GB2032740A

GB2032740A - Programmable color mapping

Info

Publication number: GB2032740A
Application number: GB7930441A
Authority: GB
Original assignee: Tektronix Inc
Current assignee: Tektronix Inc
Priority date: 1978-10-16
Filing date: 1979-09-03
Publication date: 1980-05-08
Also published as: DE2941841A1; NL7907101A; FR2439431A1; JPS5598782A

Abstract

A circuit and method of operation for selectively mapping a first digital signal representative of an image to be produced into a second digital signal representative of the color quality of said image in terms of hue, saturation, and lightness. The eight possible 3-bit pixel signals which can occur in a raster line of image data read from memory 20 via register 23 are each mapped into a 6-bit signal selected from the 64 possible via conversion code stored in a PAM in colour map unit 24. The 6-bit signal controls the displayed picture element according e.g. to a bit pair for each colour gun in CRT 30, as in Fig. 3A. A method is also disclosed for using such a mapping circuit to select a particular image to be formed from a group containing a mutually independent plurality of such images. <IMAGE>

Description

SPECIFICATION Programmable color map BACKGROUND OF THE INVENTION The subject matter of the present invention pertains to color display systems, and especially to such systems that are capable of producing both alphanumeric and graphic type display presentations.

In known prior art color display systems, for example the system disclosed in Hayashi et al U.S. Patent No. 3,771,155, the various colors in which information may be displayed are formed by combining predetermied fixed quantities of the three primary colors, red, green, and blue. This is accomplished most often by the use of a three-gun color cathoderay tube (CRT), the guns of which are selectively activatable to produce electron beams of fixed predetermined density. These beams, in turn, activate associated phosphors on the faceplate of the CRT to produce in a conventional manner the multicolored display presentation.

A particular disadvantage of known prior art color display systems is that the colors forming the display presentation are selectable in terms of hue, or color, only. In other words, the red, green, and blue electron guns are either fully on or fully off depending on their selection, and the colors produced thereby are either present in their full intensities or absent completely. This inability to select colors in terms other than hue severely limits the intelligibility of the display presentation, especially when the information contained therein is overly crowded.

Accordingly, there exists a need for a color display system capable of generating a color display in colors characterized by dimensions other than hue alone.

SUMMARY OF THE INVENTION The present invention is directed to a color display system capable of producing a color presentation wherein the colors may be selected according to the dimensions of hue, saturation, and lightness. More particularly, the present invention comprises a color mapping circuit and method of operation of mapping an ambit digital color code in to any 2m of 2 possible bit digital color codes and then converting such bit codes into analog color signals of varying magnitudes for use in controlling the density of the electron beams produced by the electron guns in a conventional three-gun color cathode-ray tube.

As used herein, the terms "hue," "lightness," and "saturation" are understood to have their standard dictionary definitions; that is, "hue" means the attribute of colors that permits them to be classified as red, green, blue, or an intermediate between any contiguous pair of these colors, "saturation" means the degree of difference from the gray having the same lightness, and "lightness" means the attribute of colors by which an object appears to reflect or transmit more or less of the incident light. A method of selecting an image to be formed is also disclosed whereby the color mapping circuit is employed to select any of a predetermined number of mutually exclusive display presentations.

It is, therefore, a principal objective of the present invention to provide a system for producing a color display wherein colors may be selected in terms of their hue, saturation, and lightnèss.

It is an additional principal objective of the present invention to provide a method for producin a color display wherein colors are presented in terms of their hue, saturation, and lightness.

It is a further objective of the present invention to provide a display system permitting the ready selection of any of a predetermined number of mutually exclusive display presentations.

The foregoing objectives, features, and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a logic-level diagram of a color display system incorporating the color mapping circuit of the present invention.

Figure 2 is a conceptual diagram of a threeplane memory cell.

Figure 3 is an exemplary address table and memory map for the color map module of the color mapping circuit of Fig. 1.

Figure 4 is a conceptual diagram of a second three-plane memory cell.

Figure 5 is an address table and three alternate memory maps for the color map module of the color mapping circuit of Fig. 1.

DESCRIPTION OF THE PREFERRED EMBODI MENT Referring to Fig. 1, there is shown a color display system incorporating the color map circuit of the present invention. As disclosed in the figure, the color map circuit 10, enclosed within the dashed line 12, comprises a digital register 22, a color map module 24, s axis circuitry 26, and a map control circuit 28, and the color display system includes, besides the color map circuit 10, an associated memory module 20, a cathode-ray tube type display device 30, a display controller 32, a processor 34, an input output (I/O) device 36 and a system control device 38 interconnected as indicated. Omitted from the figure for clarity are those other conventional circuits, such as power supplies and the like, necessary to form an operable system.

The memory module 20 may be any suitable random access memory device capable of receiving and storing alphanumeric and graphic information in digital form and transmitting such information to the register 22 on command of the processor 34. In one embodiment of the disclosed circuit, a read-only memory (ROM) module is employed to store standard alphanumeric information and a random-access memory (RAM) module is employed to store computer or processor generated graphics information.

The color map module 24 maybe any suitable random access memory device capable of providing the requisite number of input and output terminals. In the description that follows, the color map module 24 will be considered to comprise an 8 by 6 random access memory module having three input address terminals 23 and six output data terminals 25. Other suitable configurations may also be employed without departing from the invention as disclosed.

Configured as indicated in Fig. 1, the color mapping circuit 10 of the present invention is capable of receiving a 3-bit data word representative of an image to be formed on the faceplate 40 of the display device 30, and mapping the data word into any of eight 6-bit data words preselected from a group of 64 possible 6-bit data words representative of the color quantity of the image defined in terms of the three dimensions of hue, saturation, and lightness. In a particular instrument within which the color mapping circuit 10 of Fig. 1 has been incorporated, alphanumeric and graphic information is stored in memory in the form of cells comprising conceptually 14 rows of 8-bit words each of which is three bits, or planes, deep. Such a cell is shown in Fig. 2 of the drawings with the three planes of the cell labeled P.2, P.1, and P.O, respectively.Each 3-bit word comprising the bit from each plane P.O-P.2 defining a single cell location will be referred to hereinafter as a pixel with the understanding that each pixel defines a specific quantity of information that is displayable on the screen 40 of the display device 30.

In a conventional color display system, the 3-bit word of each pixel is employed to define the color characteristics of its corresponding information point in terms of hue, only; that is, in terms of the basic combinations of the three primary colors, red, green, and blue, with each primary color being either present in its full intensity or absent completely. In the circuit of the present invention, the three bits are used to define a color map address (CMA) which is employed to generate a 6-bit color map number (CMN) defining the color characteristics of the datum point in the full three dimensions of hue, saturation, and lightness; that is, in terms of variable color intensity as well as presence.Such a color map 32 740address 50 is shown in Fig. 1 as existing at the three input address terminals 23 of the color map module 24 and such a color map number 52 is shown as existing at the six output data terminals 25.

The operation of the color map circuit 10 of Fig. 1, and the method of the present invention, will best be understood with reference to a specific bit map configuration for the color map module 24. Such a bit map configuration is shown in Fig. 3 where a different one of the 64 possible color map numbers has been assigned to each of the eight possible combinations of the color map address. For ease of understanding, the three bits of the color map address are labeled A.2, A.1, and A.O, respectively, and the six bits of the color map number are labeled in pairs to indicate their relationship to the primary colors, with RR = red, GG = green, and BB = blue.Each digital value represented by the two bits of a particular bit-pair of the color map number defies the intensity of its associated color (00 = zero intensity, 01 = 1/3 intensity, 10 = 2/3 intensity, and 11 = full intensity).

As indicated earlier, the 6-bit color map numbers produceable by the color map module 24 may assume any of 64 possible forms, only eight of which may be selected with a 3-bit color map address. (In general, of course, assuming a 2"-by-n color module, an ambit color map address may be used to select any 2m of 2" possible orbit color map numbers.) The preselected color map numbers are loaded into the color map module 24 in a conventional manner via the processor 34 and the map control circuit 28, and may be changed at any time to provide program or operator control of the color mapping process.

During operation, the system of Fig. 1 generates a diplay on the screen 40 of the display device 30 in a raster-line-by-raster-line manner by assembling in a buffer memory, located for example in the memory module 20, a full line of selected memory cells and then streaming each row of each cell line to the display device 28 in a pixel-oriented serial fashion. As indicated earlier,each pixel is three bits deep and all three bits are transferred from the memory module 20, through the register 22, to the color map module 24 at the same time to form the color map address 50. Assuming for the moment that each plane of the cell shown in Fig. 2 contains data relating to the same information; that is, the letter E indicated by the small x's and the diagonal graphic line indicated by the small +'s, the color map address associated with the upper right hand pixel 60 will be 000, and, according to the bit map of Fig. 3, will be transformed by the color map module 24 into a 6-bit color map number containing all O's to indicate that the particular point on the faceplate 40 of the CRT device 28 corresponding to the pixel 60 should be nonillumi nated or black. The color value of the 6-bit color map number will be so interpreted by the taxis circuitry 26 with the result that none of the three color guns within the cathode ray tube of the display device 28 will be activated.

As indicated by the diagram of Fig. 3A, each digital value of each color map number bit-pair is converted by the z-axis circuitry 26 in a conventional manner into an analog signal the magnitude of which corresponds to the digital value. The analog signal is employed, in turn, to control the density of the respective electron beam generated within the display device 30 to produce a given display presentation. Although only the RR (red) bitpair and the corresponding R analog signal are shown in Fig. 3A, it is understood that a similar relationship exists between the bitpairs GG and BB and the analog signals G and B, respectively.

Consider now pixel 62. Its color map address will be 101 and its color map number, again according to the example of Fig. 3, will be 001100 which will result in the generation of a full intensity green spot at the point on the faceplate 40 represented by the pixel. As a last example, pixel 64 of the data cell of Fig. 2 will have a color map address of 110 producing a color number having a value of 010101 and causing the generation on faceplate 40 of a white spot of 1/3 intensity.

Thus, the information depicted in the cell of Fig. 2 will result in the generation by the display device 30 of a full intensity green letter E superimposed over a 1/3 intensity white diagonal line, the colors being defined by the digital values of the preselected color map numbers. As will be apparent to those persons familiar with the art, other configurations of the color map module 24 may be employed to cause the information contained in the cell of Fig. 2 to be displayed in any 64 possible combinations of hue, saturation, and lightness.

A significant feature of the color map circuit 10 of the present invention is that it may also be employed to select, under program control, any of three mutually independent images to be formed. Since, as indicated earlier, each pixel is three bits deep, each display presentation formed from a plurality of such pixels is also three bits, or planes, deep. Normally, the three-bit depth of a particular presentation is employed as described earlier to generate a multicolored display; however, it is also possible, by selective programming of the color map module 24, to use the thFee-bit depth of each cell to define three mutually independent planes of information each of which may be selected independently for presentation.

The use of this plane-selecting capability of the color mapping circuit of the present invention might also be best described by way of an example. Referring to Fig. 4, there are shown three planes 70, 72, and 74 of a simplified four-row-by-three-pixel memory cell.

Although the three planes 70-74 are shown in a side-by-side manner, they exist conceptually as parts of a single cell such as that described above with reference to Fig. 2.

Interpreting the small x's in Fig. 4 as positive data bits, the information contained in plane 74 of the simplified cell may be interpreted as the letter "C", and that contained in planes 72 and 70 as the letters "I" and "L", respectively. Assuming as before that the bits of plane 74, 72, and 70 form bits 2, 1, and 0, respectively, of each pixel, and therefore of each color map address word, the color map address for the upper left hand pixel 80 is seen to be 101, that for the upper middle pixel 82, 110, and that for the upper right hand pixel 84, 1 00. If the color map module 24 is configured, for example, according to the color map 90 of Fig. 5, each color map address with a O in bit position 2 will produce a color map number containing all O's, and each color map address with a 1 in bit position 2 will produce a color map number of all 1 's. Thus, only the bits contained in plane 74 of the cell of Fig. 4 will affect the color guns of the display device 30. Therefore, the presentation produced will be the full intensity white letter "C".

If the color map module 24 is now reconfigured according to color map 92 of Fig. 5, each color map address with a bit set in bit position 1 will produce a color map number of all 111100, with the other color map addresses producing color map numbers of all O's, and the result is that only a yellow letter "I" will be displayed. Similarly, when the color map module 24 is configured according to the color map 94 of Fig. 5, only a green letter "L" will be displayed. It is to be understood, that although the bit maps 90, 92, and 94 of Fig. 5 have been configured to produce only full intensity white, yellow, and green displays, presentations in other hues and intensities can also be selected as described earlier.

The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.

Claims

1. A color mapping circuit comprising: (a) means for receiving a first digital signal representative of an image to be produced; (b) means for selectively mapping said first digital signal into a second digital signal representative of the color quality of said image in preselected terms of hue, saturation, and lightness; and (c) means for converting said second signal into a visual presentation of said image in colors defined by said preselected terms of hue, saturation, and lightness.

2. The color mapping circuit of claim 1 wherein said first digital signal comprises m digital bits and said second digital signal comprises n digital bits, with n greater than m, and wherein said mapping means includes means for mapping the m bits of said first signal into any 2m of 2" possible combinations of the n bits of said second signal.

3. The color mapping circuit of claim 2 wherein said converting means includes means for converting a selected bit-pair of said second digital signal into an analog signal having a magnitude corresponding to the digital value of said bit-pair, and means responsive to said analog signal for controlling the intensity of a preselected color component of said visual presentation.

4. The color mapping circuit of claim 2 or 3 wherein m= 3 and n= 6.

5. The color mapping circuit of claim 2 wherein said mapping means includes a random access memory module having m input address terminals and n output data terminals.

6. In an improved color display system of the type including means for producing a digital signal representative of the hue characteristics of an image to be produced and means for converting said digital signal into a visual presentation of said image in colors defined by said hue characteristics, the improvement comprising: (a) means interposed operably between said producing means and said converting means for mapping said digital signal into a second digital signal representative of the color quality of said image in preselected terms of hue, saturation, and lightness; and (b) means within said converting means for converting said second signal into a visual presentation of said image in colors defined by said preselected terms of hue, saturation, and lightness.

7. A method of producing a color image in a color display system, said method comprising the steps of: (a) receiving a first digital signal representative of an image to be produced; (b) selectively mapping said first digital signal into a second digital signal representative of the color quality of said image in preselected terms of hue, saturation, and lightness; and (c) converting said second signal into a visual presentation of said image in colors defined by said preselected terms of hue, saturation, and lightness.

8. The method of claim 7 wherein said digital signal comprises digital bits and said second digital signal comprises n digital bits, with n greater than m, and wherein said step (b) includes mapping the m bits of said first signal into any 2m of 2" possible combinations of the n bits of said second signal.

9. The method of claim 8 wherein said step (c) includes the steps of converting a selected bit-pair of said second digital signal into an analog signal having a magnitude corresponding to the digital value of said bitpair and thereafter using said analog signal to control the density of an electron beam produced within a color display system, said density of said beam defining the intensity of a preselected color component of said visual presentation.

1 0. The method of claim 8 or 9 wherein hand n= 6.

11. A method of selecting an image to be formed in a color display system, said method comprises the steps of: (a) receiving a first digital signal representative of a plurality of images to be formed; (b) selectively mapping said first digital signal into a second digital signal representative of a preselected one of said images, said second digital signal defining the color quality of said preselected image in terms of hue, saturation, and lightness; and (c) converting said second signal into a visual presentation of said preselected image in colors defined by said terms of hue, lightness, and saturation.

1 2. A color mapping circuit substantially as hereinbefore described with reference to the accompanying drawings.

1 3. A color display system substantially as hereinbefore described with reference to the accompanying drawings.

14. A method of producing a color image in a color display system substantially as hereinbefore described with reference to the accompanying drawings.

1 5. A method of selecting an image to be formed in a color display system, substantially as hereinbefore described with reference to the accompanying drawings.