Computer graphics processing and selective visual display system – Computer graphics processing – Graph generating
Reexamination Certificate
1998-06-25
2002-05-07
Cuchlinski, Jr., William A. (Department: 3661)
Computer graphics processing and selective visual display system
Computer graphics processing
Graph generating
C382S267000
Reexamination Certificate
active
06384825
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of controlling a sparse vector rasterizer.
An oscilloscope presents the activity of an electrical signal to its user. Referring to
FIG. 1
, a conventional raster scan digital oscilloscope includes a display panel
10
having a two-dimensional array of pixels, with each pixel location being uniquely defined by a row number and a column number. The oscilloscope also includes a raster scan memory
14
having a two-dimensional address space. The memory locations in the raster scan memory map on a one-to-one basis with the pixel locations of the display panel
10
. The state of each pixel depends on the contents of the corresponding memory location in the raster scan memory
14
.
In the case of the oscilloscope shown in
FIG. 1
, the raster scan memory stores n bits of information for each pixel, where n is an integer greater than one, which allows each pixel to have 2
n
illumination states. One of the states is off, and in the other 2
n
−1 states, the pixel is illuminated at different respective intensities. Thus, for example, a 4-bit deep raster scan memory can support fifteen levels of partial to maximum illumination (gray scale levels) as well as the dark or off state.
Depending on the nature of the signal and the settings of the oscilloscope, a given column of pixels may contain one or more illuminated pixels (hereinafter referred to as dots). Each column displays a vector, defined as the segment of the column between the uppermost dot in the column and the lowermost dot in the column. The vector has a length (in pixel units) equal to one plus the difference between the row numbers of the top and bottom dots in the column. Thus, if the column contains only one dot, the vector has a length of one unit.
The digital oscilloscope shown in
FIG. 1
also includes an A/D converter
18
having an input terminal for acquiring an electrical signal at a test point in an electronic circuit. The A/D converter samples the signal during an acquisition interval and quantizes the samples to generate a sequence of digital data words. The data words generated by the A/D converter and having values D
1
-DN are stored as a linear waveform record in an acquisition memory
22
having a one-dimensional address space A
1
-AN.
When the acquisition is complete, the linear waveform record stored in the acquisition memory is supplied to a rasterizer
26
which generates a rasterized waveform record and stores it in a rasterizer memory
30
having a two-dimensional address space (X
1
-XN, Y
1
-YN). (The common suffix N is used for economy and is not intended to indicate that the number of elements in the set {Xi}, for example, is the same as the number of elements in the set {Ai}.) The X component of the address of a data word in the rasterized waveform record stored in the rasterizer memory
30
is derived from the address Ai of at least one word of the linear waveform record and the Y component of the address is derived from the value Di of at least one word of the linear waveform record.
Each combination of addresses (Xi, Yi) at which a data word is stored in the rasterizer memory
30
represents an event, characterized by a unique combination of time (dependent on Xi) and signal level (dependent on Yi).
The rasterized waveform record may be added to an existing display record stored in the raster scan memory
14
to control the state of the display panel
10
. Referring to
FIGS. 2A-2C
, in which the numerical values designate units of intensity,
FIG. 2A
represents the original display record for three adjacent columns of the display panel prior to addition of the rasterized waveform record for a new acquisition,
FIG. 2B
represents the rasterized waveform record for the corresponding interval of the new acquisition, and
FIG. 2C
represents the updated display record obtained by adding the rasterized waveform record of
FIG. 2B
to the display record of FIG.
2
A. Thus, if the same event occurs during multiple acquisitions, the value of the data word representing that event in the raster scan memory
14
increases.
As also shown in
FIG. 1
, the contents of the raster scan memory may be influenced by a decay process
34
, which reduces the value stored at each location in the raster scan memory by a selected amount per unit time, so that events that occur only infrequently will be shown with reduced intensity as compared with events that occur more frequently.
The oscilloscope includes a controller
38
, which controls operation of the other components shown in
FIG. 1
, and operator controls
42
which allow the user to adjust the settings of the oscilloscope. The controller
38
is implemented as a state machine, which advances from one state to another in accordance with a stored program and in dependence on inputs received by the state machine.
In one known technique of rasterizing, referred to as the dot mode, the address (Xi, Yi) of a data word of the rasterized waveform record is derived from a single data-address pair of the linear waveform record. Thus, the data words in the rasterized waveform record correspond on a one-to-one basis with the data-address pairs of the linear waveform record.
It is generally considered desirable that the waveform presented to the user of an oscilloscope be substantially continuous, without significant horizontal or vertical gaps between dots. However, when the rasterizer operates in the dot mode, there may be gaps between dots in the display. Accordingly, depending on the signal and the settings of the oscilloscope, the dot mode of rasterizing may not be considered optimum.
In another known mode, referred to as the full vector mode, the rasterized waveform record includes not only data words derived respectively from the data-address pairs of the linear waveform record but also additional data words which are synthesized by the rasterizer to ensure that the waveform is continuous, so that an end point of a vector is offset vertically from the end point of an adjacent vector by no more than one pixel, and all the pixels between the two end points of the vector, as well as the two end points themselves, are illuminated.
The advantage of full vector mode rasterization is also a disadvantage: since there are no gaps in a vector created by the rasterizer, rasterization may require many memory accesses, delaying completion of rasterization.
U.S. Pat. No. 6,104,374, the entire disclosure of which is hereby incorporated by reference herein, discloses a sparse vector mode of rasterizing in which the end points of a vector may be vertically offset from an adjacent vector by more than one pixel and there may be a gap of one or more pixels between two dots in a given vector. Randomization is built into the sparse vector mode, so that even if the linear waveform records for successive acquisitions are identical, the respective arrays of dots will generally not be precisely the same, and gaps in a vector created on one acquisition will be filled in on a subsequent acquisition. An advantage of the sparse vector mode is that it reduces the number of dots that are generated during rasterizing of an acquisition and therefore reduces the time taken to rasterize the acquisition.
One of the variables used in processing the linear waveform record to generate the rasterized waveform record in sparse vector rasterization is the maximum number of dots per vector. The quality of the display increases as the maximum number of dots per vector increases, because with more dots per vector, there are smaller gaps between adjacent dots in a vector. In a practical implementation of the oscilloscope shown in
FIG. 1
, the maximum number of dots D
max
is specified by the variable M, where D
max
is equal to 2{circumflex over ( )}M. In this practical implementation, there are 500 pixels in each column and the maximum value of M is 9, so that D
max
exceeds 500 and it is therefore possible to display a full height vector in full vector mode.
In the sparse vector mode, the actual number of dots per vect
Gerlach Paul M.
Yost Jeff W.
Bucher William K.
Cuchlinski Jr. William A.
Nguyen Thu
Smith-Hill John
Tektronix Inc.
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