JPH0410767A - Contour emphasizing circuit - Google Patents

Abstract

PURPOSE:To inexpensively attain a high quality contour emphasis independently of correlation between lines of an image by digitizing a video signal, detecting a difference between the value of a current picture element and the value of the just preceding picture element and executing the arithmetic processing of the difference. CONSTITUTION:A video signal inputted to an input terminal 1 is restricted at its band through an LPF 2, the band-restricted signal is converted into a digital signal by A/D converter 3, the data of the current picture element and the data of the just preceding picture element through a delay element 11 are supplied to a difference detecting current 6, and a difference between both the data is detected by comparison. A difference signal C obtained by the circuit 6 is supplied to an adder circuit 7, a video signal delayed by the circuit 11 is also supplied to the adder circuit 7 and the signal C is added to the signal B by the adder circuit 7 and a contour-emphasized signal D is obtained. Consequently the high quality contour emphasis can be obtained without using an expensive line memory.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit that converts a video signal into digital signals and emphasizes the outline of an image.

[Prior Art] Conventionally, a method for emphasizing the outline of an image by digitizing a video signal has been proposed, such as in Japanese Patent Application Publication No. 59/23974.

[Problem to be solved by the invention] However, in the above conventional example, a delay circuit that outputs a plurality of delayed signals sequentially shifted by one horizontal interval is used,
The correlation between these signals is calculated and output. Therefore, it is expensive because it requires a plurality of expensive line memories, and it is also necessary to calculate the correlation between lines, which has the disadvantage that sufficient characteristics cannot be obtained depending on the content of the image.

[Means and effects for solving the problem] According to the present invention, the outline of an image is emphasized by providing a circuit that detects the difference between the value of the current pixel and the value of the previous pixel. Therefore, an expensive line memory is not required, and since the difference between the previous pixel and the previous pixel is detected and calculated, high-quality contour enhancement can be obtained even when there is no image correlation between lines.

[Embodiment] The first embodiment is an embodiment of the present invention, in which 1 is a video signal input terminal, 2 is a low pass for limiting the video signal to a desired band for digitizing, and filter 3 is an analog/analog/video signal input terminal. The digital converter 4 has a conversion table for performing digital/digital conversion and has non-linear characteristics, and in order to be able to rewrite the conversion table values (non-linear characteristics), it uses RAM (random, access, memory). used.

5 is a controller 99 combination b for supplying data to rewrite the value of the conversion table in 4 in order to obtain the desired contour enhancement. 6 is a comparison between the data of the pixel at the current sample time and the data of one pixel before, and there is a difference of 1. After detecting the difference detector and the specified difference level, if the polarity of the difference level is N-inverted or the difference value is less than the predetermined level, add a difference value that is the same as the previous difference value but with the polarity reversed. The data processing circuit 7 is an adder circuit for adding differential data to the delayed Hiteoi Iris data, and the limiter circuit 8 is a limiter circuit 9 to prevent the minimum and maximum values of the tesital data from being exceeded at the peak levels of black and white. is a digital/analog converter; ]O is a low-pass filter 11 for limiting the video signal to a desired band; a delay element (memory) for delaying data for one pixel;

Next, in the above configuration, the video signal inputted to the input terminal 1 is band-limited to a desired band by the LPF 2, and then sampled and quantized by the A/D converter 3 and converted into a digital signal 6. is fed to a differential detector.

The difference detection WL of 6 is the data of the current pixel of 3 and jl
Data from one pixel before is supplied via the delay element, and a difference is compared and detected.

In FIG. 3, the difference C (excluding the shaded area) is obtained by subtracting the data A of the current pixel from the data B of the previous pixel. (T l, T 2T,, T, and Ding,,
...T, 7. is an example of Sunflink timing for sampling) The difference value obtained from FIG. The characteristics of the conversion cheatle are as shown in Figure 2.When the level of the difference value is small, there is no output to the next stage.
This is a non-linear characteristic such that a differential value of a limited level is output at a predetermined level even below a specific level.

Also, the value of the conversion table in 4 (nonlinear characteristics) is
The roll section requires RAM (random, access, memory) T4 so that it can be rewritten to the desired edge enhancement level.

The difference signal obtained by the difference detection circuit 6 and the conversion table 4 (C> in Figure 2 is the difference signal obtained, after which the difference value is less than the predetermined 17 Herre, or the polarity is reversed by 1). If obtained, a difference value of the same level as the previous difference value but with inverted polarity is added by the data processing circuit.

Figure 2 C's sting! It is a differential signal with partial addition.

This difference signal C is supplied to an adder circuit 7 at the next stage, and the video signal delayed by an 11 delay circuit is also supplied to this adder circuit and added.

By adding the video signal B and the difference signal C, an edge-enhanced signal is obtained, which is supplied to the limiter circuit 8.

The limiter circuit of 8 has a white peak (the maximum value represented by the digitized signal) and a black level (the minimum value represented by the digitized signal or the leading edge value of the synchronization signal, when it is digitized, the maximum value is below the best value level and synchronization The limiter (specified at a level that does not cause instability) cannot be applied. Further, after being converted into an analog signal by 9 digital/analog converters, band-limiting is performed by 10 LPFs, and a contour-enhanced hiteo signal is obtained.

Figure 4 shows that in the mid-range frequency band, the video signal is I:, -! Waveforms of various parts of the town (Actually, they are digital signals, but to make the explanation easier to understand, Figures 3, 4, and 5 are shown as analog signals. ) is shown.

FIG. 5 shows a waveform in which the hiteo signal is processed in an even lower frequency range. As you can see from these figures,
Contour enhancement is not performed for signals that change smoothly,
There is no harm in image quality.

``Effects of the invention'' - After digitizing the hiteo signal as explained,
By detecting the difference between the value of the current pixel and the value of the previous pixel and performing arithmetic processing, it is possible to perform high-quality contour enhancement at a low cost, regardless of the correlation between lines of the image. .

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of an edge enhancement circuit according to the present invention. FIG. 2 shows an example of characteristics of a nonlinear conversion table (see FIGS. 3, 4, and 5) for explaining the present invention. 1 is an input terminal 2 is a low-pass filter 3 is an analog/digital converter 4 is a nonlinear conversion table 5 is a control section 6 is a difference detection and data processing circuit 7 is an addition circuit 8 is a limiter 9 is a digital/analog converter 10 is a low-pass The filter 11 is a delay circuit.

Claims (3)

[Claims] (1) A detection means for detecting a difference value between the current pixel value and the previous pixel value of a digital video signal, and when the difference value is less than a predetermined threshold level or the polarity is reversed, the detection means detects the difference value between the current pixel value and the previous pixel value, and a data processing circuit that replaces data with data of the same value and inverted polarity. (2) The contour emphasizing circuit according to claim (1), further comprising a table for non-linearly converting the difference value. (3) The nonlinear conversion table is capable of changing the level of the nonlinear slope to a desired value by external control.
Contour enhancement circuit described in ).