Page buffer system for an electronic gray-scale color printer

A data storage system for an electronic color printer which stores data according to the type of information the data represents. When the data represents area fill and image information, the data is stored in the page buffer according to mode A of the invention wherein a plurality of pixels are all defined to have the same color with varying luminance levels. This color is defined in the memory in a uniform color space format. When the data to be stored is representing text or line graphics information, the data is stored in the page buffer according to mode B of the invention. In mode B, two-bit binary values in the page buffer are assigned to each pixel of a multiple-pixel cell. These two-bit values point to additional bytes in the memory block of the page buffer which in turn point to discrete colors in spectrums of 256 colors. Additional data indicates whether the output device is to reproduce the colors by halftoned or non-halftoned techniques. Thus, each pixel within the pixel cell can be printed in a color selected by the color portion of the page buffer. According to mode C of the invention, three separate color maps are defined in binary form by the bit patterns stored in the page buffer memory. Also in mode C, the method used to produce blacks in the output page is specified. By standardizing on the memory allocated to the page and utilizing this memory in different ways according to the nature of the inputted information, the printed page can be accurately stored with a minimum of memory space and without a reduction in perceived printing quality.

CROSS-REFERENCE TO RELATED APPLICATION 
This invention relates to the commonly assigned application filed on May 
18, 1989, and bearing Ser. No. 07/353,715. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates, in general, to electronic color printers and, more 
specifically, to apparatus and methods of storing page data in memory 
buffers of electronic color printing devices. 
2. Description of the Prior Art 
Color printers capable of printing pages with text, graphics, and image 
information can have very demanding memory requirements. In order to 
obtain the highest quality text and line graphics printing, the data 
transferred to the printhead must contain all of the necessary information 
to make the printed data visually accurate. For text and line graphics 
data, this can be in the form of direct, high resolution "bit-mapped" data 
with several bits of data associated with each printed pixel. However, for 
area fill graphics and images, the need for a wider color gamut than the 
direct bit-mapping system can provide is desirable. This is because more 
colors can be produced by using halftoning for the rendition of filled 
area and images. 
The conventional approach is to fill a printing buffer using a general 
purpose CPU to render the full page in memory, and then to print it. To 
fully utilize a multi-bit gray-level printhead in this fashion, four page 
buffers would be required, one for each color separation of the colors 
black, cyan, magenta, and yellow. A gray-level printhead which can have a 
four-bit gray scale per pixel for each of the color separations would 
require a tremendous amount of memory for each page in the buffer. At 400 
dots per inch (dpi), a full 11".times.17" page would require approximately 
64 Mbytes. Such a size is prohibitive, and it is desirable to store the 
information in a much smaller memory area without materially detracting 
from the quality of the finished product. 
There are three requirements that need to be met in the design of a data 
structure capable of Providing the memory space needed to economically 
store multi-bit, gray-level, color page data. Along with maintaining the 
memory at the smallest size possible consistent with maintaining an 
acceptable level of image quality, it is desirable that the memory or 
buffer system be expandable from a binary system to a multi-bit printing 
system. In addition, a desirable implementation of a page buffer memory 
system would be one in which the data structure keeps the hardware costs 
to a minimum. 
In order to obtain a more efficient memory structure for the page buffer of 
a color printer, it is important to recognize that the sharpness or 
resolution of printed information must be stored more precisely than color 
information so that the printed page will be perceived by an observer as 
having full memory storage. In other words, it is possible to sacrifice 
some of the resolution defining the color of the printed data without that 
sacrifice being perceived by the observer. On the other hand, sharp 
contrast areas such as text and line graphics require more precise data 
storage and cannot tolerate the sacrifices acceptable in storing color 
information. The invention disclosed herein uses these principles. 
The cross-referenced application, Ser. No. 07/353,715, describes two 
patents which are known to be relative to the concepts taught by this 
invention. The cross-referenced application itself describes a system for 
data storage which overcomes some of the problems encountered according to 
the Prior art. However, it is desirable, and it is an object of the 
present invention, to be able to more accurately store in memory the image 
information which will be used to ultimately print the output page. 
In some images, optimum print quality cannot be obtained by using a single 
luminance level for an entire 16-pixel array, as is taught by the 
referenced patent application. The buffer system of the present invention 
adequately provides for variations in luminance levels throughout the 
pixel cell. 
Another problem associated with the prior art is the handling of a 
transition area within the boundaries of the pixel cell. This can occur 
where text or line graphics begins adjacent to image or area fill 
graphics. The portion of the pixel cell which is high contrast text or 
lines needs to be printed in a solid color whereas the portion which is 
image or area filled would often be halftoned. However, since the pixel 
cell can only be specified for one type of representation according to the 
prior art, a mixture of solid and halftones within the same pixel cell 
cannot be realized. As a result, solid pixels are often printed near the 
border of text and lines in areas adjacent to halftoned pixels. The result 
can be an objectionable staircase effect along the edges of the lines. It 
is, therefore, desirable and another object of this invention to provide a 
system whereby transitions in types within the pixel cell are adequately 
handled. 
Although it is possible to produce black from a process of printing three 
colors, some black images or graphics are easier to represent in the 
actual operating environment with only black toner. This additional 
information about black printing must be stored in the page buffer to be 
of use to the output device or printer. Thus, the present invention also 
provides the desirable capability of storing in the page buffer data 
concerning the type of process to be used in reproducing black in the 
output page. 
SUMMARY OF THE INVENTION 
There is disclosed herein a new and useful system and method for storing 
color page information in the page buffer of a color electronic printer. 
The system stores image and area fill data in the page buffer according to 
one format or first mode and stores text and line graphic information into 
the page buffer according to another format or second mode. A third mode 
of storage is used when the information from the host computer is in the 
form of device dependent bit mapped data which can be directly inserted 
into the memory cells of the page buffer. 
According to mode A of the storage system, a predetermined number of bytes 
are used to store color space information for the entire area defined by a 
pixel cell associated with and corresponding to the memory cell. In a 
specific embodiment of this invention, the memory block contains seven and 
one-half bytes and the corresponding pixel cell contains 16 pixels 
arranged in a 4.times.4 area. Three of the memory bytes contain the color 
space data and the other four bytes of the memory block contain bits which 
define a variance in luminance level for the 16 pixels. A half byte is 
used to store data about the mode of storage and the range of variable 
luminance levels. As stated, this mode is used for area fill and image 
information where sharpness is not a prime concern and true color 
reproduction is important. Thus, even though individual pixels within the 
16 pixel cell cannot be printed differently in color, the color 
represented by the entire 16 pixel cell will be very accurate and appear 
to an observer to have all of the sharpness needed for image and area fill 
information. Luminance, however, can be changed for each pixel. 
According to mode B of the data storage system, a predetermined number of 
bytes in a memory block are associated with a predetermined number of 
pixels in a memory cell. For consistency with mode A, the specific 
embodiment illustrates a memory block containing seven and one-half memory 
bytes and a pixel cell containing 16 pixels in a 4.times.4 arrangement. 
Four of the eight-bit bytes in the memory block contain the bits which 
correspond to the individual pixels in the pixel cell, with two bits 
corresponding to each pixel. Thus, each pixel can have a decimal value of 
0, 1, 2 or 3. The other three complete memory bytes of the memory block 
contain three separate color bytes which point to one of two lookup tables 
of 256 colors, with each byte indicating a specific color in those ranges 
of 256 colors. The four decimal values associated with each pixel select 
one of the three colors indicated in the memory block or, in the case of 
the 0 decimal value, do not pick any color for printing. The one-half byte 
is used to indicate the mode of storage and whether the pixels are to be 
reproduced using halftoned or non-halftoned techniques. This, in effect, 
also selects which color spectrum is used by a color byte. Thus, within a 
16 pixel cell, three different colors, or no color at all, can be printed 
at each pixel, either for halftoned or solid reproduction. Mode B of the 
invention is used primarily for sharp contrast data, such as text and line 
graphics. 
In mode C of the invention, six of the seven and one-half allocated memory 
bytes are directly bit mapped for three separate single color pixel cells 
of 16 pixels each. Mode C is used when the data coming from the host 
computer is in device dependent form and directly bit-mapped into the page 
buffer memory. A half byte is also used to indicate the mode used and how 
black areas will be produced by the output device. By combining the three 
modes and storing the data in the page buffer according to the mode which 
will produce the desired results, an efficient and accurate data buffer 
can be provided without the need for the large amount of memory required 
for gray-level representation of color pages according to prior art 
techniques.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Throughout the following description, similar reference characters refer to 
similar elements or members in all of the figures of the drawings. 
Referring now to the drawings, and to FIG. 1 in particular, there is shown 
a block diagram of a data storage system constructed according to this 
invention. The data source 10 provides the pixel information or print data 
to the storage system which includes the data processor 12 and the page 
buffer 14. The data from the data source 10 typically would be in page 
description format and usually would originate from a device remote from 
the memory storage system. In most cases, the data would be in device 
independent form according to a known and predetermined format, such as 
PostScript, which is a registered trademark of Adobe Systems Incorporated. 
In some cases, however, the data applied to the storage system can be in 
device dependent format where the data can only be faithfully reproduced 
on the particular printing device associated with the memory storage 
system, such as the printing device 16 shown in FIG. 1. 
Data applied to the data processor 12 is processed and manipulated in such 
a fashion that it can be stored in the page buffer 14 according to a 
memory efficient system as described herein. Once stored in the page 
buffer 14, the data is, at the appropriate time, transferred to the 
printer device 16 for producing the hard copy output from the electronic 
data. In certain applications, data may be read for printer use while more 
data is being stored in the buffer, and direct memory access (DMA) 
techniques may be employed with the buffer memory. In some cases, the 
printer device 16 must further process the data from the page buffer 14 to 
ascertain the correct printing sequence for reproducing the information 
stored in page buffer 14. In other words, in order to faithfully reproduce 
a color defined in the page buffer 14, the printer device 16 must take 
into consideration the exact colors of the pigments, toners, or inks used 
in its printing process, and other factors of the printing process, such 
as the intensity of the color printed in a specific pixel to give the 
desired gray level. The data in the page buffer 14 can be outputted to the 
printer device 16 under the control of the data processor 12 or, in the 
case of direct memory access, the data in the buffer 14 can be accessed 
directly at the appropriate time by the printer device 16. 
FIG. 2 is a diagram illustrating page content and memory organization, in 
general, for the data storage system of this invention. The information 
page 18 contains four types of print information which are to be stored in 
the memory 20. Text information 22 is illustrated in one quadrant of page 
18. This is characterized by high contrast, sharp lines, and predominant 
white areas. Another quadrant of page 18 includes an image 24 which could 
be a continuous pictorial image generated from a high resolution source, 
such as a photograph or video signals. Another quadrant of page 18 
contains area fill information 26 which is characterized by the fact that 
it is a continuous shaded or solid color region covering a wide area of 
the page. The fourth quadrant of page 18 contains line graphics 28 which 
are characterized by sharp lines similar to the text 22. Because of the 
nature of the various print information on page 18 and its degree of 
perceivable deviation from exact reproduction, different methods of 
storing the data can be used in an efficient system for storing all of the 
data necessary to represent page 18. In other words, to efficiently store 
the print information on page 18, various memory formats can be used with 
the ultimate result being an efficient use of overall memory space 
consistent with high quality reproductions. 
Memory 20 shown in FIG. 2 illustrates the general organization of a solid 
state memory which can be used to store the information shown on page 18. 
The memory 20 consists of a series of memory Positions, or bytes, such as 
bytes 30 and 32 shown randomly in the memory 20. The memory 20 includes a 
plurality of such bytes, with each byte being addressable at a different 
location within the memory 20, and thus being illustrated at a different 
location within memory 20. The size of the memory 20 is dependent upon the 
level or detail at which the information is stored, the size of the 
information, the color content of the information, and upon other 
variables. In a typical system, the memory 20 could contain several 
million bytes. Each byte contains a plurality of bits which can store 
binary data, and in this embodiment of the invention, each complete byte 
contains eight bits. 
The memory 20 is organized into blocks or slots of memory containing a 
predetermined number of bytes. In FIG. 2, the memory cell or block 34 
contains seven and one-half bytes of memory similar to byte 32. The number 
of bytes per allocated block or slot of memory may be changed depending 
upon the particular format being used. In any event, the data stored in a 
block of memory corresponds to an area on the page of information. In 
other words, a particular area or group of pixels on the page 18 
corresponds to the block 34 In the memory 20, and consequently the data 
which will be reproduced from block 34 is expected to provide the 
reproduction of that portion of the page shown in FIG. 2. This is not to 
say that a particular memory block is always allocated to the same 
position on the page 18. More accurately stated, a particular area on the 
page 18 is stored in a particular block of data in the memory 20, although 
the block may be at a different position in the memory for different pages 
of information. 
FIG. 3 is a diagram illustrating the general memory allocation for the 
corresponding pixel locations according to this invention. In FIG. 3, the 
memory cell or block 36 contains the memory bytes 38, 40, 42, 44, 46, 48 
and 50, and the half-byte 51. This seven and one-half byte block 
corresponds to the pixel cell, set, or area 52 also shown in FIG. 3. Pixel 
area 52 contains 16 pixels arranged in a 4.times.4 pixel format. Thus, 
the data stored in the memory block 36 of the page buffer 14, shown in 
FIG. 1, corresponds to a 4.times.4 pixel area 52 for the page being stored 
and ultimately reproduced. 
The manner of storing the data in the memory block 36 depends largely upon 
the type of information represented by the memory data. In other words, 
depending upon whether the information is text, image, area fill, or line 
graphics, the particular format used for storage in the block 36 is 
customized or tailored to adequately store the information efficiently 
consistent with a perceivable quality in the finished product, or page 
reproduced from the stored data. Since some of the types of information 
contained on the page 18, FIG. 2, require higher reproduction contrast or 
sharpness, while others require lower contrast but more faithful color 
reproduction, the storage requirements and methods for different data are 
handled differently by this invention, as will be discussed herein. 
FIG. 4 is a diagram illustrating a specific memory format and the 
corresponding pixel area layout according to mode A of the invention. In 
mode A, the page description data is describing an area fill or pictorial 
image area of the page. With this type of information, detailed sharpness 
or fineness of an individual line is not of primary importance. It is the 
faithful reproduction of the colors over a relatively wide area of the 
image that is the desired storage criteria for efficient use of the memory 
consistent with accurate image reproduction. Consequently, in storage mode 
A of this invention, such data is stored for a large pixel area containing 
several pixels as opposed to storing it for each individual pixel. In 
other words, the seven and one-half byte memory slot is used efficiently 
to store color information for a group of pixels rather than for detailed 
fineness or sharpness information for the area, which would require 
storage for each individual pixel. 
According to FIG. 4, the seven and one-half byte memory cell or block 54 
contains three bytes 56, 58 and 60 of device independent color space 
information. Although shown in the L*a*b* format, other color space 
designations may be used such as L*u*v*. The remaining four complete bytes 
of the memory block 54 contain bit patterns which indicate variations in 
the luminance level of each of the pixels in pixel area 62. Two bits are 
used to identify a luminance level for a particular pixel in the pixel 
area 62. For example, bits 57 and 59 correspond to pixel 61, and bits 63 
and 65 correspond to pixel 67. The other bits in the four complete bytes 
of block 54 correspond to the pixels in pixel area 62 at the corresponding 
locations. 
The four values which can be defined by each of the two-bit locations 
govern the luminance for the corresponding pixel. In addition to the four 
levels of luminance defined by the bit pairs, the bits 69 and 71 in the 
one-half byte 109 of the block 54 deFine up to four different data 
registers or lookup tables in which the luminance can be obtained. Thus, 
with the combination of the bits in the four complete bytes and the two 
bits in the one-half byte, 16 levels of luminance are possible for the 
pixels in the pixel area 62. Bits 73 and 75 define the mode of storage, 
which in this case is mode A. The two-bit pattern provided by these bits 
allows up to three other modes to be stored at this location, and the 
printing or output device is able to get the information in these two bits 
to determine in which mode the data is stored and how it will print or 
output this data consistent with the storage method. 
According to FIG. 4, all of the pixels in the pixel area 62 are to be of 
the same exact color, which is defined by bytes 58 and 60 in the memory 
block 54. In mode A, sharpness of the reproduced copy is not of prime 
importance, and, therefore, the memory has been organized to sacrifice 
individual pixel color descriptions as opposed to more accurate 
descriptions of the color content for all 16 pixels as a group. In 
general, according to mode A, the data from the data source is stored 
using a plurality of bytes to define the color of the complete pixel area, 
and the remaining bytes of the memory block are used to indicate that the 
data storage is according to mode A and that certain variations in 
luminance for individual pixels are desired. It is emphasized that, 
although discussed and shown in FIG. 4 as each pixel having the same 
color, the printing or output device may perform other processing on the 
stored information to achieve the overall color for the complete pixel 
area 62. In other words, in some cases, processing, such as halftoning, 
may be used to create the overall color specified in the memory block 54. 
It is the memory which has only one color for the 16-pixel area 62, not 
the actual arrangement of the pixels on the printed page that achieves, to 
the observer, the rendition of the desired color. 
Since the color information is in device independent form as received from 
the data source, the storage in the same format into the memory block 54 
is easily handled by the processor in the memory system. The processor 
handles the additional function of generating the identifying bits which 
are stored in the remaining bytes of the memory block 54 when mode A is to 
be indicated. Consequently, the reproduced page derived and printed from 
data included in the memory block 54 would include the Pixel area 62 which 
is accurately defined in color for all the pixel, although there is no 
distinguishing color information between any particular pixel. Storage in 
this format is most efficient when the color information is to be 
faithfully reproduced and sharpness of the reproduction is not a 
perceivable limitation at the resolution of the 4.times.4 pixel area. 
The luminance level of each pixel is determined by the base luminance value 
or level indicated in byte 56 of memory block 54 in combination with a 
change or variation in the base luminance value for a specific pixel as 
indicated by the bits in the remaining four complete bytes of the memory 
block 54. In other words, the luminance value in byte 56 provides the base 
value to start with, and the deviations from this base value are indicated 
by the individual two-bit quantities contained in the four complete bytes 
corresponding to each pixel. In this specific embodiment, the base 
luminance value is the minimum value existing in the complete 4.times.4 
pixel area 62. Therefore, the individual bit pair locations allow up to 
three increases above the base luminance value to be used for each pixel. 
In addition to the three increases, which provide for four different 
luminance values, the amount of increases can be determined from different 
data banks, or look-up tables. Bits 69 and 71, shown in FIG. 4, specify up 
to four lookup tables which may be used to determine the adjustments to 
the base luminance value addressed by the two-bit pairs which correspond 
to particular pixel locations. This adds more versatility to the luminance 
variation system, and allows the total variation for the pixel area 62 to 
more correctly match the actual luminance desired. 
FIG. 5 represents a lookup table which would be used by the data in FIG. 4 
to determine the actual luminance value for the particular pixel. In this 
case, the lookup table corresponds to the binary bits 69 and 71, which 
have the binary value "1 0" therein. Three other lookup tables could be 
specified by other two-bit binary values. In the lookup table 77 of FIG. 5 
which is selected by the binary value "1 0" in bits 69 and 71, bit pair 
values 79, 81, 83 and 85 correspond to the bit pair values in the four 
complete bytes shown in FIG. 4. Depending upon the particular binary 
number, a certain deviation or variance in luminance level is specified by 
the lookup table 77. This quantity, which may be an eight-bit binary 
number, is added to the base luminance level contained in byte 56 of 
memory block 54 shown in FIG. 4. The first luminance variation, 
.DELTA.L.sub.1 *, ordinarily would indicate an additional value of 0 to 
the base luminance level. Therefore, binary bits 79 would indicate that 
the pixel would be stored with the luminance level equal to the base 
luminance level in byte 56. On the other hand, bit pair 85 indicates that 
the luminance level would be increased by the amount .DELTA.L.sub.4 *, 
which is the highest luminance level for any of the pixels in the complete 
4.times.4 area. The processor storing this data would first determine the 
minimum and maximum values of luminance in the pixel area 62 and select 
the base luminance level and the largest differential luminance value to 
give these two quantities. The intermediate luminance variations, 
.DELTA.L.sub.2 * and .DELTA.L.sub.3 *, would be equally divided between 
the two values. Thus, every pixel in the 4.times.4 pixel area could be 
specified at the maximum and minimum values of the luminance for the area 
and at two intermediate levels. Since other 4.times.4 pixel areas in the 
page may contain other ranges of luminance levels, the other lookup tables 
which can be defined by bits 69 and 71 are used to cover additional or 
other ranges between base and maximum luminance levels. Thus, the 
combination of the individual bit pairs and the lookup table designator 
bits can provide individual pixel variations of four levels within four 
different ranges for the pixel areas. 
FIG. 6 is a diagram illustrating general memory format and the 
corresponding pixel area layout according to mode B of the invention. In 
mode B, which is used when text or line graphics information is to be 
stored, sharpness is of primary concern, and each pixel of the 4.times.4 
pixel area is described separately in the memory block. According to FIG. 
6, the memory block 64 contains the Four sharpness or location memory 
bytes 66, 68, 70 and 72, and the three color memory bytes 74, 76 and 78. 
Each byte contains eight bits as indicated in FIG. 6 for the first 
sharpness byte 66. All seven and one-half bytes of the memory block 64 are 
used to define the information needed to accurately reproduce each of the 
pixels in the pixel area 80. Each pixel of the pixel area 80 corresponds 
to a two-bit number or value in the memory block 64. For example, bits 82 
and 84 correspond to pixel 86, and bits 88 and 90 correspond to pixel 92. 
Therefore, all 16 pixels of the pixel area 80 correspond to a two-bit 
number contained in the four bytes 66, 68, 70 and 72 of the memory block 
64. The location of a bit pair in the memory block 64 effectively defines 
the location in the pixel area 80 of the individual pixel represented by 
the bit pair. 
The color to be printed in the pixel area depends upon the value of the bit 
pairs in memory block 64. With two bits, each bit pair can select four 
options or colors to be printed in the corresponding pixel. One of the 
four bit pair values is used to indicate that no color will be printed in 
the corresponding pixel. The other three values are used to indicate and 
point to an additional byte in the memory block, or a three-byte lookup 
table. In other words, when a bit pair indicates that the pixel should be 
printed, it selects one of the three color bytes 74, 76 or 78, which 
further points to, with an eight-bit quantity, the specific color to be 
printed in that pixel. Having eight bits to point to a particular color 
allows each of the color bytes 74, 76 and 78 to point to a single color in 
a range of 256 colors, as shown in the color spectrum 94. Consequently, 
the 16 pixels in the pixel area 80 can be left blank or printed in any of 
three total colors, with the three colors being selected from a range of 
256 colors. 
In FIG. 6, the one-half byte 87 contains data which indicates that mode B 
has been selected for storage and that certain of the color bytes define 
colors which are to be represented by either halftoned output methods or 
non-halftoned output methods. Depending upon whether the colors are to be 
specified as halftoned or non-halftoned, the particular colors are 
selected from different color spectrums, such as spectrums 94 and 95. 
Thus, even though the same binary number may exist in one of the color 
bytes, the information in half-byte 87 would determine which color 
spectrum the color will be selected from as well as whether the color will 
be halftoned or non-halftoned by the output device. In this respect, the 
colors selected by the same binary number for halftoned and non-halftoned 
reproduction may be different. 
FIG. 7 illustrates the effect of the data contained in the half-byte 87 of 
the memory block 64 shown in FIG. 6. Bits 89 and 91 contain the binary 
number "0 1" which indicates that the mode of storage is according to mode 
B. Bits 93 and 97 contain data which indicates whether the color bytes 
will be reproduced using halftoned or non-halftoned output techniques. 
This data is defined by the table 99 shown in FIG. 7. If bits 93 and 97 
are both binary "0's", then all three color bytes will be and will 
effectively pick colors from the color spectrum 94 in FIG. 6. If the bits 
93 and 97 are binary "0" and "1" as indicated in FIG. 7, the first two 
color bytes will be non-halftoned, and the third color byte will be 
halftoned. The third condition, which occurs when the binary 
representation is "1 0", indicates that the first color byte will be 
non-halftoned and the second and third color bytes will be halftoned. 
Finally, binary "1's" in both bits 93 and 97 indicate that all three 
color bytes will be halftoned by the output device and, consequently, will 
select their colors from color spectrum 95 as shown in FIG. 6. 
FIG. 8 is a diagram illustrating specific memory values and the 
corresponding pixel colors for mode B of the invention, and is included 
herein to further define the memory and pixel arrangement according to 
mode B of the invention. In this particular example of mode B operation, 
the specific bit values for all of the bytes in the memory block 96 ate 
illustrated. Pixel value chart 98 indicates the decimal equivalent of the 
binary bit pairs contained in the first four bytes 100, 102, 104 and 106 
of memory block 96. For example, bits 108 and 110 correspond to a decimal 
value of 2 which is indicated in the chart 98 at position 112. This 
location also corresponds to the pixel 114 of the pixel area 116. Bits 118 
and 120 of memory block 96 represent a 0 decimal value corresponding to 
the position 122 and pixel 124 in the chart 98 and area 116, respectively. 
Each of the values in the chart 98 can have four decimal values, 0, 1, 2 
or 3. A value of 0 indicates that no color will be printed in the 
corresponding pixel as shown at pixel 115 in pixel area 116. The decimal 
values of 1, 2 and 3 indicate which of the color bytes 126, 128 or 130 are 
to be used for the particular pixel in defining the color to be printed in 
that pixel position. A decimal value of 1 corresponds to byte 126, a 
decimal value of 2 corresponds to byte 128, and a decimal value of 3 
corresponds to byte 130. 
The three color bytes 126, 128 and 130 define three specific colors in the 
color spectrums 132 and 133 which will be produced when that particular 
color byte is specified by the bit pair corresponding to a particular 
pixel. For example, position value 112 is a decimal 2 in chart 98 which 
points to byte 128 in memory block 96. This byte in turn has a decimal 
value of 131 which points to the 131st color in the color spectrum 132 
which contains 256 color selections. Bit pair 101 selects the first, or 
non-halftoned, spectrum 132 for color byte 128, as well as for color byte 
126, and halftoned spectrum 133 for color byte 130. If the pixel position 
value is 1, the byte 126 would be specified and the color 68 would be 
printed for that particular pixel. If the value of 3 is indicated for a 
pixel, the byte 130 would be selected and the color 200 would be "printed" 
for that pixel. Although the "memory" pixel area 116 shows all four pixels 
which correspond to the value of 3 "printed" in the same 200 color, the 
actual "printed" pixel area may not have all of the four pixels printed in 
color 200 since halftoning will be used by the printer. 
Note that 68, 131 and 200 are the decimal values of the three bytes 126, 
128 and 130, respectively. Thus, the complete 4.times.4 pixel area 116 can 
include three separate colors, or an absence of color, as defined for each 
pixel of the pixel area, and a pattern of halftoned or non-halftoned 
outputs. Although only two bits are used to indicate which color will be 
printed, a range of 256 colors in each spectrum is available for selection 
due to the increased bit capacity of the color selection bytes. By using 
this technique for storage mode B, some sacrificing of a full range of 
colors is made to obtain the advantage of being able to specify a color 
and a reproduction technique for each pixel within the 4.times.4 pixel 
area. 
FIG. 9 is a diagram illustrating specific memory values and the 
corresponding pixel area lay-outs according to mode C of the invention. 
Mode C is used for configuring the storage memory for corresponding pixel 
locations when the data obtained from the data source is in device 
dependent form or, in other words, the data has been formed with the 
knowledge of which particular colors must be printed in a specific area to 
provide the desired reproduction of the stored page. In mode C, six of the 
seven and one-half bytes in memory block 134 are used to define three 
separate overlapping pixel areas. Bytes 136 and 138 define the pixels in 
the pixel area 140. Bytes 142 and 144 define the pixels in pixel area 146. 
Bytes 148 and 150 define the pixels in pixel area 152. Typically, pixel 
area 140 would correspond to a printing or toner color of cyan, pixel area 
146 would correspond to magenta, and pixel area 152 would correspond to 
yellow. Byte 151 is in the "don't care" state since it is not used in this 
mode. One-half byte 153 contains additional data regarding the mode of 
storage and the process to be used in reproducing blocks. 
In FIG. 9, each pixel in the corresponding color pixel area is represented 
by a single bit in the corresponding two bytes of memory. If the bit is a 
binary "0", nothing is printed in the pixel area. If the bit is a binary 
"1", the corresponding color is printed in the pixel area. For example, 
the top row of pixels in the pixel area 140 is represented by the four 
most significant bits in the byte 136. Thus, bit 154 indicates that pixel 
156 should be printed in cyan. The next row of pixels in pixel area 140 is 
represented by the four least significant bits of byte 136. Thus, pixel 
158 is not printed in cyan because of the "0" at bit 160. The third and 
fourth rows in pixel area 140 are represented by the most significant and 
least significant four bits in the byte 138, respectively. By similar 
analysis, the corresponding pixels in pixel areas 146 and 152 are 
represented by the bits in bytes 142, 144, 148 and 150. Mode C of the 
invention is a storage format which is a bit mapped technique having more 
conventional aspects than the memory storage formats used in modes A and 
B. Mode C is used as an alternative to modes A and B when the data coming 
from the data source has already taken into consideration the parameters 
of the printing device 16 and is giving device dependent data in 
bit-mapped form to the page buffer 14. 
Although the individual bits in the memory block 134 can specify the colors 
necessary to produce black in the output device, certain types of outputs 
and printing are better produced by using a black toner as opposed to 
creating black from a process of using three component colors. FIG. 10 
illustrates the information which is also included in the memory block 134 
in the one-half byte 153 according to mode C. This information is 
specified by the incoming data and is stored in the memory system of this 
invention so that the printing device can most efficiently reproduce the 
colors, including black, of the output page. When the indicated bit pair 
155 in one-half byte 153 corresponds to a binary "0 0", the output device 
knows that the complete 4.times.4 pixel area is intended to be blank 
without further consulting the data in the remaining bytes of the memory 
block 134. Note that bits 103 and 105 are stored with binary "0's" which 
are used to indicate that mode C is the current mode of data storage. When 
the corresponding bits in one-half byte 153 are a binary "0 1", processed 
black is indicated to the output device, and the pixels properly colored 
by the bit pattern in memory block 134 to produce black will be produced 
in thatt method. When the binary number is "1 0", toner black is indicated 
to the output device, and those pixels in the 4.times.4 pixel area which 
are to be black according to the data in memory block 134. will be printed 
by using black toner. Binary value "1 1" tells the output device that the 
output page is to be reproduced without color and all of the pixels will 
be represented by contrasting black and white areas. 
It is emphasized that the page buffer memory formats shown for modes A and 
B do not take into consideration further processing by the printing device 
which would involve conventional and ordinary processing as known by those 
skilled in the art for reproducing the colors indicated by the data in the 
page buffer. For example, in mode A, although a particular shade of color 
is to be depicted for all 16 pixels of the pixel area 62, the printer may 
combine different colors in each pixel to produce the resultant color, 
vary the "gray" level to intensify one or more colors to produce a certain 
level or intensity of the desired color, or use halftone techniques 
throughout the pixel area. The important aspect is that the 16 pixel area 
62 appears, to an observer at normal distance, to represent for the entire 
pixel area 62 the color defined by the color space quantities contained in 
bytes 58 and 60 of the memory block 54. As regarding mode B, particular 
pixels within the pixel area 116 are produced in the proper color by the 
capabilities of the printing device. For example, with a conventional gray 
level color printing scheme, a particular pixel may contain up to three 
overlayed subtractive colors each having an intensity depending upon the 
level needed to produce the resultant color. In some cases, the printer 
device electronics may interpolate between adjacent 16-pixel areas and 
vary the printed pixel colors from those stored in the corresponding 
memory block to obtain more accurate color reproductions across the page. 
FIG. 11 is a block diagram illustrating data processing which occurs prior 
to storage of the data in the page buffer, as shown generally in FIG. 1. 
According to FIG. 11, page description information or data is applied to 
the raster image processor (RIP) 136 where, according to techniques known 
by those skilled in the art, the information is converted or processed 
into specific pixel and color data. In the case of text or graphics, this 
data is transferred to the page buffer interface 138 which is described in 
more detail in connection with FIG. 12. In the case of area fill 
information existing in the description data, the information is 
transferred directly to the page buffer 14, as no further processing by 
the interface 138 is necessary to provide the data format needed for 
storage into the page buffer 14. 
Image information, which normally would come from a separate source, is 
processed by the image processor 140 to provide the mode A format for 
storage of the image data in the page buffer 14. The function of the 
processor 140 is to convert the image information, which may be in analog 
form, into digital form and arrangement for proper insertion into the page 
buffer, although the exact location of the data of the page may be defined 
in the page description information. Image processors for converting image 
or video for storage in a solid state memory are well know to those 
skilled in the art. The processing means provided by devices 136, 138 and 
140 supplies the appropriate data formatt and identity to the page buffer 
14. 
FIG. 12 is a block diagram illustrating the operation of the page buffer 
interface shown in FIG. 11. When the raster image processor 136 (FIG. 11) 
generates data for one page, it fills the page buffer by writing to the 
x,y position address registers 142, the color register 144, and the 
32-bit, one dimensional, bit map or pixel register 146. The bit map 
register 146 associated with the position registers 142 determines the 
pixels which are printed with the color specified in the color register 
144. Linear address generator 166 provides the address data to the buffers 
152 and 156 from the data in the registers 142. 
By having the memory structure organized with 4.times.4 pixels for each 
cell, the conversion requires eight memory read and write operations. The 
32-bit register 146 covers eight 4.times.4 cells. In order to write the 
data into the page buffer, each cell in the page buffer needs to be read 
and checked with the incoming data to determine the modification of the 
sharpness cell word and the color cell word. 
As shown in FIG. 12, the 24-bit color information in the register 144 is 
compressed or reduced in possible variations by the 8-bit extractor 148. 
This extractor provides for up to 256 colors out of the 24-bit color 
designation contained in register 144. A similar extraction is 
accomplished by the 8-bit extractor 150 for the 24 bits of color 
information in the color cell buffer 152, although the format of 
representing colors in the buffer 152 is different than that used in the 
register 144. The extracted color data is compared in the eight-bit 
comparator 154 to determine whether the two colors are in the same range. 
The sharpness buffer 156 is arranged in 4.times.4 cells which contain 32 
bits. The locator 158 locates the largest two-bit number in the 4.times.4 
pixel sharpness buffer 156. This value is used by the bit mapper 160 to 
encode the sharpness value of the current pixel as accomplished by the 
cell modifier 162. According to the result of the color comparison, the 
cell in the color buffer 152 will be modified by the color cell modifier 
164 and written back to the color cell buffer 152. The sharpness buffer 
data is modified by adding the current pixel value and writing the result 
back to the sharpness buffer 156. 
It is emphasized that numerous changes may be made in the above-described 
system without departing from the teachings of the invention. It is 
intended that all of the matter contained in the foregoing description, or 
shown in the accompanying drawings, shall be interpreted as illustrative 
rather than limiting.