Method and apparatus for automatic pixel clock phase and frequency correction in analog to digital video signal conversion
a technology of analog to digital video signal and phase and frequency correction, which is applied in the direction of automatic control, instruments, television systems, etc., can solve the problems of improper setting of the number n of pixel clocks, degrading the quality of the lcd image, and imperfect a/d conversion
Inactive Publication Date: 2009-03-24
SEIKO EPSON CORP
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Benefits of technology
This solution provides automatic correction of phase and tracking errors, ensuring high-quality digital video signals for multimedia projection systems, improving user-friendliness and reducing manual intervention by iteratively adjusting the pixel clock settings to align with the active video region.
Problems solved by technology
Unfortunately, such A / D conversion is often imperfect due to errors in the pixel clock sampling of the analog signal.
Such sampling imprecision gives rise to frequency (also know as “tracking”) and “phase” errors, both of which may degrade the quality of the LCD image.
Referring to the analog video signal 1 and pixel clock signal 4′ in FIG. 1b, tracking error results from the number n of pixel clocks being improperly set.
On the other hand, if n is set too small (i.e. the pixel clock signal frequency is too low), the dispersion of the pixel clock pulses results in a rightward drift wherein sampling may also occur in the transition regions.
In all of these cases, the erroneous sampling provides erroneous video signal data that may degrade the LCD image quality.
Phase error may occur even if the pixel clock signal frequency equals the analog video data signal frequency.
In any case, phase error is undesirable in generating undesirable noise, or “snow” in the LCD video image.
While such manual error control is usually effective in achieving an acceptable image quality, such manual control is time-consuming and inhibits the user-friendliness of the projection system.
Method used
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[0064]An exemplary image edge detection method will now be described in conjunction with the exemplary screen image shown in FIG. 6. The determination of the actual image width W for a single frame will be described, with the assumption that that the original image has a resolution of 640×480. Referring to the look-up table, the number of lines / frame is 525, and n is 800. In this example, the pixel position will be designated by Cartesian coordinates corresponding to the horizontal line position and vertical line of the pixel.
[0065]The exemplary screen image 140 is a diamond-shape 142 above a horizontal menu bar 144. A margin of blanked pixels 146 (bounded by a dashed line) extends along the sides and the top and bottom of the active image region 148. The diamond has an upper point at horizontal pixel position 400, 20. The diamond widens to a pair of side points on the same horizontal pixel line at respective pixel positions 200, 300 and 600, 300. The diamond has a lower point at ho...
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A methodAn apparatus and system for producing a digital video signal from an analog video signal, the analog video signal including an analog video data signal that is raster scanned in lines across a CRT screen to form consecutive frames of video information, the raster scanning controlled by use of a horizontal synchronizing signal (Hsnyc)(Hsync) that controls a line scan rate, and a vertical synchronizing signal (Vsnyc)(Vsync) that controls a frame refresh rate, to produce consecutive frames of video information, wherein the digital signal is produced by generating a pixel clock signal with pixel clocks for repetitively sampling instantaneous values of the analog video data signal, and digitizing the analog video data signal based on the pixel clock sampling. An expected width E, measured in number of pixel clocks, of a video image producible by the analog video signal is estimated, and an actual width W, measured in number of pixel clocks, of the video image producible by the analog video signal is calculated. The actual width W is compared with the expected width E. When E does not equal W, at least one of a frequency component and a phase component of the pixel clock signal is adjusted until E equals W.
Description
[0001]Notice: More than one reissue application has been filed for the reissue of U.S. Pat. No. 5,805,233. The reissue applications are application Ser. Nos. 09 / 660,435, now issued as RE38,618, and 10 / 851,979 (the present application), which is a continuation reissue application of Ser. No. 09 / 660,435.<?insert-end id="INS-S-00004" ?>FIELD OF THE INVENTION[0002]The present invention pertains to converting from an analog video signal to a digital video signal, and in particular to converting from an analog signal to a digital signal, and particularly for .BACKGROUND AND SUMMARY OF THE INVENTION[0003]Presentations using multimedia projection display systems have become popular for purposes such as sales demonstrations, business meetings, and classroom sessions. In a common mode of operation, multimedia projection display systems receive analog video signals from a personal computer (PC). The video signals represent still, partial-, or full-motion display images of the type render...
Claims
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IPC IPC(8): H04N5/04G09G5/08H04N5/12H04N5/46H04N5/74G09G3/20G09G5/00G09G5/18
CPCG09G3/20G09G5/008G09G5/18H04N5/126H04N5/46H04N5/7441H04N2005/745
InventorWEST, MICHAEL G.
OwnerSEIKO EPSON CORP