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Claims  |
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I claim:
1. A raster display device refresh system comprising:
a refresh memory store having coded image information segments representing
a visual image and stored in addressible locations;
converter means for converting said coded image information into
non-overlapping non-coded raster information for visual display on a
raster display, said converter means including a plurality of decompressor
means for decompressing said coded image information segments into
non-coded raster information and a plurality of refresh buffer means, one
associated with each decompressor means for intermediate storage of said
non-coded raster information for use by the raster display;
means for generating control information representative of the storage
addresses and content information for each of said coded image information
segments;
an increment directory storage means for storing said control information
at incrementally addressible locations; and
cyclic image refresh control means for incrementally retrieving control
information from said increment directory store and responsive thereto for
generating address locations for cyclically and sequentially retrieving
said coded image information from said refresh memory store for conversion
by said converter means and display on said raster display.
2. A raster display device refresh system as defined in claim 1 further
including:
means responsive to said increment directory storage means for generating
an overflow indicator signal indicative of an overflow image too large for
a single display, said overflow indicator signal controlling said refresh
memory store to limit the coded image information segments stored therein.
3. A raster display device refresh system as defined in claim 2 further
including:
means for partitioning the coded image information segments in response to
said overflow indicator signal; and
means for generating a partition boundary representation in said increment
directory storage means to define the partitioned visual image data for
display on the raster display.
4. A raster display device refresh system as defined in claim 3 including:
means for retrieving the remaining coded image information for storage in
said refresh memory store; and
means for activating said means for generating a partition boundary to
identify the retrieved remaining coded image information as part of an
overflow image for display on the raster display.
5. A raster display device refresh system comprising:
compression means for compressing coded image data representative of a
visual image to be displayed into compressed image segments;
a refresh image store for storing said compressed image segments of visual
image data at addressible storage locations;
means for generating control information representative of the storage
address for each of said compressed data segments of said image stored in
said refresh storage means;
an increment directory storage means for storing said control information
at incrementally addressible locations;
a plurality of decompressor means for decompressing said compressed image
segments;
a plurality of refresh buffer means, one associated with each decompressor
means; and
cyclic image refresh control means including means for incrementally
retrieving control information from said increment directory storage means
said cyclic image refresh control means cyclically and sequentially
gating, under control of said retrieved control information, compressed
image segments from said refresh storage means to one of said decompressor
means and then gating decompressed image segments to one of said refresh
buffer means, each of said plurality of decompressor means and refresh
buffer means gated in turn for refresh of the image produced by a display
device at a data rate to adapt the decompression data rate to the data
rate requirement of said display device.
6. A raster display device refresh system as defined in claim 5 wherein
said increment directory storage means includes an overflow indicator that
generates a signal indicative of an overflow image too large for a single
display and further including:
means for generating a partition boundary signal in response to said
overflow signal for display on said display device; and
means for retrieving further coded data of the visual image, said partition
boundary generating means generating a partition boundary to identify said
further coded data.
7. A raster display device refresh system including conversion means for
compressing coded image data representative of a visual image to be
displayed, a refresh storage means for storing said compressed coded image
data, image processing control means for dividing said image data into a
plurality of non-overlapping image segments, said image processing control
means including logic means for sequentially activating said conversion
means to compress individual data segments of said coded data and to place
the data representing the compressed data segment in said refresh storage
means at addressible storage locations; wherein the improvement comprises:
means for generating control information representative of the storage
address for each of said compressed data segments of said image stored in
said refresh storage means;
an increment directory storage means for storing said control information
at incrementally addressible locations;
a refresh regulator means for decompressing said compressed data segments
of said image into non-overlapping image segments for use by the raster
display, said refresh regulator means including a plurality of
decompressor means for decompressing said compressed data segments of said
image into non-overlapping image segments for use by the raster display
and a plurality of refresh buffer means, one associated with each
decompressor means for storage of said image segments intermediate said
associate decompressor means and said raster display; and
cyclic image refresh control means including means for incrementally
retrieving control information from said increment directory storage
means, said cyclic image refresh control means cyclically and sequentially
gating, under control of said retrieved control information, compressed
data segments of said image from said refresh storage means to one of said
decompressor means and then gating said decompressed image segments to one
of said refresh buffer means for refresh of the image produced by a raster
display at a data rate to adapt the decompression data rate to the data
rate requirement of said raster display.
8. A raster display device refresh system as defined in claim 7 further
including:
overflow indicator means for generating an overflow signal indicative of
coded image data too large for a single display, said overflow indicator
signal controlling the accessing of coded image data for compression by
said conversion means;
means for generating a partition boundary signal in response to said
overflow signal for display on the raster display device; and
retrieving means for retrieving further coded image data of the visual
image, said means for generating a partition boundary being activated by
said retrieving means for generating a partition boundary to identify said
further coded image data.
9. A raster display device refresh system including:
a refresh memory store having coded image information segments
representative of a visual image and stored in addressible locations;
converter means for converting said coded image information into
non-overlapping non-coded raster information for visual display on a
raster display; and
cyclic image refresh control means for generating address locations for
cyclically and sequentially retrieving said coded image information from
said refresh memory store for conversion by said converter means and
display on said raster display;
wherein the improvement comprises:
means for generating control information representative of the storage
addresses and content information for each of said coded image information
segments;
an increment directory storage means for storing said control information
at incrementally addressible locations;
means responsive to said increment directory storage means for generating
an overflow indicator signal indicative of an overflow image too large for
a single display, said overflow indicator signal controlling said refresh
memory store to limit the coded image information segments stored therein;
means for partitioning the coded image information segments in response to
said overflow indicator signal; and
means for generating a partition boundary representation in said increment
directory storage means to define the partitioned visual image data for
display on the raster display;
said cyclic image refresh control means including means for incrementally
retrieving control information from said increment directory store and
responsive thereto for generating said address locations for said refresh
memory store.
10. A raster display device refresh system as defined in claim 9 wherein
said converter means includes:
a plurality of decompressor means for decompressing said coded image
information segments into non-coded raster information; and,
a plurality of refresh buffer means, one associated with each decompressor
means for intermediate storage of said non-coded raster information for
use by the raster display.
11. A raster display device refresh system as defined in claim 9 including:
means for retrieving the remaining coded image information for storage in
said refresh memory store; and
means for activating said means for generating a partition boundary to
identify the retrieved remaining coded image information as part of an
overflow image for display on the raster display.
12. In a raster display device, the combination comprising:
a processor including a memory store for storing visual image data;
compression means for compressing the visual image data retrieved from said
processor memory store under control of the raster display device, into a
plurality of individual compressed non-overlapping image segments;
a refresh image store for storing said image segments at addressible
storage locations;
means for generating control information representative of the storage
address for each of said compressed image segments of said image stored in
said refresh storage means;
an increment directory storage means for storing said control information
at incrementally addressible locations;
a plurality of decompressor means for decompressing said image segments
into visual signals for use by the raster display;
a plurality of refresh buffer means, one associated with each decompressor
means for intermediate storage of said visual signals; and
cyclic image refresh control means including means for incrementally
retrieving control information from said increment directory storage
means, and responsive thereto for generating address locations for
cyclically and sequentially gating compressed data segments of said image
from said refresh storage means to one of said decompressor means and then
to one of said refresh buffer means for refresh of the image produced by
said raster display at a data rate to adapt the decompression data rate to
the data rate requirement of said raster display.
13. In a raster display device as defined in claim 12 further including:
means for generating an overflow indicator signal indicative of an overflow
image too large for a single display, said overflow indicator signal
controlling said processor to limit the visual image data retrieved and
directed to said compression means.
14. In a raster display device as defined in claim 13 including:
means for partitioning the visual image data from said processor in
response to said overflow indicator signal; and
means for generating a partition boundary representation in said increment
directory storage means to define the partitioned visual image data for
display on the raster display.
15. In a raster display device as defined in claim 14 including:
means for retrieving the remaining visual image data from said processor
memory store for compression by said compression means and storage by said
refresh image store; and
means for activating said means for generating a partition boundary to
identify the retrieved remaining visual image data as part of an overflow
image for display on the raster display.
16. A raster display device designed to present image data comprising:
conversion means for compressing binary coded data representative of a
visual image to be displayed;
refresh storage means for storing said compressed binary coded data;
image processing control means for dividing said image data into a
plurality of non-overlapping image segments; said image processing control
means comprising gating means for sequentially activating said conversion
means to compress individual segments of said image data and to place the
data representing the compressed segment in said refresh storage means;
increment directory storage means for storing control information
representative of the storage address for each of said independent
segments of said image in said refresh storage means;
a plurality of decompressor means for decompressing said compressed binary
coded data;
a plurality of refresh buffer means; and
image refresh control means for sequentially gating, under control of said
increment directory storage means, compressed segments of said image from
said refresh storage means to one of said decompressor means and to one of
said refresh buffer means for refresh of the image produced by said
display device.
17. A raster display device refresh system comprising:
a refresh memory store having coded image information segments representing
a visual image and stored in addressible locations;
converter means for converting said coded image information into
non-overlapping non-coded raster information for visual display on a
raster display;
means for generating control information representative of the storage
addresses and content information for each of said coded image information
segments;
an increment directory storage means for storing said control information
at incrementally addressible locations;
cyclic image refresh control means for incrementally retrieving control
information from said increment directory store and responsive thereto for
generating address locations for cyclically and sequentially retrieving
said coded image information from said refresh memory store for conversion
by said converter means and display on said raster display;
means responsive to said increment directory storage means for generating
an overflow indicator signal indicative of an overflow image too large for
a single display, said overflow indicator signal controlling said refresh
memory store to limit the coded image information segments stored therein;
means for partitioning the coded image information segments in response to
said overflow indicator signal; and
means for generating a partition boundary representation in said increment
directory storage means to define the partitioned visual image data for
display on the raster display.
18. A raster display device refresh system as defined in claim 17 wherein
said converter means includes:
a plurality of decompressor means for decompressing said coded image
information segments into non-coded raster information; and
a plurality of refresh buffer means, one associated with each decompressor
means for intermediate storage of said non-coded raster information for
use by the raster display.
19. A raster display device refresh system as defined in claim 17
including:
means for retrieving the remaining coded image information for storage in
said refresh memory store; and
means for activating said means for generating a partition boundary to
identify the retrieved remaining coded image information as part of an
overflow image for display on the raster display. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The invention relates generally to a display image processing system and
more particularly to a refresh system that stores compressed information
of the image.
FIELD OF THE INVENTION
In a display device such as a cathode ray tube type, it is necessary to
continually refresh or retransmit the data to the display since the
retention of the displayed image by the display device is insufficient for
a complete scanning by a human operator. The refresh device continually
retransmits the same image until a new image is required.
The refresh of a display device can be accomplished in either of two ways.
First, the refresh information can be obtained from an uncompressed
representation of the information to be displayed or the refresh
information can be obtained from a compressed representation. Refresh
information from the compressed representation can result in a much less
expensive display subsystem by reducing the amount of memory storage
required to store the refresh information for a single image. The use of a
compressed representation reduces the refresh memory store capacity from
one half to one twentieth of the capacity of that required in a display
that refreshes from the uncompressed representation of the image. A major
cost item in a CRT image display is the cost of the refresh buffer. A
display system based on storage of a compressed representation may offer a
significant cost advantage over a display which refreshes from an
uncompressed representation of the image.
In order to implement a raster display designed to present image data which
accomplishes refresh from a compressed representation of the image, both
of the following problems must be overcome. First, a means must be
provided which permits the display operator to examine the contents of an
image whose compressed representation will not fit in the display refresh
storage. This is known as the partition problem. Second, the instantaneous
peak decompressor data rate problem must be solved. A means must be
provided to permit the use of multiple decompresors in order to reduce the
instantaneous data rate required by a single decompressor.
Existing Alphanumeric (A/N) and vectorgraphic CRT displays generally
refresh from a compressed representation of the information to be
displayed. Alphanumeric displays do not have the partition or data rate
problems because the decompression ratio is constant and always
significantly greater than seven to one. Vector graphic display systems
limit the amount of information which can be presented through the use of
sophisticated system software and thus avoid the partition problem.
Because of the serial nature of the compressed representation used in
vector graphic displays, beam directed presentation formats are used as
opposed to raster presentation formats. Where a raster format is used at
the CRT, a scan conversion process must be employed. The compressed
refresh image display of the present invention can be applied to a vector
graphics display after the scan conversion process, with significant cost
savings as contrasted with an uncompressed refresh display of scan
converted data.
It is, therefore, a prime objective of the present invention to provide
improved apparatus for display image refreshing from a compressed
representation.
DESCRIPTION OF THE PRIOR ART
A refresh system for storing and refresh driving a display system including
a storage for compressed refresh data is disclosed in a copending patent
application SN707,803, filed on July 22, 1976, now U.S. Pat. No.
4,074,254, entitled "An XY Addressable and Updatable Compressed Video
Refresh Buffer for Digital TV Display" and assigned to the assignee of the
present invention. That refresh system discloses a scheme for compressing
the data information of the image for storage in the refresh store
together with a means for mapping and controlling the retrieval of the
stored information. There is no showing of a means to control an overflow
situation.
U.S. Pats. Nos. 3,444,319 to Artyt et al and 3,480,943 to Marber also
discloses schemes for compressing data for driving a scanning display
device. Neither patent discloses a complete refresh system nor a situation
where the pattern is too large to place into the scanning display device
at one time.
Therefore, another object of the present invention is to provide a refresh
system that can control the overflow and partitioning problems using
compressed refresh schemes of the prior art.
Yet another object of the present invention is to provide a refresh
compression system that uses an improved partitioning scheme for the image
display and uses multiple decompression systems for an orderly raster
scan.
SUMMARY OF THE INVENTION
A reproduction system according to the present invention includes a scanner
and a compression processor for compressing the scanned image data output
for storage in a central processing unit memory store. The image data is
selectively retrieved by the display device. The selected image data is
decompressed and recompressed for storage in a refresh image store in the
display system. An indicator is stored in an increment directory store for
each compressed string length stored in the refresh image store and for a
store overflow condition. The compressed refresh image is retrieved from
the image refresh store as needed for initial display and cycled for
refreshing the display. The compressed refresh image is transferred to a
refresh controller under control of a synch generator that keeps track of
the display scanning line and the necessary image data for that scan line.
The compressed refresh image is sequence decompressed in a plurality of
decompressors and stored in associated raster buffers for eventual
serialization to the display device. An overflow indicator in the
increment directory store is provided to alert the operator that, via a
system request, more image data can be obtained to complete the image. The
image and the new data with appropriate indicators is retrieved and
recompressed for storage and display.
The present invention raster display device is designed to present image
data and comprises a conversion means for compressing binary coded data
representative of a visual image to be displayed and a refresh storage
device for storing the compressed binary coded data. Image refresh
processing control means are included for dividing the image data into a
plurality of non-overlapping image segments. The image processing control
means comprises gating means for sequentially activating the conversion
means to compress individual segments of the image data. Increment
directory storage means are included for storing the control of
information representative of the storage address for each of the
independent segments of the image as stored in the refresh storage means.
A plurality of decompressor means and a plurality of refresh buffers
decompress the compressed data and store scan lines for use by the raster
display device. Image refresh control means sequentially gate, under
control of the increment directory storage means, data segments of the
image to one of the plurality of decompressor means. The decompressed
image is then directed to an associated refresh buffer. The refresh buffer
stores scan lines of the image for reproduction by the raster display
device.
The present invention is concerned principally with a refresh system for a
raster display device. Standard refresh systems include a refresh memory
store for storing compressed coded image data, image processing control
means for dividing the image data into a plurality of non-overlapping
image segments, and logic control means for accomplishing the function.
The present invention further provides an incrementally accessible
directory store that stores control information representative of the
storage addresses and content information for each coded image information
segment together with cyclic image refresh control means for incrementally
retrieving the control information and responsive thereto for generating
address locations for cyclically and sequentially retrieving the coded
image information for conversion and display on the raster display.
Further with the present invention, the conversion of the coded image
information is performed by a plurality of refresh systems including a
plurality of sets of decompression processors and refresh buffer stores.
It is, therefore, an object of the present invention to provide enhanced
refresh apparatus for a raster display device.
Another object of the present invention is to reduce the memory store size
requirements in a refresh apparatus for a raster display device by the use
of an incrementally addressed storage means for storing control
information of the image data.
Another object is to provide a reproduction system with an enhanced method
and apparatus for controlling the image display and refresh for a raster
display device.
Yet another object is to provide a refresh control system for a raster
display device that solves the partition problem and the decompressor data
rate problem of prior art compressed refresh systems by the use of an
incrementally addressed storage means and a plurality of decompression
systems.
Still another object is to provide refresh control means for a raster
display device that can be used with compression apparatus which process
the image as a linear string or which process the image in a two
dimensional area scheme.
The display refresh control system of the present invention provides a
means for indicating the starting and trailing edges of a partition of an
image and a means to control the starting raster scan line for the
presentation of an image partition, together with partitioning means for
facilitating the use of displays with differing amounts of refresh memory
store.
Yet another object is to provide refresh apparatus for a raster display
device that operates multiple decompressors in parallel while handling
image partitioning with display control logic together with an ability to
operate with line and area oriented decompressor schemes.
These and other objects of the present invention will become apparent to
those skilled in the art as the description proceeds.
BRIEF DESCRIPTION OF THE DRAWING
The various novel features of this invention along with the foregoing and
other objects as well as the invention itself both to its organization and
method of operation, may be more fully understood from the following
description of illustrated embodiments when read in conjunction with the
accompanying drawings wherein:
FIG. 1 is a block diagram of the refresh apparatus for use with the raster
display device according to the present invention;
FIG. 2 is a block diagram of apparatus for use as the refresh controller of
FIG. 1;
FIG. 3 is a representation of the contents of the increment directory store
of FIG. 2 for an image with three partitioned displays;
FIG. 4 is a block diagram of apparatus for use as the refresh regulator of
FIG. 2;
FIG. 5 is a logic diagram of a typical circuit for use as the increment
controller of FIG. 2; and
FIG. 6 is a representation of the data in the Controller Interface for a
fourteen segment image example.
FIG. 7 is a logic diagram of a typical circuit for use as the IDS
interpretation controller of FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, a complete scanner/display system is shown with a refresh
controller 10 according to the present invention. The scanning portion of
this system includes a scanner 12, a compression processor 14, and a
central processing unit 16 with a memory store 18. The scanner 12 scans an
image, picture element by picture element, to obtain binary data
information representative of each picture element. The binary data
information is directed to the compression processor 14. The compression
processor 14 compresses the data information received from the scanner 12
to a binary data format that represents the image in a reasonable number
of bits for storage by the central processing unit 16 into its memory
store 18.
When the stored image data information is ready for reproduction on a
display device 20, control signals are directed to the central processing
unit 16 to retrieve the compressed image information. In the preferred
embodiment, the display device 20 is preferably a cathode ray tube (CRT)
device. To display the compressed image information on the CRT, the data
information is directed to a decompression processor 22 of a graphics
generator 24 where the data information is reconverted to its original
picture element format.
The output of the decompression processor 22, the picture element data
information, is directed to the refresh controller 10 which recompresses,
stores, decompresses and converts the image data into a visual image on
the CRT device 20.
Display information consisting of Alpha Numeric A/N text and line drawings
(graphics) can be merged with the image data information in the graphics
generator. The ability to merge A/N and vector graphic information with
image information at the display provides the ability to "annotate" or
"mark up" a scanned image with text or line drawing information.
The data image information from the central processing unit 16 can be
directed to an A/N memory store 26 and a graphic memory store 28 of the
graphics generator 24. The data information placed into the A/N memory
store 26 is directed to an A/N generator 30. The output of the A/N
generator 30 is directed to the display 20.
The data information placed in the graphic memory store 28 is directed to a
vector generator 32. The vector generator 32 output is directed to the
display device 20. U.S. Pat. No. 3,973,245 to Karl Belser entitled "Method
and Apparatus for Point Plotting of Graphical Data from a Coded Source
into a Buffer and for Rearranging that Data for Supply to a Raster
Responsive Device", and assigned to the assignee of the present invention,
discloses a computer controller graphics display apparatus which is
representative of the function provided by the graphic memory store 28 and
the vector generator 32.
In general, the refresh controller 10 comprises a refresh compression
processor 34, an image refresh store 36, and a refresh regulator 38. The
refresh controller 10 takes the individual binary information of the
picture elements from the decompression processor 22 and compresses this
information according to the best scheme for refresh compression. This
compressed data from the refresh compression processor 34 is stored in the
image refresh store 36. The compressed refresh data information is
retrieved from the image refresh store 36 by the refresh regulator 38 as
required to continually refresh the data image displayed on the CRT
display device 20. Each dot of each scan line of the CRT device must be
continually repeated in order to keep the image visible on the CRT screen.
There are numerous compression algorithms which can be used within the
refresh controller 10, of FIG. 1. The key requirements are ease of
implementation and control of maximum data expansion for rare input image
bit combinations with compression performance as a secondary factor. The
null suppression technique by S. S. Ruth and P. J. Kreutzer, discussed in
Datamation, September 1972 at pages 62-66 is a good example of a usable
algorithm. There are several suitable algorithms described by T. S. Huang
in the International Conference on Communications, Vol. I, Section 7 pp.
7-11.
The algorithm used in the Compression Processor 14 and it the Decompression
Processor 22 of FIG. 1 should be selected to maximize compression.
Algorithms which maximize compression generally have large data expansion
factors (4 or more to 1) for rare input image bit combinations.
The refresh controller 10 controls the amount of data retrieved from the
central processing unit 16 for display according to the amount of data
information that can be placed onto the screen of the device. This
information is compressed by the refresh compression processor 34 and
placed into the image refresh store 36. The refresh controller 10 recalls
the stored information and controls the decompression of the data in turn
through the refresh regulator. The refresh controller 10 retains an
indication of the amount of information that is being displayed in the
event that the data information to be displayed exceeds the size of the
image data store 36 and the amount of information that can be displayed at
one time. When the amount of data information overflows the display
capacity, the refresh controller 10 recalls, under operator control, the
next block of data from the central processing unit 16 for decompression
by the decompression processor 22 for compression by the refresh
compression processor 34 and for storage in the image data store 36 to
display the next block of data information through the refresh regulator
38. A block diagram for the refresh controller 10 is shown in FIG. 2.
Referring to FIG. 2, the refresh controller includes the refresh
compression processor 34 directing data to the image refresh store 36 via
an IRS bus 40. The compressed data stored in the image refresh store 36 is
directed by the IRS bus 40 to the refresh regulator 38 which includes two
refresh decompression processors 44 and 46, two raster buffers 48 and 50,
and a refresh logic control 52. More than two decompression processors and
two raster buffers can be used to reduce instantaneous peak decompression
data rates. The refresh regulator 38 generates the image data signal which
provides the image to be displayed on the CRT device. The refresh
regulator 38 is controlled by an increment controller 54 which includes a
length increment generator 56 and a control register 58. A logic diagram
of a typical logic circuit that could be used for the increment controller
54 is shown in FIG. 5 and will be discussed later.
The control register 58 accepts the control signals from the central
processing unit 16 and also generates the control signals from the refresh
controller 10 to the central processing unit 16 when more data or a new
image is to be displayed. The increment controller 54 controls the refresh
regulator 38 by a REFRESH ENABLE signal directed to the refresh logic
control 52. The length increment generator 56 via an IDS bus 60 stores an
indication of the data information stored in the image refresh store 36 in
an increment directory store 62. The increment directory store 62 stores a
set of control indicators which is representative of the image data being
displayed. The increment directory store 62 contains information required
by the refresh regulator 38, in order to locate the starting address in
the image refresh store 36 of variable string lengths which contain the
compressed representation of each image increment. There is one entry in
the increment directory store 62 for each image increment on the CRT
display surface. For example, if a simple linear compression scheme were
used, then there would be one entry per raster scan line on the display
device. In a linear compression scheme, one image increment represents one
scan line. If a two-dimensional compression scheme were used, then there
would be one entry in the increment directory store 62 for every two
dimensional area image increment on the CRT display surface. The image
refresh store 36 holds the compressed representation of the image actually
being presented on the CRT display. The refresh compression processor 34
processes the entire image as a collection of non-overlapping image
increments each of which is compressed separately.
The refresh regulator 38 and in particular, the refresh logic control 52,
provides the means for interpreting the contents of the increment
directory store 62 in order to control the refresh data access to the
image refresh store 36 and to control the generation of the starting and
trailing edge indication of a partition image. To provide a better
description of the refresh controller 10 of FIG. 2, the process of
retrieving an image from the memory store of a central processing unit and
its eventual display will be discussed.
A particular compressed image is requested from the memory store 18 by
sending a location address to the central processing unit 16. The
compressed data from the memory store 18 is directed to the decompression
processor 22 (see FIG. 1). The image data from the decompression processor
22 is directed to the refresh compression processor 34 (see FIG. 2). A
description of loading an uncompressed image whose compressed
representation will fit into the image refresh store 36 will be provided
first. Then a description of loading an image which is too large for the
image refresh store will be provided.
The central processor starts by loading the control register 56 with a set
value such as all zeroes to indicate that a new image is being processed.
The uncompressed image data serial bit stream is compressed by the refresh
compression processor 34 which implements the display refresh system
compression scheme. The data output of the refresh compression processor
34 is assembled into words for storage in the image refresh store 36. When
the compressed representation of the first image increment has been stored
in the image refresh store 36, the length of the compressed representation
of the first image increment is placed into the first entry in the
increment directory store 62. The next image increment is compressed and
stored in the image refresh store 36 with subsequent storage of the
compressed representation in the next entry in the increment directory
store 62. This process continues until all image increments have been
processed. At the completion of the input process, the image refresh store
36 will contain the compressed representation for each image increment on
the display and the increment directory store 62 will contain the length
information required to locate the start of the compressed representation
of each image increment.
An absolute addressing scheme for the image refresh store 36 could be
developed rather than the relative length based addressing used in the
preferred embodiment. The absolute addressing scheme would require more
address bits in each entry of the increment directory store 62 and a
slightly more complex control means for handling partition information. In
this preferred embodiment, the image refresh store address of the start
compressed representation of an image increment i can be easily computed
from the first i-1 entries in the increment directory store 62.
When the number of image increments sent from the central processing unit
to be displayed is less than the maximum number to fill the CRT screen,
the unused entries in the increment directory store 62 are filled with the
value 0. An increment directory store entry value of 0 when detected
during the refresh process means that there are no information bits in the
image increment and therefore the refresh regulator 38 will emit an all
"white" image increment.
The next process assumes that the compressed representation of the image as
compressed by the refresh compression processor 34 will not fit into the
image refresh store 36.
First, the manner in which the partition boundaries are generated will be
described. The refresh regulator 38 generates a partition boundary pattern
when the entry in the increment directory store 62 is equal to a special
value, called partition mark. The partition mark could have the value the
nth power minus 1, where n is equal to the number of bits per entry. If
the indicator in the increment directory store 62 is not 0 (the special
indicator for emitting an all white pattern) or the partition mark value,
the associated image increment is generated from the compressed
representation stored in the image refresh store 36 directly. Such direct
reproduction can take place through the refresh regulator. The partition
boundary pattern is used to provide the operator with a visual indication
of the image boundary when a partial image is being displayed and is
generated when a partition mark value is the controlling value in the
increment directory store.
In the most simple case, the boundary pattern could be an all black image
increment. In the general case, the partition boundary pattern would be
stored as a fixed pattern in a "read only storage" extension to the image
refresh store. This would allow the use of complex boundary indicator
patterns without incurring the cost of special purpose pattern generator
logic. Loading of the image proceeds as in the previous example. When the
image refresh store overflow condition is reached, the image increment
number causing the overflow condition is placed into the control register
58 by the length increment generator 56. The value indicator associated
with the partition boundary pattern is stored in the increment directory
store 62 in the next several positions and the value 0 is stored in each
remaining position of the increment directory store. The contents of the
control register 58, the overflow increment value denoted j, is
transmitted back to the central processing unit as part of the ending
status. When all data has been stored in the IRS, the length increment
generator starts the refresh process by sensing the refresh enable signal.
FIG. 3 summarizes the contents of the increment directory store 62 for an
image which requires 3 partition showings on a display device having 1000
scan lines. A linear compressor is used, that is, each image increment is
equal to one full scan line. Under contents, the L(x) representation is
the length in bytes of the compressed representation of scan line i as
stored in the image refresh store. The partition mark value is equal to
255 in the example shown in FIG. 3. Thus, the partition boundary will be
displayed for each line having the indication 255. Partition 1 contains
image lines 1 through 385 with a partition mark displayed in 386, and an
all white image for the remainder. Partition 2 starts all white; has a
partition mark in line 376, then shows image lines 377 through 892 and a
partition mark in line 893 followed by an all white image representation
through line 1000. Partition 3 starts with an all white image, has a
partition mark in 883 and then shows an image at lines 884 through 1000.
To display the subsequent partition of the example image, the central
processing unit preloads a starting image increment value into the control
register 58. Normally, this value will be some number of image increments
earlier in the image than where the overflow occurred, j-10 for the
example shown in FIG. 3. For partition 1, j is equal to 386 and for
partition 2, j is equal to 893. The earlier image increments provides a
visual overlap of the previous image partition with the current partition.
The central processing unit retransmits the entire image for refresh
preprocessing. The image is decompressed by the decompression processor
22, compressed again by the refresh compression processor 34 and directed
to the image refresh store 36. When the control register 58 contains a
value other than 0, the increment controller 54 controls the loading of
the image refresh store and the increment directory store 62. The value 0
is placed in each entry of the increment directory store 62 by the
increment controller 54 until the IDS entry i being processed by the
refresh compression processor 34 is equal to that specified in the control
register 58. A value that generates the partition boundary pattern is
placed in entry i in the IDS. The compressed representation for subsequent
image increment (i+1, i+2, etc.,) is directed to the image refresh store
starting with the first address of the image refresh store. the
development of the compressed representation proceeds as before for the
remainder of the image to be displaced.
After the compressed representation of the image has been stored in the
image refresh store 36 and the refresh control data has been stored in the
increment directory store 62, the refresh regulator 38 takes control to
initiate the display of the image and the refresh process. A block diagram
of the refresh regulator 38 is shown in FIG. 4. The refresh regulator 38
provides the means for controlling the starting and stopping of each
refresh decompression processor and for generating the address used by
each decompression processor to access the image refresh store. The
refresh regulator interprets the contents of each entry in the increment
directory store to insure that the appropriate data is produced by each
refresh decompression processor. T | | |
