JPH04369176A - Automatic black level adjustment circuit for infrared ray video image - Google Patents

Abstract

PURPOSE:To set adaptively a black level being a reference level of a video image decided by a blanking level to be constant independently of an absolute level of an effective infrared ray video signal. CONSTITUTION:A selector 1 extracts an effective infrared ray video signal for a signal block in an infrared ray video signal. A peak hold circuit 2 extracts a signal of a lowest level in the extracted effective infrared ray video signal and a sample-and-hold circuit 3 outputs minimum level information expressed by a voltage for each frame. A clip circuit 4 clips a blanking level of the inputted infrared ray video signal with a level of a minimum signal level information and a clamp circuit 5 adjusts the signal level so that the clipped blanking level is set to a prescribed value and outputs the result.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a black level adjustment circuit for an infrared image signal, and more particularly to a black level adjustment circuit for an infrared image signal that automatically adjusts a black level, which is a reference level of an infrared image signal, to a constant level.

0002

[Background Art] When displaying an infrared video signal on a display such as a CRT, blanking, which blanks the effective infrared video signal used as the video, sets a black level that represents the standard level of the displayed video. are doing.

Conventionally, such black level adjustment, ie, blanking level adjustment, was performed manually while observing the displayed signal level.

0004

In the conventional black level adjustment described above, the dynamic range of the infrared video signal is extremely large, and there is no absolute reference level (black level). Therefore, in order to effectively utilize the dynamic range of the signal processing system, the black level is often determined based on the lowest signal level of the effective infrared video signal.

However, since the level of the lowest level signal changes greatly depending on the object to be imaged, there is a problem in that the black level must be changed each time.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic black level adjustment circuit for infrared images that eliminates the above-mentioned drawbacks and eliminates the need to change the black level each time depending on the object to be imaged.

[0007]

SUMMARY OF THE INVENTION The circuit of the present invention provides an infrared video signal that automatically adjusts a blanking level that determines the black level of an infrared image displayed by an infrared video signal that includes an effective infrared video signal and a blanking signal. The automatic video black level adjustment circuit replaces the blanking level of the infrared video signal with the lowest level of the effective infrared video signal, and then converts and sets the effective infrared video signal to a predetermined constant value. It has a configuration that allows the signal level to be adjusted so as to adaptively set a constant black level for the infrared video signal.

Further, the circuit of the present invention has a configuration in which the constant black level is an absolute reference level of the infrared video signal.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

The embodiment shown in FIG. 1 includes a selector 1 that selects and outputs only the effective infrared video signal excluding the blanking signal from the infrared video signal, and a peak hold circuit 2 that detects and holds the lowest signal level of the output of the selector 1. and a sample hold circuit 3 that samples and holds the lowest signal level detected by the peak hold circuit 2 for each frame.
and a clip circuit 4 that cuts the blanking level of the input infrared video signal using the signal minimum signal level information sampled and held by the sample and hold circuit 3, replaces the blanking level with the lowest level of the effective infrared video signal, and outputs the same. and a clamp circuit 5 that converts the blanking level of the output of the clip circuit 4 to a certain constant level and outputs the same.

Next, the operation of this embodiment will be explained.

[0013] From the input infrared video signal, only the valid infrared signals are selected and extracted by the selector 1 and supplied to the peak hold circuit 2, and the level of the blanking period is set to a level sufficiently higher than the level of the infrared video signal. .

The peak hold circuit 2 detects the lowest signal level of the input effective infrared video signal for each frame.

The sample and hold circuit 3 samples and holds the output detected by the peak hold circuit 2 for each frame, and outputs it as minimum signal level information of a constant voltage value.

The clipping circuit 4 clips the blanking level in the infrared video signal using the lowest signal level information supplied from the sample and hold circuit 3, and replaces the blanking level with the lowest signal level information. The signal blanking level is set to the lowest level of the valid infrared video signal.

The clamp circuit 5 adjusts the signal level by setting the blanking level, ie, the black level, of the infrared video signal thus set as a certain constant level.

In this way, a constant black level can be adaptively set without depending on the absolute level of the effective infrared video signal.

[0019]

As explained above, the present invention replaces the blanking level of the infrared video signal with the lowest level of the effective infrared video signal, and then clamps it to a certain level. This has the effect of being able to adaptively set a constant black level for the signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an automatic black level adjustment circuit for infrared images according to an embodiment of the present invention.

[Explanation of symbols]

1 Selector 2 Peak hold circuit 3 Sample hold circuit 4 Clip circuit 5 Clamp circuit

Claims (2)

[Claims] 1. An automatic black level adjustment circuit for an infrared image that automatically adjusts a blanking level that determines the black level of an infrared image displayed by an infrared image signal including an effective infrared image signal and a blanking signal, comprising: , by replacing the blanking level of the infrared video signal with the lowest level of the effective infrared video signal and then converting and setting it to a predetermined constant value, the blanking level of the infrared video signal is adaptively constant for effective infrared video signals of different levels. An automatic black level adjustment circuit for infrared images, characterized in that the signal level can be adjusted so as to set the black level of an infrared image. 2. The automatic black level adjustment circuit for infrared images according to claim 1, wherein the constant black level is an absolute reference level of the infrared image signal.