JPS63123282A - Image signal processor - Google Patents

Abstract

PURPOSE:To prevent a color jump, white collapse, etc., in case of high luminance by driving one usual field period into two long and short sections, and when the accumulated change is saturated at a long section, correcting this with the accumulated charge of a short section. CONSTITUTION:The charge accumulated in a first 0.8 F section 1' is transferred at a high speed pulse PHI 5 to a section 2' of 0.2 F, written to a memory 4 and read by a usual clock PHI 1 in a next field period. The charge accumulated in a succeeding 0.2 F section 2' is transferred by a usual 5/4-fold pulse PHI 5/4 in the field period succeeding to the section 2' and written into a memory 9. Usually, only the contents of the memory 4 are outputted through an adder 6, and when an object is of the high luminance and the accumulated charge of an image pick-up element 1 arrives at the saturated limit value, a switch 10 is closed. As the result, to the accumulated charge of the section 1' which is the output of the memory 4, the accumulated charge of the section 2' which is the output of the memory 9, is synthesized by a synthesizing device 6 and corrected.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an image signal processing device, more specifically, a CCD
The present invention relates to a device for processing image signals in an image recording device using a solid-state image sensor such as the above.

[Prior Art] In image recording devices such as video cameras and electronic still cameras that use conventional solid-state imaging devices such as COD, the charge accumulation time corresponding to one field of pixels of the solid-state imaging device is longer than the television signal. The scanning time of one field is 1/60 second, and this accumulated charge is divided into 1/60 seconds.
Reading is performed by a read pulse every 60 seconds. That is, as shown in FIG. 5(A), the pixel output of one field of the solid-state image sensor is sequentially transferred using transfer pulses for 1760 seconds, and the clock pulse is read every 1 field period F of 1/60 seconds. It is generated and read out.

[Problems to be Solved by the Invention] However, when a subject is photographed using such a conventional image recording device, if the subject is very bright, the image will disappear within 1/60 second, as shown in Figure 6 (A). The accumulated charge of the solid-state imaging probe may reach the saturation limit value V8AT, and in such a case, problems such as white collapse and color skipping occur in high-luminance portions that exceed the saturation limit.

On the other hand, the applicant first extracted one frame of analog image signal from the solid-state imaging probe and A/D converted it.
Provided is an image recording device that prevents deterioration in image quality during long exposure by accumulating digital signals of multiple frames and recording them as one frame of digital image.
(See Japanese Patent Application Laid-Open No. 59-34772). However, in this device, signal processing that increases the saturation limit itself is not particularly performed for a high-luminance subject that exceeds the saturation limit.

This invention was made in view of these points, and aims to increase the saturation limit of photoelectric conversion of the solid-state imaging element, expand the dynamic range, and prevent white collapse and color scattering in high-brightness areas. The object of the present invention is to provide an image signal processing device that achieves the following.

[Means for Solving the Problems] The image signal processing device of the present invention uses a solid-state imaging device, divides one field period in television signal mode into a long period and a short period, and performs solid-state imaging in each time period. A two-part charge storage means for accumulating charges for one screen in each cell, a means for reading out and transferring accumulated charges in a long time period during a short time period, and a means for storing the transferred charges as an image signal. means for reading out the stored image signal within the next one field period; means for detecting when the level of the image signal read from the storage means reaches a saturation limit; and means for adding the image signal of the short period to the image signal read out from the memory storage means when activated.

[Operation] Normally, charges accumulated in a long period of one field are read out as an image signal from a solid-state imaging probe. However, when the brightness of the subject is bright and the accumulated charge exceeds the saturation limit, the image signal of the short time period is added to the image signal of the long time period to correct and increase the saturation limit.

[Embodiment] FIG. 1 is a block diagram of an image signal processing device showing an embodiment of the present invention.

In the image signal processing device shown in FIG. 1, a solid-state imaging probe 1 made of a CCD or the like is supplied with a clock signal having a frequency 574 times the normal clock frequency from a clock pulse generator (not shown) via a charge transfer mode changeover switch 12. A clock pulse Φ5 with a frequency five times that of the pulse Φ5/4 is given, and as shown in FIG. 5(B),
1 field period F in television signal mode is 4:1
In the first long time interval 0.8F of the time division, charge is transferred by clock pulse Φ5/4, and in the subsequent short time interval 0.2F, charge is transferred by clock pulse Φ5. That is, in a normal television signal, if, for example, 250 transfer pulses are given in one field period F as shown in FIG. 5(A), in this embodiment, as shown in FIG. 5(B), As shown, 250 transfer pulses are applied within the first time interval of 0.8F, and charge transfer is performed slightly faster than the normal transfer rate, and the same 250 transfer pulses are applied within the subsequent time interval of 0.2F.
High-speed charge transfer is performed by applying 0 transfer pulses.

Then, the photoelectrically converted image signal of one field period F of this solid-state imaging element 1 is read out from this solid-state imaging device 1 by a sample-hold circuit 2, and similarly, for the first 0.8F time interval, Clock pulse Φ5/4
Therefore, the remaining 0.2F time period is sampled by the clock pulse Φ5, and the sampled image signal is distributed and guided to the long-time exposure path 13 and the short-time exposure path 14.

That is, as shown in Figure 2 (A), the initial 0.8F
The charge accumulated in the time interval ■ follows this < 0.
Within the time interval ■ of 2F, it is transferred by a clock pulse Φ5 of five times the normal frequency, converted into a digital value by the A/D converter 3 of the long-time exposure system path ui1, and written into the field memory 4. .

Then, the digital image signal of the time interval ■ written in this field memory 4 finishes the time interval ■ and returns to the normal frequency fC within the next one field period F.
It is read out by the clock pulse Φ1 of LK.

In addition, the charge accumulated in the remaining 0.2F time interval ■ is transferred to the next one field bright F following this time interval ■ by a clock pulse Φ5/4 with a frequency 5/4 times the normal frequency. , a short time exposure system 14 after being amplified by an amplifier 7.
The A/D converter 8 converts the data into a digital value and writes it into the field memory 9. The digital image signal of the time interval ■ written into the field memory 9 is written into the field memory 9 at the same time that writing is started.
Reading from is started. To read the digital image signal from the field memory 9, a clock pulse Φ1 of a normal frequency is used.

The image signal sent to the yarn path 14 corresponds to the exposure amount in the short time interval (2) of 0.2F, and since this signal level is low, the image signal sent to the yarn path 14 is transmitted to the long time interval (2) of 0.8F by the amplifier 7.
The image signal is amplified to a level comparable to that of the image signal corresponding to the exposure amount.

Here, the field memory 9 of the short-time exposure system path 14
A normally off switch IO is provided on the output side of , and normally the image signal passing through the short-time exposure path 14 is not led to the adder 6, but is read out from the field memory 4 of the long-time exposure path 13. Only the image signal of the long time interval (2) is converted into an analog signal by the D/A converter 11 via the adder 6 and output.

Normally, when the subject brightness is not so high and the level of the image signal does not reach the saturation limit value "SAT", as described above, the relatively long 0.
The accumulated charge in the time interval (3) of 8F is converted to the time axis and taken out in the next one field period.

When the subject is of high brightness, the accumulated charge of the solid-state imaging probe 1 is as shown in Fig. 6 (
As shown in B), when the saturation limit value vsAT is reached, the saturation detection circuit 5 detects the digital image output of the field memory 9. The detection principle is shown in Figure 2 (B).
The explanation will be based on.

The relationship between the amount of light and the image signal level (accumulated charge) changes as shown by the characteristic line a for the image signal in the long-time exposure system path 13, and as shown in the characteristic line 2 for the image signal in the short-time exposure system path 14. . Therefore, when the image signal level of the long-time exposure system 13 reaches the saturation limit value v8AT, the image signal level of the short-time exposure system 14 also exceeds a certain constant @Vref'. This property is used to detect the saturation limit. That is, if the image signal level in the short-time exposure system 14 is greater than the constant value Vre[', it can be seen that the image signal level in the long-time exposure system 13 has reached the saturation limit. and,
The switch 10 is turned on by the detection output of the saturation detection circuit 5. Then, in order to correct the part of the digital image signal accumulated in the 0.2F time interval ■ and passed through the short-time exposure system path 14 that exceeds the saturation limit, the adder 6 applies the digital image signal to the long-time exposure system path 13. The digital image signal is added to the digital image signal that has passed through the . The added image signal is D/A
The converter 11 converts it into an analog value.

In this way, when the subject has high brightness, the accumulated charge in the 0.2F time interval ■ after one field period F is used as a correction signal in the 0.8F time interval ■
It is added to the accumulated charge of , and is taken out after converting the time axis to the brightness of the next field.

FIG. 3 is a block diagram of an image signal processing device showing another embodiment of the present invention.

This image signal processing device is used, for example, when displaying the field of view of an endoscope on a video monitor. In such cases, the video monitor usually does not use all of its screen to form images; about 80% is used, and the remaining 20% is used for indexes such as the date of imaging, patient name, and other medical information. It is designed to be photographed. Therefore, even in the image signal processing apparatus shown in FIG. 3, the image signal processing device shown in FIG.
As shown in C), the charge accumulated in the solid-state imaging probe 21 during the first 0.8F time period of one field period (1/80 seconds) F in the television signal mode is taken as the normal image signal, and the rest is The accumulated charge in a time interval of 0.2 F is used as a correction image signal that is added to the image signal at high brightness, but since it is not necessary to use approximately 20% of the monitor screen for image formation, one field period F is normally used. If 250 transfer pulses are given to
It is possible to form a screen of 100%, and charge transfer can be performed at a normal speed during this 0.8F time interval. In the remaining 0.2F time period, 200 transfer pulses are applied to perform high-speed charge transfer.

In order to drive the solid-state imaging probe 21 such as a COD in such a charge transfer mode, a clock pulse Φl of a normal frequency and a clock pulse Φl of four times A clock pulse Φ4 with a frequency of 0.
In the time interval of 8F, charge transfer is performed by the clock pulse Φ■, and in the time interval of 0.2F, the clock pulse Φ
Charge transfer is performed by 4.

The photoelectric conversion output of the solid-state imaging probe 21 is sampled by the sample-and-hold circuit 22 using different clock pulses for each time interval, and then branched into a long-time exposure path 33 and a short-time exposure path 34.

To explain the following operation using the time chart shown in Fig. 4, the charge planted in the first 0.8F time interval ■ is changed to the normal charge by clock pulse Φ4 in the subsequent 0.2F time interval ■. The data is transferred at four times the speed, converted into a digital value by the A/D converter 23 in the long-time exposure path 33, and written into the field memory 24. The digital image signal of the written time interval (2) is read out by the clock pulse Φ1 of the normal frequency within the first 0.8F time interval (2) of the next one field period F after the time interval (2).

Furthermore, the charge accumulated in the remaining 0.2F time interval ■ is transferred by the same clock pulse Φ1 within the first 0.8F time interval ■ of the next one field period F following this time interval ■. The amplifier 2 of the short-time exposure system 34
9, and is amplified by the amplifier 29 to a level comparable to the level of the image signal read out from the field memory 24 according to the exposure amount in the time interval (3).

Also in this image signal processing device, normally the switch 30
is off, the image signals of the short-time exposure path 34 output from this amplifier 29 are not added by the adder 26, and the 0, Only the image signal of time interval ■ of 8F is D
/A converter 31 performs analog conversion and output from adder 26.

The subject brightness is high and the accumulated charge of the solid-state imaging probe 21 is
As shown in Figure (B), when the saturation limit value vSAT is reached, the saturation detection circuit 25 detects the output of the amplifier 29 and turns on the switch 30. The image signal of the time interval ■ of 0 and 2F that has passed through is added to the image signal of the time interval ■ of 0 and 8F that has passed through the long exposure system path 33 in the adder 26, and the high brightness portion that exceeds the saturation limit is added. Corrections are made for.

In this way, also in the embodiment shown in FIG. 3, when the subject is of high brightness, the following 0.
The image signal of time interval ■ of 2F is 0.8F as a correction signal.
This will be added to the image signal of the time interval ■, and this will be added to the image signal of the first 0.
The time axis is converted to the time interval ■ of 8F and extracted.

In the embodiment shown in FIG. 3, even the peripheral parts of the endoscope field of view that are difficult to see due to halation due to conventionally strong illumination light can be treated without color scattering or blurring.
Improves reproducibility.

[Effects of the Invention] As described above, according to the present invention, one normal field period is time-divided into a long time period and a short time period, and one screen (one field) is divided into a long time period and a short time period. If the accumulated charge in a long time period reaches the saturation limit when the solid-state imaging probe accumulates a charge of The saturation limit value of the accumulated charge of the element is increased, and the ditic range is expanded, so that even in the case of high brightness, images with excellent reproducibility can be obtained without color scattering or blurring.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an image signal processing device showing an embodiment of the present invention, and FIGS. 2(A) and (B) are for explaining the operation of the image signal processing device shown in FIG. 1 above. 3 is a block diagram of an image signal processing device showing another embodiment of the present invention. FIG. 4 explains the operation of the image signal processing device shown in FIG. 3 above. Figure 5 (A) to (C)
) is a time chart of driving pulses showing the conventional driving method of the solid-state image sensor and the driving method in each embodiment of the present invention, respectively. 3 is a time chart showing the accumulated charges according to the driving method and the accumulated charges according to the driving method according to the embodiment of the present invention. 1.21...Solid-state image sensor 4.24...
・・・・・・Field memory (storage means) 5.25
......Saturation detection circuit (detection means) 6.26
・・・・・・・・・Adder (addition means) Φ, Φ
Φ Φ 5145° 1" 4

Claims (1)

[Claims] One field period of the solid-state image sensor and television signal mode is divided into two, a relatively long time period and a short time period, and the charge for one screen is charged to the solid-state image sensor in each time period. a two-divided charge integrating means for accumulating the charge; a means for reading and transferring the accumulated charge in the long time interval from the solid-state image sensor during the short time interval; a storage means for storing the transferred charge as an image signal; reading means for reading out the stored image signal within one field period following the one field period; and detection means for detecting when the level of the image signal read from the storage means reaches a saturation limit. . An image signal processing device comprising: adding means for adding the image signal of the short time interval to the image signal read from the storage means when the detection means is activated.