JP3292960B2 - Circuit for translating pixel data stored in a frame buffer into pixel data to be displayed on an output display of a computer device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output display device, and more particularly to an integrated device for supplying color pixel data to an output display device.

[0002]

2. Description of the Related Art A typical computer system generates data to be displayed on an output display. This output display is typically a cathode ray tube that sequentially produces a complete screen image in which the screen displays such movements as fast as the viewer can see when the program being displayed produces certain movements. is there. Data can be sequentially written to a frame buffer to produce individual images (frames) that are displayed sequentially. The frame buffer stores information about each location on the display. The location can be illuminated (each pixel) to produce a full screen image. For example, one display device has about 100
Pixels can be displayed using about 1000 horizontal rows of 0 pixels. All of that information in each frame is written to the frame buffer before being scanned by the display.

[0003] Data describing the entire picture resides in the frame buffer. The frame can be transferred to a display device. Typically, data goes from the frame buffer to the display pixel by pixel and line by line, starting from the upper left corner of the display and moving line by line from left to right horizontally to the lower right corner of the display. In order for the picture to appear continuously on the output display, the frames in the frame buffer must be constantly scanned at a rate of 30 frames per second or more.

[0004] Data can be stored for individual pixels in several forms. In the simplest form,
The pixels presented to the display can be one color or another color, typically white and black. Since there are only two states, this display form is one of the pixel data.
It can be implemented using only one bit of data to indicate one color or another. Pixel data can also be stored in several gray tones that vary from white to black. In a grayscale representation, several bits are used to represent each pixel. The number of bits must be sufficient to provide the required number of shades. For example, 5 types of 32 shades can be represented.

[0005] Color display devices can use 8 bits, 12 bits, 24 bits or other numbers to represent the color information of each pixel. However, there are basically two acceptable ways to present colors on an output display. First
In the method, the available pixels are divided into three pixels, each representing a red, green, or blue shade. For example, 2
When 4 bits of data are used, the device typically uses 8 of those bits to represent the red shading and 8 of those bits to represent the green shading. Typically used, eight of those bits are typically used to represent blue shading. Each of those shades can vary from transparent to fully saturated. The three values of red shading, green shading and blue shading can be combined in a manner well known to those skilled in the art to produce the final color. Of course, a color device could use a smaller number of bits to represent each shade and have a smaller number of shades of each color.

[0006] Alternatively, color devices can be based on color indexing. In the color indexing device,
The bits allocated to define a pixel are color
Used as code to look up a particular color in a look-up table (color index map). With such a device, called a color indexing device, the selection is made.
With a very large number of specific colors to choose from,
For example, a 24-bit color can be used . One particularly desirable feature of the color indexing device is that different colors can be provided for different programs simply by changing the color values stored in the color map.

[0007] However, to change the color in the color index map requires that written into the map. The writing must be done so as not to interfere with the presentation of the information on the output display. The method used in many devices is relatively slow, and may not produce optimal results, especially if the color index is changed frequently. This often meant that the sign interference was simply accepted.

In general, 24-bit colors are more realistic and more desirable. However, this requires a large amount of frame buffer memory. Therefore, more application programs are written for the color indexing device. In order to use these programs, a computer device configured for 24-bit color must also be provided to translate the color index values. Typically, if a computer device could operate with a program that utilizes a different type of color display technology, the device did so by adding hardware as a separate circuit configuration to each different technology. As such, such circuitry tends to be very complex, as it requires handling pixels encoded in different formats in the same frame buffer. Typically, those circuit elements appear as parts of a separate integrated circuit, wherein the individual functions are often duplicated. Such dual incorporation of functions increases the cost of the computer device, slows down the operation of the device, and is generally detrimental to the operation of the entire device.

One of the desirable features of modern color devices has been the ability to display video information in real time in a window on an output display device. As with devices utilizing different types of color devices, the hardware for presenting the video in the window of the output display device typically appears as individual integrated circuits or circuits that are added to already designed devices. This method of adding features adds circuit elements and is typically a waste of resources.

[0010]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an integrated device which allows various color formats to be presented on an output display. Another object of the present invention is to provide an integrated device that allows the color map to be changed without disturbing the display on the output display. Still another object of the present invention is to provide a video signal to an output display device, which can be used to supply a signal used for separate video display from a frame buffer, and to display a pixel on the output display device. It is to get an integrated device to control.

[0011]

SUMMARY OF THE INVENTION These and other objects of the present invention are directed to a plurality of colors for providing a first set of shaded digital values in response to a color index value provided by a frame buffer. Pixel data to be displayed on an output display of a computer device comprising an index map and a plurality of gamma correction maps for providing a second set of digital shade values in response to the first set of digital shade values. Is realized in a circuit for translating.

Notation and Terminology The following detailed description is primarily directed to symbolic representations of operations on data bits within a computer memory. These descriptions and representations are used by experts in the field of data processing to most effectively communicate their work to other experts in the same field. These operations and expressions require physical handling of physical quantities. Usually, but not necessarily, their amounts are stored, transferred, combined,
Takes the form of electrical or magnetic signals that can be compared and otherwise processed. At times, it has proven convenient to refer to those signals as bits, values, elements, symbols, objects, characters, terms, numbers, or the like, primarily because they are commonly used. However, all such terms and similar terms should be related to the appropriate physical quantities,
It should be remembered that it is just a label applied to those quantities.

Further, the manipulations performed are often referred to in terms, such as adding or comparing, which are commonly associated with mental activities performed by humans. In any of the operations described herein that form part of the present invention, such human capabilities are unnecessary or undesirable in most cases. The operation is a machine operation. Useful machines for performing the operations of the present invention include general purpose digital computers or other similar devices. In every case, it should be remembered that the method operation in operating a computer is different from the method of calculation itself. The present invention relates to a method of operating a computer in the processing of electrical or other (eg, mechanical, chemical) physical signals to generate other desired physical signals.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a functional block diagram of a circuit of an output display device 10 constructed according to the present invention is shown in FIG.
See This circuit 10 is used to send pixel data to an output display. Circuit 10 includes an address mode selector circuit 12. In the present invention, this address mode selector circuit 12 controls the translation of the various color modes to be displayed and allows the video signal to be placed on the output display for use in peripheral devices. To be able to retrieve the video signal from the data stored in the frame buffer (not shown).

The circuit 12 receives the pixel data (P_DATA) from the frame buffer. This data can be one of two color modes. In the preferred embodiment, the modes are a 24-bit color mode and a 12-bit color mode. In the 24-bit color mode, the data stored in the frame buffer and defining each pixel represents the color by three individual 8-bit values. Each of those values defines a shade of red, green or blue. Those shades are combined into another of the three values to produce the final color pixel value. The eight bits defining red indicate the amount of any of the final colors from zero to fully saturated red. The eight bits representing green and blue represent their colors in a similar manner. In the 24-bit color mode, about 16 million kinds of colors can be expressed and displayed on the output display device. However, to use the 24-bit color mode, at least a full 24 bits must be stored in the frame buffer in order to display each pixel on the output display. The frame buffer memory is typically a two-port video random access memory, which is very expensive.

On the other hand, the indexed color mode is about 1
Provides a sufficiently small number of colors selected from the same 6 million total spectra. In the preferred embodiment, one of the data is selected so that only 4096 colors can be selected at a time.
Only two bits are used. In fact, the index is 2
A code used to select a particular one of all the colors available on a 4-bit color device. However, values encoded with 12 bits must be decoded to provide the correct 24-bit color to be displayed on the output display. The use of indexed color modes allows for fewer bits of data to be stored, and therefore, smaller frame buffer space. Therefore, cheaper devices tend to use color indexing, and many programs are written for this color format.

In order for a 24-bit color device to execute the indexed program, the color index values must be able to be decoded. To perform this decoding of the color represented by the color index value, the apparatus of the present invention
The color index value supplied to an arbitrary pixel is sent to three color map circuits 14, 15, and 16. Assuming that the mode of operation indicates that the data is color index data, each of the three color maps 14, 15, 16 looks for the value stored at the location indicated by the encoded index. , 8 bit colors.
Each 8-bit output signal defines one of three shaded representations (red / green / blue) of a 24-bit color. Thus, for example, color map circuit 14 receives the index value and looks for that value to provide an 8-bit output indicating the value of the red shade in the final 24-bit color. Color map circuit 15, 1
6 operates similarly to provide output data indicating the shades of green and blue in the final color for each pixel receiving the index value.

To enable the index value stored in the frame buffer and supplied to the address mode selection circuit 12 to be a color index value rather than a 24-bit color value, a pixel mode signal P_
MODE is supplied to the address mode selector circuit 12 together with each pixel value. The pixel mode signal can be 1 bit,
One condition indicates one color format and another condition indicates another format. In this way, pixel values encoded in the 24-bit color format and the 12-bit color index format can be simultaneously stored in the frame buffer. This offers significant benefits over those devices, as the application program can function in any of these various color modes.

In the preferred embodiment of the present invention, the color mode signal provided to the address mode selector circuit 12 causes the address mode selector circuit 12 to assign the lower 12 bits of the color index value to each color map circuit. 1
4, 15 and 16 for translation by a color table with one color mode bit in the most significant bit position. By examining the mode bits, the color map circuits 14, 15, 16 recognize their values as color index values. In a preferred embodiment of the present invention, each color map circuit 14, 15, 16 includes 4 kilobytes of memory to store more than 4000 color shades.

On the other hand, if the information is 24-bit color data, the shade value is sent to color map circuits 14, 15, and 16. However, no translation is necessary or necessary for that value. The address mode selector circuit 12 concatenates the five higher order bits of the three groups of eight bits representing the shades of red, green, and blue. The most significant bit of those bits is a mode bit indicating that the data is 24-bit color data. The other four lower bits simply fill the 12 bits used to address the color index map, and make sure that the data transmitted is not color index data and is not translated by the color table. Discarded by the color map circuits 14, 15, 16 when the mode bits indicate. Therefore, the lower 8 bits that define each shadow of the 24-bit color pixel remain unchanged with the color map circuit 14,1.
It is only transmitted directly via 5 and 16. With this configuration, two types of color formats can be used
It allows processing via maps, thereby simplifying the circuit and reducing operating time. This greatly simplifies the operation of the output display device and makes it possible to obtain a very compact device without redundant circuits.

From the color map circuits 14, 15, 16 the 8 bits of data for each color shade (transmitted directly from the color index map or frame buffer)
3 by one of the three multiplexers 20-22
To one of the gamma correction maps 24-26.
Each of these maps performs a color correction so that the colors actually provided to the output display are relatively accurate representations of the desired colors. Gamma color correction is necessary because of the varying responses of the phosphors used by various output displays. Essentially, there is a direct relationship between the display signal and the voltage applied to the display monitor, but not the output of the screen phosphor. Therefore, there is a need to translate the linear 8-bit color values used in computer devices into 8-bit values that make the phosphors on the screen more like the desired color. A detailed description of gamma color correction can be found in Van Nostrand Rein.
Holder, Inc., edited by Connrac Corporation in 1985, "Raster Graphics.
Handbook (Raster Graphics Hans)
dbook) "Second Edition, page 215 and later.

The 8-bit binary values provided by the gamma correction maps 24-26 are provided to three individual digital-to-analog converter circuits 28-30. Their circuits 2
8 to 30 provide three analog signals used to drive an analog color display. The details of those circuits are well known to those skilled in the art, and thus description thereof is omitted here.

To enable video information already encoded in a 24-bit color format to be superimposed on the image being displayed on the output display device, an external video input data source is provided with three 8-bit data sources. It is shown connected to supply color shades to each of the multiplexers 20-22. Using the video input signal VI_KEY to the address mode selector circuit 12, the multiplexers 20-22 can be used to select whether to transmit video information or data from the frame buffer to the output display. Typically, if video is present, the video is placed on top of the graphics data held in the frame buffer. The video input signal from the video source indicates whether video is present. The pixel key signal P_KEY is provided by the frame buffer and the graphics or video information indicates whether to control if a video signal is present. Typically, the information for obtaining the P_KEY signal is
It is included in the pixel data stored in the frame buffer.

Also, 8-bit red, green, and blue color data can be selected for transmission from the output terminal of each color map for use by other circuits, such as a video recording circuit. In that case, a signal VO_KEY indicating that data is to be used is sent from the address mode selector circuit 12 to a circuit for receiving data used for video. The data can be used by a video cassette recorder, for example, to record graphics data stored in a buffer memory.

One major problem encountered in computer systems that use color indexing is that some application programs, such as animation programs, frequently change the array of colors supplied. Each such change calls for storing those values in a color index map so that the various shade values can be decoded by the color index values. Other situations also require rapid changes in the colors used for display. For example, when some individual application programs are multitasking and their output is displayed in multiple windows on the output display screen, each application allows the selection of an array of different colors. . Assuming that each program uses a different array of colors, different values must be used for each shade value in the color map. Assuming that all window color index maps do not fit into the memory space provided by the color map,
As the various application windows are activated, they must be reloaded frequently.

[0026] Thus, the values used in the color map Ru is rapidly changed in Table <br/> While browsing. To do this, such is the control circuit as a central processing unit, the values stored in the color map, it is necessary to change to adapt to the color that is desired by the application program.

In a typical computer system, a control circuit (eg, a central processing unit) simply writes to a color map and changes the stored value whenever a change is desired. However, since the color map handles the search for various color values for color indexing while the data is being transmitted to the display device, changes in the values stored in the color map do not interfere with the displayed data. Is desirable. This is done if a two-port memory is used for the color map. By using such a two-port memory, changes to the color map can be written to the display while data is being provided to the display. However, it is much more economical to utilize a conventional one-port memory for the color table because the two-port memory is very expensive. Using one-port memory means that while the colors are being changed in the color map, the map cannot be used to supply data for display. In conventional devices, the display is affected. Of course, the color map can be changed abruptly, causing interference as an acceptable side effect.

Another way to address the problem is to modify the color table while the display scanning process is during a vertical retrace operation and no data is being directed to the display. This works well when the values stored in the map change occasionally. For example, it may work well if only one application program is run that does not change color values frequently and the device changes to a new program that uses different color values. However, the device cannot correctly handle changes to the color map that occur during the time one frame is scanned into the display.

The present invention solves the problem when color values need to be changed very frequently and very quickly. The present invention relates to the method of
Use the available horizontal retrace period to create a color table
Make any changes . In conventional circuits, this time is so short that a write operation that typically takes 500 nanoseconds for each address that changes shading cannot be performed. However, to be able to do so within each such period, the system uses a first-in first-out buffer circuit (FIFO) to store the data written to change the color index map.
Prepare Accordingly, occurs a horizontal retrace period, the data output from the color index maps stop malt, FI
Write the data in the FO to the color index map,
It intends line the appropriate changes.

In order to perform this operation, a circuit 31 shown in a block diagram in FIG. 2 is used. This circuit 31
Includes a control circuit 32 that receives a control signal for controlling an operation of changing a color map. This circuit 32 has a write FIFO
33 is controlled. In the write FIFO, data to be written to the color map and address information for the data are stored by a host (not shown) such as a central processing unit. The control circuit 12 receives a read command or a write command, and instructs the FIFO to perform a required specific operation according to the command. Typically, the color index map is not read except during a test operation. Thus, a read operation is not an operation that needs to interface data scanning to the display device. However, it is possible to store the read operations in the FIFO, perform those operations during the flyback period if the FIFO operation is cleared after the write operation is completed.

In the normal case, the action to be taken is to write a value to one of the color index maps 14-16. In this case, a typical operation when the FIFO is not full, the host of data and address for the FIFO33
That begins with writing. This information signal from the scanning control circuit (not shown) indicating that the blanking period of the horizontal or vertical and Tsu beginning a (blanking) to kicking received, FIFO 33
Is stored in the queue. At this point, the circuit 35
The first part of the data in the FO queue is read and the first part is written to one of the color maps at the address stored with the data. This reading is not that horizontal (or vertical) indicated by the reception of the retrace signal from the scanning control circuit continues for a period allocated for retrace. In the preferred embodiment of the present invention, the time required to write each data portion from the FIFO is about 9 nanoseconds. Thus, a very large number of data portions can be written during a horizontal blanking period (typically about 4 microseconds). Usually, the size of the FIFO is limited by the time that the host writes to the FIFO. Since host access in the preferred embodiment requires about 500 nanoseconds, about 22 microseconds of data during the 11 microseconds of an active horizontal scan.
This part is written to the FIFO.

By utilizing the horizontal blanking interval to change the values in the color index map, the color can be changed while one frame is scanned into the display. This only changes during the vertical blanking interval
One port memory for color index map
In contrast to conventional devices used or using two-port memories.

The FIFO shown, when used in the preferred embodiment, provides memory for storing 64 portions of 8-bit data along with 16-bit addresses. Thus, it is unlikely that the FIFO will be full. However, if the event FIFO is full, de by circuit can not provide sufficient storage space
To prevent data loss, the control circuit 32 controls the color
Write to the cable and disturb the display. To do this, FI
Depending on the condition of FO, from input pixel or write FI
A multiplexer (FIG. 5a) can be provided in the device to provide the address of the memory from the FO.

As can be seen from FIG. 2, an address bank decoding circuit 35 is provided for addressing various color maps. As can be seen from FIG. 2, if it is found that the gamma correction color maps 24 to 26 can be accessed by the host and it is desirable to correct the gamma, those gamma correction color maps are stored in the FIFO circuit 33.
Can be modified using

A display mode in which data is transmitted through a color map to a color map memory and displayed on an output display device;
Switching between a host access mode in which the values stored in the color map can be changed is accomplished by a series of two-to-one multiplexers (FIG. 5) at the address input to each color map.
This is performed using b). In the display mode, the multiplexer selects a color map address from the address mode selector circuit 12 for the color map memories 14, 15, 16 and a color map address from the multiplexer 20 for the map 24. , A color map address from multiplexer 22 for map 26.
In host access mode, the color map address comes from the write FIFO address output.

A second device that allows the host to access the color map of the output display to change the data stored for color indexing is shown in FIGS. In the device 40 shown in FIG. 3, the input write FIFO 33 of FIG. 2 has been removed so that the host data and address are supplied directly to the particular color map whose contents are to be modified. I have.
A control circuit 41 is provided to control this operation.
To eliminate interference with the normal functioning of the color map search process, the device 50 of FIG. 4 is provided. In this device, FIFOs 51, 52 and 53 are provided at output terminals of a color index map (in this figure, indicated by the same numbers as those used in FIG. 1). FIFO5
1-53 are provided by the associated color maps 14-16 so that the host can access the color maps 14-16 without disrupting the flow of pixel data to the color display. , Green, or blue pixel shading data.

Thus, during the horizontal retrace interval, the pixel values for the next data row to be scanned to the display are sent to the color map, and the FIFO is filled with pixel data when the next horizontal scan line begins. Assuming that the pixel data is clocked by the FIFOs 51 to 53, the pixel data supplied to the display device via the gamma correction map is
Can be obtained from Data from the first row in the FIFO continues to be written to the FIFO from color maps 14-16, and output pixel data is written to those color maps to change the values of color maps 14-16. Is not desired, the output pixel data is supplied to a gamma correction map. In that case, the pixel enable (P_E
The NAB) signal is deasserted to allow the host to write to the color map. During this period, pixel data is available in FIFOs 51-53 for display.
When the host finishes changing it in the color table, the pixel data from the frame buffer flows to the color table and
The P_ENAB signal is again asserted to enter the IFOs 51-53.

Of course, it is necessary that the FIFOs 51-53 have sufficient storage to supply the pixels during the period during which the host writes to the color maps 14-16. In general, the length of time available to the host for writing without disturbing pixel data is equal to the length of the horizontal retrace period. Therefore, to keep the number of pixels equal to the time that the color map may be occupied by host accesses divided by the pixel duration,
The IFO must be large enough. For example, a row scan time of 16 microseconds on a display device, the host can request a memory cycle every 500 nanoseconds,
Assuming that the host cycle occupies the color map for 18 nanoseconds, the FIFO becomes (16000/500) at (18
/ 9) The product of the pixels must be stored. Thus, in the preferred embodiment, FIFOs 51-53 must provide storage for 64 pixels.

Although the present invention has been described with reference to preferred embodiments, those skilled in the art can make various modifications to the embodiments without departing from the spirit and scope of the present invention. For example, as described above, the proposed arrangement for changing the values in the color indexing map can be used to change the values in the gamma correction map if desired.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a circuit for supplying pixel data to an output display device according to the present invention.

FIG. 2 is a block diagram of a circuit for writing data to a color map of an output display circuit according to the present invention.

FIG. 3 is a functional block diagram of an additional circuit for supplying pixel data to an output display device according to the present invention.

FIG. 4 is a block diagram of an additional circuit for writing data to a color map of an output display circuit according to the present invention.

FIG. 5 is an example of a multiplexer used in the present embodiment.

[Explanation of symbols]

 Reference Signs List 10 output display circuit 12 access mode selector circuit 14, 15, 16 color map circuit 20, 21, 22 multiplexer 24, 25, 26 color gamma correction circuit 28, 29, 30 digital-analog converter circuit 32 control circuit 33 writing FIFO

Continuation of front page (56) References JP-A-2-16598 (JP, A) JP-A-62-119583 (JP, A) JP-A-53-8523 (JP, A) JP-A-59-116992 (JP) , A) European Patent Application Publication No. 466374 (EP, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G09G 5/02 G09G 5/06

Claims (10)

(57) [Claims] 1. Apparatus for providing digital shading values for display on a display for a data processing system, comprising: a) transmitting pixel data received from a frame buffer to one or more pixels during an active scan of the display; A color index map comprising digital shade values configured to translate into digital shade values; b) receiving updated digital shade values from the data processing system during the active scan; A FIFO buffer that is displayed on a display line of the display device and sends an updated digital shading value to the color index map during a time period during which the next line is displayed; c) the FIFO buffer has a digital shading value. When full, it is detected and the digital shader value is read from its FIFO buffer during the active scan. A control circuit for initiating writing to the volume map. 2. The system of claim 1, wherein the FIFO buffer is further configured to receive from the data processing system an address of a memory location in the color index map to which the updated digital shade value is sent. 2. The apparatus of claim 1 wherein said digital shade values are stored in each of a plurality of color index map memories comprising said color index map. 3. The apparatus of claim 2, wherein the pixel data received from the frame buffer includes color index data or digital shade values, and the color index map outputs the digital shade values received from the frame buffer without translation. The device of claim 1 wherein 4. Apparatus for providing digital shading values for display on a display for a data processing system, comprising: a) transmitting pixel data received from a frame buffer to one or more pixels during an active scan of the display; A color index map configured to translate to digital shade values and including digital shade values; b) receiving updated digital shade values from the data processing system during the active scan; Connected to the color index map and configured to send an updated digital shade value to the color index map during a period of time between the display of the next line and the display of the next line. C) said color index map and said color index map connected to said FIFO buffer; A) a gamma correction map configured to receive digital shading values from the digital shading values and to translate the digital shading values into corrected digital shading values during an active scan; and d) the FIFO Apparatus further configured to receive updated corrected digital shade values from the data processing system during a period and to send the updated corrected digital shade values to the gamma correction map. 5. A frame buffer for storing image data representing at least a portion of an image received from a host processor; and b) a series of frames indicated by the image data stored in said frame buffer. A color index map circuit configured to output a digital shade value and store an updated digital shade value received from a host processor during an update operation; and c) updating the color index map circuit. While the digital shade values are being stored, the series of digital shade values is received from the color index map circuit, and each digital shade value of the series of digital shade values is updated during the update operation by the display device. A device for providing digital shade values to a display device having a FIFO buffer for output for display at a corresponding location. 6. The color index map circuit further receives a color map address from a host processor and writes each of the configured digital shading values to a respective color map address of the color index map circuit. And the color index map circuit includes a plurality of color index map memories, and the digital shade values of the different colors are stored in each of the plurality of color index map memories. An apparatus according to claim 5. 7. A gamma correction map circuit coupled to the FIFO buffer for translating a digital shade value output from the FIFO buffer into a modified digital shade value and displaying the modified digital shade value. 6. The device of claim 5, wherein the device is configured to output for display on the device. 8. The image data received from the frame buffer includes color index data or digital shade values, and the color index map circuit further converts the digital shade values received from the frame buffer by the color index map circuit. 6. The apparatus of claim 5, wherein the apparatus is configured to send to a FIFO buffer without translation. 9. A method for updating a color index map of a display of a data processing device, comprising: a) receiving a plurality of digital shading values by a FIFO buffer from a data processing device during an active operation; Sending the plurality of digital shading values from the FIFO buffer to the color index map during a period between the display of the next line and the display of the next line; c) determining whether the FIFO buffer is full; d) sending a plurality of digital shade values to the color index map during the active scan in response to detecting that the FIFO buffer is full. 10. The method of claim 9, further comprising receiving, from a data processing device, an address of a memory location in a color index map to which said plurality of digital shade values are to be sent.