JP4715057B2 - Image signal conversion method and image display apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image signal conversion method and an image display device. Specifically, when the signal format of the input image signal is determined and it is determined that the input image signal is a progressive scanning method and has a horizontal synchronization frequency higher than the horizontal synchronization frequency that can be followed by the image display device, the input image signal In addition, the vertical synchronization frequency is changed and an interlace scanning type signal is displayed as a signal of a horizontal synchronization frequency that can be followed by the image display device.
[0002]
[Prior art]
The image display apparatus can display an image using a plurality of image signals having different formats. For example, in a television apparatus using a cathode ray tube, the number of effective scanning lines is 1080, the field frequency is about 60 Hz, and an interlace scanning signal, that is, a so-called 1080i / 60 system high-definition format signal is used to display an image. Has been done. When an image is displayed using this 1080i / 60 format signal, the horizontal synchronization frequency is 33.75 kHz. In addition, when the number of effective scanning lines is 720, the frame frequency is about 60 Hz, and image display is performed using a 720p / 60 format signal that is progressive scanning, the horizontal synchronization frequency is 45 kHz. As described above, since the horizontal synchronization frequency varies depending on the format, a horizontal deflection circuit capable of operating not only at 33.75 kHz but also at 45 kHz is used. In addition, an interpolation process is performed on a 720p / 60 format signal and converted to a 1080i / 60 format signal to display an image with a horizontal synchronization frequency of 33.75 kHz.
[0003]
[Problems to be solved by the invention]
By the way, if the horizontal deflection circuit can be operated not only at 33.75 kHz but also at 45 kHz, the horizontal synchronization frequency becomes high, so that the circuit scale is increased and the heat sink and the like are enlarged due to an increase in loss in the horizontal deflection circuit. The horizontal deflection circuit cannot be made inexpensive and downsized.
[0004]
Also, in the method of performing interpolation processing on a 720p / 60 format signal and converting it to a 1080i / 60 format signal, the signal waveform becomes dull due to the interpolation processing, resulting in image quality degradation. For example, when the signal of the 720p / 60 system is a signal as shown in FIG. 5A, the pixel position Ps1 in the second field in the signal of the 1080i / 60 system shown in FIG. 5B from the signals of the pixel position Pp1 and the pixel position Pp2. Are generated. The signal level of the generated signal is higher than that of the pixel position Pp2 having a low signal level. Further, a signal at the pixel position Pf2 in the first field is generated from the signals at the pixel position Pp2 and the pixel position Pp3, and the signal level of the generated signal is higher than that at the pixel position Pp2 having a low signal level. .
[0005]
Therefore, if image display is performed using the converted 1080i / 60 format signal, display is performed in the first field at the pixel positions Pf1, Pf2, Pf3. In the second field, display corresponding to each signal level is performed at the pixel positions Ps1, Ps2, Ps3..., And display according to the signal level of the pixel position Pp2 is not performed. Since the display is made according to the signal levels of Ps1 and Pf2, the signal waveform becomes dull and the image quality deteriorates.
[0006]
Therefore, in the present invention, even when image signals having different formats with different horizontal synchronization frequencies are used, the image signals can be displayed without increasing the scale of the horizontal deflection circuit and without conspicuous deterioration in image quality. A conversion method and an image display device are provided.
[0007]
[Means for Solving the Problems]
The image signal conversion method according to the present invention changes the vertical synchronization frequency of an input image signal in a progressive scanning system and converts it into an interlace scanning signal, and has a horizontal synchronization frequency different from the horizontal synchronization frequency of the input image signal. An image signal is generated.
[0008]
Further, the image display device includes an image display device that displays an image using an image signal having a predetermined horizontal synchronization frequency, a format determination unit that determines a signal format of the input image signal, and a signal format that is determined by the format determination unit. Is a progressive scanning method, and when it is determined that the horizontal synchronizing frequency is higher than the predetermined horizontal synchronizing frequency, the vertical synchronizing frequency of the input image signal is changed and an interlaced scanning method signal is used as the predetermined scanning frequency. It has an image signal conversion means for converting into an image signal having a horizontal synchronizing frequency.
[0009]
In the present invention, when the input image signal is a progressive scanning method and the horizontal synchronization frequency is higher than the frequency capable of horizontal scanning in the image display device, the input image signal is thinned out in line units. To obtain an interlaced scanning signal, and the vertical synchronizing frequency of the interlaced signal is changed to make the horizontal synchronizing frequency a frequency that can be horizontally scanned by the image display device. For example, a 720p / 60 format signal is converted into a 720i / 90 format signal that is a lower frequency than the horizontal synchronization frequency of the 720p / 60 format signal.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the invention will be described with reference to the drawings. FIG. 1 shows a configuration of an image display device, for example, a television device. A terrestrial broadcast reception signal received by the antenna 11 and a satellite broadcast reception signal received by the antenna 12 are supplied to the tuner unit 15. The tuner unit 15 selects a desired broadcast wave signal and performs demodulation processing. Here, when the signal obtained by performing the demodulation process is a signal encoded based on, for example, the MPEG (Moving Picture Experts Group) standard, the obtained signal is used as the encoded signal Dte in the decoder unit. 16 is supplied. When not encoded, the obtained signal is supplied to the signal switching unit 20 as an image signal Dtu.
[0011]
When the image signal input from the signal input unit 17 is an encoded signal, this signal is supplied to the decoder unit 16 as an encoded signal Die, and when it is not an encoded signal, the signal is converted into an image. The signal Din is supplied to the signal switching unit 20.
[0012]
The decoder unit 16 performs a decoding process on the supplied encoded signal Dte and supplies the obtained signal to the signal switching unit 20 as an image signal Dtd. Further, the supplied encoded signal Die is decoded, and the obtained signal is supplied to the signal switching unit 20 as an image signal Did.
[0013]
In the signal switching unit 20, based on the selection control signal CS supplied from the control unit 30, the image signal Dtu supplied from the tuner unit 15, the image signals Dtd and Did supplied from the decoder unit 16, or the signal input unit 17 One of the image signals Din supplied from is selected and supplied to the synchronization detection unit 21 and the signal format conversion unit 22 as the image signal Dga.
[0014]
The synchronization detection unit 21 detects the synchronization signal SY of the image signal Dga and supplies it to the control unit 30. The signal format conversion unit 22 includes a memory, and controls writing of the image signal Dga to the memory and reading of the image signal written to the memory based on the conversion control signal CC from the control unit 30. Thus, the signal format conversion process is performed. An image signal Dgb obtained by performing signal format conversion processing by the signal format conversion unit 22 is supplied to a signal processing unit 23 and a deflection processing unit 24.
[0015]
The signal processing unit 23 generates the three primary color signals SR, SG, SB based on the supplied image signal Dgb, and drives the cathode ray tube 40 based on the three primary color signals SR, SG, SB. The deflection processing unit 24 separates the synchronization signal from the image signal Dgb, and generates a horizontal synchronization signal and a vertical synchronization signal based on the synchronization signal. Further, the horizontal deflection circuit of the deflection processing unit 24 drives the horizontal output transistor based on the horizontal synchronization signal, and supplies the deflection current IdH to the horizontal coil of the deflection yoke 45 attached to the cathode ray tube 40. Further, the vertical deflection circuit of the deflection processing unit 24 drives the vertical output transistor based on the vertical synchronization signal, and supplies the deflection current IdV to the vertical coil of the deflection yoke 45. The high voltage generator 25 generates the anode voltage HV by using the switching operation of the horizontal output transistor and supplies it to the cathode ray tube 40.
[0016]
An operation unit 31 is connected to the control unit 30, and a selection control signal CS is generated and supplied to the signal switching unit 20 in response to a signal selection operation at the operation unit 31. Further, based on the detection signal SD from the synchronization detection unit 21, the signal format of the image signal Dga supplied to the signal format conversion unit 22 is determined from the horizontal synchronization frequency, the vertical synchronization frequency, etc., and conversion control is performed based on the determination result. A signal CC is generated and supplied to the signal format converter 22. That is, when the image signal Dga is progressive scan and the horizontal synchronization frequency is not a frequency operable by the deflection processing unit 24, the conversion control signal CC is generated so that the signal format conversion unit 22 executes the conversion process.
[0017]
The signal format of the converted image signal Dgb generated by the signal format conversion unit 22 is set in advance by the signal format conversion unit 22. Alternatively, the signal format of the converted image signal Dgb is set by the conversion control signal CC.
[0018]
In addition, the determination of the signal format of the image signal Dga is not limited to the case where it is performed based on the detection signal SD from the synchronization detection unit 21, and the sequence of the encoded signals Dte and Die supplied to the decoder unit 16 is not limited. When the control signal enabling the signal format to be determined together with the image signal is input to the signal input unit 17 by reading out information on the included signal format, the signal format is determined using this control signal. It is good as a thing.
[0019]
Next, the conversion processing operation of the signal format conversion unit 22 will be described. In this signal format conversion unit 22, when a progressive scanning signal having a horizontal synchronization frequency higher than the horizontal scanning frequency that can be handled by the deflection processing unit 24 is supplied as the image signal Dga, an interlace having a higher vertical synchronization frequency is provided. By converting to a scanning signal, the horizontal synchronizing frequency of the image signal Dgb is output as a horizontal scanning frequency range that can be handled by the deflection processing unit 24.
[0020]
For example, as shown in FIG. 2A, when a 720p / 60 format signal is supplied as the image signal Dga, the interlace signal is obtained by thinning out and reading out the image signal Dga written in the memory for each line. Generate. Further, the vertical synchronization frequency is increased, and signals of 3 fields from 2 frames are sequentially generated. That is, as shown in FIG. 2B, a 720i / 90 format signal is generated and output as an image signal Dgb. This 720i / 90 format signal is an interlaced scanning signal having a scanning line number of 750 and a field frequency of 90 Hz. Therefore, the horizontal synchronization frequency is 33.75 kHz, and the horizontal synchronization frequency is 45 kHz. Also, image display can be performed using a horizontal deflection circuit having a horizontal synchronization frequency of 33.75 kHz. For this reason, the scale of the horizontal deflection circuit is not increased.
[0021]
Note that the vertical synchronization frequency increases from the frame frequency of 60 Hz to the field frequency of 90 Hz. However, the vertical synchronization frequency is low, so the vertical deflection circuit has the same scale as the horizontal synchronization circuit even if the frequency increases. Will not increase significantly.
[0022]
In addition, as shown in FIG. 2, the image signal Dgb is generated by thinning out the image signal Dga for each line, so that it is possible to prevent the image degradation that occurs when the vertical interpolation process is performed. In particular, in the still image portion, the number of effective lines per frame is 720 lines for the image signal Dga and the image signal Dgb. For this reason, even if the image signal Dgb is used, an image can be displayed with an image quality equivalent to that in the case of the image signal Dga. Further, although interlaced scanning is performed even in the moving image portion, since the image is moving, the degradation of the image is at a level that does not matter.
[0023]
Further, it is known that when the vertical synchronization frequency is increased, flicker is not conspicuous and, for example, when a pattern in which brightness changes in a sine wave pattern is displayed, a change in brightness cannot be felt at a frequency higher than about 70 Hz. . Here, the signal format conversion unit 22 converts the progressive scanning signal into the interlace scanning signal. However, since the field frequency of the 720i / 90 system signal is 90 Hz, the signal signal Dgb is converted into the image signal Dgb. Line flicker is not noticeable even if the image is based on interlace scanning.
[0024]
By the way, the sampling frequency is 74.25 MHz in the 720p / 60 format signal, and the horizontal synchronization frequency of the 720i / 90 format signal is 33.75 kHz if the sampling frequency is the same in the 720i / 90 format signal. Therefore, 2200 samples are required in the horizontal direction. For this reason, horizontal interpolation processing is performed to generate a signal with 2200 samples per line from a 720p / 60 format signal with 1650 samples per line.
[0025]
FIG. 3 shows a signal format. FIG. 3A shows a 720p / 60 format signal format, and FIG. 3B shows a 720i / 90 format signal format. FIG. 3C shows the signal format of the above-described 1080i / 60 system.
In the 720p / 60 format signal format shown in FIG. 3A, the number of scanning lines is 750, the number of horizontal samples is 1650 samples, and an area of 720 pixels in the vertical direction × 1280 pixels in the horizontal direction is an effective screen. In the 720p / 60 format signal format, as described above, the horizontal synchronization frequency is 45 kHz, the vertical synchronization frequency is 60 Hz, and the sampling frequency is 74.25 MHz.
[0026]
In the signal format of the 720i / 90 system signal obtained by the signal format conversion unit 22 described above, the number of scanning lines is 750 lines and the number of horizontal samples is 1650 samples, as shown in FIG. An area of pixels × 1280 pixels in the horizontal direction is an effective screen. In the 720i / 90 signal format, as described above, the horizontal synchronization frequency is 33.75 kHz, the field frequency is 90 Hz, and the sampling frequency is 74.25 MHz. That is, similarly to the 1080i / 60 format signal format shown in FIG. 3C, it is possible to display an image with a horizontal synchronization frequency of 33.75 kHz and an effective screen of 1920 pixels in the horizontal direction.
[0027]
By the way, in the above-described embodiment, the signal is converted into a signal having a field frequency of 90 Hz. However, the field frequency may be different from 90 Hz. For example, as shown in FIG. 4, when the field frequency is 70 Hz, the number of lines in one frame is 964 lines when the horizontal synchronization frequency is 33.75 kHz. If the field frequency is 80 Hz, the number of lines in one frame is 843 lines when the horizontal synchronization frequency is 33.75 kHz.
[0028]
Here, when the field frequency is 70 Hz due to the difference in vertical synchronization frequency and the difference in scanning method, for example, by generating a signal of two fields from the same frame of a 720p / 60 method signal once every seven fields, A 7-field interlaced scanning signal is generated from a 720p / 60 frame signal. In addition, when the field frequency is 80 Hz, for example, once every four fields, a two-field signal is generated from the same frame of the 720p / 60 format signal, so that a 4-field interface is generated from the 720p / 60 format 3-frame signal. A race scan signal is generated.
[0029]
Further, the effective screen signal selected in units of lines from the 720p / 60 signal is used as the effective screen signal after conversion. For example, when the field frequency is 70 Hz, the number of lines is 964i, but the signal for 720 lines selected from the 720p / 60 signal is used as the effective screen. Similarly, when the field frequency is 80 Hz, the number of lines is 843i, but the signal for 720 lines selected from the 720p / 60 signal is used as the effective screen.
[0030]
As described above, since the 720p / 60 signal is used as it is without performing the vertical interpolation, it is possible to prevent the display image quality deterioration caused by the vertical interpolation. Further, when the field frequency of the converted image signal Dgb is high, flicker on the screen can be made inconspicuous, and when the field frequency is low, an image display with smooth motion can be performed.
[0031]
Some conventional television apparatuses have a two-screen display function for displaying two screens and an index display function for displaying one screen and a plurality of index screens. A television apparatus having such a function is provided with an image conversion unit that enables display of a plurality of screens by controlling writing and reading of an image signal to and from a memory. Therefore, if the image conversion unit is used instead of the signal format conversion unit 22 and the image conversion unit performs the conversion process described above, horizontal synchronization can be performed without newly providing a signal format conversion unit. An image can be displayed by converting a signal having a high frequency format into a signal having a low horizontal synchronization frequency.
Of course, the signal formats shown in the above embodiments are illustrative and not restrictive.
[0032]
【The invention's effect】
According to the present invention, the vertical synchronizing frequency of the progressive scanning input image signal is changed and converted into an interlace scanning signal to generate an image signal having a horizontal synchronizing frequency different from the horizontal synchronizing frequency of the input image signal. Is done. For this reason, even when an image signal whose horizontal synchronization frequency is higher than a frequency that can be horizontally scanned by the image display device is input, the input image signal is Thus, since image display is performed, it is possible to perform image display using image signals of formats having different horizontal synchronization frequencies without increasing the scale of the horizontal deflection circuit.
In addition, since the progressive scanning method input image signal is thinned out in units of lines to generate an interlace scanning method signal, it is possible to prevent image quality deterioration of the displayed image.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of an image display device.
FIG. 2 is a diagram illustrating an operation of a signal conversion unit.
FIG. 3 is a diagram illustrating a signal format.
FIG. 4 is a diagram showing the number of lines when the vertical synchronization frequency is changed.
FIG. 5 is a diagram for explaining an operation when vertical interpolation processing is performed;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11, 12 ... Antenna, 15 ... Tuner part, 16 ... Decoder part, 17 ... Signal input part, 20 ... Signal switching part, 21 ... Synchronization detection part, 22 ... Signal conversion unit, 23 ... Signal processing unit, 24 ... Deflection processing unit, 25 ... High voltage generation unit, 30 ... Control unit, 31 ... Operation unit, 40 ... Cathode ray tube, 45 ... deflection yoke

Claims (3)

An image signal conversion method in an image display device having a horizontal deflection circuit operable at a predetermined horizontal synchronization frequency, and performing image display using an image signal of the predetermined horizontal synchronization frequency,
Determining the signal format of the input image signal;
When it is determined that the signal format determined in the determining step is a progressive scanning method and a horizontal synchronization frequency higher than the predetermined horizontal synchronization frequency, the vertical synchronization frequency of the input image signal is changed and the interface is changed. Converting the image signal of the predetermined horizontal synchronization frequency as a signal of the race scanning method,
In the converting step, the interlace scanning method signal is generated by thinning out the line unit of the progressive scanning method input image signal . In an image display device having a horizontal deflection circuit operable at a predetermined horizontal synchronization frequency and performing image display using an image signal of the predetermined horizontal synchronization frequency,
Format discriminating means for discriminating the signal format of the input image signal;
When it is determined that the signal format determined by the format determination means is a progressive scanning method and is a horizontal synchronization frequency higher than the predetermined horizontal synchronization frequency, the vertical synchronization frequency of the input image signal is changed and the interface is changed. An image signal conversion means for converting the image signal of the predetermined horizontal synchronization frequency as a signal of the race scanning method ;
The image display device , wherein the image signal conversion unit generates the interlaced scanning method signal by thinning out the input image signal of the progressive scanning method in units of lines .   The image display apparatus according to claim 2, wherein the input image signal has a signal format of a 720p / 60 system.

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