JPH1155461A - Illuminance adjusted image pickup system and image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the inexpensive image pickup device that picks up an image with a constant noise level without dispersion in the luminance level over the entire photographing range. SOLUTION: This system is provided with a lighting means consisting of a combination of a main lighting device 2 lighting a photographing object 1 under a prescribed illuminance and an auxiliary lighting device 30 that adjusts the illuminance, an image pickup element 4 that converts a light into an electric signal, and a lens 5 forming an image of a reflected light (a) from a photographing object onto the image pickup element 4, obtains an analog image signal (b) of the object, a signal processing unit 6 amplifies and A/D-converts the analog image signal (b), a digital image signal (c) is obtained and stored an image storage device 7. An image processing unit 80 applies image processing to the image signal stored in the image storage device 7 and dispersion in the luminance of the image signal is obtained and power is supplied to the auxiliary lighting device 30 to light part of the object with lower luminance and an illuminance command (f) is given to increase the illuminance and an image signal with a uniform luminance level is obtained within the photographing range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illuminance-adjusted image pickup system and an image pickup apparatus which take in an image by correcting characteristics of an optical system of the image pickup device by illumination.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a configuration of an image pickup apparatus using a conventional image pickup method. In FIG. 6, reference numeral 1 denotes an object to be imaged, 2 denotes a main illumination device for illuminating the object to be imaged 1 with a constant illuminance, 3 denotes an auxiliary illumination device, 4 denotes an image pickup device (CCD) for performing photoelectric conversion, and 5 denotes an image pickup object The lens 6 couples the reflected light a from 1 to the element surface of the image sensor 4 and converts the analog image signal b output from the image sensor 4 into a digital image signal c by performing signal processing such as amplification and A / D conversion. 7 is an image storage device that stores the digital image signal c converted by the signal processing device 6, and 8 is an image processing device that performs image processing on the digital image signal c stored in the image storage device 7. , 13 are illumination power supplies for the auxiliary lighting device 3.

[0003] With this configuration, the main illuminating device 2 uniformly illuminates the imaging object 1 with the auxiliary illuminating device 3 at the four corners, and the reflected light a is imaged on the image sensor 4 via the lens 5.
The reflected light a formed on the image pickup device is input to the signal processing device 6 as an analog image signal b, amplified to a certain level as necessary, A / D converted, and the digital image signal c is stored in the image storage device 7. Output. The digital image signal c stored in the image storage device 7 is subjected to image processing by the image processing device 8 and output.

FIG. 7 shows a change in luminance due to the optical system of the image pickup apparatus having the above-described configuration. That is, the object 1 is irradiated from the main illumination device 2 with uniform illuminance.

At this time, the brightness of the image combined on the image sensor 4 by the lens 5 is determined by the characteristics of the lens.
That is, the brightness of an image passing through the peripheral portion of the lens and being imaged on the image sensor becomes lower than the brightness of an image passing near the center of the lens and being imaged on the image sensor, and is reduced at the four corners of the screen. Darkens. For this reason, the lens 5 is preferably used so that an image can be captured only with an image passing near the center of the lens 5 as much as possible.
Must be selected so that the luminance level of the image signal formed on the image sensor 4 is substantially constant.

However, in practice, when an image is taken over a wide range using an image pickup device having a large number of pixels, particularly when a line sensor CCD is used, the peripheral portion of the lens must be used for image pickup. In addition, a wider-angle lens having a wider field of view has a larger decrease in luminance at a peripheral portion of an image to be formed. Therefore, when an imaging system with a wide imaging range is to be realized, variations in luminance in the visual field occur. In such a case, (1) Design a lens that does not significantly reduce the luminance within a necessary range.

(2) By using the auxiliary lighting device 3 to increase the illuminance of the portion where the luminance of the range to be imaged is reduced when only the main lighting device 2 illuminates, it can be obtained in advance. Make the brightness of the image uniform.

(3) Brightness information of an image obtained from the image sensor 4 when an image of an object having uniform brightness is captured is stored, and the brightness level of the entire image signal becomes uniform at each position. Find a correction coefficient, and correct the image signal when the actual object is imaged according to the correction coefficient,
A so-called shading correction is performed. Such methods have been adopted.

FIG. 8 is a conceptual diagram of shading correction when a line sensor CCD is used. The left side (1) shows the variation in characteristics (white level signal d and image signal e) for each image sensor, and the right side (2) ) Shows the corrected image signal E, which has a substantially flat luminance level. The shading correction amount at this time is shown in FIG. 9, the horizontal axis is the diameter dimension of the image sensor 4, the vertical axis is the correction amount from the center to the peripheral portion of the image sensor, and the periphery of the image sensor from the center. Shading correction is performed largely to make the luminance level uniform.

[0010]

However, the above-mentioned conventional method for equalizing the variation in luminance has the following problems.

(1) When designing a lens for an image pickup system, there is a problem that the lens cost is higher than when a commercially available lens is employed, and as a result the cost of the entire apparatus is increased.

(2) In the case where the auxiliary lighting device is used, there is a problem that there is no guarantee against the illumination fluctuation of the main lighting device (change over time, fluctuation of ambient temperature, fluctuation of power supply, etc.). In particular, in a fluorescent lamp illumination or the like, since the rate of decrease in illuminance due to aging changes between a portion near the electrode and a portion not near the electrode, the luminance of the auxiliary portion may increase with the use time of the illumination.

(3) In the shading correction, the image signal of the low luminance portion is amplified to the same degree as the signal of the high luminance portion. At this time, since the noise signal included in the image signal is also amplified, it is amplified. High rate of result correction
Deterioration of image information in a (high amplification factor) portion occurs.

In view of the above problems, the present invention obtains a luminance level for an image taken using an image processing device, and controls the illuminating device to illuminate a portion having a low luminance level so as to increase the illuminance. It is an object of the present invention to provide an illuminance-adjusted imaging method capable of capturing an image with a constant noise level without variation in luminance level in the entire imaging range, and a low-cost image capturing apparatus.

[0015]

According to the present invention, in order to achieve the above object, the illumination means can be adjusted by combining a main illumination for illuminating an object to be imaged with a constant illuminance and an auxiliary illumination capable of adjusting the illuminance, or the illuminance can be adjusted. An illumination unit that illuminates the entire imaging target using a plurality of illumination devices, an imaging unit that converts light into an electric signal, and an optical unit that forms reflected light from the imaging target on an element of the imaging unit, The image processing apparatus includes image processing means for performing image processing on an image signal obtained by the imaging means and further calculating a variation in luminance of the image signal, and illuminance adjustment means for adjusting illuminance of the illumination means according to a command from the image processing means. is there.

According to the present invention, the auxiliary illumination is arranged in a portion where the luminance of the image signal is reduced by the optical system, and the variation in the luminance of the image signal obtained by imaging the object having the uniform luminance is obtained by the image processing apparatus. By controlling the brightness of the auxiliary lighting that illuminates the low-brightness part or the illuminance of some of the plurality of lighting devices based on the value, the characteristics of the optical system are corrected by the illuminance of the illumination to capture an image. The purpose is to obtain an image with uniform brightness over the entire area of the element.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. (Embodiment 1) FIG. 1 is a block diagram showing a configuration of an image pickup apparatus using an illuminance adjustment image pickup system according to Embodiment 1 of the present invention.

In FIG. 1, blocks having the same functions as those shown in FIG. 6 of the conventional example are denoted by the same reference numerals, and description thereof will be omitted. Here, 80 performs image processing on the digital image signal c stored in the image storage device 7,
Auxiliary lighting device 30 for finding variations in digital image signals
An image processing device 9 for outputting an illuminance command value f of the illuminance 9 is an illuminance control device having a dimming function for controlling the illuminance of the auxiliary lighting device 30 in accordance with the illuminance command value f from the image processing device 80. Connected to the image processing device 80.

The main illumination device 2 always illuminates the imaging target 1 with a constant illuminance. The auxiliary lighting device 30 is arranged so as to illuminate a portion where the luminance of the image signal obtained by the characteristics of the lens 5 becomes low. FIGS. 2 and 3 show examples of the arrangement of the auxiliary lighting device 30 using the line sensor and the area sensor in this case. Here, FIG. 2 shows an arrangement example viewed from the side surface, and FIG. 3 shows an arrangement example viewed from the upper surface side.

FIG. 4 is a block diagram showing the configuration of an image pickup device using a line sensor. One main lighting device 2 is provided with a fixed illumination power supply 12, and an auxiliary portion is provided at the periphery of the object 1. The lighting device 30 is arranged. Further, the relationship between the image signal (1) and the illuminance (2) is shown on the right side of FIG. 4, and the control of the illuminance is reciprocal to the magnitude of the image signal.

Next, the operation of the present embodiment will be described.
Is converted to an analog image signal b by the image sensor 4. When the dynamic range of the analog image signal b output from the image sensor 4 is small, the signal processing device 6 amplifies the signal, performs A / D conversion, converts the signal into a digital image signal c, and inputs the digital image signal c to the image storage device 7. I do. The image processing device 80 includes, among the digital image signals c stored in the image storage device 7,
The difference between the luminance of the signal output from the central portion of the image sensor 4 and the luminance of the signal output from the peripheral portion of the image sensor 4 is obtained, and the illuminance command value f of the auxiliary lighting device 30 is set so that the difference becomes smaller. The signal is output via the signal line 14. Illuminance control device 9
Controls the illuminance of the auxiliary lighting device 30 according to the illuminance command value f output from the image processing device 80. As a result, variations in luminance within the visual field of the imaging target are eliminated and uniformized.

The image pickup device according to the present embodiment is not limited to the above-described configuration, and various modes are possible. For example, the lens 5 and the imaging device 4 can be realized by an analog camera. Further, the lens 5, the imaging device 4, and the signal processing device 6 may be realized by a digital camera.

When the present invention is applied to an image inspection apparatus or the like, an image processing apparatus for inspection often includes an image memory and a CPU for image processing. The processing device 80 can be realized.

(Embodiment 2) FIG. 5 is a block diagram showing a configuration of an image pickup apparatus using an illuminance adjustment image pickup system according to Embodiment 2 of the present invention. In FIG. 5, only a portion different from FIG. 4 of the first embodiment will be described, but a case where a line sensor is used as in FIG.

The illuminating device 10 according to the second embodiment is constituted by a set of a plurality of illuminating devices whose illuminance can be adjusted. The whole of the imaging target 1 is illuminated by the plurality of lighting devices. Reference numeral 11 denotes a multiple lighting control device that individually controls the illuminance of each of the multiple lighting devices 10. Image processing device
80 separates the image signal into a plurality of sections of a fixed size corresponding to the number of each lighting device of the plurality of lighting devices 10, images an object having a uniform color, and measures the illuminance in each section,
A plurality of illuminance command values g are output to the plurality of illumination control devices 11 so that the luminance of the image signal obtained over the entire imaging range becomes uniform. The multiple lighting control device 11 adjusts the illuminance of each lighting device according to the multiple illuminance command values g given from the image processing device 80.

[0026]

As described above, according to the present invention, the luminance level of a captured image is fed back to control the illuminating device that illuminates a portion having a low luminance level so as to increase the illuminance. It is possible to realize, at low cost, an image pickup apparatus that suppresses variations in the luminance level due to the optical system in the entire region, is less affected by illuminance fluctuation of the illumination unit, and can capture an image with a constant noise level in the entire image pickup region.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image capturing apparatus using an illuminance adjustment method according to Embodiment 1 of the present invention.

FIG. 2 is an example of an arrangement of an auxiliary lighting device when a line sensor is used.

FIG. 3 is an example of an arrangement of auxiliary lighting devices when an area sensor is used.

FIG. 4 is a block diagram illustrating a configuration of an image capturing device according to Embodiment 1 of the present invention.

FIG. 5 is a block diagram illustrating a configuration of an image capturing device according to a second embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a conventional image pickup device.

FIG. 7 is a diagram illustrating a change in luminance due to an optical system of the image capturing apparatus.

FIG. 8 is a conceptual diagram of shading correction when a line sensor CCD is used.

FIG. 9 is a diagram illustrating a shading correction amount in FIG. 8;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image pick-up object, 2 ... Main illumination device, 3, 30 ... Auxiliary illumination device, 4 ... Image sensor, 5 ... Lens, 6 ... Signal processing device, 7 ... Image storage device, 8, 80 ... Image processing device, 9 ... illuminance control device, 10 ... multiple lighting devices, 11 ...
Multiple lighting control device, 12, 13… Lighting power supply, 14… Signal line,
b: analog image signal, c: digital image signal,
f: Illuminance command value, g: Multiple illuminance command values.

Claims (4)

[Claims] An object to be imaged is illuminated by an illumination device, and reflected light from the object to be imaged is formed on a photoelectric conversion element that converts light into an electric signal using an optical system such as a lens. In an image capturing method for obtaining an image signal of an object,
Using the main illumination that constantly illuminates the imaging target with a constant illuminance and the auxiliary illumination with variable illuminance, according to the luminance level of an image signal obtained when an image of an object having uniform luminance is captured, the auxiliary illumination Controlling the illuminance of the optical system to correct the characteristics of the optical system by the illuminance of the auxiliary illumination so that the luminance level of the obtained image signal is always constant irrespective of the position of the image sensor. Adjusted imaging method. 2. An illumination unit comprising a main illumination for illuminating an object to be imaged with a constant illuminance and an auxiliary illumination capable of adjusting the illuminance, an imaging unit for converting light into an electric signal, and a light reflected from the object. An optical unit coupled to an element of the imaging unit, a signal processing unit for performing amplification, A / D conversion, and the like on an image signal obtained by the imaging unit; and an image signal from the signal processing unit. An image pickup apparatus comprising: an image processing unit that performs various image processings and simultaneously obtains a variation in luminance of an image signal; and an illuminance adjustment unit that adjusts illuminance of the auxiliary illumination unit according to a command from the image processing unit. . 3. An object to be imaged by illuminating the object to be imaged with an illuminating device and coupling the reflected light from the object to a photoelectric conversion element for converting light into an electric signal using an optical system such as a lens. In an image pickup method for obtaining an image signal of
Using an illumination device that illuminates the entire imaging target with a plurality of illuminance-controllable illuminations, the illuminance of the auxiliary illumination is individually adjusted according to the luminance level of an image signal obtained when an object having uniform luminance is imaged. An illuminance-adjusted imaging system characterized in that the characteristics of the optical system are corrected by the illumination illuminance by controlling such that the luminance level of the obtained image signal is always constant irrespective of the position of the imaging element. 4. The illuminance adjustment imaging system according to claim 3, wherein the illuminating means illuminates the entire imaging target with a plurality of illuminating devices capable of adjusting the illuminance in accordance with a command from the image processing means.