JPH1123982A - Signal processing circuit of electron endoscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an endoscope image with a stereoscopic effect, an excellent color reproducibility, and moreover improved resolution at a time of high brightness. SOLUTION: This signal processing circuit has a γ-correction circuit 15 for providing corrections corresponding to γ-characteristics of CCD 10, CDS (correlation double sampling) 12, and display monitor, and the gamma coefficient γof the gamma correction curve Lr (L: input optical signal value, γ: gamma coefficient) of this gamma correction circuit 15 id set to a value in a range 0.45<γ<1. Thus, in a case of an endoscope where shades of red are main, a dark part is enhanced darker to become a stereoscopic image, and the color is well-modulated to have an excellent color reproducibility and be improved in resolution at a time of high brightness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit of an electronic endoscope for performing gamma correction on an image signal obtained by an image pickup device in order to obtain an image with optimum brightness and high color reproducibility. About the content.

[0002]

2. Description of the Related Art An electronic endoscope apparatus incorporates a CCD (Charge Coupled Device) as a solid-state image pickup device at the distal end of a scope, and captures an image of a body to be observed such as in a body cavity or a cavity into which the scope is inserted. And a TV monitor (CRT
Monitor). In a signal processing circuit of this type of electronic endoscope, a gamma correction circuit is incorporated to improve a gamma characteristic of a CRT monitor or the like.

FIG. 4 shows a gamma characteristic (brightness I, voltage E, I = E ^{1 / r} ,
γ = 0.45), and FIG. 5 shows a gamma correction curve in the signal processing circuit. The figure shows the relationship between the voltage E applied to a CRT (picture tube) and the brightness of the display screen (light emission output).
As shown in FIG. 1, the brightness I of the screen does not change linearly with the increase in the voltage E, but gradually at first,
It changes in a curve so that it becomes slightly brighter as the voltage rises.

In order to improve such gamma characteristics, a conventional gamma correction curve 102 shown in FIG.
The correction based on is performed. In other words, the gamma correction curve 102 is a curve obtained by inverting the gamma characteristic curve 101 around a 45-degree line on the coordinates when the horizontal axis represents the input optical signal (voltage) L and the vertical axis represents the output voltage. This curve is represented by L ^0.45 (gamma coefficient γ, where L is the input optical signal).
= 0.45). Then, the gamma correction circuit outputs a voltage obtained by converting the input optical signal based on the curve 102, thereby forming a straight line 103.
As shown by, the brightness proportional to the input optical signal is reproduced on the screen.

[0005]

However, the object to be observed (in the body cavity) imaged by the electronic endoscope has a color such as a mucous membrane or the like.
That is, it is mainly composed of red-based colors, and when displayed on a CRT monitor, has a problem in that it is somewhat lacking in three-dimensionality and color reproduction is not sufficient when compared with a general subject composed of all colors. was there. In other words, in an endoscopic image in which pink, red, skin color, etc. are mainly used, a three-dimensional effect can be obtained by darkening a dark place, and if a minute change in color is captured, the color is turned on, The reproduction is also good.

Further, in an endoscope image (an image including a mucous membrane) composed of the same system colors, the resolution at the time of high luminance tends to slightly decrease.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to obtain an endoscope image having a three-dimensional effect, good color reproducibility, and improved resolution at high luminance. It is an object of the present invention to provide a signal processing circuit for an electronic endoscope that can be used.

[0008]

In order to achieve the above object, the present invention provides an electronic electronic device having a gamma correction circuit for correcting an image signal obtained by an image sensor in accordance with a gamma characteristic of a display monitor. In the signal processing circuit of the endoscope, when the gamma correction curve set by the gamma correction circuit is represented by ^Lr where L is the input light signal value and γ is the gamma coefficient, the gamma coefficient γ is set to 0.45 < It is characterized in that the value is in the range of γ <1.

According to the above configuration, the gamma coefficient γ is set to 0.
Compared to the case of 45, the curve of the gamma correction curve is a gentle curve, and as a result, even on the display screen, the change in brightness with respect to the input light (signal) is not linear,
The characteristic becomes a gentle curve approaching the original gamma characteristic of the CRT. Therefore, on the display screen in the object to be observed in which the red and pink colors are mainly used, dark places are emphasized more darkly to provide an image with a three-dimensional effect, and the color reproducibility is improved, so that the color reproducibility is improved. Furthermore, there is an advantage that the resolution is improved at the time of high luminance.

[0010]

FIG. 1 shows a configuration of a signal processing circuit of an electronic endoscope as an example of an embodiment.
1, a CCD 10 which is a solid-state imaging device is arranged at the tip of the electronic endoscope. This CCD 10 is a CCD
The output signal of the CCD 10 is driven by a driver 11 and supplied to a CDS (correlated double sampling) circuit 12. The CDS circuit 12 clamps the output video signal of the CCD and samples and holds the image data portion with a sampling pulse phase-adjusted in relation to the clamp pulse, thereby obtaining a video signal with reduced noise. it can.

The CDS circuit 12 includes an A / D converter 1
A gamma correction circuit 15 is connected via the line 4, and a matrix circuit 16 for forming each color signal of red (R), green (G), and blue (B) is connected to the gamma correction circuit 15. In the matrix circuit 16, for example, in a simultaneous electronic endoscope, an operation for converting a color difference signal into an RGB signal is performed, and in a field sequential electronic endoscope, an operation of multiplying by a coefficient set for each color is performed. Will do.

At the stage subsequent to the matrix circuit 16, RGB
An image memory 17 for storing each video signal is provided.
A D / A converter 18 is connected to the image memory 17. And, in order to control each of the above circuits,
A CPU 20 is provided.

In the gamma correction circuit 15, when the input optical signal (voltage) is L and the gamma coefficient is γ, the video signal obtained by the CCD 10 is L ^0.45 <L
^r <correction is performed calculating a gamma correction curve L ^r in the range of L ^1. That is, the gamma correction circuit 15 is configured by a circuit that changes the gain of the amplifier for each stepped voltage value or a circuit that has a table that stores a correction coefficient by which the input value is multiplied. The coefficient is set according to the above-mentioned gamma correction curve.

FIG. 2 shows that the above gamma coefficient γ is 0.6
5 shows a gamma correction curve 104 when (L ^0.6 ) [the horizontal axis represents the input optical signal (voltage) L and the vertical axis represents the output (voltage)], and this correction curve 104 is shown in FIG. It is a gentle curve having a lower output level than the corrected correction curve L ^0.45 .

The embodiment has the above-described structure, and includes a CCD
The video signal obtained in 10 is DC-reproduced by a CDS circuit to be a signal from which noise has been removed, converted into a digital signal, and input to a gamma correction circuit 15. The gamma correction circuit 15 applies the above L ^{0.6 to the} video signal.
The gamma correction is performed by the gamma correction curve 104, and is temporarily stored in the image memory 17 as RGB signals via the matrix circuit 16. The data is read out based on the read control of the CPU 20 and is read out via the D / A converter 18.
The endoscope image is output to the C monitor
Displayed on the monitor.

FIG. 3 shows the display characteristics on the monitor screen. The horizontal axis represents the input light signal L, and the vertical axis represents the brightness. According to the gamma correction circuit 15 described above, the gamma characteristic 101 of the CRT monitor shown in FIG. The characteristic curve 105 has a gentler characteristic than the conventional linear characteristic 103 (FIG. 5), and becomes darker when the input optical signal level is low.
The dark places are emphasized to give an image with a three-dimensional effect.

In addition, in the case of an endoscope image of the same system color, color reproducibility is improved due to color turning, and at high luminance, brightness is suppressed and resolution is improved.

In the above example, the gamma coefficient γ has been described as 0.6, but this γ can be selected from values larger than 0.45 and smaller than 1. Or a remarkable improvement in resolution at high brightness 0.5
It is preferable to set in the range of 0.7.

[0019]

As described above, according to the present invention,
Since the gamma gamma coefficient of the gamma correction curve L ^r set in the gamma correction circuit and a value in the range 0.45 <γ <1, and in the body cavity image color reddish is the main, there are three-dimensional effect, It is possible to display an image with good color reproducibility and improved resolution at high luminance.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a signal processing circuit of an electronic endoscope according to an embodiment of the present invention.

FIG. 2 is a graph showing a gamma correction curve of the gamma correction circuit of FIG.

FIG. 3 is a graph showing a state of brightness of an image on a monitor screen when the image is corrected by the gamma correction circuit of FIG. 1;

FIG. 4 is a graph showing gamma characteristics of a CRT monitor.

FIG. 5 is a graph showing a state of brightness on a monitor screen when corrected by a conventional gamma correction circuit.

[Explanation of symbols]

 10: CCD, 12: CDS, 15: gamma correction circuit, 17: image memory, 20: CPU.

Claims (1)

[Claims] 1. A signal processing circuit for an electronic endoscope having a gamma correction circuit for correcting an image signal obtained by an image sensor according to a gamma characteristic of a display monitor, wherein the signal processing circuit is set by the gamma correction circuit. When the gamma correction curve is represented by ^Lr where L is the input optical signal value and γ is the gamma coefficient, the gamma coefficient γ is set to a value in the range of 0.45 <γ <1. Endoscope signal processing circuit.