Television – Image signal processing circuitry specific to television – A/d converters
Reexamination Certificate
1998-11-20
2001-11-06
Eisenzopf, Reinhard J. (Department: 2614)
Television
Image signal processing circuitry specific to television
A/d converters
C348S537000, C341S155000, C375S355000
Reexamination Certificate
active
06313881
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a signal processing method for an analogue picture signal.
The invention is based on a signal processing method for an analogue picture signal of the generic type of the independent Claim
1
. The invention is concerned with the problem of displaying a picture originating from a computing unit (for example personal computer) on the screen of a television set. In other words, therefore, the intention is for a picture which has been generated by a computer in accordance with a set graphics standard (for example EGA, VGA or (S)VGA) to be output via a television set instead of a computer monitor. For this problem area, EP-A-0 697 689 has provided a multiplex unit which enables either the output signal of the computer or the TV video signal to be selected and fed directly to a monitor without any analogue/digital or digital/analogue conversion being carried out. In this case, therefore, use is made of a computer monitor which also has a mode in which standard TV signals can be displayed.
SUMMARY OF THE INVENTION
In a departure from the abovementioned prior art, the intention according to the present invention is for the screen of a television receiver to be used for the display of the computer-generated picture. If the television receiver is equipped with digital signal processing, e.g. for the known 100 Hz technology or for format matching (zoom function in the case of widescreen television receivers) the problem arises whereby the analogue picture signals coming from the personal computer have to be digitized for matching to the picture resolution and picture size of the television receiver. In order to be able to recover the original picture data as faithfully as possible to the original, the analogue picture signals should be sampled at the same frequency and as far as possible also with the same phase as they were originally generated in the graphics card of the personal computer. In other words, pixel-synchronous sampling should be performed.
The method according to the invention, having the features of Claim
1
, solves the problem of sampling at the correct frequency in such a way that first of all analogue/digital conversion is carried out with a pre-set sampling clock pulse and then the picture stored in the process is investigated for picture disturbances in order to determine the correct sampling frequency.
This method enables the computer graphics signals of any desired standard to be reproduced on a TV receiver faithfully to the original.
Advantageous developments of the method are possible by virtue of the measures evinced in the dependent claims. It is advantageous for the investigation of the sampled picture for picture disturbances if the picture signal is divided into a number of sections (for example columns) and the pixel values in the individual sections are added. Afterwards, the same picture is sampled anew at a slightly altered sampling frequency and the pixel values (as before) are added anew in the individual sections. The difference between the summation values in the individual sections for the two sampling operations is then formed. The number of maxima and minima in the distribution of the difference values is counted. The result corresponds in practice to the picture disturbances that occur in the picture. The number of maxima and minima allows a conclusion to be drawn about the difference with regard to the optimum sampling frequency. After the corrected sampling frequency has been set, the operation can be repeated in order to verify that the optimum sampling frequency has been found.
Further specific, advantageous measures for the algorithm regarding the sampling frequency determination are specified in Claims
3
to
14
. A very advantageous measure is the use of a table having the possible sampling frequencies for the known graphics standards in accordance with Claim
10
. If none of the values stored therein has led to the desired result, it is advantageous if a further search operation is carried out such that, proceeding from the first sampling frequency in the table, the sampling frequency is progressively incremented by a defined value until the optimum sampling frequency has been found (see Claims
12
and
13
). If this measure does not lead to the desired result either, the option still remains of varying the division of the picture line into sections and of starting the search anew.
The use of high-pass filtering before the investigation of the data of a sampled picture has the advantage that only the relevant frequencies in the picture are considered.
It is advantageous for the determination of the optimum sampling phase if, for the sampled picture, the absolute value of the difference between two successive pixel values is in each case summed, the sampling phase is progressively incremented or decremented, the sum of the pixel difference values for the picture is in each case calculated anew and then the maximum is determined in the distribution of the summation values for the different sampling phases. The phase setting associated with the maximum then specifies the optimum sampling phase value. The measures are evinced in Claim
16
.
In order to achieve exact determination of the initially unknown horizontal and/or vertical position of the active picture to be displayed, it is advantageous, in accordance with Claim
18
, if the inactive pixels at the edges of the picture to be displayed are counted. In accordance with Claim
19
, the counting of the pixels at the left-hand or right-hand edge of the picture can take place in such a way that the picture is once again divided into a number of sections and the pixel values in the individual sections are added. The summation values are then compared with a threshold value in order to define which sections are filled with pixel values of the edge of the picture and which sections have pixel values of the computer picture to be displayed. The number of sections with summation values below the threshold value at the left-hand and right-hand edge of the picture is counted. Progressive shifting of the sections relative to the pixel values in one direction then takes place. The summation values are in each case determined anew for the new sections and a comparison is once again performed to see whether the summation values lie below the threshold value or now lie above the threshold value. As an alternative, it is also possible to ascertain whether a sum that was previously above the threshold value now lies below the threshold value. The number of pixels in the left-hand or right-hand edge region is then determined using the number of shifts by in each case one pixel and the number of sections with a sum below the threshold value at the beginning of the shifting operations. The exact determination of the position of the picture is required, for example, for subsequent centring of the picture on the screen of the television receiver.
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“Display Mode Detection for Multimode Monitors”. In: IBM Technical Disclosure Bulletin, vol. 37, No. 04B, Apr. 1994, pp. 255-258.
German Search report translated into English citing the above-listed documents: AA, AB, AC, AM, AN, AR.
Article: “Low-Cost IC Provides Quality Video Conversion” by Paul McGoldrick—Electronic Design/Jul. 22, 1996.
European Search Reportwith references identified as AA,AM, AN and AR.
Correa Carlos
Croise Dimitri
Reinhart Wolfgang
Zwing Rainer
Deutsche Thomson-Brandt GmbH
Eisenzopf Reinhard J.
Liao Frank Y.
Shedd Robert D.
Tran Trang U.
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