Apparatus for shade gradation enhancement and flicker reduction in multishade displays

• US 5,313,224 A
• Filed: 04/08/1992
• Issued: 05/17/1994
• Est. Priority Date: 04/10/1989
• Status: Expired due to Term

• Current Assignee: NVIDIA Corporation
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Singhal, Dave M., Richter, Bryan, Abudayyeh, Jihad Y., Bassetti, Chester F. Jr.
• Primary Examiner(s): BRIER, JEFFERY A
• Application Number:
  US07/865,091
• Time in Patent Office: 769 Days
• Field of Search: 340/793, 340/767, 340/701, 340/703, 345/89, 345/99, 345/148
• US Class Current: 345/89
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 2320/0266 Reduction of sub-frame artefacts
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2360/18 Use of a frame buffer in a display terminal, inclusive of the display panel
• CPC Class Codes: G09G 3/20 for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
• CPC Class Codes: G09G 3/2003 Display of colours specific for liquid crystal displays G09G3/3607
• CPC Class Codes: G09G 3/2007 Display of intermediate tones
• CPC Class Codes: G09G 3/2025 the sub-frames having all the same time duration
• CPC Class Codes: G09G 3/2051 with use of a spatial dither pattern
• CPC Class Codes: G09G 3/2092 Details of a display terminals using a flat panel, the details relating to the control arrangement of the display terminal and to the interfaces thereto suitable for both CRT and flat panel G09G5/003; specific for a CRT G09G1/165
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers
• CPC Class Codes: H04N 3/127 using liquid crystals

Abstract

A method and apparatus for increasing the perceived gradation of the shades in visual displays is disclosed. A plurality of signals control the intensity of a sub-pixel of a display so that display can exhibit a native number of shades. Frame rate modulation techniques are used to increase the perceived gradation. Finally, flicker is reduced by spreading the phases of the modulating pixels across time, and the horizontal and vertical axes of the display.

Claims

1. In a display system having a multishade display panel in which a plurality of pels are arranged as dots within a plurality of lines, so that each pel is identifiable by a line number and a dot number, wherein the shade of each pel is selectable from N different native shade levels, where N is greater than two, and the shade of each pel can be selected on a frame by frame basis in a sequence of frames, an apparatus for increasing the number of selectable shade levels comprising

means for specifying from the N different native shades a first native shade to which a pel is to be driven;

and

means coupled to the specifying means and responsive to the dot and line number of the pel being driven and to the frame number in the sequence of frames for selecting a second shade different from the first shade so that the pel is driven to the second shade over selected frames in the sequence of frames, and so that, with respect to neighboring pels which are being driven with more than one shade during the sequence of frames, the change between the native shades in any one pel is out of phase with the change between native shades in neighboring pels.

2. In a display system having a multishade panel in which a plurality of pels are arranged as dots within a plurality of lines, so that each pel is identifiable by a line number and a dot number, wherein the shade of each pel is selectable from N different native shade levels, where N is greater than two, and the shade of each pel can be selected on a frame by frame basis in a sequence of frames, an apparatus for increasing the number of selectable shade levels comprising

means for specifying a first native shade for driving a pel in one frame and a second native shade, different from the first native shade, for driving the pel in a different frame in the sequence of frames to provide an apparent shade for the pel which is an average of the number of times the selected first and second native shades are driven in the sequence of frames;

and

means coupled to the selecting means and responsive to the dot and line number of the pel being driven and to the frame number in the sequence of frames for controlling the specifying means so that the change from frame to frame between the native shades in any one pel is out of phase with the change between native shades in neighboring pels.

3. In a display system having a plurality of pels arranged as dots within a plurality of lines, so that each pel is identifiable by a line number and a dot number, wherein the shade of each pel is selectable from N different native shade levels, where N is greater than two, and the shade of each pel can be selected on a frame by frame basis in a sequence of frames, an apparatus for increasing the number selectable shade levels comprising

means for selecting a native shade to which a pel is to be driven wherein the selected native shade is alternated between a first native shade in one frame and a higher second native shade in a next frame in the sequence of frames to provide an apparent shade for the pel which is an average of the selected first and second native shades;

and

means coupled to the selecting means and responsive to the dot and line number of the pel being driven and to the frame number in the sequence of frames for controlling the selecting means from frame to frame with respect to neighboring pels which are being driven between more than one native shades so as to minimize the number of times that a change from the first native shade in one frame to the higher native shade in the next frame for any one pel occurs when the change in neighboring pels is also from a lower native shade to a higher native shade.

4. In a multishade display system having a plurality of pels arranged as dots within a plurality of lines, so that each pel is identifiable by a line number and a dot number, wherein each pel produces one of N different native shades when it is driven with an associated one of N different drive levels during each frame in a sequence of consecutive frames, where N is greater than two, an apparatus for increasing the number of shades comprising

means for driving a subject pel during the sequence of consecutive frames in a selected phase-pattern and frame rate duty cycle to produce a first native shade in one or more of the frames and to produce a second native shade, different from the first native shade, in the other frames, so that the subject pel has an apparent shade over the sequence of consecutive frames which is intermediate the first and second native shades, wherein the apparent shade is determined by the selected frame rate duty cycle which specifies the number of frames in the sequence of consecutive frames in which the subject pel is driven to produce the first native shade and the number of frames in which the subject pels is driven to produce the second native shade, and further wherein the selection of the particular frames in which the first native shade is produced and of the frames in which the second native shade is produced is determined by the selected phase-pattern;

and

means responsive to the dot number, the line number and the frame for the subject pel for selecting a phase-pattern for driving the subject pel and selecting phase-patterns for driving neighboring pel so as to minimize from frame to frame the number of neighboring pels in which the transition between native shades is in the same direction as the direction of the transition between native shades in the subject pel.

5. In a display system of the type which includes a multishade display panel in which a plurality of pels are arranged as dots within a plurality of lines, so that each pel is identifiable by a line number and a dot number, and in which each pel can be driven with one of N discrete drive levels to provide one of N native shade levels, an apparatus for increasing the number of shades comprising

means responsive to the dot and line numbers of a subject pel for generating frame rate cycling waveforms and which are associated with pels of the multishade display panel according to phase-placement patterns, wherein the frame rate cycling waveforms and the phase-placement patterns are of the type which can be used with passive liquid crystal display panels to obtain multiple gray scale intensities in a manner which minimizes in-phase relationships of neighboring pels;

and

means responsive to the frame rate cycling waveforms from the generating means and to a selected native shade for modulating the selected native shade to provide a display data waveform which varies from the selected native shade in accordance with the frame rate cycling waveform, and providing a shade which is intermediate the selected native shade and a next native shade.

6. In a display system having a multishade display panel in which a plurality of pels are arranged as dots within a plurality of lines, so that each pel is identifiable by a lie number and a dot number, wherein each pel produces one of N different native shades when it is driven with an associated one of N different drive levels during each frame in a sequence of consecutive frames, an apparatus for increasing the number of shades comprising

incrementer means responsive to a specified native shade and to a modulation control signal for supplying a pel driving signal to drive a subject pel in the multishade display panel, wherein the pel driving signal is formed from the specified native shade as modulated by the modulation control signal, so that the pel driving signal to be either the specified native shade or the specified native shade which has been incremented by a specified amount;

modulation phase generation and separation means responsive to the dot number, the line number, the frame in the consecutive sequence of frames, and to a gradation command, for providing the modulation control signal to the incrementing means, the modulation phase generation and separation means including;

first means which are toggled by the dot number and reset by the line number of the subject pel for providing an indication of when the subject pel is at an "even" dot position;

second means which are toggled by the line number of the subject pel and reset by the frame number in the consecutive sequence of frames for providing an indication of when the subject pel is at an "even" line position;

third means which are toggled by the frame number for providing an indication of when the frame is at an "even" frame position;

exclusive-OR logic means for providing an output which is the logical exclusive-OR of the "even" dot position indication, the "even" line position indication, and the "even" frame position indication from the first, second and third means; and

AND logic means for providing an output which is the logical AND of the gradation command and the output from the exclusive-OR logic means and for supplying the output to the incrementer means as the modulation control signal;

so that from frame the number of neighboring pels in which the transition between native shades is in the same direction as the direction of the transition between native shades in the subject pel is minimized.

7. In a display system having a multishade display panel in which a plurality of pels are arranged as dots within a plurality of lines, so that each pel is identifiable by a line number and a dot number, wherein each pel produces one of N different native shades when it is driven with an associated one of N different drive levels during each frame in a sequence of consecutive frames, an apparatus for increasing the number of shades comprising

decrementer means responsive to a specified native shade and to a modulation control signal for supplying a pel driving signal to drive a subject pel in the display panel, wherein the pel driving signal is formed from the specified native shade as modulated by the modulation control signal, so that the pel driving signal is controlled by the modulation control signal to be either the specified native shade or the specified native shade which has been decremented by a specified amount;

modulation phase generation and separation means responsive to the dot number, the line number, the frame in the consecutive sequence of frames, and to a gradation command, for providing the modulation control signal to the decrementing means, the modulation phase generation and separation means including;

first means which are toggled by the dot number and reset by the line number of the subject pel for providing an indication of when the subject pel is at an "even" dot position;

second means which are toggled by the line number of the subject pel and reset by the frame number in the consecutive sequence of frames for providing an indication of when the subject pel is at an "even" line position;

third means which are toggled by the frame number for providing an indication of when the frame is at an "even" frame position;

exclusive-OR logic means for providing an output which is the logical exclusive-OR of the "even" dot position indication, the "even" line position indication, and the "even" frame position indication from the first, second and third means, and

NAND logic means for providing an output which is the logical NAND of the gradation command and the output from the exclusive-OR logic means and for supplying the output to the decrementer means as the modulation control signal;

so that from frame to frame the number of neighboring pels in which the transition between native hades is in the same direction as the direction of the transition between native shades in the subject pel is minimized.