JPH0530350A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To simply correct ununiformity of sensitivity between picture elements in the solid-state image pickup device provided with a solid-state image pickup element having a characteristic in which an output voltage with respect to a light received quantity is changed in natural logarithm. CONSTITUTION:An image pickup data for each picture element at uniform light exposure is stored in a memory MEM. A correction arithmetic operation circuit COR subtracts an image pickup data at uniform exposure stored in the memory MEM from the image pickup data for each picture element at an actual image pickup to correct the ununiformity of the sensitivity among picture elements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device,
In particular, the present invention relates to a solid-state imaging device including a solid-state imaging device having a characteristic that its output voltage changes logarithmically with respect to the amount of received light.

[0002]

2. Description of the Related Art Conventionally used solid-state image pickup devices have a characteristic that the output voltage thereof changes linearly with the amount of received light. The solid-state image sensor having this linear characteristic has different sensitivities for each pixel, and even if uniform light is irradiated, a difference occurs in the output between each pixel due to the difference in sensitivity.

FIG. 1 is a diagram showing the relationship between the received light amount L and the output voltage V0 of the conventional solid-state image pickup device, which can be expressed by the following equation. ⋅ V0 ∝ L ◇ If there is a difference in the sensitivity ai of each pixel, and the light receiving amount of each pixel is Li, the output voltage Vi is as follows. However, i = 1,2,3, ... ◇ Vi ∝ ai ・ Li ◇ Here, even when the solid-state imaging device is irradiated with the uniform light L, that is, when L = L1 = L2 = L3 = ..., the output voltage Vi of each pixel is as follows. Therefore, it can be seen that there is a difference between the output voltages of the pixels. ◇ Vi ∝ ai ・ L ◇ In order for the output voltage difference between each pixel to be zero, a uniform light L
The output voltage Vi of each pixel when all the values are given must be equal. If all pixels have the same sensitivity ai,
The output voltages Vi of the pixels are all equal, but it is virtually impossible to make the sensitivities ai equal.

Therefore, in the conventional solid-state image pickup device, the output difference between each pixel is corrected by the following calculation. That is,
The correction is performed by multiplying the output voltage Vi of the corresponding pixel by the reciprocal of the sensitivity ai of each pixel. The corrected output voltage Vi 'is expressed by the following equation. ◇ Vi '∝ (1 / ai) Vi ◇ ∝ (1 / ai) ・ (ai ・ Li) ◇ ∝ Li ◇ As a result of the above correction calculation, as shown in FIG. The relationship of can be matched with the reference straight line. Therefore, it can be considered that all pixels have the same amount of received light and output voltage characteristics.

[0005]

However, in a solid-state image pickup device provided with a solid-state image pickup device having a characteristic that its output voltage changes logarithmically with respect to the amount of received light, the conventional solid-state image pickup device and the photoelectric conversion device described above are used. Since the characteristics are different, the above method cannot correct the nonuniformity of the sensitivity of each pixel.

The present invention has been made in view of the above problems, and in a solid-state image pickup device having a solid-state image pickup device having a characteristic that its output voltage changes logarithmically with respect to the amount of received light, each pixel is An object of the present invention is to provide a solid-state imaging device capable of correcting nonuniformity in sensitivity between the solid-state imaging devices.

[0007]

In order to achieve the above object, the solid-state image pickup device of the present invention includes a "storage means for storing image pickup data for each pixel at the time of uniform light irradiation" and an "actual image pickup time. Correction means for correcting the non-uniformity of sensitivity between pixels of the solid-state image pickup device by subtracting the image pickup data of the corresponding pixel stored in the storage means from the image pickup data of each pixel.

[0008]

FIG. 3 is a diagram showing the relationship between the received light amount L and the output voltage V0 of a solid-state image pickup device having a characteristic that its output voltage changes naturally logarithmically with respect to the received light amount. It is as follows when expressed by. ⋅ V0 ∝ lnL ◇ Here, when the sensitivity ai of each pixel is non-uniform, the light receiving amount of each pixel is Li, and its output voltage Vi is as follows. ◇ Vi ∝ ln (ai ・ Li) ◇ ∝ lnai + lnLi ◇ Here, since the sensitivity ai is different for each pixel, when the uniform light L is irradiated, that is, when L = L1 = L2 = L3 = ... However, a difference occurs in the output voltage of each pixel. In order to correct this output voltage difference, it is sufficient to remove the term including the sensitivity ai, and the calculation can be performed by subtracting lnai from Vi. The corrected output voltage Vi 'is expressed by the following equation. ◇ Vi '∝Vi − lnai ◇ ∝ (lnai + lnLi) − lnai ◇ ∝ lnLi ◇ By the above correction calculation, as shown in FIG. 4, the relationship between the received light amount and the output voltage, which is different for each pixel, matches the reference straight line. Can be made Therefore, it can be considered that all pixels have the same amount of received light and output voltage characteristics.

[0009]

FIG. 5 is a block diagram of a solid-state image pickup device to which the present invention is applied. The CCD is a solid-state image sensor having a characteristic that its output voltage changes logarithmically with respect to the amount of received light. The A / D is an A / D converter for digitally converting the voltage output from the solid-state image sensor CCD.
The MEM is a memory for storing the digital value converted by the A / D converter, and includes a RAM or a PROM. The memory MEM stores the output voltage of each element when the solid-state image sensor CCD is irradiated with predetermined uniform light. COR is a digital correction arithmetic circuit, which outputs the output voltage of the solid-state imaging device CCD converted by the A / D converter at the time of image capturing, to the output voltage of the solid-state imaging device CCD stored in the memory MEM during uniform light irradiation. The corrected image data is output to the device DEV (storage device, printer, etc.).

An example of correcting non-uniformity in sensitivity of a solid-state image pickup device having a characteristic that its output voltage changes logarithmically with respect to the amount of received light will be described below with reference to FIGS. 6 to 10. In FIG. 6, A is an output example when a certain bright and uniform light (hereinafter referred to as A level light) is applied to a solid-state imaging device having a characteristic that its output voltage changes logarithmically with respect to the amount of received light. .. B in the figure is an output example when the solid-state imaging device is irradiated with uniform light darker than A-level light (hereinafter, B-level light). Here, when the output of the B level light is subtracted from the output of the A level light for each pixel, the result is as shown in FIG. 7, and it is understood that the sensitivity variation for each pixel can be corrected.

Next, the case of receiving an actual image will be described. When light having a distribution as shown in FIG. 8 is applied to a solid-state image sensor having a characteristic that its output voltage changes logarithmically with respect to the amount of received light, the sensitivity becomes non-uniform for each pixel. The output is as shown in FIG. 9, which is very different from the actual light distribution. Therefore, the output of the B level light of FIG. 6 is subtracted from the output of FIG. Then, the result is as shown in FIG. 10, which coincides with the light distribution given to the solid-state imaging device (see FIG. 8). In other words, even when an actual image is captured, it is possible to correct the non-uniformity of sensitivity between pixels by simply subtracting the imaging data for each pixel obtained when uniform light is emitted from the imaging data. it can.

FIG. 11 is a block diagram of another embodiment of the solid-state image pickup device to which the present invention is applied. The CCD is a solid-state image sensor having a natural logarithmic relationship between the amount of received light and the output voltage.
Both / D1 and A / D2 are A / D converters. Also,
MEM is a memory, D / A is a D / A converter, COR is an analog correction arithmetic circuit, and DEV is a storage device or printer.

The output voltage of each pixel of the solid-state image pickup device CCD at the time of uniform light irradiation is A / D converted by the A / D converter 1
It is D-converted and stored in the memory MEM. At the time of image capturing, the difference between the image pickup data for each pixel and the actual image pickup data for each pixel at the time of uniform light irradiation converted into an analog value again by the D / A converter is the analog correction arithmetic circuit C.
It is calculated by OR and the imaging data is corrected. The corrected image data is converted into a digital value by the A / D converter A / D2 and output to the device DEV. With this configuration, the correction arithmetic circuit can be an analog circuit.

[0014]

As described above, according to the present invention, in the solid-state image pickup device provided with the solid-state image pickup element having a characteristic that its output voltage changes logarithmically with respect to the amount of received light,
By subtracting the imaging data at the time of uniform light irradiation from the imaging data of the subject, it is possible to correct the nonuniformity of the sensitivity between the pixels. Further, since the calculation for correction needs only addition and subtraction, there is an effect that the calculation is simple and the speed can be increased.

[Brief description of drawings]

FIG. 1 is a diagram showing a received light amount / output voltage characteristic of a solid-state imaging device having a characteristic that its output voltage changes linearly with respect to a received light amount.

FIG. 2 is a diagram showing a difference in received light amount / output voltage characteristic of a solid-state imaging device having a characteristic that an output voltage thereof linearly changes with respect to a received light amount, depending on a pixel.

FIG. 3 is a diagram showing a received light amount / output voltage characteristic of a solid-state imaging device having a characteristic that its output voltage changes logarithmically with respect to a received light amount.

FIG. 4 is a diagram showing a difference in received light amount / output voltage characteristic of a solid-state imaging device having a characteristic that its output voltage changes logarithmically with respect to a received light amount depending on pixels.

FIG. 5 is a block diagram of an embodiment of the present invention.

FIG. 6 is a diagram showing an output example at the time of uniform light irradiation in a solid-state imaging device having a characteristic that its output voltage changes logarithmically with respect to the amount of received light.

FIG. 7 is a diagram showing a correction result of nonuniformity of sensitivity of a solid-state imaging device having a characteristic that its output voltage changes logarithmically with respect to the amount of received light.

FIG. 8 is a diagram showing a light distribution given to a solid-state imaging device having a characteristic that its output voltage changes logarithmically with respect to the amount of received light.

9 is a diagram showing the output of a solid-state image sensor having a characteristic that its output voltage changes in a natural logarithmic manner with respect to the amount of received light having received the light distribution shown in FIG.

FIG. 10 is a diagram showing a result of performing sensitivity nonuniformity correction on the output of FIG. 9;

FIG. 11 is a block diagram of another embodiment of the present invention.

[Explanation of symbols]

 MEM memory COR correction calculation circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H04N 1/028 A 9070-5C 5/335 P 8838-5C

Claims (1)

Claim: What is claimed is: 1. A solid-state image pickup device comprising a solid-state image pickup device having a characteristic that its output voltage changes logarithmically with respect to the amount of received light. Non-uniformity of sensitivity between each pixel of the solid-state image sensor by subtracting the image data of the corresponding pixel stored in the memory means from the image data of each pixel at the time of actual image pickup A solid-state imaging device comprising: a correction unit that corrects