JP2000137469A - Pixel number conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pixel number conversion device improved in picture quality at the time of converting the number of pixels. SOLUTION: An enlargement interpolation means 10 generates an enlargement interpolation picture signal Im by enlarging and interpolating a picture signal I. A high frequency component extraction means 21 extracts high frequency components from the enlargement interpolation picture signal Im. A high frequency emphasis means 22 adds the high frequency components, which have been changed in the high frequency characteristic according to an enlargement ratio, to the enlargement interpolation picture signal Im, and outputs it by emphasizing the high frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pixel number converter, and more particularly to a pixel number converter for converting the number of pixels of an image signal.

[0002]

2. Description of the Related Art A television screen has 483 effective scanning lines for a standard television signal and 1035 effective scanning lines for a high-definition television signal.

Therefore, when displaying a standard television signal on a television monitor for a high-definition television signal, the number of scanning lines is converted to 7:15. When a standard television signal is displayed on a fixed single display pixel such as a liquid crystal display, an SVGA (Super Video Graphi
For cs Array), the number of pixels is 800x600,
The scan lines are converted and displayed at approximately 4: 5.

Further, when a television signal is slightly over-scanned on a liquid crystal display, it is necessary to enlarge the image by less than 10%, or when a personal computer signal is displayed on a CRT displaying an overscan, an image is not displayed. In order to reduce the image by about 10%, which is necessary to prevent the image from protruding outside the screen, conversion is performed at a ratio of 10:11 or 10: 9.

[0005] When image quality is emphasized by such conversion of the number of scanning lines, interpolation is generally performed using an interpolation filter that approximates the interpolation function sin (x) / x.

[0006]

However, in contrast to the above-described conventional conversion of the number of scanning lines (hereinafter referred to as pixel number conversion), at the time of enlargement conversion, the scanning when the number of scanning lines of the input original signal is displayed. Since the number of lines is smaller than the number of lines, the number of pixels must be increased by interpolation. For this reason, there is a problem that the signal looks blurred compared to the original signal of the display device.

Further, even if an ideal interpolation filter is used, it is not possible to create information finer than the information of the original image by interpolation, so that there is a problem that the image quality deteriorates.

SUMMARY OF THE INVENTION The present invention has been made in view of such a point, and it is an object of the present invention to provide a pixel number conversion device which improves image quality at the time of pixel number conversion.

[0009]

According to the present invention, in order to solve the above-mentioned problems, in a pixel number conversion device for converting the number of pixels of an image signal, the image signal is enlarged and interpolated based on an enlargement ratio. Expansion interpolation means for generating an image signal, high-frequency component extraction means for extracting a high-frequency component from the expansion interpolation image signal, and, for the expansion interpolation image signal, a high-frequency characteristic according to the expansion ratio. A high-frequency emphasizing means for adding the changed high-frequency components and emphasizing and outputting the high-frequency, and an enhancer comprising: You.

[0010] Here, the enlargement interpolation means performs enlargement interpolation of the image signal to generate an enlarged interpolation image signal. The high frequency component extracting means extracts a high frequency component from the enlarged interpolation image signal. The high-frequency emphasis unit adds a high-frequency component obtained by changing a high-frequency characteristic according to an enlargement ratio to the enlarged interpolation image signal, and emphasizes and outputs the high-frequency.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a principle diagram of a pixel number conversion device according to the present invention. The pixel number conversion device 1 performs enlargement conversion of the number of pixels of an image signal.

The number-of-pixels conversion apparatus 1 includes an enlargement interpolation unit 10 and an enhancer 20. In addition, enhancer 20
Is composed of a high-frequency component extraction means 21 and a high-frequency emphasis means 22.

The enlargement interpolation means 10 is a low-pass filter (hereinafter, LPF) and performs enlargement interpolation on the input image signal I based on an enlargement ratio to generate an enlarged interpolation image signal Im.

The high frequency component extracting means 21 performs a high pass filtering process to extract a high frequency component from the enlarged interpolation image signal Im. The high-frequency region emphasis unit 22 adds, to the enlarged interpolation image signal Im, a high-frequency component obtained by changing the high-frequency characteristic according to the magnification. Then, the image signal Ia after conversion is output by emphasizing the high frequency band.

Here, when the high-frequency emphasis means 22 emphasizes the high-frequency in two dimensions, the high-frequency component extraction means 21 is constituted by a two-dimensional transversal high-pass filter. The coefficients at this time are shown in FIG.

As described above, the pixel number conversion device 1 of the present invention
Is an enhancer 2 comprising a high-frequency component extraction means 21 and a high-frequency emphasis means 22 at the output of the enlargement interpolation means 10.
0 is provided.

Then, a high frequency component is added to the enlarged interpolated image signal Im whose pixel number has been converted, and the high frequency is emphasized in accordance with the enlargement ratio, thereby suppressing image blur.
This makes it possible to improve the image quality.

Next, before the conversion: the pixel number ratio after the conversion is 10:
As an example, an LPF having a cosine roll-off characteristic as a finite response filter of an interpolation function sin (x) / x
The conversion of the number of pixels in the case of using is described.

Consider a cosine roll-off interpolation LPF that processes with the least common multiple clock fm of the input signal clock fi and the output signal clock fo and cuts off fi / 2. FIG. 3 is a diagram showing the frequency characteristics of the cosine roll-off interpolation LPF in the case of 10:11. The vertical axis shows the gain (|
A |), and the frequency (fi × 10) is plotted on the horizontal axis.

FIG. 4 is a diagram showing a table of coefficients of the cosine roll-off interpolation LPF in the case of 10:11. Te
The coefficient Cn (n = 0 to 20) of the bull t1 indicates only a half from the center, and is 6 assuming an actual circuit for integer processing.
After scaling by a factor of four, it is rounded to the integer part.

FIG. 5 is an overall block diagram of the cosine roll-off interpolation LPF in the case of 10:11. In the figure, IC1
a to IC4a and IC11a are D flip-flops, IC
5a to IC8a are 2-input, 1-output multipliers, and IC9a is 4
An adder with one input, SW1a to SW4a are switches for selecting the coefficient Cn, and IC10a is an 11-digit counter for switch switching control.

The coefficient Cn is for an interpolation filter (operated at fm) not shown. Note that IC1a is a D flip-flop for timing adjustment. Next, the connection relationship between the circuit elements of the cosine roll-off interpolation LPF 100a will be described. IC1a to IC4a are serially connected. The image signal before conversion is input to the D terminal of the IC 1a. The Q terminal of IC1a is connected to the D terminal of IC2a, the Q terminal of IC2a is connected to the D terminal of IC3a, and I terminal
The Q terminal of C3a is connected to the D terminal of IC4a. Also,
The input clock fi synchronized with the image signal before conversion is IC1
a to the clock terminals of the IC 4a.

On the other hand, SW1a is a switch for selecting one coefficient from the coefficients C12 to C20, and SW2a is
SW3a is a switch for selecting one coefficient from C0 to C10 coefficients, and SW4a is a switch for selecting one coefficient from C11 to C20 coefficients. It is.

The Q terminals of IC1a to IC4a are connected to one input terminal of IC5a to IC8a.
The other input terminals of IC5a to IC8a are SW1a to SW
4a is connected to the switch terminal.

The clock terminals of the ICs 10a and 11a have output clocks fo synchronized with the converted image signals.
That is, (11/10) × fi is input. IC10a
Are connected to control terminals for switching the switches SW1a to SW4a, respectively. Four input terminals of the IC 9a are connected to output terminals of the ICs 5a to 8a, respectively, and an output terminal of the IC 9a is connected to a D terminal of the IC 11a. Then, the IC 11a outputs the converted image signal in which the number of pixels has been converted.

In this block diagram, the frequency relationship is fo =
(11/10) × fi, fm = 11 × fi. The coefficient Cn is that of an interpolation filter operating at fm. In practice, only one sample is input for every 11 samplings. Therefore, the filter is calculated by, for example, C11 + C0.
+ C11, C10 + C1 + C12, C20 + C9 + C2
+ C13,..., And this calculation output may be output as fo.

In the pixel number expansion conversion such as 10:11 described above, the number of pixels must be increased by interpolation from the input original signal and output. Therefore, the blur is smaller than the original signal of the display device. The image looks bad and the image quality deteriorates.

Next, the deterioration of the image quality will be described based on the waveform response. For the sake of simplicity, an example will be described in which the interpolation filter is not cosine rolled off but is linear interpolation.

FIG. 6 is a diagram showing the waveform response of the interpolation filter. (A) is a diagram of a waveform response before pixel number conversion, (B) is a diagram showing sample points interpolated to the waveform response before pixel number conversion, and (C) is a diagram of a waveform response after pixel number conversion. . The vertical axis is amplitude, and the horizontal axis is time.

In (A), the white circles in the figure indicate the sample points of the original signal S. The rising slope of the original signal S is defined as Sa. In (B), the black circles in the figure are sample points obtained by calculating the sample points 11 times as large as the sample points (white circles) of the original signal S by interpolation, and the square marks are one of the sample points (black circles). / 10 sample points are shown.

(C) shows an enlarged signal S-1 obtained by extending the sample point (square mark) of (B) to the sampling cycle of the original signal S. Enlarged signal S-
The rising slope of 1 is Sb.

As shown in the figure, the rising slope Sa of the original signal S becomes the slope Sb after the enlargement, so that the rising slope becomes small and the image is visually blurred. This is more remarkable as the enlargement ratio increases.

Therefore, in the pixel number conversion device 1 of the present invention, the output signal after the enlargement interpolation is enhanced to make the image blur at the time of enlargement less noticeable. Next, the enhancer 20 will be described. FIG. 7 is a diagram showing a configuration of the enhancer 20. The enhancer 20
High frequency component extraction means 21 and high frequency frequency emphasis means 22
Consists of

The ICs 21a and 21b are D flip-flops, the ICs 21c and 21d are multipliers, and the IC 21e is a 3-input / 1-output adder. The IC 22a is a multiplier, and the IC 22b is a two-input one-output adder.

The connection relation of the circuit elements will be described. I
The enlarged interpolation image signal Im output from the enlargement interpolation means 10 is input to the D terminal of C21a. Q terminal of IC 21a, D terminal of IC 21b, input terminal of IC 21c and IC
The input terminal 22b is connected. An output clock fo synchronized with the converted image signal is input to clock terminals of the ICs 21a and 21b.

The three input terminals of the IC 21e are connected to the IC 21
D terminal of a, output terminal of IC 21c, and Q terminal of IC 21b
Connect to each terminal. Then, the outputs are added at a ratio of −1: 2: −1.

The output terminal of the IC 21e is connected to the input terminal of the IC 21d, and the output terminal of the IC 21d is connected to the input terminal of the IC 22a. The output terminal of IC22a is IC22b
Connect to the input terminal of

As described above, the enhancer 20 which operates by the fo clock is provided at the output (enlarged interpolation image signal Im) of the pixel number conversion of the linear interpolation. And the enhancer 20 is-
A high-frequency component is extracted by the HPF of 1: 2: -1, and an appropriate amount thereof (according to the enlargement ratio) is added to the enlarged interpolation image signal Im.

FIG. 8 is a diagram showing the frequency characteristics of the present invention in the case of 10:11. The vertical axis represents gain (| A |), and the horizontal axis represents frequency (fi × 10). As can be seen from the characteristics, compared to the cosine roll-off frequency characteristics in FIG.

Next, this will be described with reference to a waveform response. FIG.
FIG. 7 is a diagram showing a waveform response of the present invention in the case of 0:11. The vertical axis is amplitude, and the horizontal axis is time. The sample points obtained by the interpolation calculation are indicated by squares, and the output through the enhancer 20 is indicated by black squares.

Here, the values of the sample points (squares) obtained by the interpolation calculation are represented by 20, 20, (s), 20 (t), 65
(U), 75 (v), 75, 75. By the processing in the high frequency component extracting means 21 of the enhancer 20 shown in FIG.
-1 * u) / 4) * 0.5.

When the values at each sample position are calculated in this way, 0 (s), -5.6 (t), 4.4 (u),
1.3 (v) and 0. Then, the values of the output (black squares) passed through the enhancer 20 are added to obtain the values of 20, 20 (s), 14.4 (t), 69.4 (u),
76.3 (v), 75, 75.

Compared with FIG. 6, the slope Sb of the rising edge before the enhancement is changed to the slope Sc after the enhancement.
And the rising slope rises, and the slope Sa of the original signal
It can be seen that it is approaching. Therefore, the visual blur is improved.

Next, a case where the enhancement amount is adaptively controlled according to the enlargement ratio will be described. The extent to which the slope of the rising edge of the original signal becomes smaller after enlargement and is visually blurred increases as the enlargement ratio increases.

Therefore, the effect can be further enhanced by increasing the amount of enhancement (the amount of enhancement of the high frequency band) in conjunction with the enlargement ratio. FIG. 10 is a diagram showing the configuration of the present invention when the enhancement amount is controlled according to the magnification.

In the circuit described with reference to FIG. 7, a new coefficient setting means 22a is provided in the high frequency emphasis means 22. In the figure, for example, if the enlargement ratio is 1.1, the enhancement amount is 0.1.
5. If the enlargement ratio is 1.2, the enhancement amount can be adaptively controlled based on the enlargement ratio, for example, the enhancement amount is 0.7.

The HP of the high frequency component extraction means 21
The characteristics of F do not consider the conversion ratio of pixel conversion or seek characteristics that bring pixel conversion closer to ideal characteristics.
Since the purpose is to make the blur of the image as a result of the display less noticeable, a good effect can be obtained by setting the frequency near the display upper limit of the display device. If it is lower than this, interference such as ringing is worrisome, and if it is higher, the effect is reduced.

Therefore, when the resolution of the display device is lower than the upper limit of the Nyquist frequency determined by the output clock frequency, the high frequency component extracting means 21
1: 2: -1 transversal HPF (BP
It is better to use F).

Next, a description will be given of the configuration and operation in the case where the processing of the nonlinear characteristic is provided inside the enhancer 20. FIG.
FIG. 1 is a diagram showing an enhancer in a case where processing of nonlinear characteristics is provided. The same circuit elements as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted.

In the enhancer 20a, a nonlinear characteristic processing means 23 is provided between the output of the high frequency component extracting means 21 and the input of the high frequency emphasizing means 22. The nonlinear characteristic processing means 23 performs nonlinear characteristic processing on the output of the high frequency component extraction means 21. That is, when the output from the high frequency component extraction means 21 is added by the IC 22b, the small amplitude component is removed so that the noise component included in the input signal is not emphasized together with the signal.

Further, even if the large amplitude signal is emphasized, if it exceeds the dynamic range of the display device, the number of pixels may be increased, the color may be added, or the effect may be adversely affected. Limit the amplitude signal.

Next, a description will be given of a pixel number conversion apparatus for performing both horizontal pixel number conversion and vertical pixel number conversion. FIG.
FIG. 3 is a diagram illustrating a pixel number conversion device when both horizontal pixel number conversion and vertical pixel number conversion are performed.

The enlargement interpolation means 10b includes a horizontal pixel number conversion means 11 (LP in the horizontal direction) for performing linear interpolation of the number of horizontal pixels.
F) and vertical pixel number conversion means 12 (LPF in the vertical direction) for performing linear interpolation of the number of vertical pixels.

The two-dimensional enhancer 20b includes a 3 × 3 two-dimensional transversal HPF 21-1 (having the coefficients shown in FIG. 2), a multiplier IC 22b, and an adder IC 22a. Further, a nonlinear characteristic processing means 23 may be provided.

As described above, when both the horizontal pixel number conversion and the vertical pixel number conversion are performed, only one set such as a non-linear circuit is required if the two-dimensional enhancer 20b is used after interpolating with the horizontal and vertical linear linear LPFs. Also, an image having good visual characteristics can be obtained.

Next, a description will be given of a pixel number conversion device that shares a band-limited LPF and an enhancer. In pixel number conversion, both reduction and enlargement processing are often performed. For example, when switching between a standard television signal and a high-definition television signal for display on a VGA display panel, the number of effective scanning lines per field of the original signal is about 240
Since the number of pixels is about 517, if the number of pixels is converted to 480 vertical dots of VGA, the former is enlarged and the latter is reduced.

In the case of reduction, the frequency of the signal is increased by the conversion of the number of pixels, and the aliasing of sampling occurs. Therefore, the band is generally limited by the LPF before the conversion of the number of pixels.
Since the LPF often uses a transversal filter, its configuration is similar to that of an enhancer.

The enlargement and reduction are not performed simultaneously. Therefore, the circuit can be reduced by sharing the band-limited LPF before the pixel number conversion and the enhancer after the pixel number conversion. In particular, when the vertical filter is integrated into an IC, the line memory used for the delay can be shared. Thus, the circuit scale can be reduced.

FIG. 13 is a diagram showing a configuration of a pixel number conversion device sharing a band-limited LPF and an enhancer. IC3
3a and IC33b are line memories, IC33c and IC3
3dIC33e and IC32a are multipliers, IC33f and I
C33g and IC32b are adders.

The connection relation of the circuit elements of the pixel conversion device 3 will be described. A terminal of switch SW1 and switch SW
2, an image signal is input to the b terminal. The terminal c of the switch SW1 is connected to the input terminal of the line memory IC 33a and one input terminal of the adder IC 33f.

The output terminal of the line memory IC 33a is connected to the input terminal of the multiplier IC 33c and the input terminal of the line memory IC 33b. The output terminal of the line memory IC 33b is connected to the other input terminal of the adder IC 33f.

The output terminal of the adder IC33f is connected to the terminal a of the switch SW3 and the input terminal of the multiplier IC33d. The output terminal of the multiplier IC33d is connected to the terminal b of the switch SW3.

One input terminal of the adder IC 33g is connected to the output terminal of the multiplier IC 33c, and the other input terminal is connected to the c terminal of the switch SW3. Adder IC 33g
Is connected to the input terminal of the multiplier IC 33e, and the output terminal of the multiplier IC 33e is connected to the c terminal of the switch SW4.

The terminal a of the switch SW4 is connected to the switch SW2.
The terminal c of the switch SW2 is connected to the input of the pixel number conversion means 30. The output of the pixel number converting means 30 is connected to the terminal b of the switch SW1 and one input terminal of the adder IC 32b.

The terminal b of the switch SW4 is connected to the multiplier IC32
a, and the output terminal of the multiplier IC 32a is connected to the other input terminal of the adder IC 32b. Next, the operation will be described. Switches SW1 to SW4
In the case of reduction, which switches upward during reduction and downward during expansion, an input signal first enters a vertical LPF of 1: 2: 1 using the line memory ICs 33a and 33b, and its output is input to the pixel number conversion means 30. The result is output as is. In the case of reduction, there is no blur, so no enhancement control is required.

In the case of enlargement, the input signal is first input to the pixel number conversion means 30, and the conversion result is stored in the line memory IC3.
Enter the -1: 2: -1 vertical HPF using 3a, 33b and enhance its output.

In the case of enlargement, an input band-limited LPF is not required. With such an operation, the line memory ICs 33a,
Since 3b and the filter addition part are shared, 1
Processing of two circuits can be performed by a set of circuits.

In particular, the line memory ICs 33a and 33b
For example, in the case of performing RGB3ch processing on an 8-bit HDTV signal, 90 kbits (1920 x
(Dots * 2 lines * 8 bits * 3 ch). Therefore, it is possible to enhance the effect of reducing the circuit scale, power consumption, and the like, as compared with the case where the common use is not performed.

As described above, the pixel number conversion device 1 of the present invention has a configuration in which the output is enhanced at the time of enlargement to reduce the blur for the pixel number conversion of a television or the like. In the pixel number conversion device 3 of the present invention, the LPF for limiting the band of the input for reduction and the enhancer for enlargement are shared. Thus, the circuit can be reduced. In this case, the effect of reducing the vertical line memory is particularly great.

In the above description, the signal delay in the digital processing is omitted, but the circuit scale is almost the same as the circuit scale in consideration of the signal delay.

[0071]

As described above, the pixel number conversion device of the present invention adds the high frequency components whose high frequency characteristics have been changed in accordance with the enlargement ratio after the image signal has been enlarged and interpolated. High frequency is emphasized and output. This makes it possible to improve the image quality at the time of converting the number of pixels.

[Brief description of the drawings]

FIG. 1 is a principle diagram of a pixel number conversion device of the present invention.

FIG. 2 is a diagram illustrating coefficients of a two-dimensional transversal high-pass filter.

FIG. 3 shows a cosine roll-off interpolation L for 10:11
It is a figure showing the frequency characteristic of PF.

FIG. 4 shows a cosine roll-off interpolation L for 10:11
It is a figure showing the table of the coefficient of PF.

FIG. 5 shows a cosine roll-off interpolation L for 10:11
FIG. 3 is an overall block diagram of a PF.

FIG. 6 is a diagram showing a waveform response of an interpolation filter.
(A) is a diagram of a waveform response before pixel number conversion, (B) is a diagram showing sample points interpolated in the waveform response before pixel number conversion,
(C) is a diagram of the waveform response after the pixel number conversion.

FIG. 7 is a diagram showing a configuration of an enhancer.

FIG. 8 is a diagram illustrating frequency characteristics of the present invention in the case of 10:11.

FIG. 9 is a diagram showing a waveform response of the present invention in the case of 10:11.

FIG. 10 is a diagram showing a configuration of the present invention in a case where an enhancement amount is controlled according to an enlargement ratio.

FIG. 11 is a diagram illustrating an enhancer in a case where processing for nonlinear characteristics is provided.

FIG. 12 is a diagram illustrating a pixel number conversion device when both horizontal pixel number conversion and vertical pixel number conversion are performed.

FIG. 13 is a diagram illustrating a configuration of a pixel number conversion device that shares a band-limited LPF and an enhancer.

[Explanation of symbols]

1 ... pixel number conversion device, 10 ... enlargement interpolation means, 20 ...
... enhancer, 21 ... high frequency component extraction means, 22
... high frequency emphasis means, I ... image signal, Im ... enlarged interpolation image signal, Ia ... output signal.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 5/262 G06F 15/66 355C 7/01 15/68 405 F-term (Reference) 5B057 CA16 CB16 CD06 CD11 CE03 CH09 CH11 CH18 5C023 AA02 AA07 CA02 DA02 EA03 EA06 EA11 EA13 5C063 AA02 AA11 AC01 BA03 BA08 BA14 CA03 CA25 5C080 BB05 DD07 EE19 JJ01 JJ02 JJ03 JJ04 JJ05 KK02 KK43 5C082 BA41 BC19 CA21 CA33

Claims (6)

[Claims] 1. A pixel number conversion device for converting the number of pixels of an image signal, comprising: an expansion interpolator for expanding and interpolating the image signal based on an expansion ratio to generate an expansion interpolation image signal; A high-frequency component extracting means for extracting a high-frequency component from the high-frequency component obtained by changing a high-frequency characteristic in accordance with the magnification to the enlarged interpolation image signal. And a high-frequency emphasis means for emphasizing and outputting a frequency. 2. The pixel number conversion device according to claim 1, wherein said high frequency component extraction means is a transversal high-pass filter having a coefficient of −1: 2: −1. 3. The apparatus according to claim 1, further comprising a non-linear processing means for performing non-linear processing on the high frequency component.
The pixel number conversion device according to the above. 4. The pixel number conversion device according to claim 1, wherein said high frequency component extraction means is a two-dimensional transversal high-pass filter. 5. The pixel number conversion device according to claim 4, wherein said high-frequency emphasis means emphasizes said high-frequency in two dimensions. 6. A pixel number conversion device for converting the number of pixels of an image signal, comprising: a number-of-pixels conversion means for performing a reduction conversion or an enlargement conversion of the number of pixels; A low-pass filter that limits a band of a signal, an enhancer that shares the line memory during the expansion conversion to emphasize a high-frequency component of the image signal; A switch for switching according to enlargement conversion.