GB2262407A

GB2262407A - Television display apparatus for screen and video signals with different aspect ratios

Info

Publication number: GB2262407A
Application number: GB9223952A
Authority: GB
Inventors: Eiichi Yokoyama
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1991-11-29
Filing date: 1992-11-16
Publication date: 1993-06-16
Anticipated expiration: 2012-11-16
Also published as: GB9223952D0; FR2684510A1; GB2262407B; DE4139403C2; FR2684510B1; DE4139403A1

Description

2262407 1 A SCAN DISPLAY APPARATUS The invention relates to a scan display

apparatus.

When a picture reproduced from a video signal is displayed on a screen whose aspect ratio differs from that of the picture itself or when the picture is displayed after enlargement, a part of the original picture may be missing from the screen of the display due to the difference in aspect ratio.

In order to avoid losing the missing part, methods are well known in which the input video signal is subjected to signal processing such as picture compression or expansion to conform to the constants of the deflection system of the display device prior to display (for example, is Japanese laid open patent publications Nos. 1-221067, 2-92077 and 2-277383) and in which the amplitude of the vertical or horizonal deflection system is modified to compress or expand the picture (for example, Japanese laid open patent publication Nos. 57-206178, 60-119183, 62-128669, 62-271579 = British patent application no. 8602644).

The former signal processing methods, suffer from the defect that picture quality is deteriorated due to the signal processing which compresses or expands the picture.

This tendency is especially noticeable in cases involving a reduction in the number of the scanning lines to be used for displaying the picture. Namely, for example, there are total 525 scanning lines and 483 effective scanning lines appearing on the screen in the NTSC system with an aspect ratio 4:3. When a picture of the aspect ratio 16:9 is displayed on a display device of the NTSC system after signal processing to compress the picture so as to have the same horizontal width as that of the display device, the number of the scanning lines to be used for displaying the picture is decreased (for example, Japanese laid open patent publication no. 2-92077) to only 383 scanning lines. As a 2 result, the details and the preciseness of the picture become insufficient and the so called zig-zag effect may be caused in oblique line parts of the image in certain signal processing methods.

In the latter methods which involve modification of the vertical or horizontal deflection, there is no deterioration in picture quality. However, because in the deflection system the amplitude of a deflection involving a large power is changed, not only are problems experienced with the linearity of the deflection system and in the amplifying elements of the deflection system, but also kinds of display forms will be limited. For example, no display is possible in an area in which no scanning line exists so that that area is wasted. Namely, when the aspect ratio is changed by reducing the vertical scanning width or amplitude to compress the vertical width of the picture, while the number of the effective scanning lines, 483, in the display device remains unchanged, the area which is not scanned remains above or below the displayed picture as much as the vertical amplitude is compressed. Furthermore, there is the problem that signals in the vertical retracing period or data signals or an automatic adjustment signal superimposed during the vertical retracing period are very visible on the screen, because these signals have no relation with the picture. Although it is known to physically blank the part involved so as not to be visible (for example, Japanese laid open patent publication no. 62-128670), this involves a significant increase in cost.

Moreover, if there is an area which is not scanned on the screen and in which the beam current does not flow at all, differences between the screen phosphor in that area and the area in which the current always flows for displaying the picture are caused, resulting in the socalled screen burn or print phenomenon in the course of time. This phenomenon is a serious problem especially in 3 projection tubes for projectors in which a large driving current flows.

It is also well known, that a picture or character information can be displayed by means of the over scanning lines appearing on the screen when the vertical amplitude is reduced or additional scanning lines are inserted in the period generated by shortening the vertical retracing period, (for example, Japanese laid open patent publication Nos. 57-206178 and 60-119183, Japanese laid open utility model publication No. 61-37668). In these cases, the number of scanning lines which can be utilized is few and there is less freedom of display forms.

According to the present invention there is provided a scan display apparatus comprising:

video signal input terminal means to be supplied with an input video signal; sampling means for sampling at least the picture signal part of the input video signal at a predetermined sampling rate; time base conversion means into which, in use, the sampled picture signal or digital data corresponding thereto is written at the sampling rate and from which the same is read out at a rate different from the sampling rate so that a picture signal compressed or expanded in time base is obtained; display means supplied, in use, with the time base compressed or expanded picture signal and for displaying a picture image or images by a scanning beam or beams modulated by the time-base-compressed or -expanded picture signal; and deflection means for generating vertical and horizontal deflection currents to drive the scanning beam or beams; wherein the deflection means is adapted to generate the horizontal deflection current with a frequency different from the horizontal frequency of the input video signal.

4 The invention will be further described by way of non-limitative example with reference to the accompanying drawings, in which:- Figures 1A and 1B of the accompanying drawings are schematic diagrams showing examples of the display forms in a scan display apparatus according to the invention; Figure 2 is a schematic block diagram showing an embodiment of a scan display apparatus according to the invention; Figures 3A through 3F and Figures 4A through 4F are timing charts showing the operation of the scan display apparatus shown in Figure 2; Figure 5 is a schematic block diagram showing another embodiment of a scan display apparatus according to the invention; and Figures 6A through 6L are schematic diagrams showing other examples of display forms to be displayed in the scan display apparatus shown in Figure 5.

When a picture of the aspect ratio 16:9 which is constituted by 525 lines is displayed on a display device having a screen of the aspect ration 4:3 a shown, for example, in Figures 1A and 1B, 525 lines are less than necessary to scan the whole screen of the display device. According to this invention, the oscillating frequency of the horizontal oscillating circuit of the display device is set corresponding to the ratio of the vertical width of the #screen of the display device to the vertical width of the picture to be displayed, so that the number of the scanning liens is increased, for instance. In the example shown in Figure 1A and 1B, this ratio is 4:3, so that the horizontal oscillating frequency is set as 4/3 times as the oscillating frequency for displaying a picture of the aspect ratio 4:3 so as to generate 643 effective scanning lines and 700 lines in total. Thereby the same density of scanning lines as in the part displaying a picture of aspect ratio 16:9 are obtained throughout the screen. Figure 1A shows a case in which the picture is arranged in the middle of the screen and Figure 1B shows a case in which the picture is arranged in the upper side of the screen.

Referring to Figure 2, an embodiment of a scan display apparatus according to the invention is now explained. The scan display apparatus fundamentally consists of a video signal input terminal 1, a synchronizing signal separation circuit 2, time base conversion circuit 3 which includes field memories 3a and 3b or the like, a horizontal oscillating circuit 4, a horizontal deflection circuit 5, a vertical deflection circuit 6 and a display tube 7.

in a case in which a picture is to be displayed is using the same number of the scanning lines as in the picture originally transmitted, the horizontal and vertical synchronizing signals S. and Sv are extracted from the video signal P supplied to the video signal input terminal 1, while the video signal P is supplied to the time base conversion circuit 3 so that a time base compressed or expanded picture signal Pc is produced. The time base conversion circuit 3, for converting the time base of the picture signal contained in the video signal P, consists of a couple of field memories 3a and 3b and a control circuit 3c controlling the field memories 3a and 3b by write and read clock signals and write and read addresses generated in basis of the horizontal synchronizing signal SHf the vertical synchronizing signal Sv and a horizontal synchronizing signal S'., which is independently generated in the horizontal oscillating circuit 4 within the scan display apparatus in synchronism with the vertical synchronising signal Sv. The picture signal Pc is compressed or expanded in time base by the time base conversion circuit 3 is supplied to the display tube 7 in which the 6 scanning beam is driven correspondingly to the horizontal deflection current i. and the vertical deflection current iv derived from the horizontal deflection circuit 5 and the vertical deflection circuit 6 mentioned below, respectively, so as to display the picture.

Referring to Figures 3 and 4, the time base conversion operation will be explained in more detail by taking an example of time-base-compressing a picture of the aspect ratio 16:9 and displaying it on a screen of the aspect ratio 4:3.

The video signal P, for displaying a picture of the aspect ration 16:9 and supplied to the video signal input terminal 1, has the horizontal periods H and the vertical periods V as shown in Figures 3A and 4A, respectively. The picture to be displayed is constituted by effective picture parts H,, within the horizontal periods H which are contained in effective picture parts V, of the vertical periods V. The effective picture parts H, of the video signal P are sampled and analog to digital converted at a predetermined sampling frequency, though not shown in the drawings. The digital picture signal is written in alternation by field in the field memories 3a and 3b at the write addresses and using the write clock signals from control circuit 3c. The write clock and the write addresses are generated in the control circuit 3c on the basis of the horizontal synchronizing signal SH and the vertical synchronizing signal Sv extracted in the synchronising signal separation circuit 2. The digital picture signal written in the memories 3a and 3b is read out in alternation by field from the read addresses determined by the control circuit 3c and using the read clock signals. The read clock signals and the read addresses are generated on the basis of a horizontal synchronizing signal SfH which is generated in the horizontal oscillating circuit 4 in synchronism with the

7 vertical synchronizing signal Sv so as to have a frequency of 413 times the sampling frequency and on the basis of the vertical synchronizing signal Sv. The read out digital picture signal is digital to analog converted to an analog signal so as to become a picture signal Pc consisting of the compressed effective picture parts H, within the compressed effective picture parts V, which is obtained by time base compressing the effective picture parts H, and V, by 3/4, as shown in Figures 3B and 4B, but in practice, for example, one field later respectively. The picture signal Pc is supplied to a picture signal input of the display tube 7. Since the read-out from the memories is so controlled that the digital picture signal is not read out during the periods in which there is no effective picture parts H, in the horizontal periods, according to the horizontal synchronizing signal StHI the pedestal level signal is supplied to the display tube 7.

Meanwhile, the horizontal deflection circuit 5 generates the horizontal deflection current iH as shown in Figure 3E, based on the horizontal synchronizing signal S,, produced in the horizontal oscillating circuit 4, and the vertical deflection circuit 6 generates the vertical deflection current iv having a wave form of the tracing periods V, and retracing periods V, as shown in Figure 4E, based on the vertical synchronizing signal Sv, so that the scanning beam of the display tube 7 is driven by the horizontal and vertical deflection currents i. and iv. Thereby, a picture of with an aspect ratio 16:9 is displayed in the display form as shown in Figure 1A. In this case, if the timing for reading out the digital picture data from the field memories 3a and 3b is adjusted with respect to the vertical synchronizing signal Sv as shown in Figure 4C, the picture is displayed form the top of the screen as shown in Figure 1B. Furthermore, if the level of the picture signal

8 supplied to the display tube 7 is set higher than the pedestal level, as shown by the broken line in Figures 3B, 4B, 3C and 4C during the period in which the time base compressed picture signal Pc does not exist, the beam current flows even where the picture is not displayed, so that the screen burn or print phenomenon is prevented. For this purpose, a combination of a level signal generating circuit 8 or 81 and a switch 9 or 91 is provided as an option before or after the time base conversion circuit 3 as shown in Figure 2. In this structure, either field memories 3a and 3b having a capacity of more than the amount of picture data of one field are used and the level signal from the level signal generating circuit 8 and the video signal from the video signal input terminal 1 are supplied in alternation through the switch 9 at the predetermined timing to the corresponding area of the memories 3a and 3b, or the level signal from the level signal generating circuit 81 and the video signal from the memories 3a and 3b are supplied in alternation through the switch 91 at the predetermined timing to the display tube 7.

In the case that the supplied video signal is a picture having a 4:3 aspect ratio, the 4:3 aspect ratio picture can be displayed on the whole screen by compressing the video signal in time base at the timing as shown in Figure 4C and by modifying the duty ratio of the tracing periods Vt and retracing periods V, of the vertical deflection current i1v as shown in Figure 4F but keeping the amplitude thereof the same as shown in Figure 4E.

Now referring to Figures 5 and 6, other embodiments of the scan display apparatus according to the invention will be explained. In the embodiment explained above, when a picture with an initial aspect ratio 16:9 is displayed on a screen with an aspect ratio 4:3, there are one or more areas which do not display any picture on the upper or lower part of the screen. Since usable scanning 9 lines exist in that area, however, it is possible to display in that area other information such as information generated from a signal/data generating device built-in the display apparatus or information received from characters broadcasting, i.e. teletext or video text in a manner such as not to be overlapped with the picture already displayed. Especially, when subtitles or caption and so on are to be displayed on the area, there is no problem because there is no overlapping of imaging within the displayed picture.

To implement the above, instead of the level signal generating circuit 8 or 81 in the embodiment shown in Figure 2, a picture processing circuit 10 or 101 as shown in Figure 5 may be used. The picture processing circuit 10 or 101 may produce characters or picture data by itself or handles video signal supplied from outside the apparatus. The picture processing circuit 10 or 101 and/or the switch 9 or 91 changes over the picture signals and the picture signal from the picture processing circuit 10 or 101 is supplied to the display tube 7 after the picture data of the main picture area are read out from the field memories 3a and 3b as shown in Figure 4D. In order to do this, either field memories 3a and 3b having a capacity of more than the amount of picture data amount of one field are used and the picture processing circuit 10 and/or the switch 9 is controlled so that digital picture data from the picture processing circuit 10 is written in the remaining area of the field memories 3a and 3b other than the area for the main picture data, or the picture processing circuit 10, and/or the switch 9f is controlled so that the picture signal form the picture processing circuit 101 is supplied to the display tube 7 after the main picture data are read out from the field memories 3a and 3b.

Several examples of the above described scan display apparatus will be explained below. In the case that main picture HM1 with an initial aspect ratio 16:9 is displayed with 525 scanning lines on a display apparatus having a screen with an aspect ratio 4:3 from the top as shown in Figure 6A, since the lower area of the screen in which the main picture HM1 is not displayed can be utilized for displaying three sub-pictures HSI, HS2 and HS3 of 16:9 aspect ratio or four sub-pictures SS1, SS2, SS3 and SS4 of 4:3 aspect ratio as shown by the broken line, respectively by 175 scanning lines, namely 525/3 lines, the original picture data of the sub-pictures is compressed by 1/3 by thinning out in the horizontal and vertical directions and the obtained compressed pictures are displayed there. In order to display the sub- pictures HSI, HS2 and HS3 or SS1, SS2, SS3 and SS4, the compressed picture data are arranged, as shown in Figures 3D, 4D, 3D' and 4D1, in the positions of the respective horizontal and vertical periods corresponding to the area in which the sub-pictures are arranged on the screen. This display form is well known as the Picture out Picture (POP) function and the respective compressed pictures may be pictures from different sources or pictures form a single source at different times. In the above case, since the number of scanning lines for displaying the compressed picture is in integral proportion to that for the original picture, only the signal processing necessary to thin the data out is required and is very simple.

As other variations, the display forms as shown in Figures 6B through 6L are also possible. Because the above methods are applied to display in these forms, detailed explanation will be omitted. Figures 6B through 6H relate to a display apparatus having the aspect ratio 4:3 and Figures 61 through 6L relate to a display apparatus having the aspect ratio 16:9. In Figure 6B, a main picture of the aspect ratio 4:3 which is compressed by 9/16 to the screen size of the display tube is displayed by 525 lines and 7 sub-pictures of 35 the aspect ration 4:3 which are compress by 1/16 to the 11 screen size are displayed by 175 lines respectively on the surrounding area thereof. In Figure 6C, four pictures of 4:3 aspect ratio which are compressed by 114 to the screen size are displayed equally by 525 lines respectively. in Figure 6D, two main pictures of 4:3 aspect ratio which are compressed by 1/4 to the screen size are displayed on the middle of the screen equally by 525 lines and five sub pictures of 4:3 aspect ratio which are compressed by 1/16 to the screen size or other character information and so on are displayed on the above and below the main pictures by 52512 lines respectively. In Figure 6E, two main pictures of aspect ratio 4:3 which are compressed by 1/4 to the screen size are displayed on the upper side of the screen equally by 525 lines or 52512 lines and other information is is displayed on the above and below the main pictures by suitably distributed number of lines respectively. In this case, it is not always necessary that the density of the lines for displaying the main pictures are equal to that for displaying the other information. In Figure 6F six pictures of aspect ratio 4:3 which are compressed by 1/9 to the screen size are displayed separately on the upper side and lower side of the screen by 525 lines or 525/2 lines and other information is displayed therebetween by suitably distributed number of lines. In Figure 6G, a high definition picture of aspect ratio 16:9 is displayed by 1125/2 lines or 1125/3 lines. Figure 6H, a high definition picture of aspect ratio 16:9 is displayed on the upper side of the screen by 112512 or 112513 lines and a sub-picture or other information is displayed on therebelow. In Figure 6E or 6F, although the number of scanning lines is reduced by a ratio of an integer to the original number, it is appropriate to display the pictures in this method in the case that the performance of the display apparatus is inferior to the original signal in fineness of detail and the preciseness even if the same number of scanning lines as 12 the signal has are used to display the picture. This is especially suitable to display the HDTV signal on a normal display apparatus. As in the above, the number of the scanning lines to be added may be selected to obtain the highest quality on the display apparatus.

Similarly to the above, in Figure 61, two main pictures of aspect ratio 4:3 are displayed equally on the middle of the screen by 525 or 52512 lines and other information is displayed on above and below the main pictures by the suitably distributed number of lines. In Figure 6J, three pictures of aspect ratio 4:3 are displayed equally on the upper side of the screen by 525 lines and two pictures of aspect ratio 16:9 are displayed equally on the lower side of the screen by 525 lines and other information is displayed on the remaining part. In Figure 6K, a main picture of aspect ratio 4:3 is displayed by 1050 lines (525 lines times two) and three sub-pictures of aspect ratio 4:3 are displayed vertically on the right side thereof by 1050/3 lines and other information is displayed on the remaining part. In Figure 6L, two main pictures of aspect ratio 4:3 are displayed by 525 lines and two sub-pictures of aspect ratio 4:3 and other information is displayed on the remaining part thereof by 525 lines.

Various forms of display other than the above are applicable, if necessary. The display apparatus to be utilized is not only limited to a display tube; any display of projection type, for example, such as direct beam scanning type or projection tube type, can be used as well.

According to the invention, the quality of the picture which is displayed is not degraded and the screen burn or print phenomenon caused on a display screen is prevented, so that the technology is suitable for projector or such like. This invention is applicable to display apparatuses of any kind of aspect ratio. In case of displaying a picture by thinning out by a ratio of an 13 integer, the apparatus can be very simply constructed without any interpolation between scanning lines.

14

Claims

1. A scan display apparatus comprising: video signal input terminal means to be supplied with an input video signal; sampling means for sampling at least the picture signal part of the input video signal at a predetermined sampling rate; time base conversion means into which, in use, the sampled picture signal or digital data corresponding thereto is written at the sampling rate and from which the same is read out at a rate different from the sampling rate so that a picture signal compressed or expanded in time base is obtained; display means supplied, in use, with the time base compressed or expanded picture signal and for displaying a picture image or images by a scanning beam or beams modulated by the time-base-compressed or -expanded picture signal; and deflection means for generating vertical and horizontal deflection currents to drive the scanning beam or beams; wherein the deflection means is adapted to generate the horizontal deflection current with a frequency different from the horizontal frequency of the input video signal.

2. A scan display apparatus according to claim 1, wherein the aspect ratio of the picture to be displayed by the input video signal is different from the aspect ratio of the screen of the display means.

3. A scan display apparatus according to claim 2, wherein the picture to be displayed by the input video signal has the aspect ratio 16:9 and the screen of the display means has the aspect.ratio 4:3.

is

4. A scan display apparatus according to claim 3, wherein the picture to be displayed by the input video signal is constructed by 525 scanning lines and the screen of the display means is scanned by 700 scanning lines.

5. A scan display apparatus according to claim 2, wherein other information than the above said picture can be displayed on the remaining area which is left by the difference of the aspect ration of the above said picture and the screen of the display means and in which the above said picture is not displayed.

6. A scan display apparatus constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.