GB2146868A - Television receiver - Google Patents

Abstract

In a television receiver the received video signal is processed to increase the displayed number of lines, e.g. by spot-wobble or line frequency doubling, so that each received pixel (1, 2, 3) produces two corresponding pixels to be displayed (4 to 10). The luminance values of two spatially adjacent pixels from different fields (e.g. 10 and 7), or the average luminance value of a group of pixels from one line and the luminance value of a spatially adjacent pixel from a different field are compared. The result of this comparison controls the degree of interpolation between one of the compared pixels (10) and the corresponding pixel in the previous line of the same field (5). If the compared pixels have the same luminance value then no interpolation occurs. <IMAGE>

Description

SPECIFICATION Television Receiver The present invention relates to a television receiver in which the input display signals are proceeded to provide an improved picture.

One well known method of improving a television picture is to increase the number of lines displayed by spot-wobbling the video signal. In this technique, an oscillation (whose frequency is much higher than the line frequency) is applied in order to produce a raster with an undulatory waveform which dwells at the crests and troughs; this results in effectively forming two lines for display from each line received at the television, thereby giving the appearance of greater definition. However, there is no real improvement in definition because each pair of new lines produced by spot-wobbling have video information identical to that of the line that they replace.

In order to produce a real improvement in definition, a line of video information received at the television is interpolated with the temporally prior line in that field; the video information after interpolation is displayed in the upper of the two lines produced by the spot-wobble and the unmodified video information (i.e. in the form in which it arrived at the television) is displayed in the lower of the two lines. However, this arrangement may produce artifacts due to a line of video information from an adjacent field being interleaved with the two lines subject to the interpolation.

While an improved image could be obtained by interpolating between spatially adjacent lines, this would require the storage of an entire field of video information, which would be costly.

In the present invention, a comparison is made of video information in spatially adjacent lines of separate fields, in order to determine what degree of interpolation should be done between temporally adjacent lines of the same field.

Thus the present invention provides a television receiver having: means to store video information of at least some of the scanning lines of a field; means to spot-wobble a scanning line of a field; means to compare video information of one scanning line with stored video information of a spatially adjacent scanning line from the previous field; means to interpolate video information of the one scanning line with video information of a temporally adjacent scanning line in the same field, the degree of interpolation being dependent on the result from the comparison means.

Thus, the difference in video information between the incoming signal and its spatially adjacent line (which is from the previous field) is considered before interpolation, if any, occurs. In this way interpolation is controlled so that the possibility of forming artifacts is significantly reduced.

Preferably the interpolation means is operable only when the comparison indicates there is a substantial difference of video information between the incoming signal and its spatially adjacent line.

The interpolation means may operate with a single predetermined interpolation factor or it may operate with any one of a nubmer of interpolation factors dependent on the result from the comparison means.

A receiver embodying the present invention acts to prevent the formation of artifacts which would occur whenever video information from spatially adjacent lines is the same, while differing from that of the line temporally adjacent to the incoming line.

Also, in the present invention, a comparison can be made between pixels in one scanning line and values of video information, said values being representations of divisions of the spatially adjacent scanning line of the previous field, in order to determine the degree of interpolation between temporally adjacent lines of the same field.

Thus the present invention provides a television receiver having: means to determine a value of video information representative of each of a number of divisions of a scanning line in a field; means to store the representative values of at least some of the scanning lines of a field; means to spot-wobble a scanning line of a field; means to compare the value of video information of a pixel in a scanning line with the stored representative value of the corresponding division of the spatially adjacent scanning line from the previous field; means to interpolate the video information of said pixel with that of a corresponding pixel of the temporally adjacent scanning line in the same field, the degree of interpolation being dependent on the result from the comparison means.

By making a comparison with representative values of divisions of the lines in the prior field, a store of comparatively small capacity is used, thereby maintaining cost of the apparatus low. The representative value may be the mean of the video information within a division; alternatively the value of video information of the middle pixel in a division may be used as the representative value.

A division may have a representative value for each of a number of different parameters; thus for a colour television receiver, a division may have one representative value corresponding to the luminanice contents and another for the chrominance contents.

According to another aspect of the present invention, double frequency scanning can be used either in addition to, or as an alternative to, spotwobbling.

Thus the present invention also provides a television receiver having: means to store video information of at least some of the scanning lines of a field; means to provide double frequency scanning of a scanning line of a field; means to compare video information of one scanning line with stored video information of a spatially adjacent scanning line from the previous field; means to interpolate video information of the one scanning line with video information of a temporally adjacent scanning line in the same field, the degree of interpolation being dependent on the result from the comparison means.

In order that the invention may more readily be understood, a description is now given, by way of example only, reference being made to the accompanying drawings in which: Figure 1 is a diagrammatic representation of signal processing in a conventional monochrome television receiver; Figure 2 is a diagrammatic representation of signal processing in a monochrome television receiver embodying the present invention; and Figure 3 is a block diagram of apparatus which operates generally in accordance with signal processing described with reference to Figure 2.

In order to show simply how known apparatus differs from apparatus of the present invention in processing certain combinations of pixels, Figures 1 and 2 utilize simpie representations for indicating characteristics of the pixels involved. Thus a rectangular box represents a pixel of monochrome video information, with the hue of each box indicating the relative luminance value of that pixel.

The left half of each Figure shows corresponding pixels of successive lines as transmitted to the television receiver, and the right half of each Figure shows the resultant pixels after processing as they would be used for display on the television screen.

The pixels associated with the n+1 line are drawn with broken lines to indicate that they are in the earlier field of the same frame, due to the interleaving operation.

Taking in detail Figure 1 first, this shows a situation in which a television receiver receives a video signal having the form of a white pixel 1 (i.e.

with a luminance value which would result in a white dot displayed on the screen) at a given point along line n, a black pixel 2 at the same point along line n+1, and a black pixel 3 at the same point along line n+2. The prior art apparatus processes the signal by firstly spot-wobbling each pixel and then interpolating the upper resultant pixel (of each original line) with the corresponding pixel in the temporally prior line. Thus, in Figure 1, white pixel 1 is processed as described to produce an upper pixel 4 (whose luminance value is dependent on that of the corresponding pixel in line n-2) and a lower pixel 5 which is white in accordance with white pixel 1. It is assumed that the previous frame was of such a form that processing of pixel 2, resulted in two black pixels 6 and 7.Pixel 3 is spot-wobbled to produce two black pixels, of which the upper 8 becomes grey after interpolation with white pixel 5, and the lower 9 is not subject to interpolation and remains black. Thus the final image displayed on the television screen has an artifact formed by grey pixel 8 being within a group of black pixels 6,7 and 9. Thus while this processing of the transmitted video signal may produce a denser, more detailed image in that there are more lines displayed on the screen, the image will be subject to artifacts which detract from the quality of the image.

Now, the signal processing of Figure 2 differs from that described with reference to Figure 1 in that the amount of interpolation occurring to a pixel is dependent on the relative luminance values between that pixel and its spatially prior pixel; more particularly, there is no interpolation of a pixel if it has the same value as the spatially prior pixel. Thus, as before, spot-wobbling of black pixel 3 produces an upper black pixel and a lower black pixel; however, in this case, a comparison is then made between the luminance values of this upper black pixel and pixel 7 and, since they are the same, no interpolation occurs between this upper black pixel and pixel 5. Thus the signal for display on the screen has a black pixel 10 in place of the grey pixel 8 in Figure 1, so that the image on the screen will have no corresponding artifact.Clearly, similar processing occurs for pixels 1 and 2. Also, it is evident that the processing described above is equally advantageous for combinations of pixels in which pixel 1 is black and pixels 2 and 3 are white.

Figure 3 discloses, in block diagram form, apparatus which can perform generally the signal processing as described with reference to Figure 2, differing only in that the apparatus makes a comparison between individual pixels of one line with a group of pixels in the previous line.

Thus a television aerial 21 receives a broadcast video signal and feeds it to a receiver 22. There, the lines (e.g. the n+1 line in Figure 2) of a field are passed into a unit 23 which separates each line into divisions each with a predetermined number of pixels, and then evaluates an average luminance value for each division; all of these average values are then held in store 24.

The lines of the subsequent field (e.g. then and n+2 lines in Figure 2) are passed through spotwobbling unit 25 and the resultant signals are fed into store 26 where they are held to permit a comparator 27 to make a comparison between the luminance value of each pixel in this field and the average value for the appropriate group of the previous field held in store 24.

If the comparator determines that the values are the same, then it instructs store 26 to pass the luminance value of that pixel directly to a television screen 28 for display. However, if it determines that the values are not the same, it instructs store 26 to pass the luminance values of that pixel and of the corresponding pixel in the previous line of the same field to an interpolator 29 which then derives an adjusted luminance value for display on screen 28.

Comparator 27 also instructs interpolator 29 as to the amount of difference between the luminance values which were compared, in order that an appropriate degree of interpolation can be done.

The apparatus described above is used to provide an image with a doubling of line density (e.g. a 1250 line image derived from the conventional broadcast signals of 625 lines) with a minimal risk of producing artifacts and at a low cost compared to existing equipment. The apparatus can be used to improve the quality of the image on a domestic-size screen, or to provide a iarge-screen image of acceptable quality whether for domestic or commercial purposes.

In a modification, the luminance value of the middle pixel in a division is used as the value representing that division, instead of using the average luminance value of all the pixels in that division.

In a modification suitable for colour video signal, the apparatus processes two values of video information for each pixel or division of a line, one value representing the respective luminance characteristic and the other the respective chrominance characteristic. Other than this increased handling capability, the components forming the apparatus are as described with reference to Figure 3.

In one example, unit 23 operates to separate each of the lines into 20 divisions and store 24 retains for each of these divisions one bit representing the luminance characteristic and one bit representing the chrominance characteristic, the total storage per frame necessary in a 625 line format being 11 K bits.

However, since each of the colour difference signals (i.e. R-Y and B-Y) may be either positive or negative, it is necessary to store the "most significant bit" of both to record accurately the line quadrant of the instantaneous colour signal. If this resolution is equated in the luminance signal, then a total of 5 bits is required for each line division of the previous field. A commonly adopted format for the conventional approach to interpolation is to store 6 lines of video information, temporally adjacent, to produce one additional interpolated line of video. To digitize one line of a composite signal requires approximately 13 K bits, so that six lines would require 78 K bits.Thus if storage in the current field is restricted to two lines for interpolation, then 78 K bits minus 26 K bits are available for storing the information of the previous field, if the total amount of storage in the compared systems are equal.

Thus a line can be divided, for interpolation purposes, into sections each of 52x1024 -50 pixels.

275x4 At this degree of division, artifacts of the chrominance characteristics are substantially eliminated, and artifacts of the luminance characteristics are nearly so.

The apparatus shown in Figure 3 can be modified by providing in suitable manner double-frequency scanning of the lines as an addition to, or as an alternative to, the spot-wobbling operation. In one example, incorporating both spot-wobbling and double-frequency scanning, interpolation is applied only to the double frequency scanning, i.e. the two lines produced by the spot-wobble would be identical; also different degrees of interpolation could be applied to three of the four lines.

Any form of the apparatus could be used to provide a 625/50 frame/field display from a 625/50 field source signal if it were considered of paramount importance to eliminate the flicker effect which occurs in conventional television receivers.

Claims (8)

1. Atelevision receiver having: means to store video information of at least some of the scanning lines of a field; means to spot-wobble a scanning line of a field; means to compare video information of one scanning line with stored video information of a spatially adjacent scanning line from the previous field; means to interpolate video information of the one scanning line with video information of a temporally adjacent scanning line in the same field, the degree of interpolation being dependent on the result from the comparison means.

2. A television receiver having: means to store video information of at least some of the scanning lines of a field; means to provide double-frequency scanning of a scanning line of a field; means to compare video information of one scanning line with stored video information of a spatially adjacent scanning line from the previous field; means to interpolate video information of the one scanning line with video information of a temporally adjacent scanning line in the same field, the degree of interpolation being dependent on the result from the comparison means.

3. A television receiver having; means to determine a value of video information representative of each of a number of divisions of a scanning line in a field; means to store the representative values of at least some of the scanning lines of a field; means to spot-wobble a scanning line of a field; means to compare the value of video information of a pixel in a scanning line with the stored representative value of the corresponding division of the spatially adjacent scanning line from the previous field; means to interpolate the video information of said pixel with that of a corresponding pixel of the temporally adjacent scanning line in the same field, the degree of interpolation being dependent on the result from the comparison means.

4. Atelevision receiver according to claim 3, wherein the representative value is the mean of the video information within a division;

5. A television receiver according to Claim 3 or Claim 4wherein a division has one representative value corresponding to the luminance contents and another for the chrominance contents.

6. A television receiver according to any one of the preceding claims wherein the interpolation means is operable only when the comparison indicates there is a substantial difference between the incoming signal and its spatially adjacent line.

7. A television receiver according to any one of the preceding claims wherein the interpolation means operates with any one of a number of interpolation factors dependent on the result from the comparison means.

8. A television receiver substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.