Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-10-26
2004-08-17
Evans, Arthur G. (Department: 2622)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S001100
Reexamination Certificate
active
06778294
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to color printer technology and, more particularly, to a color printer that employs cache memories for conversion of received computer-generated color values to printer color values.
BACKGROUND OF THE INVENTION
Eight bit values (bytes) are used by personal computers (PC's) to designate colors in a Red Green Blue (RGB) color space. The colors Red, Green, and Blue are the primary colors in a RGB color space. Each byte represents one primary color. Colors are selected by assigning values to the bytes representing each primary color. To produce colors, a PC uses combinations of values for the bytes to control the computer's display device (e.g. a color monitor). Together these three byte (i.e. 24 bit) color value can represent over 16 million different colors. Each color is reproduced by appropriate control of the monitor's color producing devices. When, however, a color laser printer is called upon to accurately reproduce that many color values, extensive color processing is required that adds significantly to the execution time of the printer.
Color laser printers use a Cyan Magenta Yellow (CMY) color space. As a result, each RGB color value sent from the PC to a color laser printer must be converted to a CMY color value. A simple color space conversion is represented by the equation:
[
C
M
Y
]
=
[
1
1
1
]
-
[
R
G
B
]
However, ink pigments are not perfect. Thus, in order to match screen colors on paper, extensive modification of the simple equation is required.
In order to reproduce a received color value, a color laser printer must convert the color value into a color command that is recognized by the laser printer engine. It is impractical to produce a color table map that will map all possible PC-generated input colors to laser engine color codes. As a result, many color laser printer drivers employ a cache scheme that is combined with a color table/map to accomplish the conversion. The procedures employed by the prior art color laser printers will be better understood by referring to
FIGS. 1 and 2
.
In
FIG. 1
, a high level block diagram illustrates a color laser printer
10
and a connected personal computer (PC)
12
. PC
12
generates three byte color values to enable display
14
to display any of over 16 million colors. If hard copy is required of the displayed image, a three byte value
16
defining red, green, and blue values, is transferred as a PC-RGB value over interface connection
18
to PC-RGB register
20
in printer
10
. A microprocessor
22
in printer
10
then truncates the received PC-RGB value into a cache address and stores the address value in a cache address register
24
. The truncation action uses only the four least significant bits of each byte to make up a 12 bit address value. That address value is then utilized to address a color cache
26
to determine if, at that address, a source RGB value is stored that matches the value in PC-RGB register
20
. If the color values matches, a corresponding “destination” CMY value is accessed from the same address in color cache
26
and is employed by microprocessor
22
to control color print engine
28
. If no match is found, the value in PC-RGB register
20
is fed to a color map
30
.
It will be understood that employing only the four least significant bits of each of the red, green and blue bytes in PC-RGB value
16
allowed many possible addresses are ignored. Thus, at any designated address, there is a substantial possibility that the source RGB value
42
will not match the PC-RGB value. In such cases, resort to color map
30
becomes necessary. To preserve memory space, color map
30
only contains a limited number of selected color values and corresponding color print engine control values. As a result, if a received PC-RGB value is not found in color map
30
(as is likely), an interpolation procedure is executed using bracketing color values from color map
30
. This action, while enabling an interpolated color print engine control value to be determined, is time consuming and slows the performance of color laser printer
10
.
In
FIG. 2
, a diagram illustrates further detail of the above-described procedure employed by color laser printer
10
in response to a received PC-RGB value
16
. Microprocessor
22
accesses the lower-most four significant bits of each of the red, green, and blue bytes to create a 12 bit concatenated address value
40
. Address value
40
is then used to access one of the positions within color cache
26
.
Color cache
26
contains two entries at each 12 bit address, i.e., a “source” RGB value
42
comprising three eight bit bytes of red, green, and blue values and an associated “destination” CMY color value which also comprises three color value bytes, which color values are employed to control color print engine
28
(FIG.
1
). Different destination CMY color values
62
are required due to the fact that color print engine
28
operates in a “dither” mode to reproduce PC-RGB color values. The dither mode, in essence, calls for the interspersal of color dots of plural color values, which when viewed from a distance, appear to reproduce the desired PC-RGB value.
Initially (decision box
46
), if it is determined that source RGB value entry
42
is equal to a received PC-RGB value, destination CMY color value
44
is returned to color print engine
28
(box
48
). If however, source RGB value
42
is found not to match the PC-RGB value, then color map
30
is accessed at a source RGB color value that most closely matched the value in PC-RGB register
20
. An interpolation procedure then obtains a destination CMY color value to be used to control color print engine
28
(box
50
).
To update color cache
26
(box
52
), the source RGB and destination CMY color values are replaced at the previously accessed address, as follows: the value in PC-RGB register
20
replaces source RGB value
42
at the address and the interpolated destination CMY color value replaces destination CMY color value
44
. As a result of the described replacement procedure, color cache
26
is continually updated with newly interpolated values.
Color cache
26
is most effective when an image or document is printed which includes many slight variations of a particular color. When a color is varied slightly, the most significant bits of the color value remain unchanged and the least significant bits are altered. As color values with the same most significant bits are received and processed by color laser printer
10
, color cache
26
is filled with the most of or all of the variations of the least significant bits. Thus any incoming color value with the same most significant bits will find a match in color cache
26
.
SUMMARY OF THE INVENTION
According to principles of the present invention in a preferred embodiment, a color printer includes a palette color cache preloaded with predetermined palette colors. The palette color cache includes source and destination entries at each cache address. Each source entry includes values indicative of a computer generated color and each destination entry includes values usable by the color printer to reproduce the color indicated by the source entry.
According to further principles of the present invention, the color printer receives P, N-bit values indicating a computer generated color to be printed. Each N-bit value has a most significant bit (MSB). Upon receiving P, N-bit color values, the color printer creates an address from P combined multiple-bit segments of each of the received N-bit values, each multiple bit segment including at least a MSB of each N-bit value. A processor determines if there is a match at the address created from a received computer color value between a source entry and the received computer color value. The processor is responsive to a determined match to access the destination entry at the address and to employ the destination entry to control the color printer.
It has been noticed that many application provide a default color palette. The default color pa
LandOfFree
Palette color cache does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Palette color cache, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Palette color cache will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3314850