines the first said and said second values to develop said signal which is a measure of said latitude angle.

11. A color identification unit that comprises: a light source that can direct light onto a document; a light sensor that can receive light from said document; said light sensor developing an essentially DC signal in response to light received from the base material of said document and developing an essentially AC signal in response to light received from a colored area on said document, said essentially AC signal developed by said light sensor including information on the position of the pigment used in preparing said colored area with respect to the black end of the locus of achromatic light of a color solid; a first circuit that responds to signals developed by said light sensor to provide a signal which is a measure of the latitude angle of said pigment within said color solid; said first circuit having a subcircuit which determines a value corresponding to said position of said pigment along said achromatic locus; said first circuit having a second subcircuit which includes a squaring circuit and a delay circuit and a rejection filter that coact to provide a second value corresponding to the contrast of said pigment; said first circuit having a third subcircuit which combines the first said and said second values to develop said signal which is a measure of said latitude angle; said light from said light source being modulated at a predetermined frequency; and said delay circuit providing a time delay equal to one-half of a cycle of said predetermined frequency.

12. A color identification unit as claimed in claim 8 wherein said second circuit senses the phase of said AC signals developed by said light sensor.

13. A color identification unit that comprises: first means to determine the hue of a pigment on a document relative to the hue of the base material of said document; second means to determine the position of said pigment with respect to the black end of the locus of achromatic light of a color solid relative to the position of said base material of said document with respect to said black end of said locus of achromatic light of said color solid; third means to determine the saturation of said pigment relative to the saturation of said base material of said document; and fourth means responsive to the relative hue, the relative position along said achromatic locus, and the relative saturation of said pigment to identify said pigment.

14. A color identification unit that comprises: first means to determine the hue of a pigment on a document relative to the hue of the base material of said document; second means to determine the position of said pigment with respect to the black end of the locus of achromatic light of a color solid relative to the position of said base material of said document with respect to said black end of said locus of achromatic light of said color solid; third means to determine the saturation of said pigment relative to the saturation of said base material of said document; fourth means responsive to the relative hue, the relative position along said achromatic locus, and the relative saturation of said pigment to identify said pigment; and said first means including a circuit that senses the longitude angle of said pigment within said color solid by sensing zero crossings of signals developed by a light sensor as said light sensor ''''sees'''' said pigment.

15. A color identification unit that comprises: first means to determine the hue Of a pigment on a document relative to the hue of the base material of said document; second means to determine the position of said pigment with respect to the black end of the locus of achromatic light of a color solid relative to the position of said base material of said document with respect to said black end of said locus of achromatic light of said color solid; third means to determine the saturation of said pigment relative to the saturation of said base material of said document; fourth means responsive to the relative hue, the relative position along said achromatic locus, and the relative saturation of said pigment to identify said pigment; and said second means including a circuit which essentially filters out the AC components of the signals developed by a light sensor as said light sensor ''''sees'''' said pigment to provide essentially DC values corresponding to said position of said pigment along said achromatic locus.

16. A color identification unit as claimed in claim 13 wherein said third means includes a squaring circuit and a delay circuit and a rejection circuit that coact to provide a signal which is a measure of the contrast of said pigment.

17. A color identification unit as claimed in claim 13 wherein said first means includes a circuit that senses the longitude angle of said pigment within said color solid by sensing zero crossings of signals developed by a light sensor as said light sensor ''''sees'''' said pigment, wherein said second means includes a circuit which essentially filters out the AC components of the signals developed by a light sensor as said light sensor ''''sees'''' said pigment to provide essentially DC values corresponding to said position of said pigment along said achromatic locus, and wherein said third means includes a squaring circuit and a delay circuit and a rejection circuit that coact to provide a signal which is a measure of the contrast of said pigment.

18. A color identification unit as claimed in claim 13 wherein said document is scanned by a spot of light composed of a plurality of chromatically-different spots of light.

19. A color identification unit as claimed in claim 13 wherein said document is scanned by a spot of light composed of a plurality of chromatically-different spots of light and wherein the intensities of said chromatically-different spots of light are modulated.

20. A color identification unit that comprises: first means to determine the hue of a pigment on a document relative to the hue of the base material of said document; second means to determine the position of said pigment with respect to the black end of the locus of achromatic light of a color solid relative to the position of said base material of said document with respect to said black end of said locus of achromatic light of said color solid; third means to determine the saturation of said pigment relative to the saturation of said base material of said document; fourth means responsive to the relative hue, the relative position along said achromatic locus, and the relative saturation of said pigment to identify said pigment; said document being scanned by a spot of light composed of a plurality of chromatically-different spots of light; and the intensities of said chromatically-different spots of light being set to cause the light received from said base material to be essentially white.

21. A color identification unit that comprises: first means to determine the hue of a pigment on a document relative to the hue of the base material of said document; second means to determine the position of said pigment with respect to the black end of the locus of achromatic light of a color solid relative to the position of said base material of said document with respect to said black end of said locus of achromatic light of said color solid; third means to determine the saturation of said pigment relative to the saturation of said base material of said document; fourth means responsive to the relative hue, the relative position along said achromatic locus, and the relative saturation of said pigment to identify said pigment; said document being scanned by a spot of light composed of a plurality of chromatically-different spots of light; the intensities of said chromatically-different spots of light being adapted to cause the light received from said base material to develop a DC signal as long as said received light is essentially white light and to create a ripple on said DC signal whenever said received light is not essentially white; and a fifth means responding to said ripple to adjust the intensity of at least one of said chromatically-different spots of light.

22. A color identification unit which comprises: means to provide a plurality of individually-different colors of light; a light modulator which modulates the intensities of said individually-different colors of light; an optical system that directs said modulated colors of light toward a document to form a spot of light on said document; means providing relative movement between said spot of light and said document to cause said spot of light to ''''scan'''' portions of said document; a light sensor that receives light from the areas of said document which are successively illuminated by said spot of light and that responds to said light to develop waveforms; and means to sense the differences between the waveforms developed by said light sensor as it ''''sees'''' a colored area on said document and the waveforms developed by said light sensor as it ''''sees'''' the base material of said document.

23. A color identification unit which comprises: means to provide a plurality of individually-different colors of light; a light modulator which modulates the intensities of said individually-different colors of light; an optical system that directs said modulated colors of light toward a document to form a spot of light on said document; means providing relative movement between said spot of light and said document to cause said spot of light to ''''scan'''' portions of said document; a light sensor that receives light from the areas of said document which are successively illuminated by said spot of light and that responds to said light to develop waveforms; and means to sense the differences between the waveforms developed by said light sensor as it ''''sees'''' a colored area on said document and the waveforms developed by said light sensor as it ''''sees'''' the base material of said document; and said last-mentioned means including a low pass filter that effectively separates the DC components from the AC components of the waveforms developed by said light sensor.

24. A color identification unit as claimed in claim 22 wherein said individually-different colors of light include the basic components of white light so said light sensor will ''''see'''' essentially white light as it ''''sees'''' the base material of said document.

25. A color identification unit which comprises: means to provide a plurality of individually-different colors of light; a light modulator which modulates the intensities of said individually-different colors of light; an optical system that directs said modulated colors of light toward a document to form a spot of light on said document; means providing relative movement between said spot of light and said document to cause said spot of light to ''''scan'''' portions of said document; a light sensor that receives light from the areas of said document which are successively illuminated by said spot of light and that responds to said light to develop waveforms; means to sense the differences between the waveforms developed by said light sensor as it ''''sees'''' a colored area on said document and the waveforms developed by said light sensor as it ''''sees'''' the base material of said document; and said light modulator phase displacing the modulated light from said individually-different colors of light.

26. A color identification unit as claimed in claim 22 wherein said light modulator modulates the intensities of the light from said individually-different colors of light, wherein said light modulator phase displaces the modulated light from said individually-different colors of light, and wherein said color identification unit has a circuit which can be programmed to provide different phase displacements of the modulated light from said individually-different colors of light.

27. The method of identifying a pigment used in preparing a document that comprises: determining the longitude angle of said pigment within a color solid; determining the latitude angle of said pigment within said color solid; and using said longitude angle and said latitude angle to identify said pigment.

28. The method of identifying a pigment as claimed in claim 27 wherein an AC waveform is developed as said pigment is ''''seen,'''' wherein time periods are developed during which zero crossings corresponding to the longitude angles of predetermined pigments are expected to occur, and wherein the time period which is active as said AC waveform crosses zero in a predetermined direction is sensed to determine the longitude angle of said pigment.

29. The method of identifying a pigment that comprises: determining the longitude angle of said pigment within a color solid; determining the latitude angle of said pigment within said color solid; using said longitude angle and said latitude angle to identify said pigment; sensing the position of said pigment with respect to the black end of the achromatic locus of a color solid; sensing the saturation of said pigment; using said position of said pigment with respect to said black end of said locus of achromatic light of said color solid and said saturation to determine the contrast of said pigment; and using said position of said pigment with respect to said black end of said locus of achromatic light of said color solid and said contrast to determine the latitude angle of said pigment within said color solid.

30. The method of identifying a pigment that comprises: determining the longitude angle of said pigment within a color solid; determining the latitude angle of said pigment within said color solid; using said longitude angle and said latitude angle to identify said pigment; sensing the position of said pigment with respect to the black end of the locus of achromatic light of a color solid relative to the position of the base material of the document bearing said pigment with respect to said black end of said locus of achromatic light of said color solid; sensing the contrast of said pigment relative to the contrast of said base material; and using the relative positions of said pigment and of said base material along said achromatic locus and the relative contrast to determine the latitude angle of said pigment within said color solid.

31. A color identification unit as claimed in claim 8 wherein said light from said light source is modulated at a predetermined frequency, and wherein said second circuit includes means to sense the phase of said essentially AC signal developed by said light sensor relative to the modulation of said light at said predetermined frequency.

32. A color identification unit which comprises: a source of light; light-modulating means receiving light from said source of light and phase-displacing and amplitude-modulating said light; a document-receiving support mounted in the path of the phase-displaced, amplitude-modulated light from said light-modulating means; means providing relative movement between said document-receiving support and said phase-displaced, amplitude-modulated light to enable said phase-displaced, amplitude-modulated light to ''''scan'''' a document held by said document-receiving support; a light-sensor receiving light from said document held by said document-reciving support; a circuit connected to said light sensor to analyze information within the light from said document; and said phase-displaced, amplitude-modulated light from said light-modulating means being modified by light-absorbing pigments on said document.

33. A color identification unit which comprises: a source of light; light-modulating means receiving light from said source of light and phase-displacing and amplitude-modulating said light; a document receiving support mounted in the path of the phase-displaced, amplitude-modulated light from said light-modulating means; means providing relative movement between said document-receiving support and said phase-displaced amplitude-modulated light to enable said phase-displaced, amplitude-modulated light to ''''scan'''' a document held by said document-receiving support; a light-sensor receiving light from said document held by said document-receiving support; a circuit connected to said light sensor to analyze information within the light from said document; said phase-displaced, amplitude-modulated light from said light-modulating means being modified by light-absorbing pigments on said document; said source of light including three light sources; said light-modulating means including three light modulators; each of said light modulators being in register with one of said light sources; and filters interposed between said light sources and said light modulators.

34. A color identification unit which comprises: a source of light; light-modulating means receiving light from said source of light and phase-displacing and amplitude-modulating said light; a document-receiving support mounted in the path of the phase-displaced, amplitude-modulated light from said light-modulating means; means providing relative movement between said document-receiving support and said phase-displaced amplitude-modulated light to enable said phase-displaced, amplitude-modulated light to ''''scan'''' a document held by said document-receiving support; a light-sensor receiving light from said document held by said document-receiving support; a circuit connected to said light sensor to analyze information within the light from said document; said phase-displaced, amplitude-modulated light from said light-modulating means being modified by light-absorbing pigments on said document; said light sensor developing an AC waveform which has essentially the same frequency and the same phase as a component of said phase-displaced amplitude-modulated light whenever said light sensor ''''sees'''' the base material of said document held by said document-receiving support; and said circuit sensing shifts of said AC waveform as said light sensor ''''sees'''' a pigment of said document.