DE3876212T2 - METHOD AND DEVICE FOR DISPLAYING THREE-DIMENSIONAL COLOR DATA IN A ONE-DIMENSIONAL REFERENCE SYSTEM. - Google Patents

Description

The invention relates to the representation of color images on a computer screen and in particular to a method and a device for processing, storing and designating data corresponding to image colors according to the preamble of patent claim 1 or 2.

In many computer terminal systems, image color data is stored as R, G, B (red, green, blue) color component values in predetermined memory locations. Often, red values are stored in one group of memory locations, green values in another, and blue values in a third group. To select a color consisting of a color value from each of the groups, the user typically specifies a color number or index. The index, which corresponds to a single (one-dimensional) address, allows access to a specific set of RGB values corresponding to the selected color. One such prior art "single index" system is described, for example, in US-A-4,509,043, dated April 2, 1985.

Another type of prior art system is the "true color" system, which is intended to represent the true or actual colors of an object. One such true color system is described, for example, in "Model One/25 Programming Guide" published by Raster Technologies Corporation on December 12, 1983. In such a true color system, the user generally specifies the RGB color values themselves (instead of color numbers or indices) to represent a selected color. This "color value" approach corresponds to the true color system - a three-dimensional color naming system. The "color number" approach corresponds to the index color system - a one-dimensional color naming system.

True color systems are generally used to produce color-graded images, to represent images read by scanners, and to simulate physical phenomena such as colored light illuminating a scene consisting of colored objects. Index color systems are generally used to map the color of iconographic symbols, to represent scalar values, or to distinguish image segments (for example, such simple representations as points, lines, arcs, circles, rectangles, polygons, and text representations).

Often symbolic images specified in index colors are to be superimposed on shaded images specified in true colors. To achieve this, a system is needed that allows both true color and index color representation.

US-A-4,509,043 discloses an apparatus for representing three-component color data in a single index reference system, comprising processing means responsive to applied data representing color component information and memory means connected to the processing means. The known apparatus provides for independently displaying one of a plurality of images on a display and superimposing a plurality of images to produce a composite image. A color map, or color map, is constructed in the memory, which contains a plurality of brightness indices which determine the brightness of the image. Each of these indices is associated with one or more color indices. The bits associated with each pixel of the image are used as an index for the color map by locating the corresponding colors or gray indices.

The invention provides according to claims 1 and 2 a method and a device that can display both true color images and index color images. The user can specify either a color number to designate an index color or RGB color values to designate a true color.

Index color operations and true color operations are performed in an index color environment.

According to the invention, the apparatus for performing a true color operation in an index color environment calculates one-dimensional index-like data from three-dimensional true color data input by the user. The user specifies the number of color levels used to represent the range of representable red, green and blue colors and the RGB values of the colors to be represented. The apparatus derives true color data (RGB color level values) from the number of color levels specified by the user, stores the derived data in memory in a predetermined order suitable for reference by a single address or index, and derives a single address from the user-specified RGB values for reference to the stored data.

The device comprises a keyboard and connection to a host computer for entering index color data and true color data, a processing device connected to the keyboard and/or the host computer for generating index-like data from the true color data, a storage device for storing the input data and the data generated by the processing device, and a display device for displaying the stored data.

In the figures show:

Fig. 1 is a block diagram of a prior art system that can perform index color operations,

Fig. 2 is a block diagram of an arrangement of data in a memory of the system of Fig. 1,

Fig. 3 is a block diagram of a prior art system that can perform true color operations,

Fig. 4 is a block diagram of the device according to the invention for performing index color operation and true color operation in an index color environment,

Fig. 5 is a block diagram of a color image memory of the device of Fig. 4,

Fig. 6 a block diagram of the range of representable colors as a three-dimensional color coordinate space,

Fig. 7 is a block diagram of a concatenation mask used in the device of Fig. 4 and

Fig. 8 is a block diagram of multiple bit planes, a true color surface and a single index surface.

Fig. 1 shows a prior art system capable of performing index color operations. Fig. 2 shows a system color map memory, RGB data typically stored in memory, and a one-dimensional (single color index) address structure for referencing stored data. Fig. 3 shows a prior art three-dimensional address structure for referencing stored data. Based on the user-entered RGB values stored in the image memory, color values stored in three look-up tables (LUTs) are referenced. Fig. 2 shows a one-address (index) scheme, while Fig. 3 shows a three-address (true color) scheme.

Fig. 4 shows a true color single address scheme used by the Apparatus according to the invention is used. As with the prior art system described in US-A-4,509,043, the apparatus according to the invention can perform index color operations. Unlike prior art systems, the apparatus can perform true color operations in an index color environment.

The device comprises a keyboard 10 and a connection to a host computer for entering index color data and true color data, a processing device 11 connected to the keyboard and/or the host computer for generating index-like data from the true color data, a storage device 13 for storing the input data and the data generated by the processing device, and a display device 15 for displaying the stored data.

The processing device 11 comprises a microprocessor 12 having a ROM (read only memory, not shown) with a program stored therein, and a vector generator 18. The storage device 13 comprises a memory 14 for storing index information, an image display memory 20 and a color image memory 22. The display device 15 comprises an image timing and control circuit 16, a CTR (cathode ray tube) display with an associated deflection circuit and a digital-to-analog converter.

The apparatus of the present invention is similar to the system for performing indexing operations described in US-A-4,509,043, and the description of that system also applies to the present apparatus. However, in performing true color operations in such an indexing environment, the processor and color map memory of the present apparatus operate differently from that system, as described below.

Fig. 5 shows the color image memory 22 of the present Device in further detail. As in the prior art, the RGB values in memory are arranged in a table format, with each memory location containing a set of R, G and B values addressable by a single address. Unlike the prior art, the RGB values in the tables are calculated (derived) by the device from data input to the device. The calculation is performed by the processor 12 under the control of the stored program. (Examples of this stored program are given in Appendices A and B.) Also unlike the prior art, the single address used to refer to the RGB values in the table is derived by the device's processor 12 from RGB values specified by the user. Thus, according to the invention, both the RGB table values and the single address for referring to the RGB table values are derived by the device.

The first user of the device (e.g., the device supplier) specifies the RGB color values that are to constitute the table by uniformly quantizing the closed interval from zero to one for each color. For example, the user may specify the number of representable levels as Q (i.e., Q are discrete quantization levels of representable red, green, and blue primary colors). The device then computes the actual table entries (i.e., the true-color RGB values that produce the original user-specified values when subsequently referenced by a single index-like address).

As shown in Table 1, a set of representable primary color levels where the number (Q) of quantization levels is 5 can be as follows: TABLE I Quantization level representable primary color levels

The five quantization levels cover the range from 0% to 100% of the displayable red, green and blue primary colors.

As shown in Fig. 6, the range of representable colors can be seen as a three-dimensional color space, where (0, 0, 0) represents black, i.e., 0% red, 0% green, and 0% blue, (1, 0, 0) represents 100% red, (0, 1, 0) represents 100% green, (0, 0, 1) represents 100% blue, and (1, 1, 1) represents white, i.e., 100% red, 100% green, and 100% blue.

As shown in Fig. 6, the user of the device

Q1 Level Red,

Q2 level green and

Q3 Level Blue,

select when a true color object is to be displayed within the limits of the displayable colors of the device. From the displayable levels specified by the user, the device derives (calculates) appropriate color values for single index reference (single addressing) and stores the derived values in tables in memory for later use.

The device calculates the color values (table entries) and fills the RGB tables as follows

Red (address) = i/(Q₁ - 1)

Green (address) = j/(Q₂ - 1)

Blue (address) = k/(Q₃ - 1),

where

Q�1 corresponds to the number of quantization levels specified for red,

Q₂ corresponds to the number of quantization levels specified for green,

Q₃ corresponds to the number of quantization levels specified for blue,

the quantization level i = 0 to Q₁ - 1,

the quantization level j = 0 to Q₂ - 1,

the quantization level k = 0 to Q₃ - 1,

Address = i + Q�1; j + Q&sub1;Q2; s,

n the number of allowed table entries corresponds

and (Q₁ . Q₂ Q₃) < n

or Q₁ Q₂ Q₃ < 2m, where m corresponds to the number of bit planes, as shown for example in Figures 2 and 8.

The following RGB tables show color data generated (derived) by processor 12 in response to user-specified quantization levels. Processor 12 stores the derived data in memory 22 in a predetermined sequence (arrangement) as shown in Table 2. TABLE II specified color values derived single address derived and stored color data

The order in which the data is stored in memory 22 ensures that the processor derives from the RGB values specified by the user the appropriate index (individual address) to reference the correct RGB values in memory 22. The processor derives each individual address (index) using the following formula:

Index = [R (Q₁ - 1)] rounded + Q₁ [G (Q₂ - 1)] rounded + Q₁ Q2; [B (Q₃ - 1)] rounded.

Thus, as shown in Table I, the processor 12 would derive address 86 from the user-specified three-dimensional true color value (0.25; 0.5; 0.75) so that the correct RGB value in the table could be accessed.

An alternative formula for deriving individual addresses (indices) from the specified (input) RGB values is:

[RQ₁] cut off + Q₁ [G Q₂] cut off + Q₁ Q₂ [B Q₃] cut off

where 0 ≤ R < 1; 0 ≤ G < 1; 0 ≤ B < 1

and Q₁, Q₂, Q₃ are powers of 2.

If B1 bits are given for red, B2 bits for green and B3 bits for blue, and if an m-bit plane surface is given, for example as shown in Fig. 8, where m = b1 + b2 + b3 and b1 ≤ B1, b2 ≤ B2 and b3 ≤ B3, then the above-mentioned rounding operation can be performed as shown in Fig. 7, where the b1 most significant bits (MSB) of the R field and the b2 MSB of the G field and the b3 MSB of the B field are concatenated and shifted to align them with the m-bit plane surface.

Up to this point, the process for converting true color data into single index data has been described. This process includes the following steps: Deriving true color data (ie, RGB color level values) from the number of color levels specified by the user, storing the derived data in memory in a predetermined arrangement suitable for reference by a single address or index, and deriving a single address from user-entered RGB color values to reference the stored address.

Appendix A shows RGB values and associated single index addresses derived for:

Q�1 = 5 red levels,

Q₂ = 5 green levels,

Q₃ = 5 blue levels,

where the RGB values in the range of 0 to 255 correspond to 0% to 100%.

Appendix B shows RGB values and associated single index addresses derived for:

Q�1 = 7 red levels,

Q₂ = 6 green levels,

Q₃ = 5 blue levels,

where the RGB values in the range of 0 to 255 correspond to 0% to 100%.

Appendix C shows index and true color data (stored in binary form in color map memory 22) for both a single index surface (Surface 1) and a true color surface (Surface 2). For example, at the address "00 01 10 11" shown in Appendix C and Figure 8, "00" corresponds to a color index for Surface 1 and "01 10 11" corresponds to RGB color values for Surface 2. The address was calculated (derived) from index and true color values entered by the user. The address is used to designate the RGB values "01010101 10101010 11111111" is used.

Depending on which surface has priority over the other, the RGB values may differ from a given address. For example, suppose the calculated address is "01 11 11 11", if the RGB values "10000000 10000000 10000000" were designated to represent the color index "01", and the RGB values "11111111 11111111 11111111" were designated to represent the RGB color level "11 11 11", then the RGB values "10000000 10000000 10000000" would be used if the index color surface had priority, and the RGB values "11111111 11111111 11111111" would be used if the true color surface had priority. APPENDIX A (Program Listing/Data/Comments) /*Global Type and Data Definitions*/ /*The following test program calls the "Populate" and "Convert" functions and prints their results for some example cases.*/ /*Populate.C - Example of colormap mapping function. This function calculates "surface colormap" (as per Mossaides) data to simulate true color and stores the data in a main memory array of RGB values. The array position is passed to this function as an argument. This function is called in response to a user command to create a "true color surface". After this function is called, the array can be copied into the hardware colormap or combined with other "surface colormaps" as per Mossaides and the combined map is copied into the hardware colormap. The hardware colormap is assumed to contain 8 bits for both red and green and blue entries at each address. Note that the address calculation shown above is just an example; another equivalent example could have the address = i q₂ q₃ + j q₃ + k; other addresses are possible. The only condition is that the same rule is used to calculate the address in this function and to calculate the index in the "Convert" function.*/ /*Convert. C - This function takes three real numbers R, G and B (range 0.0 to 1.0) that correspond to the color of a pixel and produces a single color index to be stored at the pixel's location in the frame buffer. This function is used during the drawing of image segments in a frame buffer.*/ APPENDIX B (Program Listing/Data/Comments) /*Global Type and Data Definitions*/ /*The following test program calls the "Populate" and "Convert" functions and prints their results for some example cases.*/ /*Populate. C - Example colormap populating function. This function calculates "surface colormap" (as per Mossaides) data to simulate true color and stores the data in a main memory array of RGB values. The array position is passed to this function as an argument. This function is called in response to a user command to create a "true color surface". After this function is called, the array can be copied into the hardware colormap or combined with other "surface colormaps" as per Mossaides and the combined map is copied into the hardware colormap. The hardware colormap is assumed to contain 8 bits for both red and green and blue entries at each address. Note that the address calculation shown above is merely an example; another equivalent example could have the address = i q₁ j + q₁ q₂ k; other addresses are possible. The only condition is that the same rule is used to calculate the address in this function and to calculate the index in the "Convert" function.*/ /*Convert. C - This function takes three real numbers R, G and B (range 0.0 to 1.0) that correspond to the color of a pixel and produces a single color index to be stored at the pixel's location in the frame buffer. This function is used during the drawing of image segments in a frame buffer.*/ APPENDIX C (Program Listing/Data/Comments) The example shows a true color surface and an index color surface John C. Darrymple 10/21/1987 Assume that the index surface is in bit planes 7 and 6 and the true color surface is in bit planes 5 to 0, with planes 5 and 4 being for red, 3 and 2 for green, and 1 and 0 for blue. Also assume that 3 bits per primary color (R, G, or B) are provided in the data fields of the hardware color map, where the bits correspond to fractional values and 00000000 represents "0" and 11111111 "1". For this example, assume that the index surface color map has been set by the user as follows:

Claims (6)

1. Method for representing multidimensional data values in a one-dimensional memory addressing system, with the following method steps: - forming multidimensional data values calculated from user-specific numbers of data levels (Q₁, Q₂, Q₃), each user-specific number representing the number of data values in one dimension, - storing the multi-dimensional data values in a memory (13) in a predetermined order suitable for reference by a one-dimensional address, and - Forming the one-dimensional address calculated from a user-specific multi-dimensional data value, whereby this one-dimensional address can refer to multi-dimensional data values stored in the memory that correspond to the user-specific multi-dimensional data value. 2. Device for carrying out a method according to Claim 1, comprising: - processing means (11) responsive to applied data for forming three-component colour data (RGB) and individual index addresses for reference to said three-component colour data, wherein said three-component colour data are formed from applied colour plane data (Q₁, Q₂, Q₃) and said individual index addresses are formed from applied colour component data, said colour component data components of a selected color and the color plane data represents a number of color planes per color component, and storage means (13) connected to the processing means (11) for storing the three-component color data in an order in which the individual index addresses can refer to three-component color data corresponding to the components of the selected color. 3. Device according to claim 2, with an input device (10) for supplying the applied data to the processing device. 4. Device according to claim 3, wherein the input device (10) has at least one keyboard and/or a connection to a host computer. 5. Apparatus according to claim 4, wherein the processing means (11) has a stored program for forming single index addresses and three-component color data. 6. Apparatus according to claim 5, comprising display means (15) for displaying color corresponding to the three-component color data specified by the single index address formed from the selected color.