JP2812349B2 - Image synthesis circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image synthesizing circuit for synthesizing a signal of a wideband natural image and a signal of a high-definition image by a computer or the like. More specifically, the present invention relates to an oversampling technique for smoothing a natural image of a synthesized image. And an image synthesizing circuit capable of displaying an image by a computer or the like with high definition.

[0002]

2. Description of the Related Art Conventionally, as an image synthesizing circuit of this kind, FIG.
For example, a natural image (video data) digitally processed for picture-in-picture of a television and a superimposed image (superimposed data) such as a telop can be synthesized.

In FIG. 11, this image synthesizing circuit converts a digitally processed wideband natural image (video data) into a D / A converter 1 for analog conversion and a high-definition superimposed image (superimposed data). The D / A converter 2 for analog conversion, the clamps 3 and 4 for adjusting the DC levels of the signals independently converted by the D / A converters 1 and 2, respectively, and the clamps 3 and 4 A switching unit 5 for switching a signal passed through at a predetermined timing (switching signal), and an analog post-low-pass filter (LPF) unit for removing noise (false signal) generated at the time of the analog conversion from a signal synthesized by the switching 6 is provided.

The wide-range natural image signal and the high-definition superimposed image signal can be synthesized by the image synthesizing circuit having the above-mentioned configuration. And a high-resolution superimposed image by a computer or the like.

[0005]

However, the system of the image synthesizing circuit has the following problems. First, since an analog switch is used as the switching unit 5, the delay time by the analog switch itself and the time until the switching is actually performed by the switching signal directly affect the image quality of the synthesized image, that is, the synthesized signal and the display The phase from the position is shifted (a phase difference is generated), and the displayed composite image is deteriorated.

[0006] Then, a natural picture, a superimposed picture,
It is practically impossible to guarantee the timing of the switching signal of the switching unit 5, and the adverse effect on the synthesized image is further affected by the higher definition of the superimposed signal to be synthesized, and the effect on the display image is reduced. Becomes more noticeable.

Second, the band limitation (LPF) of the above system
(The cutoff frequency of the section 6), the image is deteriorated in the case of the high definition graphic display by the computer or the like,
Conversely, if the band limitation is not performed, the image quality of the natural image deteriorates.

That is, the output signal of the computer is L
Since the image does not pass through the PF, a superimposed image by the computer and the natural image are combined, and when the combined signal is passed through the LPF section 6, the computer image becomes dull. If the synthesized signal is not passed through the LPF unit 6, the natural image will be jagged.

FIG. 1 is a frequency spectrum diagram of FIG.
3, the conversion clock frequency (sampling frequency) of the D / A converters 1 and 2 is assumed to be fs. The frequency spectrum of the picture and superimposed picture signals has the form shown in FIG.

In this case, the frequency spectrum of the synthesized superimposed image has a fundamental wave component (arrow a in the same figure) and its harmonic component (arrow a) in the vicinity of the frequency (1/2) fs. Arrows a1 and a2 in FIG.
Becomes

The frequency spectrum of the synthesized natural image is an effective image signal (arrow b in the figure) of a natural image having a frequency (1/2) fs or less and a fake signal (fourth frequency component) of the natural image. Arrows b1 and b2 in the figure are obtained. In addition,
The false signal is a signal (shaded area in the figure) generated by the digital processing.

For this purpose, the false signal is transmitted to the LPF section 6.
However, in order to sufficiently suppress this spurious signal, the cutoff frequency of the LPF unit 6 is set to, for example, (1/2) fs.
(Arrow c in the same figure), and if this (1/2) fs or more is cut, it is attenuated to the fundamental wave component of the superimposed image (arrow a in the same figure).

As a result, assuming that the input signal waveform (D / A converted composite signal) of the LPF unit 6 is as shown in FIG. 13A, the output waveform of the LPF unit 6 is shown in FIG. ), The natural image is correctly reproduced, but the display of the superimposed image deteriorates.

Therefore, as shown by an arrow d in FIG. 12, the cut-off frequency of the LPF section 6 is increased so that the fundamental wave component of the superimposed image near (1/2) fs is not cut off. A false signal (shaded portion in FIG. 4) generated when the image is D / A converted passes through the LPF section 6.

As a result, the output waveform of the LPF section 6 has a shape as shown in FIG. 13 (c), and the superimposed image is displayed well, but the natural image is deteriorated by the block-like noise and becomes smooth. It will not be reproduced.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to combine a wideband natural image with a high-resolution superimposed image by a computer or the like to obtain a composite image. It is an object of the present invention to provide an image synthesizing circuit which eliminates the phase difference between the image and the display position, displays a natural image smoothly, and can display a superimposed image with high definition.

[0017]

In order to achieve the above object, an image synthesizing circuit according to the present invention converts video data of a digitally processed high-bandwidth natural image to a sampling frequency fs.
Oversampling at a clock that is an integral multiple (k) of
An oversampling section and a digital filter section for shifting the aliasing component included in the video data to a higher frequency side by the oversampling, and a predetermined timing between the oversampled data and the high-resolution superimposed image data. A multiplexer (MPX unit) for switching and synthesizing the data, a D / A conversion unit for converting the switched data into an analog signal, and attenuating the aliasing component on the high frequency side included in the analog-converted signal; An essential point of the invention is to provide an analog post-filter unit for extracting an effective component of the natural image and a fundamental wave component of the superimposed signal.

[0018]

With the above configuration, the video data of the natural image is oversampled and passed through a digital filter unit, whereby the aliasing component (false signal) included in the oversampled natural image signal is output. Sampling frequency (fs), close to effective components for natural images
Unnecessary signals in the vicinity of the clock (unnecessary signals other than the clock near the oversampling frequency (2 · fs); aliasing components) are removed. That is, the aliasing component included in the oversampled natural image signal is shifted to a higher frequency side.

The signal of the natural image in which the aliasing component has been shifted and the signal of the superimposed image are switched by a multiplexer, and the composite image signal obtained by the switching is analog-converted by a D / A converter. Since the analog-converted signal is passed through the analog post-filter unit, the high-frequency side aliasing component (false signal) and the harmonic component of the superimposed image signal are removed.

Therefore, there is no delay time or switching time unlike the analog switch at the time of the switching, so that there is no shift in the phase between the synthesized image signal and the display position. When displaying a composite image of a pose image, there is no difference in the phase of each display position, and the composite image can be displayed well.

Further, since the aliasing component removed by the analog post-filter section is located on the high frequency side, the cut-off frequency of the analog post-filter section can be increased, and the natural image is limited by band limitation. The aliasing component can be removed, and the band is not limited to the superimposed image.

Thus, when the composite image is displayed,
The display of the natural image can be made smooth without being jagged, and the display of the superimposed image can be made high definition.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image synthesizing circuit according to the present invention, prior to synthesizing a digitally processed wideband natural image (video data) and a high-resolution superimposed image (data) by a computer or the like, only the natural image. Over-sampling, shifting the aliasing component (false signal) included in the over-sampled signal to the high frequency side, and combining the effective component of the natural image and the false signal shifted to the high frequency side with the superimposed image. Are switched at a predetermined timing and synthesized, the synthesized signal is converted into an analog signal, and the analog-converted signal is passed through an analog post-LPF, whereby the false signal shifted to the high frequency side and the superimposed image are converted. Attenuates (removes) only the harmonic components of the signal
I do.

For this purpose, as shown in FIG. 1, the image synthesizing circuit overwrites the video data with an oversampling clock having a frequency (for example, 2 fs) that is an integral multiple (k; for example, twice) of the sampling frequency (fs). Sampling, attenuates the false signal closest to the effective component of the natural image among the aliasing components (alias) included in the sampled signal, and returns the effective component and aliasing on the high frequency side. An oversampling unit 7 and a digital filter unit 8 for outputting the components as digital signals that are analogous to analog signals;
An MPX (multiplexer) unit 9 for switching between the obtained digital signal and the superimposed image (data) by a switching signal at a predetermined timing;
A D / A converter 10 for analog-converting a signal digitally synthesized by the X unit 9 (a synthesized image signal of a natural image and a superimposed image), and an unnecessary signal from the analog-converted synthesized image signal And an analog post-LPF unit 11 for attenuating (removing) the above-mentioned high-frequency side false signal and harmonic components of the superimposed image.

The oversampling section 7 is composed of two D-type flip-flop circuits 7a and 7b and an AND gate circuit 7c as shown in FIG. 2 when the integer k = 2, for example. Natural painting (data)
Is a 1-bit data string. Note that the first flip
The clock of the flop circuit 7a is a sampling clock (frequency fs), and the clock of the second flip-flop circuit 7b is an oversampling clock (frequency 2fs).

As shown in FIG. 3, for example, as shown in FIG. 3, a digital filter section 8 configured as a block with the oversampling section 7 includes a delay register 8 for delaying a 1-bit data string (n-bit data) from the oversampling section 7.
, 8b, a multiplier 8c for multiplying 1-bit data by a filter coefficient α, and a multiplier 8d for multiplying each delayed data by a filter coefficient β,.
8e and an adder 8f for adding each multiplied data. The oversampling unit 7 and the digital filter unit 8 are separated from each other in order to explain the operation of the image synthesizing circuit on the frequency axis.

Then, the natural image (video data) is oversampled by the oversampling unit 7 and the digital filter unit 8, and the aliasing component due to the oversampling (a false signal of the natural image).
Among them, the false signal near the effective component of the natural image is attenuated, and the effective component of the natural image and the false signal on the high frequency side, that is, a digital signal similar to an analog signal can be obtained. As a result, the false signal included in the oversampled natural image signal is shifted to a higher frequency side.

As shown in FIG. 4, for example, the MPX unit 9 performs a logical product (AND) of a signal oversampled by the oversampling unit 7 and the digital filter unit 8 and a switching signal at a predetermined timing. 2 AND) circuit 9a, an invar circuit 9b for inverting the switching signal, and a logical product (2) for obtaining a logical product of the super-import image (SI data) and the inverted switching signal.
An AND circuit 9c and a logical OR (2 OR) circuit 9d for logically ORing the output signals of the two AND circuits 9a and 9c.

Then, when the switching signal is at "H" level, a signal of a natural image that has been over-salamped is output,
When the switching signal is at "L" level, a superimposed image signal from a computer or the like is output.

Next, the operation of the image synthesizing circuit having the above configuration will be described with reference to the frequency spectrum diagrams of FIGS. 5 to 9 and the waveform diagrams of FIG.

First, it is assumed that a wideband natural image (video data) from a television or the like and a superimposed image (data) from a computer or the like are synthesized at a predetermined timing, and the video data is sampled by an oversampling unit 7 and a digital filter unit 8. Frequency (fs)
It is assumed that oversampling is performed by an oversampling clock having a frequency twice as high as

Then, the MPX unit 9 switches between a digital signal that is regarded as an analog signal from the digital filter unit 8, that is, a signal obtained by oversampling a natural image and a signal of the superimposed image (data). .

By the switching of the MPX section 9, the oversampled natural image signal and the superimposed image signal are synthesized, and the synthesized signal is converted into an analog signal by the D / A conversion section 10 and displayed. Converted to an image signal.

In this case, the frequency spectrum of the natural image before passing through the digital filter section 8 has, for example, the form shown in FIG. 5, and the arrow A in the figure is an effective component of the natural image. A1 and A2 (shaded portions) are aliasing components included in the oversampled signal, that is, false signals of an integral multiple of the sampling frequency.

The interpolation filter characteristic of the digital filter section 8 has, for example, the form shown by the arrow B (inside of the broken line) in FIG. 6, that is, attenuates the false signal near the effective component of the oversampled natural image. (Removal)
And interpolate other signals. Therefore, as shown in FIG. 7, the signal of the oversampled natural image becomes a valid component of the natural image (arrow A in FIG. 7) and a false signal on the high frequency side (arrow A2 in FIG. 7).

The MPX unit 9 converts a signal based on the effective component of the natural image (arrow A in the figure) and a false signal on the high frequency side (arrow A2 in the figure) and the signal of the superimposed image. The signals are combined, and the frequency spectrum of the combined signal is, for example, as shown in FIG. The arrow B in the figure is a fundamental component of the signal of the superimposed image, and the arrows B1 and B2 in the diagram are harmonic components of the signal of the superimposed image.

Further, the signal of the synthesized image is D /
The analog signal is converted by the A-converter 10, and the frequency spectrum of the analog-converted composite signal is, for example, as shown in FIG. In FIG. 9, the same parts as those in FIG. 8 are denoted by the same reference numerals, and redundant description will be omitted. The arrow A2 in FIG.
The energy level of the false signal shown in FIG. 7 and the harmonic components shown in arrows B1 and B2 in FIG. 7 are low due to the aperture effect of the D / A conversion.

Furthermore, the D / A-converted synthesized signal is passed through the analog post-LPF unit 6, and the analog post-LPF unit 6 has a portion indicated by an arrow C in FIG.
, The spurious signal of the natural image shown by the arrow A2 in the figure and the harmonic component of the superimposed image shown by the arrows B1 and B2 in the figure are attenuated, and the effective component and the super The fundamental wave component of the imposed image is passed.

Further, the band of the analog post-LPF section 6 is set between the fundamental wave component of the superimposed image and the aliasing component (false signal) on the high frequency side of the natural image, thereby changing the basic frequency of the superimposed image. Since the wave component is not applied, the band of the signal of the superimposed image is not limited, and the band of the signal of the natural image can be limited.

Thus, for example, as shown in FIG.
Even when the output composite signal of the D / A conversion unit 10, that is, the composite image of the natural image and the superimposed image is passed through the analog post-LPF unit 11, the superimposed image deteriorates as in the conventional example. In addition, the natural image does not have a jagged shape, and a synthetic image including a smooth natural image and a high-definition superimposed image can be obtained.

Since the aliasing component (noise component near the effective component of the natural image) generated by the digital synthesis is removed by the digital filter, it is easy to increase the resolution and S / N of the natural image. Since the conventional analog clamp circuit (clamp units 3 and 4 shown in FIG. 11) is not required, the pedestal level after the above-mentioned digital synthesis can be made accurate, and the waveform can be damaged. Absent.

Further, since the natural image (video data) digitally processed and the superimposed image (data) by a computer or the like are switched and synthesized by the MPX unit 9, that is, the switching unit (MPX unit 9) Since this is nothing but a digital switch, the delay time and switching time of an analog switch can be almost neglected, the phase difference at the time of combining does not occur in principle, and the combined signal and display position , The display coordinates (position on the screen) can be easily specified.

Further, since it is not necessary to provide the analog post-filter unit 11 in the final stage with steep characteristics, the design of the analog post-filter unit 11 becomes easy, and the cost can be reduced.

[0044]

As described above, according to the image synthesizing circuit of the present invention, video data of a digitally processed wideband natural image is converted to an integer multiple (k) of the sampling frequency fs.
An oversampling unit and a digital filter unit for shifting the aliasing component included in the video data to a higher frequency side by the oversampling, and a superimpose of the oversampled data and the high-definition superimposed data. A multiplexer for switching and synthesizing the image data at a predetermined timing, a D / A converter for converting the synthesized image signal into an analog signal, and the aliasing component on the high frequency side included in the analog converted signal And an analog post-low-pass filter unit for extracting the effective component of the natural image and the fundamental wave component of the superimposed signal, so that the natural image and the superimposed image are switched and synthesized. The delay time and the analog switch Since there is almost no replacement time, it is possible to eliminate the phase difference between the combined image signal and the display position, that is, it is possible to easily specify the coordinates of the display image (the position on the screen), Since the aliasing component (false signal of the natural image) generated when the image data is oversampled is shifted to the high frequency side, the high-resolution spur imposed image is band-limited by the last analog post-LPF unit. It is possible to limit the bandwidth of the natural image, to display the superimposed image of the composite image with high definition, to display the natural image smoothly, and to obtain a good composite image. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an image synthesizing circuit showing one embodiment of the present invention.

FIG. 2 is a specific circuit diagram of an oversampling unit included in the image synthesis circuit shown in FIG.

FIG. 3 is a specific circuit diagram of a digital filter unit included in the image synthesis circuit shown in FIG.

FIG. 4 is a specific circuit diagram of an MPX unit included in the image synthesis circuit shown in FIG.

FIG. 5 is a frequency spectrum diagram of an oversampled natural image for explaining the operation of the image synthesis circuit shown in FIG. 1;

FIG. 6 is a frequency spectrum diagram of an oversampled natural image illustrating the operation of the image synthesis circuit shown in FIG. 1;

FIG. 7 is a frequency spectrum diagram of an oversampled natural image illustrating the operation of the image synthesis circuit shown in FIG. 1;

FIG. 8 is a frequency spectrum diagram of a synthesized image for explaining the operation of the image synthesis circuit shown in FIG. 1;

FIG. 9 is a frequency spectrum diagram of a synthesized image for explaining the operation of the image synthesis circuit shown in FIG. 1;

FIG. 10 is a schematic waveform diagram of a synthesized image illustrating the operation of the image synthesis circuit shown in FIG. 1;

FIG. 11 is a schematic block diagram of a conventional image composition circuit.

FIG. 12 is a frequency spectrum diagram of a synthesized image for explaining the operation of the conventional image synthesis circuit.

FIG. 13 is a schematic waveform diagram of a synthesized image for explaining the operation of the conventional image synthesis circuit.

[Explanation of symbols]

 Reference Signs List 7 oversampling section 8 digital filter section 9 MPX (multiplexer) section 10 D / A conversion section 11 analog post-filter section 7a, 7b flip-flop circuit 7c AND gate circuit 8a, 8b delay register 8c, 8d, 8e multiplier 8f Adders 9a, 9c Logical product (2 AND) circuit 9b Inverting circuit 9d Logical OR (2 OR) circuit A Effective component of natural image B Fundamental wave component of superimposed image A1, A2 Return component (false signal of natural image) ) B1, B2 harmonic components (of superimposed image)

Claims (1)

(57) [Claims] 1. A digitally processed wideband natural image video data is oversampled by a clock of an integral multiple (k) of a sampling frequency (fs), and the oversampling causes a folded component included in the video data to be on a high frequency side. An oversampling unit and a digital filter unit for shifting to a predetermined time, a multiplexer for switching the oversampled data and high-resolution superimposed image data at a predetermined timing, and a multiplexer. D / A conversion means for performing an analog conversion, for attenuating the high-frequency side aliasing component contained in the analog-converted signal, and extracting an effective component of the natural image and a fundamental wave component of the superimposed signal. Characterized in that it comprises: Synthesis circuit.