JPH0191591A - Gamma correction method for solid-state image pickup device - Google Patents

Abstract

PURPOSE:To obtain a reproduced video image with excellent gradation by correcting the reduction in the output signal level of a solid-state image pickup element as shutter speed goes to a high speed so as to apply gamma correction for each hue. CONSTITUTION:Optical systems 1-3 controlling and aperture 2 and a speed of a shutter 3 and a solid-state image pickup element 4 applying photoelectric conversion for each hue of an optical image from an object made incident via the systems 1-3 are provided. The gamma change of the solid-state image pickup element 4 is adjusted for each hue depending on the change in the speed of the shutter 3 under the condition of constant exposure. Thus, the level change is compensated for each hue to attain the high picture quality of the video image and the deterioration in the picture quality caused as the faster shutter speed is prevented.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is applicable to electronic cameras, video cameras, etc. that take pictures by controlling the aperture and shutter speed and controlling the amount of exposure to a solid-state image sensor at a constant level. The present invention relates to a gamma correction method for a solid-state AM device, which compensates for the decrease in sensitivity of a solid-state image sensor as the shutter speed increases even if the exposure amount is kept constant in a solid-state image pickup device.

(Prior Art) An electronic still camera as a conventional solid-state imaging device shown in FIG. 6 will be described. In the figure, 1 is a photographing lens provided in the optical system, 2 is an aperture, 3 is a shutter, and 4 is a COD.
It is a MOS-type solid-state image sensor, and a solid-state silver image element 4 photoelectrically converts an optical image from a subject incident through a photographing lens 1, an aperture 2, and a shutter 3 to generate video signals for each hue.

5 is a synchronization signal generation circuit for generating various control signals for controlling the entire operation of the electronic still camera at a predetermined timing; 6 is a synchronization signal generation circuit for outputting a signal generated in each pixel of the solid-state image sensor 4 according to a predetermined scanning timing; This is a drive circuit that generates drive signals.

7 is a signal processing circuit which outputs signals of various hues, namely R (blue) from the solid-state f1 image element 4;

The primary color signals of G (green) and B (red) or their complementary color signals are subjected to rTi processing, and a luminance signal and a color difference signal are formed by a matrix circuit provided inside.

Reference numeral 8 denotes a recording section, which performs so-called FM modulation on these luminance signals, color difference signals, etc., and records them on a magnetic recording medium such as a magnetic tape and a magnetic disk.

Reference numeral 9 denotes a photometric circuit, which detects the exposure interval before a shadow and transmits the detected data to the exposure amount control circuit 10.

11 is a shutter/aperture drive circuit that drives the aperture 2 and the shutter 3; when the exposure amount control circuit 10 instructs to keep the exposure M constant based on the detection data, the aperture ratio of the aperture 2 is changed according to the instruction; and adjust the shutter speed of shutter-3.

Reference numeral 12 denotes a storage circuit composed of a semiconductor memory or the like, which stores data to enable optimum photographing by keeping the exposure table constant at all times, that is, optimum data corresponding to the detection data value from the photometry circuit 9. Adjustment data specifying the aperture and/or shutter speed of the image is stored.

That is, when a shooting instruction is given using the f1 shadow release, etc.,
First, the exposure amount control circuit 10 senses the amount of exposure from the subject based on the detection data from the photometry circuit 9, and adjusts the aperture corresponding to this exposure amount and/or reads adjustment data regarding the shutter speed from the storage circuit 12 and shutters the shutter. /Supplied to the aperture drive circuit 11 and set so that photography can be performed with optimum exposure.

This type of configuration of electronic still cameras is common in those that affect performance such as aperture priority or shutter priority, and especially in solid-state imaging devices that use solid-state imaging elements with narrow latitude, such exposure Amount control has become extremely important.

(Problem to be solved by the invention) However, even if constant exposure is obtained by controlling the aperture distance and shutter speed in this way, it may not be possible to obtain optimal photographing conditions due to the characteristics of the solid-state image sensor. The inventor of the present application has studied this and as a result of this research has developed a new method that can obtain extremely superior images that have never existed before.

Even if a constant exposure is obtained by controlling the latitude and the shutter speed, it is not possible to obtain the optimum i-shadow condition due to the characteristics of the solid-state image sensor. It was assumed that optimal shooting could be achieved by setting the exposure to a certain value, but in reality, even if the exposure was constant, as the shutter speed became faster, the deterioration of the reproduced image became more noticeable. Occur.

To explain this phenomenon in detail based on Figure 7, which shows the characteristics of a solid-state image sensor at a certain hue, if the exposure amount is constant, the output will be output for each pixel of the solid-state image sensor regardless of whether the shutter speed is fast or slow. However, as shown in the figure, if the ratio of the amount of incident light to the output signal level is 100% when the shutter speed is 1760 seconds, the faster the shutter speed is, the more the signal level will be constant. The output level decreases. As a result V
In the reproduced video using the video signal that has been input, the brightness gradation will be lowered and the contrast will be deteriorated, resulting in the so-called "
This results in a "sleepy" image.

Further, since the signal level decreasing characteristic depending on the shutter speed as shown in FIG. 7 changes differently depending on the hue, a problem arises in that the color balance of the reproduced image is disrupted. In particular, according to the results of an experiment conducted by the present inventor, as shown in the figure, when the shutter speed becomes 1/1000 seconds or less, the output signal level from the solid-state*a element decreases significantly, and With regard to image pickup devices, it is not possible to achieve high image quality of images using conventional techniques that only control the exposure amount.

(Means for solving the problems) The present invention has been made in view of the above problems.
An object of the present invention is to provide a compensation method that prevents deterioration in image quality that occurs as the shutter speed increases even when the exposure amount is constant.

In order to achieve this object, the present invention includes an optical system that controls the aperture and shutter speed, and a solid-state image sensor that photoelectrically converts an optical image from a subject incident through the optical system for each hue. By adjusting the amount of change in gamma of the solid-state image sensor for each hue as the shutter speed changes under certain conditions, level changes are compensated for each hue and the image quality is improved. The technical point is to be able to achieve the following.

The signals output from the solid-state image sensor for each hue are primary color signals of red, blue, and green or color signals of their complementary colors,
To achieve this method, it is preferable to provide a gamma compensation circuit that performs gamma compensation for each signal according to the shutter speed.

(Example) Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a block diagram showing the configuration, and the same or corresponding parts as in FIG. 6 are given the same reference numerals.

First, to explain the configuration, there is J3 in the same figure, 1 is a dance lens, 2 is an aperture, 3 is a shutter, 4 is a solid-state image sensor, 5
6 is a sync signal generating circuit that generates a sync signal for controlling the operation of the camera system and a signal necessary for forming a video signal, and 6 is a drive circuit that controls signal readout of the solid-state image sensor 4.

Reference numeral 21 denotes a signal separation/sample hold circuit which separates the signal output from the solid-state image sensor 4 into signals corresponding to each pixel, and samples and bolds the signals.

22 is an automatic gain control circuit; 23 is a color separation circuit; the signal sampled by the signal separation/sample hold circuit 21 is amplified to a predetermined amplitude by the automatic gain control circuit 22; 〉.

It is divided into B (blue) color signals. In this example,
The case where primary color signals of R, G, and [3 are processed will be described, and the method of the present invention can be similarly applied when processing their complementary color signals, so the description will be omitted.

24.25 goes to Why 1・Balance adjustment circuit, 26.2
7.28 is a clamp circuit, 29, 30.degree. 31 is a blanking mixing circuit for increasing the blanking pulse by 111 during the blanking period, and 32.33.degree. 34 is a gamma correction circuit.

35 is a matrix circuit, and each gamma correction circuit 32
, 33. A luminance signal Y and a color difference signal RY based on the R, G, and B color signals corrected in 34.

Form B-Y.

36 is a luminance signal compensation circuit, which automatically changes the amplification factor of the luminance signal Y according to the shutter speed, which will be described later.

37 is an encoder circuit, and r4pox signal compensation circuit 36
Based on the luminance signal @Y and the color difference signals R-Y and B-Y from the matrix circuit 35, a standardized video signal of, for example, the NTSC system is generated.

38 is a recording section, which performs FM modulation or the like on the video signal from the encoder circuit 38 and records it on a magnetic recording medium.

The circuit within the dotted line indicated by the reference numeral 39 in the figure is an exposure amount control section, which includes a central processing circuit 40 using a microcomputer or the like, input/output interface circuits 41 and 42, an A/D converter 43, and a memory circuit 44. It is equipped with

The A/D converter 43 converts the G (green) color signal from the signal separation/sample hold circuit 21 into a digital signal and transfers it to the central processing circuit 40 .

The central processing circuit 40 measures (photometers) the light incident on the solid-state image sensor 4 based on the signal from the A/D converter 43. That is, this camera system constitutes an internal photometry system, and this photometry is performed before actual image transfer.

The storage circuit 44 stores adjustment data for adjusting the aperture 2 and shutter 3 based on the detection results obtained by photometry, and the medium heat processing circuit 40 stores A/D conversion 2.
Read the adjustment data corresponding to the signal from S43,
This is supplied via the input/output interface circuit 41 to a drive circuit (not shown) that drives the diaphragm 2 and shutter 3, and settings are made to perform photography under preset optimal exposure conditions.

In addition to the adjustment data for controlling the aperture and shutter speed described above, the storage circuit 44 also contains gamma correction data for controlling the correction values of the gamma correction circuits 32, 33, and 34 according to the shutter speed. Similarly, brightness compensation data for controlling the compensation value of the brightness signal compensation circuit 36 according to the shutter speed is stored.

That is, as shown in FIG. 2, its configuration includes an adjustment data storage area 44a that stores aperture adjustment data in an address area corresponding to the above-mentioned photometric value detected by photometry, and an adjustment data storage area 44a that stores aperture adjustment data in an address area corresponding to the above-mentioned photometric value detected by photometry. an adjustment data storage area 44b that stores shutter speed adjustment data in an address area;
Further, a storage area 44c stores brightness compensation data in an address area corresponding to the shutter speed read from the adjustment data storage area 44b, and gamma correction data is stored in an address area corresponding to the shutter speed. It is equipped with a memory area 1!44d.

An address signal A corresponding to the amount of photometry is sent from the central processing circuit 44.
D11BDi is each storage area 44a.

44b, the adjustment data Δci.

BCi is read out, and these data are transferred to the aperture 2 and shutter 3 via the input/output interface circuit 41. Further, data ACi for setting the shutter speed is stored in the storage areas 44c and 44r as an address signal.
j, the brightness compensation data YCi and gamma correction data γC1 (
R), γC1 (G), and γC1 (B) are output. still,
The subscripts R, G, and B of the gamma correction data indicate that each hue is supplied to a predetermined gamma correction circuit 32, 33, and 34. Therefore, gamma correction is performed independently for each hue.

The gamma correction circuits 32, 33, and 34 are configured to change the gain by fold line approximation, and for example, as shown in FIG. 3, they are semiconductor switches that turn on and off the current from the current source circuit according to the gamma correction data. r1. r2.・・・
, rn to change the gain adjustment current of the gamma correction circuit to obtain a gain change based on the folded line approximation.

The change in gain based on this approximation has a characteristic that it increases as the shutter speed increases in order to correct the decrease in level for each hue shown in FIG.

FIG. 4 shows a specific example of the luminance signal compensation circuit 36.

That is, an amplifier AMP is connected to a signal line for transmitting a luminance signal connecting between the matrix circuit 35 and the encoder circuit 37, and a plurality of feedback resistive elements R1, R1, and R1 having mutually different resistance values are connected to the amplifier AMP.
R2,..., Rn are provided in parallel, and the central processing unit 4
Semiconductor switches SW1 . SW2. ..., SWn are provided. That is, as shown in FIG. 5, as the shutter speed increases, the amplification factor increases to compensate for the level drop in the luminance signal.

As explained above, according to this embodiment, the gamma correction circuit corrects the decrease in the signal level output from the solid-state image sensor as the shutter speed increases even if the exposure amount is constant. It is possible to prevent deterioration of the gradation of the reproduced image, and since the same compensation is performed in the luminance signal compensation circuit, accurate correction can be performed. Note that, practically, the compensation by this luminance signal compensation circuit can be omitted.

Although internal photometry has been described in this embodiment, the present invention can also be applied to external photometry.

Furthermore, there is a place to control the photometry amount and shutter speed.ff
The present invention may be applied to a JE El structure camera, or to an aperture-priority or shutter speed-priority camera.

(Effects of the Invention) As explained above, according to the present invention, the decrease in the output signal level of the solid-state image sensor as the shutter speed increases is corrected by performing gamma correction for at least each hue. It is possible to provide reproduced video with extremely excellent gradation. Further, by performing compensation according to the shutter speed on the luminance signal synthesized from the color signal corrected in this manner, more accurate compensation can be performed.

Therefore, it is possible to provide a solid-state image carrier that can obtain excellent images that are not affected by shutter speed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of an electronic still camera configured based on the solid-state imaging Q-position gamma correction method according to the present invention, and FIG. 2 is a block diagram showing the configuration of the storage circuit shown in FIG. 1. , Fig. 3 is a circuit diagram showing the configuration of each gamma correction circuit shown in Fig. 1, Fig. 4 is a circuit diagram showing a specific example of the luminance signal compensation circuit shown in Fig. 1, and Fig. 5 is a circuit diagram showing a specific example of the luminance signal compensation circuit shown in Fig. 1. A characteristic curve diagram showing the gain characteristics of the circuit, Figure 6 is a block diagram showing the configuration of a conventional electronic still camera, and Figure 7 is a schematic diagram of changes for each hue in response to changes in shutter speed for one of the hues. FIG. 2: Aperture 3: Shutter 4: Solid-state image sensor 32.33.34: Gamma correction circuit 36:! Ei degree signal compensation circuit 40: Central processing circuit 41.42: Input/output interface circuit 43: A/D
Converter 44: Storage circuits 44a, 44b, 44c, 44d: Storage area 2nd
Figure 3 Figure 4 Figure 5 CIFf) Figure 6

Claims (3)

[Claims] (1) Equipped with an optical system that controls the aperture and shutter speed, and a solid-state image sensor that photoelectrically converts the optical image from the subject incident through the optical system for each hue, and the shutter speed is set under the condition that the exposure amount is constant. 1. A gamma correction method for a solid-state imaging device, characterized in that the amount of change in gamma of the solid-state imaging device is adjusted for each hue in response to changes in the gamma of the solid-state imaging device. (2) The signals output for each hue from the solid-state image sensor are primary color signals of red, blue, and green, or color signals of their complementary colors, and gamma correction is performed for each signal according to the shutter speed. A gamma correction method for a solid-state imaging device according to claim 1, further comprising a correction circuit. (3) Compensating means for forming a luminance signal based on the signal outputted from the gamma correction circuit for each hue, and compensating the luminance signal with a change in amplification factor corresponding to the shutter speed. A gamma correction method for a solid-state imaging device according to claims 1 and 2.