Facsimile and static presentation processing – Static presentation processing – Attribute control
Patent
1986-06-18
1988-02-23
Groody, James J.
Facsimile and static presentation processing
Static presentation processing
Attribute control
358166, 340793, H04N 967, H04N 520, G09G 300
Patent
active
047274140
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to circuit means for converting digital signals representing color information into analog voltage level signals to be applied to a monochrome CRT monitor for displaying information generated by a data processing system. The invention has application, for example, to the display monitor of a personal computer.
DESCRIPTION OF THE RELATED ART
CRT monitors display information in the form of text and/or graphics (hereinafter referred to as foreground information) against a background which may be uniform over the CRT screen. With color CRT monitors, an attribute register supplies digital data representing color information (red, green, blue or combinations thereof, with or without an intensity component) for foreground and background channels to a multiplexer The multiplexer output is applied to the color CRT as the normal RGBI signal. Some personal computers, for example, may be supplied with either a color or a monochrome CRT monitor, at the option of a customer. However, it is desirable that such computers should utilize the same software regardless of whether they have a color or a monochrome CRT monitor, and accordingly the monitor of such a computer may utilize input data representing color information even if the monitor is a monochrome CRT. If colored information is to be displayed on a monochrome CRT, each color must be converted by a digital-to-analog converter to an analog voltage representing a step in a grey scale.
A problem arising with monochrome monitors utilizing input data representing color information is that the contrast between the grey scale values for foreground information and background may be rather poor for certain color combinations, e.g. blue on black.
SUMMARY OF THE INVENTION
Thus, it is an object of this invention to provide circuit means for use with a monochrome CRT monitor which alleviates the problem referred to above.
According to the invention, there is provided circuit means for converting digital signals representing color information into analog voltage level signals for application to a monochrome CRT monitor, characterized by a resistor network to which said digital signals are applied in operation, said resistor network being arranged to generate a voltage output in response to said digital signals, said voltage output determining the analog voltage level signals for application to said monitor, and by further resistor means to which is applied in operation a further digital signal indicative of whether foreground information or background is to be displayed, said further resistor means being operatively connected to said resistor network and the value of said further resistor means being so chosen that a relative shift is brought about between the voltage range within which said analog voltage level signals lie when foreground information is to be displayed and the voltage range within which said analog voltage level signals lie when background is to be displayed, said shift being in such a sense as to enhance the contrast between foreground information and background.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way or example, with reference to the accompanying drawings, in which;
FIG. 1 is a block diagram of input circuitry for a monochrome CRT monitor, including circuit means according to the present invention;
FIG. 2 is a more detailed diagram of the circuit means according to the present invention;
FIG. 3 is a diagram showing the foreground and background colors expressed as voltage levels appearing at the output of a digital-to-analog converter;
FIG. 4 is an illustration of a character showing the voltage ranges of FIG. 3 for the foreground and background; and
FIG. 5 is a block diagram of a modified version of the input circuitry shown in FIG. 1, showing an inverse logic decoder.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, color attribute signals from an attribute register are shown as inputs to a multiplexer 10. The three color signals for
REFERENCES:
patent: 4236175 (1980-11-01), Groothius
patent: 4251755 (1981-02-01), Bryden
patent: 4274094 (1981-06-01), Noguchi
patent: 4481529 (1984-11-01), Kerling
patent: 4626835 (1986-12-01), Nienaber et al.
patent: 4688031 (1987-08-01), Haggerty
Laupheimer Wolfgang
Ranf Karl H.
Bauer Robert M.
Groody James J.
Hawk Jr. Wilbert
NCR Corporation
Salys Casimer K.
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