JP3306216B2 - Electronic endoscope device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device in which a solid-state imaging device is provided at the end of an endoscope insertion portion, and an observed image is converted into an electric signal, transmitted to the outside, and reproduced on a monitor or the like. The present invention relates to an endoscope device.

[0002]

2. Description of the Related Art In order to reproduce a video signal transmitted from a solid-state imaging device provided at the distal end of an insertion portion of an endoscope as an image that does not give a sense of strangeness, it is necessary to perform gamma correction.

Therefore, conventionally, an output value after gamma correction corresponding to a video signal (original signal) value input to a gamma correction unit is written in a lookup table constituted by a memory, and the video signal is looked up. It is applied as an address signal of a table memory to output a corresponding gamma correction value. The signal after the correction is converted into an analog signal again, then subjected to video signal processing, and displayed on a monitor as an image (JP-A-1-178235).

[0004]

However, since the gamma correction unit not only amplifies the original signal up to the correction value, but also amplifies the noise component superimposed on the original signal, the input original signal shown in FIG. For the signal, as shown in FIG. 18, especially in the low-brightness (dark) range where the gain is high, S
There is a disadvantage that the / N ratio deteriorates.

When the non-linear processing is performed using a look-up table, for example, in FIG. 19, a lookup table is used so that data 1 to 4 whose addresses are between 0 and 1 are not written in the look-up table. Some data is not written to the table.

Therefore, in a low-brightness (dark) range where data changes greatly with respect to an address, much data is not written in the look-up table, and a quantization error peculiar to digital processing occurs at the time of gamma correction. Resulting in.

Accordingly, an object of the present invention is to provide an electronic endoscope apparatus capable of performing gamma correction of a digital video signal without deteriorating the S / N ratio and with a small quantization error.

[0008]

In order to achieve the above object, an electronic endoscope apparatus according to the present invention converts a video signal sent from a solid-state imaging device provided at the end of an endoscope insertion section into a digital signal. After the conversion into a signal, the gamma correction data written in the look-up table is read out, and the gamma correction of the video signal is performed in the electronic endoscope apparatus. A first low-pass filter for writing only data corresponding to the gamma correction and reducing a noise component from the original signal input to the look-up table, and a noise filter for the signal output from the look-up table. A second low-pass filter for reducing a component, wherein the second low-pass filter is read from the look-up table, and Gamma correction of data which has passed through the filter is added to the original signal and outputs a correction signal.

The original signal to be added to the data for only the gamma correction read from the look-up table preferably does not pass through the first and second low-pass filters.

[0010]

An embodiment will be described with reference to the drawings. FIG. 2 shows an overall configuration of an electronic endoscope apparatus according to an embodiment of the present invention. For example, the electronic endoscope apparatus is provided at an image forming position of a subject by an objective optical system 3 provided at a distal end of an insertion section 2 of the endoscope 1. Charge coupled device (C
A solid-state imaging device 4 made of CD) is arranged. 5
Is a light guide fiber bundle for transmitting illumination light for illuminating the observation range.

A connector section 6 of the endoscope 1 connected to the video processor 10 includes a drive circuit 7 for amplifying signals input to and output from the solid-state imaging device 4 and data specific to the endoscope 1. And a rewritable read-only memory (EEPROM) 8 in which information such as data is stored.

The video processor 10 also serves as an illumination light source device, and illumination light is incident on the light guide fiber bundle 5 of the endoscope 1 from a light source lamp 11.
A three-color rotating filter 12 having three color filters of red (R), green (G), and blue (B) is disposed in the middle of the incident optical path so as to rotate at a constant speed.
Illumination light of each color of red, green, and blue is sequentially incident on the light guide fiber bundle 5 with a time lag.

An output terminal of the CCD processing unit 14 connected to the driving circuit 7 of the solid-state image pickup device 4 is connected to a timing circuit 15.
Is connected to the input terminal of the video processing unit 16 via the
Sent to

The operations of the CCD processing unit 14, the timing circuit 15, and the video processing unit 16 are performed by a system control unit 17 having a central processing unit (CPU).
Are controlled in conjunction with each other. Further, the endoscope-side data is read from the EEPROM 8 connected thereto via the peripheral driver 19 connected to the system control unit 17.

FIG. 3 specifically shows the structure of the above-described CCD processing section 14 and video processing section 16. In the CCD processing unit 14, the solid-state imaging device 4
Is amplified by an amplifier 23, a video signal is extracted by a sample and hold circuit 24, converted into a digital signal by an analog / digital conversion circuit 25, and then subjected to gamma correction by a gamma correction circuit 26.

The gamma-corrected video signal is switched by the timing circuit 15 in synchronization with the driving of the solid-state imaging device 4, and sequentially corresponds to each color of red (R), green (G), and blue (B). It is stored in the frame memories 28R, 28G, 28B.

The signals stored in the frame memories 28R, 28G, 28B are simultaneously read out and converted into analog color signals by digital-to-analog conversion circuits 29R, 29G, 29B, respectively.

The three color signals are output as three primary color signals, respectively, and are also input to the NTSC encoder 30 in parallel with the three primary color signals, converted into an NTSC composite video signal and output to the monitor 18.

FIG. 1 shows the contents of the gamma correction circuit 26. The gamma correction circuit 26 includes a read-only memory 32 for a look-up table and a noise component from an original signal input to the look-up table memory 32. A first low-pass filter 34 for reducing noise, a second low-pass filter 35 for reducing noise components from a signal output from the look-up table memory 32,
The output signal from the second low-pass filter 35 is formed by an addition circuit 33 for adding the original signal.

FIGS. 4 and 5 are graphs showing an example of data written in the look-up table memory 32. FIG. As shown in FIG. 4, the gamma correction value to be output from the gamma correction circuit 26 takes a large value with respect to the input original signal. However, the sum of the corrected data indicated by the oblique lines is much smaller than the sum of the gamma correction values.

Therefore, in this embodiment, only the gamma correction data shown in FIG. 5 is written in the look-up table memory 32. Then, the original signal is applied as an address signal of the look-up table memory 32, and the correction data corresponding to the address is read out of the look-up table memory 32,
, The data for the correction is added to the original signal and output as a gamma correction value.

The look-up table memory 32
May be written in advance, and gamma correction data suitable for the characteristics of the endoscope 1 and the characteristics of the subject may be selected and used.

The first low-pass filter 34 is connected to the video signal input line immediately before the look-up table memory 32, and the second low-pass filter 35 is connected to the video signal output line immediately after the look-up table memory 32. The original signal that is connected to the line and sent to the adding circuit 33 does not pass through the first low-pass filter 34 and the second low-pass filter 35.

Therefore, a video signal from which noise components have been reduced is input to the look-up table memory 32 as an original signal, but the original video signal is input to the adder circuit 33.

FIGS. 6 to 8 show examples of a low-pass filter circuit for reducing noise of a digital signal. FIG. 6 shows a horizontal filter, FIG. 7 shows a vertical filter, and FIG. 8 shows a time filter.

Each of these receives a video signal input as a digital signal in a latch 341, multiplies it by a plurality of predetermined constants k _{0 to} k ₄ in parallel, and outputs each output to a latch 342 in a horizontal filter. The vertical filter receives and adds and outputs each in the line memory 343, and the time filter receives and adds and outputs each in the frame memory 344 in the vertical filter.

When the low-pass filter processing is performed using an analog signal, the signal from the look-up table memory 32 is once converted into an analog signal by a D / A conversion circuit, and the output from the second low-pass filter 35 is output. Is converted into a digital signal by the A / D conversion circuit and then sent to the addition circuit 33.

Next, the operation of the above embodiment will be described. It should be noted that the original signal before being input to the first low-pass filter 34 is a signal transmitted to the look-up table memory 32 after passing through the first low-pass filter 34, The signal only for the gamma correction sent to the second low-pass filter 35 through the filter is the signal sent to the addition circuit 33 after passing through the second low-pass filter 35,
5 shows a gamma correction signal output from the.

FIGS. 9 and 10 show the low-luminance areas (FIG. 5).
(Between O and H) of FIG. 9 shows a change in signal level (FIG. 9) and a change in waveform (FIG. 10). Is input, the signal passes through the first low-pass filter 34, thereby becoming a signal with reduced noise components.

Between O and H where the luminance is low, the gamma correction data also increases as the original signal level increases. Therefore, when a waveform such as the signal is input to the look-up table memory 32, the data for the gamma correction is amplified and becomes a waveform as shown in FIG.

When the signal for the gamma correction output from the look-up table memory 32 is passed through the second low-pass filter 35, low-pass processing is further performed to reduce noise, and a state as shown in FIG.

As described above, by passing the output signal from the look-up table memory 32 through the second low-pass filter 35, data not written in the memory 32, such as "3" shown in FIG. Are processed as if they were output from the memory 32.

Then, the second low-pass filter 35
When the adder 33 adds the gamma-corrected signal output from and the original signal by the adder circuit 33, a gamma-corrected output as shown below is obtained, and the noise component is reduced by the low-pass effect.

FIG. 14 shows an experimental result in which random noise is input by providing a low-pass filter before and after the look-up table memory 32 as described above.
As shown in FIG.
The noise can be further smoothed as compared to the case where only the input side is provided or the case where only the output side is provided.

When the original signal is added by the adding circuit 33, the lookup table memory 32 and the first and second memories are used.
In order to adjust the delay time by the low-pass filters 34 and 35, a delay element may be inserted in the original signal transmission path sent to the addition circuit 33.

FIGS. 11 and 12 show a change in signal level in a high luminance area (between H and L in FIG. 5) (FIG. 11).
And changes in the waveform (FIG. 12). Again, in this case,
Is input, the signal passes through the first low-pass filter 34, thereby becoming a signal with reduced noise components.

Between H and L with high luminance, the gamma correction data decreases as the original signal level increases. for that reason,
Is input to the look-up table memory 32, the gamma correction data output from the look-up table memory 32 decreases as shown in FIG. Then, when the signal is passed through the second low-pass filter 35, low-pass processing is further performed to reduce noise, and a state as shown in FIG.

When the gamma correction component signal that has passed through the second low-pass filter 35 and the original signal are added by the adder circuit 33, a gamma correction output as shown below is obtained, and an enhancement effect in which the outline is emphasized appears.

By providing the low-pass filters 34 and 35 before and after the look-up table memory 32, as shown in FIG. 15, it is provided only on the input side or only on the output side of the look-up table memory 32. The outline is more emphasized than in the case.

In this case as well, a delay element is inserted in the original signal transmission path sent to the adder circuit 33, so that the delay time by the look-up table memory 32 and the first and second low-pass filters 34 and 35 is reduced. Adjustments may be made.

As described above, noise is reduced in a low luminance area, and contour enhancement is performed in a high luminance area. If one of a plurality of types of gamma correction data can be selected, the noise removal area and the enhancement area can be used as needed.

The present invention is not limited to the above embodiment. For example, as shown in FIG. 16, the gamma correction circuits 26R, 26G and 26B are
May be connected to the output terminals of the respective color frame memories 28R, 28G, and 28B to independently perform gamma correction on each of the red, green, and blue color signals. The configuration and operation of each of the gamma correction circuits 26R, 26G, and 26B in this case are the same as those in the first embodiment.

[0043]

According to the present invention, the noise component is reduced by the low-pass filter when the video signal is input / output to / from the look-up table for reading out only the data corresponding to the gamma correction. Amplification of a noise component when gamma correction is performed is suppressed, and a good S / N ratio can be obtained.

Furthermore, values not written in the look-up table can be output as gamma correction data, and quantization errors in digital gamma correction at a low signal level can be greatly suppressed.

By adding the original signal that does not pass through the low-pass filter to the data for the gamma correction, it is possible to prevent the original signal waveform from being smoothed by the low-pass filter, and to output a signal with higher precision. it can.

Further, the outline is emphasized in a bright video portion, and each effect of gamma correction, noise reduction and enhancement can be realized by one circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a gamma correction circuit according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of an electronic endoscope apparatus according to an embodiment of the present invention.

FIG. 3 is a circuit block diagram of an embodiment of the present invention.

FIG. 4 is an explanatory diagram of gamma correction data according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram of gamma correction data according to the embodiment of the present invention.

FIG. 6 is a circuit diagram of a low-pass filter according to an embodiment of the present invention.

FIG. 7 is a circuit diagram of a low-pass filter according to an embodiment of the present invention.

FIG. 8 is a circuit diagram of a low-pass filter according to an embodiment of the present invention.

FIG. 9 is a diagram showing a change in signal level in a low luminance region according to the embodiment of the present invention.

FIG. 10 is a diagram illustrating a change in a signal waveform in a low luminance region according to the embodiment of the present invention.

FIG. 11 is a diagram illustrating a change in signal level in a high-luminance region according to the example of the present invention.

FIG. 12 is a diagram showing a change in a signal waveform in a high luminance region according to the embodiment of the present invention.

FIG. 13 is an explanatory diagram of output characteristics of the embodiment of the present invention.

FIG. 14 is an explanatory diagram of output characteristics of the embodiment of the present invention.

FIG. 15 is an explanatory diagram of output characteristics of the embodiment of the present invention.

FIG. 16 is a circuit block diagram of a second embodiment of the present invention.

FIG. 17 is a diagram illustrating characteristics of digital gamma correction.

FIG. 18 is a diagram illustrating characteristics of digital gamma correction.

FIG. 19 is a diagram illustrating characteristics of digital gamma correction.

[Explanation of symbols]

 26 gamma correction circuit 32 look-up table memory 33 adder circuit 34 first low-pass filter 35 second low-pass filter

Continuation of the front page (56) References JP-A-6-30301 (JP, A) JP-A-4-373361 (JP, A) JP-A-5-14905 (JP, A) JP-A-1-206775 (JP) , A) JP-A-4-46485 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 1/00-1/32 H04N 5/202

Claims (1)

(57) [Claims] 1. A video signal sent from a solid-state imaging device provided at the end of an endoscope insertion section is converted into a digital signal, and then gamma correction data written in a look-up table is read out to convert the video signal into a digital signal. In an electronic endoscope apparatus configured to perform gamma correction of a signal, data of only a gamma correction corresponding to an input original signal is written in the look-up table and input to the look-up table. A first low-pass filter for reducing a noise component from an original signal and a second low-pass filter for reducing a noise component from a signal output from the look-up table are provided and read from the look-up table. The data for the gamma correction that has been passed through the second low-pass filter is then combined with the first and second low-pass filters. Both of Ruta
An electronic endoscope apparatus, which adds an original signal that has not passed through and outputs it as a correction signal.