JPS62200470A - Shading correcting method and its device - Google Patents

Abstract

PURPOSE:To relax an influence exerted on the shading correcting data of various noises, by forming the shading correcting data, based on a reference data to which a low-pass filter processing has been performed. CONSTITUTION:First of all, a switch 5 is connected to a side (a), and also, in case an object 3 is a transmissive object, the object 3 is removed, and when the object 3 in an reflecting object, it is replaced with a standard object and a reference data R (x, y) is read, and a low-pass filter processing of an (n)X(m) matrix size is performed. As a result, a component of dust contained in the reference data R (x, y) is smoothed, and in a shading correcting data Sf (x, y) which has been formed, based on, an influence of dust does not appear vividly. A shape of shading is varied gently as it goes to the end face of a screen from the center of the screen. Accordingly, since a high space frequency component is not contained, a digital low-pass filter of (n)X(m) is used in this embodiment.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a shading correction method and apparatus,
In particular, the present invention relates to a shading correction method and apparatus for minimizing the effects of dust and electrical noise in an optical system when creating shading correction data.

[Prior Art] Shading correction is necessary to faithfully reproduce a subject. Various types of shading correction have been proposed and attempted in the past. One method is to perform approximate correction by transforming the scanning signal on the time axis. Although this device has a simple configuration and can be made at low cost, it does not provide a sufficient approximation and cannot provide a correction result that can be put to practical use.

The other method is to remove shading by splitting the light beam from the light source and comparing the signals of the light that passes through the object and the light that does not pass through the subject. However, since the shading caused by the two optical systems is not the same, a complete correction effect cannot be obtained.

Moreover, since it has two sets of optical systems, the apparatus becomes complicated and expensive.

Still another one uses one optical system and memory 7 as shown in FIG.

FIG. 6 is a flowchart of shading correction processing performed by the apparatus shown in FIG. In step S21, reference data R(x, y) is input into the memory 7. Reference data R(x
,y) Manually, first connect the switch 5 to the a side, and if the object 3 is a transparent object, remove the object 3,
Further, when the subject 3 is a reflective object, it is replaced with a standard subject and reference data R(x,y) is read. Step S2
2, the arithmetic unit 6 calculates the maximum value Rm of the reference data R(x,y)
Calculate ax (x, y). Shading is caused by, for example, unevenness in the light source 1 or spatially nonuniform attenuation that occurs when passing through the optical system 2 or phototube 4, so the reference data R(x.

From a relative point of view, the maximum value Rmax (x, y) of y) can be treated as having not been subjected to shading. In step S23, shading correction data s (x,
y) is determined by the following formula.

S (x, y) mRaax (x, y)/R (x, y) Step 52
4, the switch 5 is connected to the b side, the subject 3 is inserted, and the data D(x, y) of the subject 3 is input. In step S25, corrected object data D' (x, y) is obtained from the data D (x, y) of the object 3 and the shading correction data s (x, y) using the following equation.

D' (x, y)=D (x, y)xS (x, y)
However, this device does not take into account the effects of electrical noise and dust on the reference data R(x, y), which occur in the optical system 2 and the phototube 4 when the reference data R(x, y) is taken in. If there is electrical noise, the reference data R(
x, y) itself.

FIG. 3(a') is a diagram illustrating the adverse effects of noise and dust on a conventional device. For example, if there is dust in the optical system 2, the reference data Rg(x, y) of that part will be changed to the reference data R(x, y) around it.

y) and appears as black with a certain area. That is, if the error amount due to dust is D arr, the shading correction data S (x, y) is affected by the following equation.

S (x, y) = Rrnax (x, y)/ (R(x, y)
y)-Derr) In the above formula, (R(x, y)
-Derr) indicates that the brightness of the part with dust is lower than the brightness of the original reference data R(x, y) by Derr. Therefore, the subject data D (x, y
) is assumed to be free of dust when reading it, the corrected object data D' (x, y) is affected by the following equation.

o' (x, y) = (Ra+ax (x, y)XD (x, y))/
(R(x, y) −Derr) Therefore, De
If the value of rr is large, D'(x.

Since the value of y) also increases, the reference data R(x.

The dust part Rg (x, y) that appears black on y) is the white part D on the corrected subject data D' (x, y).
This appears as an adverse effect on g' (x, y).

Furthermore, in the conventional device, the reference data R(x,y) is adversely affected by the electrical random noise of the phototube 4. That is, if the maximum value Rmax (x, y) of the reference data R (x, y) is
If random noise of +N err is included in y), it can be said that the noise of +N err increases the possibility of this happening, and the effect is that the corrected subject data D' (x, y
) can be easily seen to apply to the entire range.

[Problems to be Solved by the Invention] The present invention eliminates the drawbacks of the prior art described above, and its purpose is to reduce the influence of dust and noise when forming shading correction data, It is an object of the present invention to provide a shading correction method and an apparatus thereof that enable more accurate shading correction.

[Means for solving the problem] In order to solve the problem, the shading correction device of the embodiment shown in FIG.
) based on the shading correction data sr (x, y
), and the formed shading correction data S
A shading correction device that corrects subject data D (x, y) using f (x, y), wherein data Rt (x, y) is smoothed by applying low-pass filter processing to the reference data R (x, y). shading correction data forming means 8 and 9 that form shading correction data sr (x, y) based on the shading correction data sr (x, y);

A shading correction means 9 is provided for correcting object data D (x, y) according to y).

[Operation] In the configuration shown in FIG. 1, first, the switch 5 is connected to the a side, the object 3 which is the transparent object is removed, and the read reference data R(x, y) is smoothed by the low-pass filter 8. Obtained smoothed reference data Rf (x, y)
is stored in the memory 7. Next, the calculation means 9 forms shading correction data Sf (x, y) based on the smoothed reference data Rf (x, y). Next switch 5
is connected to the b side, and the subject 3 is inserted to read the subject data D (x, y), and the arithmetic means 9 uses the formed shading correction data 5f (x, y).

The subject data D(x, y) read by
Correct.

[Examples] Examples of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a block diagram of a shading correction device according to an embodiment. Components equivalent to those in FIG. 5 are given the same reference numerals and their explanations will be omitted. In FIG. 1, 8 is read reference data R(x.

y), and a low-pass filter 9 forms shading correction data Sf (x, y) based on the smoothed reference data Rf (x, y), and
It is a calculating means for correcting the read object data D (x, y) using the shading correction data Sf (x, y) formed above when reading the image data Sf (x, y).

FIG. 2 is a flowchart of shading correction processing according to the embodiment. In step S31, the operator is asked whether or not to create correction data. Since the shape of shading gradually changes due to aging of the light source 1 and its optical system 2, especially the light source 1, it is necessary to rewrite the shading correction data S(x, y) from time to time.

In step S32, reference data R(x,y) is read. First, connect the switch 5 to the a side, and if the object 3 is a transparent object, remove the object 3, and if the object 3 is a reflective object, replace it with a standard object and set the reference data R.
Read (x, y).

In step S33, the reference data R(x, y) is subjected to low-pass filter processing with an nxm matrix size. As a result, the dust components included in the reference data R (x, y) are smoothed to become the reference data Rf (x, y), and the shading correction data Sf (
x, y), the influence of dust no longer clearly appears. The shape of shading varies depending on the type of light source, but generally changes gradually from the center of the screen to the edges of the screen. Therefore, since high spatial frequency components are not included, an nxm digital low-pass filter is used in this embodiment.

FIGS. 4(a) and 4(b) are explanatory diagrams showing the state of shading correction processing using actual data, and FIG. 4(a)
) is based on the prior art, and FIG. 4(b) is based on this embodiment.

In the case of the conventional technique shown in FIG. 4(a), the influence of dust appears strongly in the subject data D' (x, y) after correction. For example, subject data D (x, y) with uniform luminance
If you input 100, the value of the corrected object data D' (x, y) including the dust part will be "2".
At 55', everything is saturated.

On the other hand, in the case of the present embodiment shown in FIG. 4(b), the reference data R(x, y) is a 3×3 low-pass filter LPFw.
F CX,y) is smoothed to FLf(x,y). Therefore, object data D (x, y)− with uniform brightness
If you input 1oo, the influence of the dust part of the reference data R (x, y) is dispersed to the surroundings, so the corrected subject data or (x, y) will still maintain an intermediate value. There is. Furthermore, - example low-pass filter L
PF averages and smoothes the reference data R(x, y), so even if the reference data R(x, y) includes electrical random noise such as that generated by the phototube 4, these noises will be ignored by surrounding noise. and cancel each other out, and have almost no effect on the shading correction data 5f(x,y).

Representing the ConvoluLton integral with the symbol “*”, Rf (x, y)=R(x, y)*)” (x, y)
It is.

In step 334, the maximum value Rfmax (x, y) of the reference data Rf (x, y) is determined. Scan the reference data Rt (x, y) and select the one with the largest value as Rf
Let max (x, y). Since the influence of electrical random noise is canceled out and the influence of dust is dispersed, the value of the reference data Rfmax (x, y) can be trusted.

In step S35, the shading correction data sf (
x, y) are determined by the following formula.

5f (x, y) = Rfmax (x, y) / Rf (x, y) For each reference data Rt (x, y), the influence of electrical random noise is canceled out, and the dust If is dispersed. Therefore, the shading correction data Sf (x, y) obtained based on this can also be confirmed.

In step 336, switch 5 is connected to side b, object 3 is inserted, and data D(x, y) of object 3 is input.

In step S37, data D (x.

y) and the shading correction data Sf (x, y), the corrected subject data Df (x, y) is obtained using the following equation.

of(x, y)=D (x, y) xsf (x, y) FIG. 3(b) is a diagram illustrating the influence of noise and dust on the apparatus of this embodiment. When the reference data R(x, y) is subjected to low-pass filter processing, the reference data Rt(x,
y), the shape of the dust and its value are smoothed, and the smoothed reference data Rgf(x, y) based on the dust part becomes smooth.

In the above embodiment, a 3×3 low-pass filter LPF=F (x, y) is used to form the reference data Rt (x, y).
y), but by changing the filter size depending on the large amount of dust, and by giving other parameters to the digital filter, for example, the MTF correction of the optical system used in this device, contour enhancement, etc. It is also possible to have this function.

[Effects of the Invention] As described above, according to the present invention, since shading correction data is formed based on reference data that has been subjected to low-pass filter processing, the influence of various noises on shading correction data can be alleviated. Furthermore, since the shape of the dust is blurred, the dust becomes less noticeable in the output image.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram of a shading device according to an embodiment, FIG. 2 is a flowchart of shading correction processing according to an embodiment, FIG. FIG. 4(b) is a diagram explaining the influence of noise and dust in the example device. FIG. 4(a) is an explanatory diagram showing the state of the conventional shading correction IA process using actual data. FIG. FIG. 5 is a block diagram of a conventional shading correction apparatus, and FIG. 6 is a flowchart of shading correction processing performed by the apparatus shown in FIG. 5. In the figure, 1... light source, 2... optical system, 3... subject, 4... phototube, 5... switch, 7... memory, 8... low pass filter, 9...・It is a calculation means. Patent Applicant Canon Co., Ltd. Rumor→- Agent Patent Attorney Yasushi Otsuka Virtue 5, Figure 2, I, Dai, I! Reference 7-Ta1shidaii1 Salary,! ! Tenita 3rd
Figure (G) (b) (a) (b)

Claims (2)

[Claims] (1) In a shading correction method in which shading correction data is formed based on reference data and object data is corrected using the formed shading correction data, the shading correction data is generated based on data obtained by performing low-pass filter processing on the reference data. A shading correction method comprising: a step of forming a shading correction data; and a step of correcting subject data using the formed shading correction data. (2) In a shading correction device that forms shading correction data based on reference data and corrects subject data using the formed shading correction data, the shading correction data is generated based on data obtained by performing low-pass filter processing on the reference data. A shading correction apparatus comprising: a shading correction data forming means for forming shading correction data; and a shading correction means for correcting subject data using the formed shading correction data.