Computer graphics processing and selective visual display system – Computer graphics processing – Graphic manipulation
Reexamination Certificate
1999-01-19
2001-12-04
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Computer graphics processing
Graphic manipulation
C345S472000, C345S681000
Reexamination Certificate
active
06326979
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method and apparatus for calibrating a video monitor relative to an external object. More particularly, the present invention relates to a method and apparatus for calibrating any video monitor such that the size of an object displayed on the calibrated video monitor will be the same regardless of monitor size and resolution.
Video monitors generate images on a cathode ray tube (CRT) or liquid crystal display (LCD) by energizing one or more pixels on the CRT or LCD to generate light visible to the user of the monitor. A line, for example, is represented by illuminating a series of adjacent pixels. Pixels are the fundamental building blocks from which all computer graphics are created. A pixel is the smallest possible dot that can be represented on a given video monitor. All pixels on a given monitor are the same size. However, pixel size varies from monitor to monitor.
When displaying to scale the image of an object having a known size, on a given monitor, it is necessary to divide the horizontal and vertical size of the object by a scale factor that is specific to the given monitor. This scale factor is related to the pixel size.
When displaying physiological patient waveforms, e.g., electrocardiogram (ECG) or blood pressure (BP), it is standard to use a vertical scale of 10 millivolts (mV)/millimeter (mm), and a horizontal scale of 25 mm/second (sec.).
If a pixel on a given monitor is known to have a height (vertical) and width (horizontal) of 0.20833 millimeters (mm), the pixel height in a vertical direction of a 1 millivolt (mV) ECG signal, using a vertical scale of 10 mm/mV, is calculated by the following equation:
height of signal=(1 mV×10 mm/mV)/0.20833 mm/pixel
height of signal=48 pixels
Similarly, the pixel width in a horizontal direction (as a function of time) of a 1 mV ECG signal at a scan rate of 25 millimeters per second is calculated by the following equation:
width of signal/time=(25 mm/sec)/(0.20833 mm/pixel)
width of signal/time=120 pixels/sec
SUMMARY OF THE INVENTION
Prior art patient monitoring systems used standardized video monitors so that the scale and scale factor of the systems are fixed. This allows the calculations necessary to accurately display an image of a given size to be programmed into the software of the system.
Present day video display monitors range greatly in size and in pixel resolution. For example, displays on notebook computers have pixel resolutions such as 640×480. Larger 21″ monitors have pixel resolutions such as to 1280×1024. Further, the size of an individual pixel is dependant not only on the dimensions of the screen, but also the resolution of the monitor. For example, a 17″ or 21″ monitor may both have a pixel resolution of 1280×1024, but the actual pixel sizes may be different.
The various sizes available in video monitors, and the various pixel sizes on those monitors, pose a unique problem in designing medical waveform display devices—namely, determining the size that waveforms should be represented on display devices. Displaying some waveforms, such as blood pressure waveforms, is straightforward. Sample values are scaled proportionally between two arbitrary coordinates on the video display. Points are chosen based on available screen area. As more waveforms are added to the display, the vertical area dedicated to a given waveform is reduced, and thus the amplitude of the waveform is proportionally decreased. The horizontal area dedicated to a given waveform is fixed at a rate of 25 millimeters per second.
Electrocardiograph (ECG) waveforms, however, are subject to an industry standard for gain and time base as specified by the Association for the Advancement of Medical Instrumentation (AAMI). The display of an ECG waveform is to be the same size, regardless of the type, size, or pixel resolution of the display monitor used. The AAMI specification is most concerned with aspect ratio (i.e., gain/time). The aspect ratio is derived from a standard value of 10 mm/mV for gain and 25 mm/sec for time. This results in an aspect ratio of 0.4 sec/mV.
Accordingly, the invention provides a method and apparatus to display a waveform such that the size of the waveform remains the same regardless of the type of monitor used to display the waveform. Specifically, the invention allows a user to easily communicate the pixel and screen size of the monitor to the computer thereby allowing the computer to accurately calculate the number of pixels to energize and the rate at which the pixels should be energized in order to accurately display an image to a given scale.
The method of the present invention calibrates a video monitor relative to an external object, such as a ruler. A video representation of an object (a “video” ruler) is displayed on the video monitor. The user then places an external object (a “real” ruler) on the surface of the video monitor. The user changes the size of the “video” ruler to substantially match the size of the “real” ruler.
The invention also provides an apparatus for calibrating a video monitor relative to an external object. The apparatus includes a video monitor for presenting a video display, and means for calibrating the video display relative to a reference external to the monitor.
It is an advantage of the invention to provide a method and apparatus of calibrating a video monitor relative to an external object regardless of the size or resolution of the monitor.
It is another advantage of the invention to display an image on the video monitor, wherein the image has the same size (relative to a scale) regardless of the display monitor being used.
Other features and advantages of the invention are set forth in the following drawings, detailed description and claims.
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patent: 5933134 (1999-08-01), Shich
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patent: 6098048 (2000-08-01), Dashefsky et al.
patent: 6104384 (2000-08-01), Moon et al.
patent: 6124841 (2000-09-01), Aoyama
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GE Medical Systems Information Technologies Inc.
Hjerpe Richard
Michael & Best & Friedrich LLP
Nguyen Kimnhung
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