JPH0366267A - Contour correction device - Google Patents

Abstract

PURPOSE:To attain the contour correction not making a contour signal thick and not incurring the deterioration in the quality by providing several kinds of contour signals whose boost frequency differs and comparing a reference level with a level of a signal being the sum of an optional contour signal and a luminance signal and selecting the contour signal proper in response to the output. CONSTITUTION:An adder 17 adds a luminance signal and an optional horizontal contour signal F1. A comparator circuit 18 compares a reference level with an output signal level of an adder 17. Horizontal contour signals F1-F4 are obtained by the simple calculation of a high pass filter. When a luminance signal subject to contour correction is clipped, the contour signal F3 or F4 with a high boost frequency is selected. Thus, the horizontal contour signal obtained by the control and a vertical contour signal from a vertical contour signal from a vertical contour signal forming section 14 are added by an adder 20 to obtain a desired contour signal. Then the signal passes through a level dependent gate circuit 3 and a noise slice circuit 4, resulting in noise reduction.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a contour corrector for improving the image quality obtained from television signals and the like.

2. Description of the Related Art A conventional contour corrector has a configuration as shown in FIG. 7, for example.

In FIG. 7, 1 is an input terminal into which a luminance signal is input;
2 is a contour signal forming circuit that generates horizontal and superimposed contour signals; 3 is a level dependent gate circuit that adjusts the amplitude of the contour signal according to the level of the input luminance signal; 4 is a noise slice circuit; 5 is a luminance signal 6 and 7 are delay lines for timing adjustment, and 8 is an output terminal.

The operation of the contour corrector configured as described above is shown in FIGS.
This will be explained using FIG. 13.

FIG. 8 is a diagram showing the internal configuration of the contour signal forming circuit 2 of FIG. 7, in which 9 is an IH (one horizontal scanning time) delay circuit;
0 is a one-time delay circuit, 11 is an amplifier that amplifies by the multiplication factor shown in the circle, and 12 is an adder. To explain the operation of each part, first, in the riding contour signal part 2A, as shown in FIG.
Assuming that the luminance signal shown in FIG.
.

The signal shown in FIG. 9(c) is obtained, and by adding the output signals of each amplifier 11, a vertical contour signal shown in FIG. 9(d) is obtained. Similarly, in the horizontal contour signal section 2B, FIG.
) are input during the IH period, the outputs of the time delay circuit 10 are as shown in FIGS. 9(f) and (g).
By adding the output signals of each amplifier 11, a horizontal contour signal shown in FIG. N'49 (h) is obtained. Therefore, a two-dimensional contour signal can be obtained by adding the output signal of the horizontal contour signal forming section 2B and the vertical contour -1 to the output signal of the signal forming section 2A in the adding section 2C. The frequency characteristics of the horizontal and vertical contour signal forming sections are shown in Fig. 10 (a) and (
b)

As described above, the contour signal generated by the contour signal forming circuit 2 is generated by the level dependent circuit 3. Further, the signal passes through the noise slice circuit 4 and is added to the IH delay luminance signal time-adjusted by the delay line 6.7 in the adder 5, and a contour-corrected luminance signal is obtained from the output terminal 8. For example, as shown in FIGS. 11(a) to 11(C), when the input signal is a staircase wave as shown in FIG. 11(a), the level-dependent circuit 3 operates as shown in FIG. A contour signal is obtained from the contour signal forming circuit 2, and this contour signal is gain controlled as shown in FIG. This is because the contour signal forming circuit 2 also amplifies high-frequency noise using a so-called bypass filter, so in order to reduce noise in dark areas, the gain of the contour signal is controlled according to the level of the luminance signal. Further, the noise slice circuit 4 is configured as shown in FIG.
) and (b), high-frequency noise that remains in flat areas of the signal (with little change in brightness) is sliced and removed by edge enhancement.

In this way, the level dependent gate circuit 3° noise slice circuit 4 prevents the SN ratio from deteriorating by emphasizing the contour. Therefore, a luminance signal with a good SN ratio can be obtained from the output terminal 8.

In the above method, the contour signal is created from the luminance signal, but another method is to create the contour signal from only the green signal and convert this signal to R(
red), G (green), and B (blue) are mixed in each process amplifier.
OF GREENJ) system (for example, "Contour Compensator for Plumbicon Color Cameras" by Hiroshi Marubayashi et al., June 26, 1961, material of the 14th Television Network System Circuit Research Committee) . This rOUT O
The F GREENJ method is often used in cameras using image pickup tubes due to the size of the register storage circuit.

Problems to be Solved by the Invention However, with the configuration of the contour corrector as described above, even if a contour signal with little noise is obtained, for example, in the case of a professional camera, a studio camera, etc., the boost frequency of the horizontal contour signal is approximately 3 MHz. ~4MHz, and as shown in Fig. 13, the contour signal is too large for sudden changes in the brightness signal as typified by step response, and the VTR
If the signal is clipped at around 110% due to the connections, the contour signal becomes thick and lacks quality. This is a big problem for professional and studio cameras that require high performance and high quality.

In view of the above, an object of the present invention is to provide a contour corrector that does not cause the contour signal to become thicker and cause no deterioration in quality even if the contour signal becomes too large and is clipped due to a sudden change in the luminance signal. do.

Means for Solving the Problems In order to achieve the above object, the contour corrector of the present invention uses a contour signal that forms several types of contour signals with different boost frequencies than a luminance signal or a signal similar to a luminance signal. a forming circuit, a selection circuit that selects a desired contour signal from the several types of contour signals, and an adder that adds the brightness signal or a signal similar to the brightness signal and any one of the several types of contour signals. and a comparison circuit that compares the output signal level of the adder with a reference level and controls the selection circuit.

According to the present invention, by setting the reference level to an appropriate value with the above-described configuration, the level of the signal obtained by adding the contour signal to the luminance signal or a signal similar to the luminance signal is compared with the reference level in the comparator. However, if the level of the luminance signal is high and the added contour signal is significantly clipped, or if the contour signal is not clipped but is close to the clip level, the selection circuit selects the contour signal with a high boost frequency. , and then switch between the normal setting contour signal and the high boost frequency contour signal.

Embodiment FIG. 1 is a block diagram showing the internal configuration of a contour corrector in an embodiment of the present invention. The difference from the conventional example shown in FIGS. 7 and 8 lies in the horizontal contour signal forming section 13, and the vertical contour signal section 14 is similar.

In FIG. 1, 14 is a vertical contour signal forming section, 15 is a horizontal contour signal forming section, 16 is a horizontal contour signal forming circuit that forms four horizontal contour signals with different boost frequencies, and 17 is a horizontal contour signal forming section.
18 is an adder that adds the luminance signal and an arbitrary horizontal contour signal Fl; 18 is a comparison circuit that compares the output signal level of the adder 17; and 19 is a horizontal contour signal that is selected based on the output of the comparison circuit 18. The selection circuit 20 is an adder 92 that adds the horizontal contour signal and the superimposed contour signal.

The operation of the horizontal contour signal section in the contour corrector of this embodiment configured as above will be explained using FIGS. 2 to 6.

In FIG. 2, 21 is a T time delay circuit, 22 is an amplifier that amplifies the signal by the multiplication factor shown in the circle, and 23 is an adder.

The horizontal axis signal Fl-F4 is obtained by calculation of a small bypass filter, its frequency characteristics are determined by each delay time as explained in the conventional example, and the boost frequency is 1.
/8T, 1/6T, 1/4T, 1/2T. Fig. 3 shows its frequency characteristic diagram.

Here, if T=35nsec, Fl, F2°F3
．． The boost frequency of F4 is approximately 3.5MHz 4.7M
Hz, 7MHz, and 14MHz. In current professional cameras, the boost frequency of the contour signal is 3MHz to 5MHz.
It is around MHz, and in this example, Fl or F2 is set. Also, F3. At F4, sharpness increases, but noise is also emphasized, which is not very desirable in terms of S/N.

Now, here, the frequency characteristic of the luminance signal is, for example, shown in Figure 4 (
If the characteristics are as shown in a), the horizontal contour signals F1 to F
4, the characteristics of 01 to G4 shown in FIG. 4(b) are obtained. In addition, for a step response exceeding 100% as shown in FIG. 5(a), the horizontal contour signal Fl,
F2. FS and F4 are shown in the same figure (b), respectively.
The contour signals shown in (c), (d), and (s) are obtained, and the contour-corrected luminance signals are as shown in (f) and (s) in the same figure.
(g), (h), (i). (However, in f), (g), (h), and (i), the negative portion of the contour signal is clipped. ) Therefore, the normally set Fl
Or F2 contour signal (boost frequency is 3MHz to 5M
Hz), when clipped, the contour signal becomes thicker and quality deteriorates, but at high boost frequencies such as F3 or F4, even if clipped, the contour signal becomes thin and quality does not deteriorate.

Therefore, if the contour-corrected luminance signal is clipped, it is sufficient to select a contour signal with a high boost frequency.In this embodiment, as a first control example, the reference level Sa is clipped. level (110% in FIG. 5), and the comparison circuit 18 compares this reference level Sa with the level PL of the signal obtained by adding the contour signal and the luminance signal in the adder 17. Control is performed so that the horizontal axis contour signal F1 is selected; and when PL>sa, the horizontal contour signal F4 is selected. Therefore, even if it is clipped,
A contour-corrected luminance signal without deterioration in quality can be obtained.

However, in the case of clipping, the contour signal becomes thinner and even if the quality does not deteriorate, the contour signal (Fl) when the level of the summed signal of the contour signal and the luminance signal is below the clip level, and the contour signal above the clip level. (F4) may make you feel uncomfortable.

In this case, as a second control example, for example, the reference level has three levels: a clip level Sa, an arbitrary level sbs smaller than the clip level, and an arbitrary level SC smaller than sb. When the signal level PL is PL≦SC, the normal horizontal contour signal Fl is
When PL≦sb, the horizontal contour signal F2 is used, and when sb<PL≦
Control is performed to select the horizontal contour signal F3 in the case of Sa, and to select the horizontal contour signal F4 in the case of PL>sa. Here, if we take the luminance signal change as shown in FIG. 6(a) as an example, how to switch the contour signal as shown in FIG. 6(b) (when the reference level is only the clip level Sa)
On the other hand, by switching the contour signal as shown in Fig. 6(C) (in the case of three reference levels, Sat ab + sc), the thickness of the contour signal can be gradually reduced as the luminance signal becomes larger. It can be made thinner, and contour correction can be performed without causing any discomfort or deterioration of quality. However, the 6th
In Figures (b) and (c), the negative portion of the contour signal is clipped. Therefore, although both the first control example and the second control example can prevent deterioration of quality, the second control example is more effective.

As described above, the horizontal contour signal obtained by the first or second control and the vertical contour signal from the vertical contour signal forming section 14 are added by the adder 20, and a desired contour signal is obtained. After this, the signal passes through the level dependent gate circuit 3 and the noise slice circuit 4 in the same way as in the conventional example, and the noise is reduced, and a contour-corrected luminance signal that does not degrade the quality even for various video signals is output. Obtained from terminal 8.

Although four horizontal contour signals are formed in this embodiment, the number may be changed so as to have desired characteristics. Furthermore, although the case where one reference level is provided and the case where there are three reference levels are shown, it is possible to set two reference levels or an appropriate number.

Also, although the signal obtained by adding the horizontal contour signal of Fl to the luminance signal was used for comparison with the reference level, it is possible to use a signal obtained by adding any horizontal contour signal other than F1 as long as the reference level is set to an appropriate value. Needless to say. In addition, the comparison between the reference level and the luminance signal to which the contour signal is added can be made by setting the reference level to an appropriate value, setting the other input to zero in the adder 17, and comparing only the luminance signal level or the contour signal. It goes without saying that the same effect can be obtained when comparing only the signal. Also,
It goes without saying that the same effect can be obtained by multiplying the outputs of each delay element 21 by coefficients and adding them together, and controlling the selection of the coefficients by the output of the comparator circuit 18 to create several types of contour signals. .

Furthermore, it goes without saying that if this embodiment is configured with a digital circuit, delay 9 multiplication, comparison, etc. can be easily performed, and stability of characteristics can be obtained.

In recent years, COD (charge coupled device)
With the rise of professional-use solid-state cameras using CCD, the clock frequency of the COD has also increased due to the increase in the number of picture elements, and when the contour signal is constructed using a digital circuit synchronized with the CCD clock, it is necessary to have several types of contour signals. It is more convenient to do so, and the configuration of this embodiment is very effective.

Furthermore, although the horizontal contour signal is switched in this embodiment, it goes without saying that similar effects can be obtained by applying similar processing to the vertical contour signal.

As described in detail, according to the present invention, there are several types of contour signals with different boost frequencies, and the level of the sum of any contour signal and luminance signal among them is compared with a reference level. By selecting an appropriate contour signal according to the output, the contour signal will not become thick even when the contour signal level is large and clipped due to sudden changes in the brightness signal such as step response. Contour correction can be performed without deteriorating quality. In addition, since it uses multiple delay elements, it has a configuration that is compatible with digital circuits, and has several types of contour signals, making it effective for COD solid-state cameras that are expected to increase the number of picture elements. It is suitable for high-performance cameras and has great implementation effects.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the configuration of a contour corrector according to an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of the internal configuration of a horizontal contour signal forming circuit according to the embodiment. 1!2-14- Figure 3 is a characteristic diagram showing the frequency characteristics of each horizontal contour signal, Figures 4 (a) and (b) are characteristic diagrams showing examples of horizontal contour correction by each horizontal contour signal, and Figure 3 is a characteristic diagram showing frequency characteristics of each horizontal contour signal. Figures 5 (a) to (i) are waveform diagrams of each contour signal with respect to the step response of the luminance signal, and waveform diagrams of the luminance signal contour-corrected by each contour signal, Figures 6 (-'i-), (b) . (C) is a waveform diagram of a contour-corrected luminance signal showing an example of contour signal control, and FIG. 7 is a waveform diagram of a contour-corrected luminance signal, and FIG.
Comparison circuit, path, 21...T time delay circuit,

Claims (1)

[Scope of Claims] A contour signal forming circuit that forms several types of contour signals with different boost frequencies from a brightness signal or a signal similar to the brightness signal, and a selection circuit that selects a desired contour signal from among the several types of contour signals. an adder that adds the luminance signal or a signal similar to the luminance signal and any one of the several types of contour signals; and comparing the output signal level of the adder with a reference level;
A contour corrector comprising: a comparison circuit that controls the selection circuit.