Image display apparatus

Abstract: An image display apparatus of this invention is an apparatus for displaying an image corresponding to an image signal. An input image signal is converted along the time base into an image signal having an aspect ratio different from that of the input image signal. An image corresponding to the converted image signal is supplied to an image display unit, thereby faithfully displaying an image corresponding to the input image signal without degrading image quality.

Description: BACKGROUND OF THE INVENTION: Filed of the Invention The present invention relates to an image display apparatus for displaying images complying with different types of display schemes. Related Background Art Conventional image display apparatuses capable of selectively switching to display a television signal of a high definition scheme and a television signal of an NTSC scheme are an apparatus having a display screen aspect ratio of 16 : 9 complying with the-high-vision scheme and an apparatus having a display screen aspect ratio of 4 : 3 complying with the NTSC scheme. In the former apparatus, in order to display a television signal of the NTSC scheme, an actual display screen is located at the central portion of the entire display screen, and both sides of the entire display screen are displayed as blank portions. In the latter apparatus, in order to display a television signal of the high definition scheme, an actual display screen is located at the central portion of the entire display screen, and the upper and lower portions of the entire screen are displayed as blank portions. In order to display a television signal of the NTSC scheme in the former apparatus, the normally interlaced NTSC television signal is subjected to interpolation processing, and the interpolated television signal is displayed in the form of a non-interlaced signal. In order to display a high definition television signal in the latter apparatus, interlaced scanning is performed in only the vertical direction or both the vertical and horizontal directions. In addition, the image is compressed, or the resolution is suppressed, and the resultant image is displayed. When an image corresponding to the high-vision television signal is to be displayed on the image display apparatus complying with the NTSC television signal, since interlaced scanning is performed in only the vertical direction or in both the vertical and horizontal directions of the high definition television signal, an image represented by the input television signal cannot be entirely displayed, or image quality may be greatly degraded. Document WO-A-8605644 discloses an image display apparatus for displaying an image corresponding to an input high definition image signal, comprising a television receiver for displaying the image corresponding to the image signal, and image converting means for receiving the input image signal, converting the input image signal with respect to the time base to obtain a standard image signal having an aspect ratio different from that of the input image signal, and supplying the standard image signal to the television receiver. Furthermore, switching means are provided for switching to a widescreen mode in which the input image signal is directly passed to the television receiver without being converted in case a high definition television receiver is used. However, in order to use this apparatus alternatively for both television formats, two complete TV receivers for each TV format are required. Furthermore, in case the high definition image having a 16:9 aspect ratio is displayed in the standard mode (4:3 aspect ratio), a selection signal is required to be input by an operating person to determine the desired portion of the high definition picture which is to be displayed to thereby prevent image distortions due to the different aspect ratios. Furthermore, document EP-A-0 298 362 relates to a device for area enlargement of a television picture, which comprises scanning control means for controlling a scanning range of an image display unit in accordance with an aspect ratio of the image signal supplied from an image converting means. However, this apparatus also requires an external selection signal in order to specify the line portion of the widescreen signal (high definition signal) which is to be displayed on the standard screen. SUMMARY OF THE INVENTION: It is therefore an object of the present invention to provide an improved image display apparatus, which is capable of completely displaying an image corresponding to an input high definition image signal on a high definition display unit as well as on a standard display unit without any distortions. This object is achieved by an image display apparatus as claimed in claim 1. Accordingly, since the scanning range of both display units can be controlled by scanning control means it is possible to convert the time base of the image signal and to encode the image signal before switching it to the desired display unit. Thus, image distortion can be prevented and only the respective display units of the television receivers are required. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a block diagram showing a schematic arrangement of an image display apparatus; Fig. 2 is a block diagram showing a schematic arrangement of an image display apparatus according to an embodiment of the present invention; and Figs 3A to 3D are views showing images displayed on a display device of a monitor apparatus so as to explain an operation of the embodiment shown in Fig. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS: The present invention will be described with reference to an embodiment of the present invention. Fig. 1 is a block diagram showing a schematic arrangement of an image display apparatus a description of which is useful for understanding the present invention. Referring to Fig. 1, a high-vision television signal is supplied to input terminals 1 R , 1 G , and 1 B in the form of R, G, and B signals. The R signal is input from the input terminal 1 R and is band-limited to about 20 MHz by an LPF (Low-Pass Filter) 2 R . The G signal is input from the input terminal 1 G and is band-limited to about 20 MHz by an LPF 2 G . The B signal is input from the input terminal 1 B and is band-limited to about 20 MHz by an LPF 2 B . Signals band-limited by the LPFs 2 R , 2 B , and 2 B are supplied to a matrix circuit 3. The R, G, and B signals input to the matrix circuit 3 are converted into a luminance signal Y, and color difference signals, i.e., R-Y and B-Y signals C R and C B . The Y signal is input to an A/D converter 4a, the C R signal is input to an A/D converter 4b, and the C B signal is input to an A/D converter 4c. The Y signal supplied to the A/D converter 4a is digitized at a 64.125-MHz sampling frequency f S . The digital Y signal is input to a vertical filter 69. The vertical filter 6a has a line delay line, and the structure of sampling points in the vertical direction is converted to perform vertical filtering so as to reduce the number of scanning lines. The digital Y signal processed by a vertical filtering process by the vertical filter 6a is supplied to a horizontal filter 7a. The horizontal filter 7a has a pixel delay line to convert a structure of horizontal sampling points to perform horizontal filtering so as to reduce the number of horizontal sampling points. The digital Y signal obtained after horizontal filtering processing by the horizontal filter 7a is supplied to a field memory 8a. The field memory 8a serves as a buffer for absorbing a time error caused by a difference between the high definition scheme and the NTSC scheme by controlling the write and read timings of the digital Y signal. The digital Y signal converted along the time base by the field memory 8a is supplied to an NTSC encoder 10. The C R signal supplied to the A/D converter 4b is digitized at a 32.0625-MHz sampling frequency f S '. The C B signal supplied to the A/D converter 4c is converted at a 32.0625-MHz sampling frequency f S ' as in the A/D converter 4b. The digital C R and C B signals digitized by the A/D converters 4b and 4c are supplied to a switch 5. For every sampling period, the switch 5 alternately outputs the digital C R and C B signals formed by sampling at the sampling frequency f S which is 1/2 the sampling frequency f S of the Y signal. A digital C signal as a time-divisional multiplexed signal of the digital C R and C B signals is formed and output to a vertical filter 6b. The vertical filter 6b has a line delay line, and the structure of sampling points in the vertical direction is converted to perform vertical filtering so as to reduce the number of scanning lines. The digital C signal obtained after vertical filtering by the vertical filter 6b is supplied to a horizontal filter 7b. The horizontal filter 7b has a pixel delay line to convert a structure of horizontal sampling points to perform horizontal filtering so as to reduce the number of horizontal sampling points. The digital C signal obtained after horizontal filtering processing by the horizontal filter 7b is supplied to a field memory 8b. The field memory 8b serves as a buffer for absorbing a time error caused by a difference between the high-vision scheme and the NTSC scheme by controlling the write and read timings of the digital C signal. The digital C signal converted along the time base by the field memory 8b is supplied to a switch 9. The switch 9 is alternately switched every sampling period to separate the digital C R and C B signals time-divisionally multiplexed as the digital C signal. The separated C R and C B signals are supplied to the NTSC encoder 10. The NTSC encoder 10 generates a digital television signal complying with the NTSC scheme by using the digital Y signal, and the digital C R and C B signals, and supplies the digital television signal to a D/A converter 11. The digital television signal has a bandwidth equal to a signal obtained by sampling an NTSC television signal at a sampling frequency 4f SC (f SC is the color subcarrier frequency). The digital television signal supplied from the NTSC encoder 10 is converted into an analog signal in the D/A converter 11, and the frequency band of the analog signal is limited to 5 MHz by an LPF 12 connected to the output terminal of the D/A converter 11. An output from the LPF 12 is supplied to a monitor apparatus 13. The monitor apparatus 13 corresponds to the NTSC television signal and has a display device having an aspect ratio of 4 : 3. The monitor apparatus 13 displays the television signal supplied from the LPF 12. In the arrangement shown in Fig. 1, the high definition television signal is converted into an NTSC television signal by using the vertical and horizontal filters. The high definition television signal can be displayed on the monitor apparatus corresponding to the NTSC television signal so as not to cause degradation of image quality of the high definition television signal and not to form a blank portion or the like in the display device of the monitor apparatus. An embodiment of the present invention will be described below. Fig. 2 is a block diagram showing a schematic arrangement of an image display apparatus according to an embodiment of the present invention. The same reference numerals as used in Fig. 1 denote the same parts in Fig. 2, and a detailed description thereof will be omitted. Referring to Fig. 2, a high definition television signal representing an image shown in Fig. 3A is supplied to input terminals 1 R , 1 G , and 1 B in the form of R, G, and B signals. The R, G, and B signals are converted into a luminance signal Y and color difference signals, i.e., R-Y and B-Y signals C R and C B by a matrix circuit 3 in the same manner as in the embodiment of Fig. 1. The Y signal is input to an A/D converter 14a, the C R signal is input to an A/D converter 14b, and the C B signal is input to an A/D converter 14c. The Y signal supplied to the A/D converter 14a is digitized at a 64.125-MHz sampling frequency f S . The digital Y signal is input to a time base compression circuit 16a. The time base compression circuit 16a compresses the time base so as to correct a horizontal scanning period difference caused by a difference between the high definition and NTSC schemes by controlling the write and read timings of the digital Y signal. The digital Y signal time-based compressed by the time base compression circuit 16a is supplied to an NTSC encoder 18. The A/D converter 14b converts the input C R signal into a digital signal at a 32.0625-MHz sampling frequency. Similarly, the A/D converter 14c converts the input C S signal into a digital signal at a 32.0625-MHz sampling frequency as in the A/D converter 14b. The digital C R and C B signals digitized by the A/D converters 14b and 14c are supplied to a switch 15. For every sampling period, the switch 15 alternately outputs the digital C R and C B signals sampled at the sampling frequency f S ' which is 1/2 the sampling frequency f S of the Y signal, thereby forming a digital C signal obtained by time-divisionally multiplexing the digital C R and C B signals. The digital C signal is supplied to a time base compression circuit 16b. The time base compression circuit 16b has a memory and compresses the time base so as to correct a horizontal scanning period difference caused by a difference between the high definition and NTSC schemes by controlling the write and read timings of the digital C signal. The digital C signal time-based compressed by the time base compression circuit 16b is supplied to a switch 17. The switch 17 is switched every sampling period to separate the digital C signal into its components, i.e., the digital C R and C B signals. The digital C R and C B signals are supplied to the NTSC encoder 18. The NTSC encoder 18 forms a digital television signal complying with the NTSC scheme by using the digital Y signal and the digital C R and C B signals. The NTSC digital television signal is supplied to a D/A. converter 19. The digital television signal has a bandwidth equal to a signal obtained by sampling an NTSC television signal at a sampling frequency 4f SC (f SC is the color subcarrier frequency). The digital television signal supplied from the NTSC encoder 18 is converted into an analog signal in the D/A converter 19, and the frequency band of the analog signal is limited by an LPF 20 connected to the output terminal of the D/A converter 19. An output from the LPF 20 is supplied to a switch 21. Note that the time base of an image represented by the television signal output from the LPF 20 is compressed in the horizontal direction, as shown in Fig. 3B. The switch 21 is arranged to supply the television signal from the LPF 20 to one of a high definition monitor apparatus 22 having a display device with an aspect ratio of 16 : 9 and an NTSC monitor apparatus 23 having a display device with an aspect ratio of 4 : 3. The switching operation of the switch 21 is controlled by a monitor apparatus selection designating signal output from a system controller (not shown). When an image display on the high definition monitor apparatus 22 is designated by the monitor apparatus selection designating signal, the switch 21 is set to the H position. The television signal output from the LPF 20 is supplied to the high definition monitor apparatus 22 through the switch 21 set at the H position. When the television signal output from the LPF 20 is displayed on the high definition monitor apparatus 22, an image shown in Fig. 3C is displayed on the display device of the monitor apparatus 22. In this embodiment, a scan control circuit 24 is arranged to increase a horizontal scanning range of the high definition monitor apparatus 22 when an image display on the high definition monitor apparatus 22 is designated by the monitor apparatus selection designating signal. An image without any distortion, as shown in Fig. 3A, is displayed on the display device. When an image display on the NTSC monitor apparatus 23 is designated by the monitor apparatus selection designating signal, the switch 21 is connected to the N position. The television signal output from the LPF 20 is supplied to the NTSC monitor apparatus 23 through the switch 21 connected to the N position. When the television signal output from the LPF 20 is displayed on the NTSC monitor apparatus 23 without any processing, an image shown in Fig. 3B is displayed on the display device of the monitor apparatus 23. When the image display on the NTSC monitor apparatus 23 is designated by the monitor apparatus selection designating signal, the vertical scanning range of the NTSC monitor apparatus is narrowed by the scan control circuit 24, thereby displaying an image without any distortion on the display device, as shown in Fig. 3D. In the embodiment shown in Fig. 2, when the image represented by the high definition television signal is compressed along the time base in the horizontal direction so as to convert it into an image size represented by an NTSC television signal, and the converted image is to be displayed on the monitor apparatus, the horizontal or vertical scanning range of the monitor apparatus is controlled in accordance with the types of monitor apparatuses. Therefore, distortion of the image represented by the high definition signal can be prevented, and a faithful display can be performed. As has been described above, according to the present invention, there can be provided an image display apparatus capable of faithfully displaying an image corresponding to an input image signal without degrading the image quality.

Claims: An image display apparatus for displaying an image corresponding to an input image signal having a first aspect ratio, comprising: a) a first image display unit (22) having a display screen of said first aspect ratio, for displaying the image corresponding to the image signal; b) a second image display unit (23) having a display screen of a second aspect ratio smaller than said first aspect ratio, for displaying the image corresponding to the input image signal; c) display selection means (21) for selectively designating on which of said first display unit (22) and said second display unit (23) an image corresponding to the input image signal representative of said image having said first aspect ratio is to be displayed; d) image signal conversion means (14 - 19) for receiving the input image signal, converting the image represented by the input image signal into an image having the second aspect ratio by compressing the time base of the received input image signal and outputting said compressed input image signal to the display unit designated by said display selection means (21) ; and e) scanning control means (24) for controlling a scanning range of the display screen of the image display unit designated by said display selection means (21) , such that the vertical scanning range is reduced if the first display unit (22) is selected, whereas the horizontal scanning range is increased if the second display unit (23) is selected. An apparatus according to claim 1, wherein said image signal converting means (14 - 19) includes: a) analog-digital converting means (14) for converting the received input image signal into a digital image signal and outputting the digital image signal; b) storage means (16) for temporarily storing the digital image signal output from said analog-digital converting means (14) and outputting the digital image signal; and c) digital-analog converting means (19) for converting the digital image signal output from said storage means (16) into an analog signal. An apparatus according to claim 2, wherein said storage means (16) is arranged so as to perform correction of a difference of a horizontal scanning interval, caused by a difference between the aspect ratio of the image represented by the input image signal and the aspect ratio of the image represented by the compressed input image signal, on the digital image signal output from said analog-digital converting means (14) . An apparatus according to claim 1, wherein the input image signal includes a luminance signal (Y) and two kinds of color difference signals (C R , C B ) . An apparatus according to claim 4, wherein said image signal converting means (14 - 19) includes: a) first analog-digital converting means (14a) for converting the received luminance signal (Y) into a digital luminance signal (D-Y) and outputting the digital luminance signal (D-Y) ; b) second analog-digital converting means (14b) for converting one of the received color difference signals (C R ) into a digital color difference signal (D-C R ) and outputting a digital color difference signal (D-C R ) ; c) third analog-digital converting means (14c) for converting the other of the received color difference signals (C B ) into a digital color difference signal (D-C B ) and outputting a digital color difference signal (D-C B ) ; d) time division multiplexing means (15) for receiving the digital color difference signal (D-C R ) output from said second analog-digital converting means (14b) and the digital color difference signal (D-C B ) output from said third analog-digital converting means (14c) , outputting one of the digital color difference signals which one is output being alternated from sample to sample to time-divisionally multiplex the digital color difference signals (D-C R , D-C B ) , and outputting a time-divisionally multiplexed signal; e) first storage means (16a) for temporarily storing the digital luminance signal (D-Y) output from said first analog-digital converting means (14a) and outputting the digital luminance signal; f) second storage means (16b) for temporarily storing the time-divisionally multiplexed digital color difference signal output from said time division multiplexing means (15) and outputting the multiplexed signal; g) separating means (17) for separating the two kinds of digital color difference signals from the multiplexed signal output from said second storage means (16b) and outputting the separated two kinds of digital color difference signals; h) digital image signal forming means (18) for forming a digital image signal by using the digital luminance signal output from said first storage means (16a) and the two kinds of digital color difference signals output from said separating means (17) ; and i) digital-analog converting means (19) for converting the digital image signal output from said digital image signal forming means (18) into an analog signal and outputting the anlog signal. An apparatus according to claim 1, wherein said first display unit (22) has a display screen having an aspect ratio corresponding to a high-definition television scheme, and said second display unit (23) has a display screen having an aspect ratio corresponding to an NTSC, PAL, or SECAM television scheme. An apparatus according to claim 1, wherein said first display unit (22) has a display screen having an aspect ratio of 16:9, and said second display unit (23) has a display screen having an aspect ratio of 4:3. An apparatus according to claim 1, wherein the input image signal is an image signal corresponding to a high-definition television scheme. An apparatus according to claim 1, wherein the input image signal is an image signal having an aspect ratio of 16:9. An apparatus according to claim 1, wherein said scanning control means (24) controls the horizontal scanning range of the image display unit designated by said display selection means (21) so as to reduce the horizontal scanning range. An apparatus according to claim 1, wherein said scanning control means (24) controls the vertical scanning range of the image display unit designated by said display selection means (21) so as to reduce the vertical scanning range.

Inventors: TANAKA YASUYUKI, TANAKA, YASUYUKI, TANAKA, YASUYUKI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: H04N5
IPC codes: H04N7, G09G5, G09G1, G03B37, H04N9, H04N5, H04N3