JPH0582784B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to signal level control of a video signal processing device.

Conventional configuration and its problems Figure 1 shows the conventional monochrome video signal or
FIG. 2 is a block diagram of a circuit that automatically adjusts an NTSC color video signal to the optimum gain.

1 is a VCA (voltage control amplifier) that amplifies the video signal a with a gain corresponding to the control signal, 2 is a peak detector that detects the peak of the output b of the VCA 1, and 3 is the output c of the peak detector 2 and the reference voltage d. This is an error amplifier that amplifies the difference between the two and controls the gain of VCA1.

When the amplitude of the video signal output b is too small, the output c of the peak detector 2 becomes smaller than the reference voltage d, and the output of the error amplifier 3 acts in the direction of increasing the gain of the VCA1, causing the output b of the VCA1 to increase. The peak will always be equal to the reference voltage d. If the amplitude of the video signal output b is too large, gain control is applied in the same manner as described above, and the output b is stabilized at a constant amplitude.

The conventional configuration is a monochrome video signal or
It can be used for gain control of NTSC color video signals, etc., but RGB video signals are divided into three signals and there is a correlation between each signal, so if you perform conventional gain control for each signal, each Since the signal gains differ and an image with incorrect color balance is output, it cannot be used to control the gain of RGB color video signals. Furthermore, since the gain is adjusted in an analog manner, the signal-to-noise ratio and frequency characteristics of the signal deteriorate, resulting in poor gain accuracy.

Purpose of the Invention The present invention improves the above drawbacks by digitalizing automatic gain control, and can simultaneously process multiple conversions with arbitrary conversion characteristics including gamma correction at high speed, and converts color video signals consisting of RGB. It is an object of the present invention to provide a video signal processing device that can perform signal level control without destroying color balance even when the color balance is not destroyed.

Structure of the Invention The present invention includes a peak detection means for detecting the peak of a video signal, an A/D conversion means for A/D converting the output signal of the selection means, a CPU, ROM, RAM,
It consists of a microcomputer section consisting of an input port and an output port.

DESCRIPTION OF EMBODIMENTS FIG. 2 is a block diagram of a video signal processing apparatus according to a first embodiment of the present invention.

In FIG. 2, 4 is a peak detection circuit that detects the peak value of the video signal e, 5 is a selection circuit that selects the video signal e and the output j of the peak detection circuit 4, and 7 is an A/D converter for the output k of the selection circuit. This is an A/D converter that performs the conversion. 10 is a CPU, 11 is a ROM that stores programs for the CPU 10, and 12 is a ROM that stores data.
RAM, 8 is an input port for reading the output data of the A/D converter 7, 9 is an output port for outputting the processed data, CPU 10, ROM 11,
RAM12, input port 8 and output port are:
They are connected to each other by an address bus and a data bus to form a microcomputer.

Further, in this embodiment, a lookup table is configured in advance by software in the RAM 12 of the microcomputer section mentioned above. This lookup table is designed to provide an arbitrary functional relationship between the video data input from the input port 8 and the data output from the output port 9, so that when the input data is given as an address, the output data is read out. It is set.

First, the CPU 10 selects an output j obtained by detecting the peak value of the video signal e by the peak detection circuit 4 and outputs it to the selection circuit 5.
, and the peak value data A/D converted by the A/D converter 7 is read through the input port 8 .

When the aforementioned peak value data is P, a lookup table with a maximum input of N and a maximum output of M as shown in FIG. Create a new lookup table as shown in Figure b.

After the above processing, the CPU 10 selects the video signal e with the selection circuit 5, reads the video data converted from A/D by the A/D converter 7 through the input port 8,
The converted data is obtained by giving the video data as an address to the lookup table shown in FIG.

Next, the operation of the address expansion/contraction means for expanding/contracting the lookup table in the address direction will be explained in detail using figures and flowcharts.

In order to simplify the explanation, a and b in Fig. 4 are
The input/output functions of the lookup table are illustrated as linear functions.

When the input parameter of the lookup table is a variable i, the variable i is a variable that points to a memory address, so it is an integer from 0 to N, but the value f(i) or g(i) of the lookup table is is determined only by the data representation type expression and does not need to be an integer.

Function f(i) in Figure 4a is not expressed as a lookup table for values other than when variable i is an integer between 0 and N. The data necessary to create the function g(i) compressed by is not necessarily present in the data of f(i).

Therefore, the new function g(i) can be written as g(i)=f(P/Ni)=f(α+β), where the integer part of N/Pi is α and the decimal part is β. Approximating by Taylor expansion around α up to g(i)f(α)+βf′(α), and replacing the first-order differential coefficient with the difference, we get g(i)f(α)+β(f It can be expressed approximately as (α+1)−f(α)). This formula calculates the value of f(α) at the integer part α of N/Pi and the following function value f(α+
This means that the value of 1) can be calculated by internally dividing the value of the decimal part β.

By compressing the lookup table of the function f(i) in FIG. 4a in the address direction at a ratio of P/N, address expansion/contraction means creates the lookup table g(i) in FIG. 4b where gain control works. A flowchart explaining the detailed operation is shown in FIG.

Variable i is the address pointer of g(i) from 0 to N
The calculated data is written to the address indicated by the variable i while incrementing the value up to the address indicated by the variable i.

The variable α and the variable β are variables to which the integer part and decimal part of the value obtained by multiplying the variable i by N/P are substituted, and the symbol [ ] in the flowchart is a Gaussian signal.

The next conditional judgment is for clipping the function g(i) when the variable α becomes larger than N. Normally, the value calculated using the approximation formula described above is used to look up the function g(i). write to the table.

The following other embodiment will be explained using FIG. 6. Peak detection circuit 4, A/D converter 7, input port 8, output port 9, CPU 10, ROM 11,
RAM 12 is similar to that of the embodiment of FIG.

6 is a color video signal consisting of RGB, f, g,
A maximum detection circuit 5 that obtains the maximum value of the amplitude of h is one from four input signals consisting of the output obtained by detecting the peak of the output of the maximum value detection circuit 5 by the peak detection circuit 4 and RGB video signals f, g, and h. This is a selection circuit that selectively passes one.

The peak voltage j of the RGB still image video signals f, g, h obtained by the maximum value detection circuit 6 and the peak detection circuit 4 is selected by the selection circuit 5, and then
The data is converted into peak value data by the D converter 7, and is taken into the microcomputer section through the input port 8.

FIG. 7 shows the relationship between an example of RGB video signals f, g, h and the peak voltage output j.

In order to perform automatic gain control without destroying the color balance of the RGB color video signal, a lookup table is created using the maximum peaks of f, g, and h as peak value data, and the same value is used when processing the video signal for each RGB color. By referring to the lookup table, you can avoid disturbing the color balance.
Automatic gain control can be performed using RGB, etc. gains.

In the embodiments described in detail above, it is possible to create a second lookup table that provides an output equivalent to performing automatic gain control by replacing the first lookup table in which an arbitrary function is set in advance. By referring to a single lookup table during execution, calculations such as gamma correction of the video signal and automatic gain control can be processed simultaneously. It has high utility value in applications such as image printers that require a number of conversions such as gamma correction and gamma correction of printing characteristics.

Furthermore, for applications requiring high-speed processing, only the lookup table can be performed by hardware.

Effects of the Invention By using the method of the present invention, which adds automatic gain control to a preset arbitrary function conversion table such as gamma correction using table address expansion/contraction means, multiple conversions, corrections, etc. can be performed by simply referring to one table. can be performed at high speed,
In the case of AGB video signals, without disturbing the color balance,
Accurate automatic gain control can be performed without degrading S/N, so when used in image printers, it is possible to obtain images with a high contrast ratio regardless of variations in the video signal level or image content. can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a video signal processing device in a conventional example, FIG. 2 is a block diagram of a video signal processing device in an embodiment of the present invention, FIGS. 3 and 4 are explanatory diagrams of the same device, and FIG. 6 is a block diagram of a video signal processing apparatus according to another embodiment of the present invention, and FIG. 7 is a signal waveform diagram for explaining the apparatus. 4...Peak detection circuit, 5...Selection circuit, 6...
...Maximum value detection circuit, 7...A/D converter, 8...
Input port, 9...Output port, 10...CPU,
11...ROM, 12...RAM.

Claims (1)

[Scope of Claims] 1. Peak detection means for detecting the peak of the signal level of a video signal, selection means for selecting the video signal and the output from the peak detection means, and an A/D converter for the output signal of the selection means. A first lookup table having an arbitrary input/output function relationship set in advance and having an A/D conversion means for converting, a microcomputer consisting of a CPU, ROM, RAM, input ports, and output ports; is selected by the selection means and converted into A/D by the A/D conversion means according to a program stored in the ROM.
a second lookup table set in the RAM that gives the converted video data read through the input port as an address and sends out the obtained data; 1. A video signal processing device comprising a table expansion/contraction means for expanding/contracting a first lookup table in an address direction to create the second lookup table. 2. The video signal is a color video signal consisting of R, G, and B, and includes a maximum value detection circuit that detects the maximum value of the color video signal, and provides the output of the maximum value detection circuit to a peak detection circuit. A video signal processing device according to claim 1.