JP2563420B2 - Endoscope device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an endoscope apparatus having a signal processing system that simultaneously performs arbitrary gamma characteristics and arbitrary gradation conversion.

[Problems to be Solved by Conventional Techniques and Inventions] In recent years, electronic endoscopes using a solid-state imaging device such as a CCD as an imaging means have been put into practical use. In this electronic endoscope system, the photoelectric conversion characteristics of the image sensor and the characteristics displayed on the CRT are different, and the displayed image is different from the actual subject. Correction means are provided.

Conventionally, as a signal means capable of performing variable digital gamma correction, a look-up
Some use the table memory 1. This is converted into an electric signal by the CCD 2, the gradation conversion circuit 5 performs gradation conversion on the analog signal 4 output as a video signal by the pre-processing circuit 3, and converted into a digital signal 7 by the analog-digital converter 6. To do. Further, the digitized signal 7 is applied as an address signal of the look-up table memory 1 to read the data for linear correction and gamma correction written in the look-up table memory 1. Further, a microprocessor (hereinafter referred to as MPU) 9 switches the address signal with respect to the data input of the keyboard 8 to select one of a plurality of gamma characteristics written in the look-up table memory 1. it can. The signal linearly corrected and gamma-corrected by the selected gamma characteristic is converted into a digital-analog converter 10.
It is input to the post-process circuit 12 as a signal 11 that is converted into an analog signal by the CRT 13 and converted into a predetermined video signal.
Is input to

By the way, when the gamma correction is performed after the video signal is digitized as shown in FIG. 9 (a), the low level has the extended characteristic as shown in FIG. 9 (b). Therefore, the quantization error in this case becomes larger than the quantization error in the case where the gamma correction is performed by analog and then the digitization is performed as shown in FIG. 9C. Therefore,
In Japanese Patent Laid-Open No. 61-208990, gradation conversion is performed before analog-digital conversion as shown in FIG. 10 (a), whereby low level is expanded and then analog-digital conversion is performed. By performing the gamma correction after performing the linear correction as shown in FIG. 10 (b), an image signal quantizer capable of reducing the quantization error at a low level as shown in FIG. 10 (c) is provided. It is disclosed.

However, with the above configuration, one tone conversion cannot be applied to arbitrary gamma characteristics, so the quantization accuracy of the output data after gamma correction is deteriorated, and the subject cannot be reproduced faithfully. Occurs.

The present invention solves the conventional problems as described above. To reduce the quantization error of an output signal after gamma correction with respect to an arbitrary gamma characteristic, an arbitrary gamma characteristic and an arbitrary level are selected. It is an object of the present invention to provide an endoscope apparatus having a signal processing system that can perform tone conversion simultaneously.

[Means for Solving Problems and Its Action] In the principle diagram shown in FIG. 1, the video signal 4 converted into an electric signal by the CCD 2 and preprocessed by the pre-processing circuit 3 is gradation conversion and analog-digital conversion. The unit 16 converts the signal into an arbitrary nonlinear characteristic (including a linear characteristic) and converts it into a digital signal. (The same can be done in an analog-digital converter that performs gradation conversion.) The digital signal is a linear correction and gamma correction unit having a look-up table memory in which a plurality of linear characteristics and gamma correction are written. Data is input to an address of any one of 17 table memories, and data in which the gradation-converted digital signal is subjected to linear correction and gamma correction is read out.

By the way, when a signal for selecting an arbitrary gamma characteristic is inputted from the external input device (keyboard) 18 to the input signal discriminating circuit section 19, the input signal discriminating circuit 19 has a look-up circuit having a plurality of table memories. A signal for switching the address of the table memory is sent, and the non-linear characteristic of gradation conversion is changed so that the quantization error of the output signal becomes small with respect to the selected gamma characteristic.

The signal read from the linear correction and gamma correction unit 17 is converted into an analog signal through the digital-analog converter 10, converted into a predetermined video signal by the post-process circuit 12, and output and displayed on the CRT 13 as a video. .

[Embodiment] FIGS. 2 to 6 relate to a first embodiment of the present invention, FIG. 2 is a block diagram of an endoscope apparatus of the first embodiment, FIG. 3 is a block diagram of a signal processing system, FIG. 4 is a block diagram of the analog-digital converter, FIG. 5 is a non-linear characteristic graph showing the input / output characteristics of the analog-digital converter, and FIG. 6 is the analog-digital conversion with the gradation characteristic corresponding to the gamma characteristic. 2 is a nonlinear characteristic graph.

As shown in FIG. 2, the endoscope apparatus 21 of the first embodiment has an electronic endoscope 22 and a light source unit 23 for supplying irradiation light to the electronic endoscope 22, and the electronic endoscope 22 A control device 25 comprising a signal processing system 24 for processing the video signal sent from
And a monitor (CRT) 13 for displaying the video signal output from the control device 25 on the screen.

The insertion part 28 inserted into the inspection part 27 of a living body or the like includes a long flexible tube part 29 and an upper / lower part connected to the tip of the flexible tube part 29.
It is composed of a bending portion 30 that can be bent in the left-right direction, and a tip portion 31 that is continuously provided at the tip of the bending portion 30. Tip 31
Is composed of a CCD 2 that converts incident light into a video signal, and an objective lens 32 and a light guide 33 that are provided in front of the CCD 2. A large-diameter operation portion 34 is continuously provided at the rear end of the insertion portion 28, and a universal cord 35 is extended from the side portion of the operation portion 34. The universal cord 35 is provided at the tip of the universal cord 35. Light source and signal connector
36 is connected to the control device 25.

In FIG. 3, an electric signal from the CCD 2 is input to the pre-processing circuit 3 and converted into an analog signal 4 as a video signal which has been subjected to pre-processing such as white balance and has a linear correction terminal (reference voltage). It is applied to a parallel comparison type analog-digital converter 40.

On the other hand, a signal for selecting an arbitrary gamma characteristic from the keyboard 41 is discriminated by the MPU 42, and the discriminated signal is a look-and-hold that holds a plurality of linear characteristic and gamma characteristic data.
It is a signal for switching the address of ROM43 as the up table memory. Further, the MPU 42 also sends a signal for controlling the voltage to the voltage generating circuit 44 which gives an arbitrary voltage to the linear correction terminal of the analog-digital converter 40. In addition, by applying the address signal, ROM43
The digital signal 45 read out from is converted into an analog signal 46 by the digital-analog converter 10 and input to the post-process circuit 12. The post-processing circuit 12 converts the analog signal 46 into a predetermined video signal of R, G, B, etc. and outputs it to the CRT 13.

FIG. 4 shows the structure of the analog-digital converter 40,
The analog signal Vin is applied to the input terminal 50, and the reference voltages VRT and VRB are applied to the reference voltage terminals 51 and 52, respectively. The input terminal 50 has 2 ⁿ comparators Ci (where i
= 1,2, ... 2 ⁿ ) is connected to one input
A voltage obtained by dividing the voltage VRT-VRB between the reference voltage terminals 51 and 52 by serially connected resistors R / 2, R, ... Is applied to the other input terminals of C1, C2 ,. These 2 ⁿ comparators C1, C2, ...
The output terminal (generally indicated by reference numeral 53) is connected to the input terminal of an encoder 54 that encodes a digital signal, and an encoded n-bit digital signal is output. A linear correction terminal 55 is connected to the midpoint of the resistors R / 2, R, ... Which divide the voltage between the reference voltage terminals 51 and 52, and the reference voltage VRM
Is applied. By changing the reference voltage VRM, it is possible to simultaneously perform gradation conversion and analog-digital conversion corresponding to a desired gamma characteristic. This reference voltage VRM determines the output signal of the keyboard 41 which is a means for selecting the gamma characteristic.
Based on the output control signal of 2, the voltage generation circuit 44 generates.

Next, the operation of the endoscope device 21 configured as above will be described.

The light emitted from the light source unit 23 is radiated from the tip 31 toward the inner surface of the inspection unit 27 via the light guide 33,
This reflected light is converted into an electric signal by the CCD 2 via the objective lens 32 and is passed through a signal cable (not shown) to a signal processing system 24 having a configuration as shown in the block diagram of FIG.
Is input to

As shown in FIG. 3, the electric signal from the CCD 2 is input to the pre-process 3 and the analog signal Vin
Is output as

This analog signal Vin is applied to the analog signal input terminal 50 of the analog-digital converter 40 having the configuration shown in FIG.

In FIG. 4, voltage VRT between reference voltage terminals 51 and 52
A reference voltage obtained by dividing −VRB by reference resistors R / 2, R, ... Is given to each comparator Ci, and the reference voltage is compared with the analog signal Vin. Further, the output of the comparator 53 is input to the encoder 54, and is encoded as an n-bit digital signal, and the analog signal is quantized.

Therefore, by moving the reference voltage VRM applied to the linear correction terminal 55 in FIG. 4 between the reference terminals 51 and 52, the nonlinear characteristic as shown in FIG. 5 can be obtained and the nonlinear analog signal can be quantized. Can be done with one analog-to-digital converter 40.

On the other hand, the keyboard 41 sends a signal for selecting one of the gamma characteristics to the MPU 42.

The MPU 42 discriminates the sent signal and sends a signal for switching the address of the ROM 43 in which the data of a plurality of gamma characteristics is written.

Further, the MPU 42 sends a signal for controlling the reference voltage VRM applied to the linear correction terminal 55 of the analog-digital converter 40 to the voltage generation circuit 44.

Upon receiving the control signal output from the MPU 42, the voltage generation circuit 44 generates a reference voltage VRM according to the signal and applies it to the linear correction terminal 55 of the analog-digital converter 40.

Therefore, the MPU 42 can simultaneously control the address of the ROM 43 and the reference voltage VRM applied to the linear correction terminal 55 of the digital-analog converter 40.

Further, in order to make the quantization error uniform with respect to an arbitrary gamma characteristic, the same non-linear correction as that of the gamma characteristic may be performed before analog-digital conversion. However, since the same characteristic as the gamma characteristic cannot be reproduced in analog, non-linear correction is performed according to each gamma characteristic as shown in FIGS. 6 (a) and 6 (b).

As shown in FIG. 6 (c), if a point a at which the slope of the gamma characteristic is 1 for an arbitrary gamma characteristic is selected and the input level at that point a is x%, the input level is x%, The quantization error can be made uniform by selecting the point b at which the output level becomes 50% as the break point of the nonlinear characteristic.

As described above, one non-linear characteristic can be determined for an arbitrary gamma characteristic, and linear characteristic data and gamma characteristic data corresponding to the non-linear characteristic can be written in the ROM 43.

Therefore, by selecting an arbitrary gamma characteristic from the keyboard 41, the address is switched so that the MPU 42 reads the data of the gamma characteristic and the linear characteristic from the ROM 43, and the reference voltage applied to the linear correction terminal 55 of the analog-digital converter 40. Since VRM is determined, gamma correction with less quantization error can be performed.

The gamma-corrected digital signal 45 is converted into an analog signal by the digital-analog converter 10, and the analog signal 46 is converted into a predetermined video signal by the post process 12 and input to the monitor 13 as a CRT. Thus, the subject can be faithfully reproduced with high quantization accuracy.

According to the first embodiment, if the signal for selecting the desired gamma characteristic is simply output by the keyboard 41, the gradation conversion and the analog-digital conversion suitable for the gamma characteristic are performed, and the quantization accuracy is lowered. Color display can be performed on the CRT13 as a gamma characteristic video signal.

In FIG. 4, the reference voltage can be applied not only to the midpoint terminal 55 between the reference voltage terminals 51 and 52 but also to the midpoint between 51 and 52, the midpoint between 55 and 52, and the like. By doing so, analog conversion is possible with gradation conversion that is closer to the gamma characteristic.
It is also possible to perform digital conversion.

FIG. 7 shows a non-linear correction circuit diagram according to the second embodiment of the present invention.

The analog video signal is input to the DC amplifier 61 from the input terminal 60 and amplified. A plurality of parallel resistors 62a, 62b, ... 62m are connected to the output terminal of the DC amplifier 61, and are connected to an analog-digital converter 64 via a switch 63. (The resistance values of the resistors 62a, 62b are indicated by r1, r2, ..., Rm.) The input terminal of this analog-digital converter 64 is a diode 65, a resistor 6
6 (whose resistance is indicated by R2), and is grounded via a series circuit of a power supply 67.

The analog video signal input to the input terminal 60 is multiplied by a constant by the DC amplifier 61.

When the voltage output from the DC amplifier 61 is below the voltage of the power supply 67, the input / output characteristics are constant, and above the voltage of the power supply 67, the diode 65 conducts and is determined by the resistances ri and R2 (R2 / ri
+ R2) Compressed by the characteristic.

Therefore, by inputting this output signal to the analog-digital converter 64, a non-linearly corrected digital signal can be obtained. Furthermore, by switching the output voltage of the DC amplifier 61 and the switch 63, an arbitrary nonlinear characteristic can be obtained.

[Effects of the Invention] As described above, according to the present invention, not only can an external gamma correction be performed on an input video signal, but also gradation conversion can be performed according to the gamma correction. , An output signal with less quantization error can be obtained, and a faithful reproduced image can be obtained.

[Brief description of drawings]

FIG. 1 is a principle diagram showing a basic configuration of a signal processing system in the present invention, FIGS. 2 to 6 are related to a first embodiment of the present invention, and FIG. 2 is a configuration diagram of an endoscope apparatus, 3 is a block diagram of the image processing system, FIG. 4 is a block diagram of the analog-digital converter, FIG. 5 is a non-linear characteristic graph showing the input / output characteristics of the analog-digital converter, and FIG. 6 corresponds to the gamma characteristic. A non-linear characteristic graph which is analog-digital converted with the same gradation characteristic, FIG. 7 is a non-linear correction circuit diagram in the second embodiment of the present invention, FIG. 8 is a block diagram of a conventional signal processing system, and FIG. A graph showing the digital output with respect to the analog input when the gamma correction is performed after digitization and when the gamma correction is performed by analog and digitized. Figure 10 shows the gradation conversion before analog-digital conversion. −
6 is a graph showing a digital output with respect to an analog input when performing linear correction after digital conversion and performing gamma correction after linear correction. 1 ... CCD, 2 ... preprocess 10 ... digital-analog converter 12 ... postprocess, 13 ... CRT 16 ... gradation conversion and analog-digital converter 40 ... analog-digital converter 41 ... … Keyboard, 42 …… MPU 44 …… Voltage generator, 53 …… Comparator 54 …… Encoder

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masahide Sugano 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Akinobu Uchikubo 2-43-2 Hatagaya, Shibuya-ku, Tokyo No. Olympus Optical Co., Ltd. (72) Inventor Katsuyuki Saito 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Inventor Katsuyoshi Sasakawa 2-43-2 Hatagaya, Shibuya-ku, Tokyo No. Olympus Optical Industry Co., Ltd. (72) Inventor Shinji Yamashita 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Industry Co., Ltd. (56) Reference JP-A-59-69055 (JP, A) Kai 61-48333 (JP, A) JP 61-208990 (JP, A)

Claims (1)

(57) [Claims] 1. An image pickup means for picking up an image of a subject and outputting an analog image pickup signal, and a linear correction terminal, the gradation change characteristic corresponding to a gradation characteristic change signal inputted to the linear correction terminal, An analog-digital conversion circuit for digitally converting the analog image pickup signal, gamma characteristic data storage means for storing a plurality of different gamma characteristic data, and gamma characteristic input means capable of selectively inputting any gamma characteristic, Gradation characteristic changing means for inputting a gradation characteristic changing signal according to the gamma characteristic inputted from the gamma characteristic input means to the linear correction terminal; and the gamma characteristic according to the gamma characteristic inputted from the gamma characteristic input means. Based on the gamma characteristic data read from the data storage means and the digital image pickup signal output from the analog-digital conversion circuit, The endoscope apparatus characterized by equipped with a gamma correction unit, the outputs of the image pickup signal.