JP3798178B2 - Peripheral dimming correction method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a peripheral darkening correction method and apparatus for correcting peripheral darkening of an image caused by an optical system such as a lens.
[0002]
[Prior art]
For example, when an image is obtained by imaging a subject with a CCD camera, an image signal is obtained by detecting an image formed by light emitted from the subject and transmitted through the camera lens, and an image formed by the camera lens is obtained at this time. It has the property of reducing the amount of light (lens periphery dimming) going from the center image formed near the optical axis of the lens to the peripheral image formed away from the lens optical axis. Due to the light attenuation, the image signal goes from the central part of the image corresponding to the central image formed near the optical axis of the lens to the peripheral part of the image corresponding to the peripheral image formed away from the optical axis of the lens. The signal value decreases by an amount corresponding to the lens periphery dimming.For example, even if the subject is originally uniform in brightness, a phenomenon occurs in which the obtained image becomes darker as it goes to the periphery. To lead to dimming phenomenon.
[0003]
Such a lens peripheral light reduction phenomenon has a small influence when the difference in the density of the subject is large and the difference in the amount of light transmitted through the lens is significantly detected because the amount of light reduction is smaller than the difference in the amount of light transmitted through the lens. However, as the difference in the density of the subject decreases and the difference in the amount of transmitted light decreases, the amount of light reduction becomes relatively larger than the difference in the amount of transmitted light.
[0004]
Conventionally, as a method of correcting the lens periphery dimming of such an image, an image corresponding to an image formed around the optical axis of the lens from the center of the image corresponding to the image formed near the optical axis of the lens. By multiplying the image signal value by a coefficient that gradually increases toward the periphery of the image, and correcting the image, the influence of the lens periphery dimming is removed, and the lens periphery decrease to obtain an image signal corrected to the same brightness distribution as the subject. Light correction methods are known.
[0005]
[Problems to be solved by the invention]
However, when such a lens periphery dimming correction method is adopted, the image signal corresponding to the peripheral portion of the image is multiplied by a larger value, so that the lens peripheral dimming is compensated and the lens peripheral dimming is affected as a whole. However, in that case, not only the image signal to be imaged but also components such as electrical noise mixed in the image signal when the subject is imaged are multiplied in the peripheral area in that case. As a result, there arises a problem that noise around the image becomes conspicuous.
[0006]
This problem also occurs in the case of an image picked up through an optical system other than the lens and which causes peripheral dimming similar to that of the lens.
[0007]
In view of the above circumstances, an object of the present invention is to provide a peripheral darkening correction method and apparatus capable of correcting peripheral darkening of an image caused by an optical system while suppressing an increase in noise in the peripheral portion. .
[0008]
[Means for Solving the Problems]
The method according to the present invention is a peripheral darkening correction method for correcting peripheral darkening of an image caused by an optical system, and an image data corresponding to a position further away from the optical axis position on the imaging plane has a larger coefficient. The image data multiplied by the coefficient is subjected to a smoothing process using a mask having a larger size as the image data corresponding to a position further away from the optical axis position on the imaging plane. To do.
[0009]
An apparatus according to the present invention is a peripheral darkening correction device that corrects peripheral darkening of an image caused by an optical system, and a larger coefficient is obtained for image data corresponding to a position farther from the optical axis position on the imaging plane. Multiplication means for multiplying and smoothing processing for image data multiplied by a coefficient by the multiplication means using a mask having a larger size for image data corresponding to a position farther from the optical axis position on the imaging plane And smoothing processing means for performing the above.
[0010]
【The invention's effect】
According to the peripheral darkening correction method and apparatus according to the present invention, the image signal corresponding to the peripheral portion of the image is multiplied by a larger value to correct the image signal that compensates for the peripheral darkening. By applying a smoothing process using a mask with a larger size toward the periphery of the image, the image signal that has been enhanced with noise as it goes to the periphery of the The influence can be corrected while suppressing an increase in noise in the peripheral portion.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0012]
FIG. 1 shows a schematic configuration of an embodiment in which a peripheral darkening correction apparatus that performs a peripheral darkening correction method according to the present invention is applied to a fluorescence detection apparatus.
[0013]
The fluorescence detection apparatus according to the embodiment of the present invention images an ultraviolet irradiation unit 100 that irradiates ultraviolet UV, a sample 30 that emits fluorescence when irradiated with ultraviolet UV from the ultraviolet irradiation unit 100, and fluorescence emitted from the sample 30. A high-sensitivity CCD camera 10 that is output as an image signal V, and an image signal V that is output from the CCD camera 10 are input, and peripheral light attenuation correction processing and noise reduction processing are performed. A peripheral dimming correction calculator 40 that outputs as W, an image display device 50 that receives the image signal W output from the peripheral dimming correction calculator 40 and displays it as an image, and a sample stage 21 on which the sample 30 is placed. And a dark box 20 that shields light from the outside and accommodates the irradiation unit 100, the CCD camera 10, and the sample stage 21.
[0014]
The CCD camera 10 includes an excitation light cut filter 14 that transmits reflected fluorescence emitted from the sample 30 by cutting the reflected light of the ultraviolet UV irradiated by the ultraviolet irradiation unit 100, a lens system 11 that forms an image of the fluorescence emitted from the sample 30, and a lens. The image pickup device 12 picks up the fluorescent image KZ imaged by the system 11 as image information, and the image output unit 13 converts the image information picked up by the image pickup device 12 into an image signal and outputs it as an image signal V. .
[0015]
Further, the CCD camera 10 has an optical axis X of its lens system 11 coincided with the center position of the sample table, and is separated from the sample 30 by an appropriate distance for photographing the sample 30 placed on the sample table 21. Separated and fixed in the dark box 20.
[0016]
The peripheral light reduction correction computing unit 40 receives the image signal V output from the CCD camera 10 and stores it, and the image signal V stored in the storage unit 43 is input and becomes larger as it goes to the periphery of the image. A multiplication unit 41 that corrects the image signal V by multiplying by a coefficient and outputs it as an image signal VA, and an image signal by performing smoothing processing using a mask having a larger size as the image signal VA is input and goes to the periphery of the image A smoothing processing unit 42 that corrects VA and outputs it as an image signal VB, and a display conversion unit 44 that receives the image signal VB, converts it into a displayable signal, and outputs it as a display signal W are provided.
[0017]
Next, the operation of the peripheral darkening correction apparatus of this embodiment will be described.
[0018]
The sample 30 is placed on the sample stage 21, and the sample 30 is irradiated with ultraviolet UV from the ultraviolet irradiation unit 100 to excite the sample 30 to generate fluorescence Ke. The fluorescence Ke generated from the sample 30 passes through the excitation light cut filter 14 and enters the lens system 11. However, the ultraviolet UV irradiated from the ultraviolet irradiation unit 100 and reflected by the sample 30 or the like is cut by the excitation light cut filter 14 and the lens system. 11 does not enter. The fluorescence Ke transmitted through the excitation light cut filter 14 is imaged on the imaging surface h of the imaging device 12 by the lens system 11. The fluorescent image KZ formed on the imaging surface h is imaged by the imaging element 12, converted into a signal, and output. A signal output from the image sensor 12 is input to the image output unit 13, converted into an image signal, and output as an image signal V. Here, the fluorescent image KZ imaged on the imaging surface h is affected by the lens periphery dimming of the lens system 11, and the image signal V converted into the image signal by the image output unit 13 is similarly lens periphery dimming. Is influenced by.
[0019]
The image signal V converted into an image signal and output by the image output unit 13 is input to the peripheral light reduction correction calculator 40, and the storage unit 43, the multiplication unit 41, the smoothing processing unit 42, and the display conversion unit 44 described above. After the processing, the display signal W is output to the image display device 50 and displayed on the image display device 50.
[0020]
Here, details of the operation of the multiplication unit 41 will be described.
[0021]
Even if the intensity of the fluorescence emitted by the sample 30 is uniform at all locations, the brightness of the fluorescent image KZ in which the fluorescence emitted by the sample 30 forms an image on the imaging surface h of the image sensor 12 by the lens 11 is reduced around the lens. As shown in FIG. 2 due to the influence of light, the optical axis X of the lens 11 becomes maximum at the portion of the fluorescent image KZ corresponding to the optical axis crossing pixel P (0, 0) intersecting the imaging surface h of the imaging device 12, and the light The portion of the fluorescent image KZ corresponding to the position of the peripheral part (position on the imaging surface h) further away from the axis crossing pixel P (0, 0) decreases. Accordingly, the amount of light received by the pixel on the imaging surface h is similarly maximized at the optical axis crossing pixel P (0, 0), and the amount of light received by the pixel is further away from the optical axis crossing pixel P (0, 0). Decrease.
[0022]
The amount of reduction in the amount of light received by the peripheral pixels of the image pickup device 12 due to the lens periphery dimming is obtained by calculation when designing the lens system 11 in advance, or a sample that actually emits a uniform amount of light at all locations. Since it can be obtained in advance by means such as placing on the sample stage 21 and photographing with the CCD camera 10, the amount of light received by the optical axis crossing pixel P (0, 0) of the image sensor 12 is set to the reference value 1, If the light quantity received by the peripheral pixel P (x, y) is q (x, y), the multiplication coefficient corresponding to the pixel P (x, y) is Q (x, y) = 1 / q ( x, y). Similar coefficients are obtained for all pixels, the coefficients are stored in the multiplication unit 41, and the signal values corresponding to the respective pixels of the image signal V that are affected by the lens peripheral dimming input to the multiplication unit 41 are obtained. A value obtained by correcting the influence of the lens peripheral dimming by multiplying the coefficient is obtained, and those signal values are output as the image signal VA.
[0023]
Note that the multiplication coefficient is not a coefficient that accurately corrects the decrease in the amount of light received by the pixels of the image sensor 12 due to the influence of the lens periphery dimming, but is simply replaced by an arbitrary coefficient value that increases toward the periphery. It can also be simplified.
[0024]
Next, details of the operation of the smoothing processing unit 42 will be described.
[0025]
Since the fluorescence emitted from the sample 30 irradiated with the ultraviolet rays UV is very weak light, there is a possibility that various noises are mixed from when the image is taken with the CCD camera until the image signal V is outputted.
[0026]
If noise is mixed when the intensity of the fluorescence emitted from the sample 30 is uniform in all places, the value of the signal carried by the image signal V is influenced by both the lens peripheral attenuation and noise as shown in FIG. Is receiving. When this signal is processed by the multiplier 41, a larger coefficient is multiplied toward the periphery, so that the decrease in the amount of light at the periphery due to the lens periphery dimming is corrected as shown in FIG. The image signal VA carries an image with enhanced noise.
[0027]
Smoothing processing is performed on the image signal VA carrying an image in which noise is emphasized as it goes to the periphery. As shown in FIG. 5A, the imaging region on the imaging surface h is divided into six regions surrounded by squares of different sizes with the optical axis crossing pixel P (0, 0) as the center. FIG. 5B shows the value of the image signal carried by each pixel on the U1-U2 cross section of the imaging surface h divided into six regions. Then, region a, region b, region c, region d, region e, and region f are set from the region close to the optical axis crossing pixel P (0, 0), and the pixels in region a are smoothed with a 3 × 3 pixel mask. That is, as shown in FIG. 6, processing for replacing the value of G22 with the average value of the image signals carried by the nine pixels G11, G12, G13, G21, G22, G23, G31, G32, and G33 The same smoothing process is performed with a 5 × 5 pixel mask in area b, the same smoothing process is performed with a 7 × 7 pixel mask in area c, and the same smoothing process is performed with a 9 × 9 pixel mask in area d. In the region e, the same smoothing process is performed with a mask of 11 × 11 pixels in the region e, and the same smoothing process is performed with a mask of 13 × 13 pixels in the region f. The effect of Since deal of processing is performed, while suppressing an increase in noise influence of vignetting as shown in FIG. 7 can be corrected, its value is output as an image signal VB1.
[0028]
Note that the size of the pixel area and the mask on which the smoothing process is performed is not necessarily limited to the above example. For example, the pixel area is located at a substantially equidistant position in the peripheral direction with the optical axis crossing pixel P (0, 0) as the center. The arranged pixels are set as the same region, and the mask only needs to have a size that is larger toward the periphery with the optical axis crossing pixel P (0, 0) as the center.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a fluorescence detection apparatus to which a peripheral dimming correction apparatus according to the present invention is applied. FIG. 2 is a diagram showing a relationship between an amount of light detected by an image sensor and a pixel position. FIG. 4 is a diagram showing the relationship between the brightness value and position of an image carried by the image signal V. FIG. 4 is a diagram showing the relationship between the brightness and position of an image carried by the image signal VA. FIG. FIG. 6 is a diagram showing the relationship between the magnitude of noise contained in an image signal and FIG. 6 is a diagram showing a pixel range corresponding to the size of a mask used for smoothing processing. FIG. 7 is the brightness and position of an image carried by the image signal VB. That shows the relationship
DESCRIPTION OF SYMBOLS 10 CCD camera 11 Lens system 12 Image pick-up element 13 Image output part 30 Sample 40 Perimeter attenuation correction calculator 41 Multiplication part 42 Smoothing process part 43 Storage part 44 Display conversion part 50 Image display apparatus

Claims (2)

A peripheral dim correction method for correcting peripheral dim of an image caused by an optical system,
Image data corresponding to a position farther from the optical axis position on the image plane is multiplied by a larger coefficient, and the image data multiplied by the coefficient is positioned farther from the optical axis position on the image plane. An image peripheral darkening correction method, wherein smoothing processing is performed using a mask having a larger size as image data corresponding to the image data. A peripheral darkening correction device for correcting peripheral darkening of an image caused by an optical system,
Multiplication means for multiplying image data corresponding to a position farther from the optical axis position on the imaging plane by a larger coefficient, and for the image data multiplied by the coefficient by the multiplication means, the optical axis on the imaging plane An image peripheral darkening correction apparatus comprising: smoothing processing means for performing smoothing processing using a mask having a larger size for image data corresponding to a position farther from the position.

Images