JPH0568258A - Image discriminating device - Google Patents

Abstract

PURPOSE:To provide an image discriminating device necessary for reproducing a correct tone even when an area occupied by a specific color is large on the screen of a video camera or VTR. CONSTITUTION:This device is provided with a sampling circuit 11 obtaining image data proper for discriminating the image from a color-separated image signal, a distributed calculating part 12 calculating a statistical quantity expressing the feature of the distribution of image data by receiving image data and a threshold value processing part 13 judging the normality/defectiveness of the image based on the calculates statistic quantity. A photographing light source can correctly be estimated by setting the discrimination of the normality/ defectiveness of the image to be that whether GWA is satisfied or not in the photographed image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image judging device for reproducing a correct color tone in a video camera or the like.

[0002]

2. Description of the Related Art In recent years, with the spread of video cameras, means for following photographing conditions have become more and more important in order to obtain beautiful colors. Among them, it is very important for color reproduction to accurately estimate the light source at the time of shooting.

Conventionally, as means for estimating the photographing light source, there are known means for estimating using a plurality of photosensitive elements having different spectral characteristics and means for performing estimation through image processing. In general, the light source estimation device has been replaced with a means using a light sensitive element, which is restricted from the viewpoints of design, cost, etc., to a means for processing an image signal to estimate a light source.

The basis of the method of estimating the light source based on image processing is the assumption that when the colors of the subject in the screen are mixed and averaged, the colors are achromatic, that is, the gray world assumption (hereinafter abbreviated as GWA). )It is in. As a method for performing color adjustment based on this assumption, Japanese Patent Application Laid-Open No.
The thing described in 6-36291 is known. Further, a method described in Japanese Patent Laid-Open No. 2-50592, which adds the assumption that the white portion has high brightness, is also considered as one of several ideas based on this assumption.

[0005]

However, the above-mentioned conventional GWA-based method is, on the assumption that the simple arithmetic mean of the colors of the entire screen is achromatic, although some measures have been taken. Since the processing is performed, the above assumption does not hold when a specific color occupies a large area on the screen, and thus there is a problem that the light source is often mistaken and the color balance is lost.

The present invention solves such a conventional problem, and provides an image determination device for enabling accurate adjustment of color balance even when the area occupied by a specific color is large on the screen. The purpose is to provide.

[0007]

In order to achieve the above object, an image judgment apparatus of the present invention comprises sampling means for sampling color-separated image signals to obtain image data suitable for image judgment, and sampling means. Further, there is provided means for calculating a statistic representing the characteristics of the distribution of the image data, and means for judging the quality of the image based on the calculated statistic.

In a preferred embodiment of the present invention, the means for calculating the statistic means is means for calculating the vertical dispersion for the black body radiation curve in the chromaticity space of the sampled image data or the light source line approximated to this curve. Yes, the means for judging the quality of the image is a means for judging whether the calculated vertical dispersion is larger or smaller than the threshold value.

[0009]

According to the present invention, with the above configuration, the statistical processing of the image data can be correctly performed. In addition, the present invention is
By applying to the WA determination, it is possible to control not to execute the light source estimation when the GWA with many errors in the light source estimation is not established, and as a result, the error rate of the light source estimation result is reduced, It is possible to further reduce the error in light source estimation.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. First, the principle of the present invention and consideration based thereon will be described.

The essence of enabling GWA lies in the phenomenon that color mixture reduces the color saturation. And if you think about this phenomenon, if you mix all enough colors, the color will be achromatic, or gray (white). Based on this, the GWA performs processing under the following expectations.

If the subject entering the screen contains a large number of colors, the average of all the subject colors is calculated as follows:
It should be achromatic. If the subject color is achromatic, the screen color reflects the light source color as it is.
That is, the light source can be estimated by looking at the average color of the entire screen. Therefore, by adjusting the color reproduction system so that the average color of the entire screen is achromatic, the color rendering of the light source can be corrected and the white balance can be adjusted.

Here, the point to be noted is that
It's usually not much emphasized, but as implied in the expression "contains enough colors ...", GWA is a statistical method (for one screen). is there. The essence of GWA being a statistical method is summarized in the talk of "the white wall illuminated by a red light source and the red wall illuminated by a white light source?" There is. As is well known, in order for statistical methods to be applicable, the subject must be sufficient to allow statistical discussion. Since the above settings deal with the case where the statistical method cannot be applied to the target, the light source cannot be properly estimated by the GWA. To be clear, the above question is a discussion beyond the limit of GWA application and has no meaning.

When considering the GWA as a premise, rather than discussing the statistically meaningless condition as described above, G
It is important to understand the WA application limits. And
In the implementation of GWA, keeping the light source estimation within the applicable limit is the most important for ensuring the estimation accuracy. The present inventors considered as described above and made the following consideration based on various data analysis.

Since the chromaticity is two-dimensional, there are two dispersion axes that describe the distribution of data. Mathematically speaking, the axis doesn't matter. However, in the problem of white balance, in the chromaticity space, the blackbody radiation curve drawn by the color of the light emitted by the blackbody radiation according to the temperature of the blackbody has a special meaning as shown in FIG. Moreover, the equivalence of directions does not hold. For convenience of calculation, the light source line is set as a line that approximates the black body radiation curve.

In fact, in view of the data, there is a remarkable difference between the tangential dispersion (horizontal dispersion) of the blackbody radiation curve and the vertical dispersion (vertical dispersion). The dispersion in the tangential direction is usually larger than the vertical dispersion, and in outdoor photography, the dispersion size greatly changes depending on whether or not there is a sky in the screen. Incidentally, in the chromaticity space shown in FIG. 5, the sky blue region is shown surrounded by a square. On the other hand, such a phenomenon is not observed in vertical dispersion. Therefore, vertical dispersion is stable and meaningful for various subjects. (Hereinafter, vertical dispersion may be simply referred to as dispersion. Also, a parameter that describes the axial direction of vertical dispersion is referred to as an axis parameter.)

In GWA, the color distribution of the subject entering the screen is a statistically natural distribution (for example, a normal distribution centered on an achromatic color), and at least the subject does not change the color distribution. , Implicitly in the expression "many colors". This assumption seems to hold with considerable accuracy when shooting a distant view outdoors, but the assumption that the color distribution does not change is not always true. On the other hand, it is clear when considering a bust shot of a person wearing highly saturated clothes.

For a subject whose GWA assumption is broken, such as a bust shot of a person wearing such highly saturated clothes, the average color of the entire screen obtained by simple addition is strongly drawn to the color of the clothes. I will end up. This is a cause of incorrect estimation of the light source.

On the other hand, in an image such as a bust shot, the saturation of some of the block average data is relatively high, and the data in the hue plane is widely distributed. This appears as an increase in the distribution of data. This phenomenon is
The screen is divided into several blocks, and it can be seen notably in the block average data obtained by performing the averaging operation on each block.

When the vertical dispersion is large, the GWA assumption is often not satisfied, and the vertical dispersion is effective as an index related to errors. Therefore, it is possible to reduce the error rate of light source estimation by performing the following processing using vertical dispersion. That is, when the vertical dispersion, which is one of the indexes indicating the application limit of GWA, becomes larger than a certain set value, it is expected that the GWA assumption does not hold in the image to be processed. In this case, the light source estimation is not executed, and the current light source estimation result is held to suppress the occurrence of an error.

It may be argued that the average color of the entire screen may be achromatic and the light source may be estimated correctly even if the variance is large.
However, such a case happens by chance when colors that occupy a considerable part of the screen are in a complementary color relationship with each other, and is not originally assumed in the white balance processing based on the assumption of GWA. That is.
Of course, if there are many such subjects, it is necessary to respond positively, but no such tendency has been seen so far.

Lastly, possible side effects of the processing using dispersion and its solution will be described. As a possible side effect, it is considered that the recoverability decreases when the light source estimation is started up in an incorrect state. In the initial estimation, it is necessary to estimate the light source under any condition. Therefore, when the rising screen is a close-up screen, it is considered that it is easy to make an erroneous decision, and the stabilizing effect due to the dispersion appears strongly. Since such a situation is outside the limits of the statistical method, it is considered that the situation is more likely to occur than the conventional method, even considering that the recovery itself is largely due to chance. However, with regard to such side effects, GWA by dispersion is at least once after startup until the vertical dispersion falls below the threshold value.
This can be avoided by not making the determination.

Each embodiment of the present invention based on the above consideration will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram showing a schematic configuration of an image judgment apparatus according to a first embodiment of the present invention. In FIG. 1, 11 is a sampling circuit for obtaining image data suitable for image determination from the color-separated image signal, and 12 is a dispersion calculation for receiving the sampled image data and calculating the vertical dispersion of the color signal with respect to the light source line. And a threshold processing unit 13 which receives the chromatic dispersion signal from the dispersion calculation unit and compares it with a threshold value set internally, and outputs GWA establishment if the dispersion is smaller than the threshold value, and outputs establishment failure in other cases. Is.

The operation of the image determining apparatus constructed as above will be described below. First, the image signal output from the color separation circuit through an image pickup device such as a CCD is taken in by the sampling circuit 11 according to an appropriate sampling rule, and sent to the dispersion calculator 12. The variance calculator 12 receives the input image data IS ((RGB),
(Y, R-Y, B-Y, etc.), and in some cases, while evaluating the data, the chromaticity space, for example, FIG.
The image data variance SGM, which is the vertical variance with respect to the light source line in the chromaticity space represented by (RY) / Y and (BY) / Y as shown in FIG.

[0026]

[Equation 1]

Hereinafter, the input image data IS is converted into (Y,
RY, BY), the operation of the dispersion calculator 12 will be described more specifically.

The image data IS is converted into C1 = (BY) / Y C2 = (RY) / Y and the chromaticity signal CS = (C1, C2). The chromaticity signal CS is projected in the direction (V1, V2) perpendicular to the light source line described in the description of the principle, and its magnitude, that is, the displacement X from the light source line is given by X = C1 · V1 + C2 · V2 .. The variance of the distribution of the displacement X calculated in this way is the vertical image data variance SGM.

The threshold value processing unit 13 receives the image data variance SGM from the variance calculation unit 12 and compares it with the internally stored threshold value θ. When SGM <θ, J = GWA is established (OK), and otherwise. , J = GWA not satisfied (NO) (However, after starting up, at least once, SGM
Until <θ, in particular, J = OK), and the GWA determination signal J is output.

As described above, according to the first embodiment,
G based on the vertical dispersion of the image data with respect to the light source line
It is possible to determine the establishment of WA, and it is possible to perform more accurate light source estimation.

The vector (V1, V2) that gives a direction perpendicular to the light source line may be approximately (V1, V2) to (1, 1) and need not be strictly determined. Further, although the GWA determination accuracy is somewhat changed depending on this axis parameter, the influence thereof is not large as a result of the data analysis.

The basis of calculation of the vertical image data dispersion SGM is that the image data is an RGB signal or Y, R-.
It goes without saying that it does not depend on whether the signals are Y and BY signals.

Further, in the above calculation, the image data is 2
I calculated the vertical dispersion after dropping it into the dimensional chromaticity space.
This can also be calculated by directly using the three-dimensional image data with a slight modification such as re-thinking the light source line as a light source curved surface.

In addition, when the three-dimensional image data is directly used, an algorithm can be constructed so as to eliminate the effect of a specific color such as the sky, which has a great influence on the light source estimation described in the principle. In this case, the variance in the light source line direction (horizontal variance) can also have a significant meaning, so it is not necessary to specify the vertical variance as the statistic for determining GWA.

Further, as the statistic representing the characteristics of the distribution of the image data, not only the variance but also the average or the Nth moment can be used.

(Embodiment 2) Next, a second embodiment of the present invention will be described in which the above image determining device is used as a light source estimating device. FIG. 2 is a block diagram showing the configuration of the light source estimation device in the second embodiment of the present invention. In FIG. 2, 21
Is an image determination device, which includes a sampling circuit 22 for obtaining image data suitable for image determination from color-separated image signals, a dispersion calculation unit 23 for calculating the dispersion of color signals of image data, and a dispersion calculation unit 23. And a threshold value processing unit 24 that outputs a GWA succession when the dispersion is smaller than the threshold value and compares it with a threshold value that is internally set by receiving the chromatic dispersion signal from. Reference numeral 25 is a light source estimation unit that receives the sampled image data and estimates the light source. Reference numeral 26 is a light source estimation unit 25 and the image determination device 21, which receive the primary light source estimation result S1 and the GWA determination signal J, respectively, and perform the GWA determination. Primary light source estimation result S based on signal J
Reference numeral 27 denotes a comprehensive determination unit that processes 1 and outputs a secondary light source estimation result S2, and reference numeral 27 denotes a light source estimation result holding unit that retains the secondary light source estimation result S2 from the comprehensive determination unit 26.

The operation of the light source estimation device configured as described above will be described below. First, the image signal output from the color separation circuit through an image pickup device such as a CCD is captured by the sampling circuit 22 according to an appropriate sampling rule, and sent to the light source estimation unit 25 and the dispersion calculation unit 23. The light source estimation unit 25 uses the input image data IS
In response to ((RGB), (Y, RY, BY), etc.), the image data average IS ave is calculated, for example, while the data is evaluated, and the light source color stored inside is calculated. The IS ave is compared, and the nearest light source is used as the estimation result, and the primary light source estimation result S1 is output. Also,
The variance calculation unit 23 of the image determination device 21 receives the input image data IS ((RGB), (Y, RY, BY), etc.) and, in some cases, evaluates the data while performing color evaluation. Degree space For example, (RY) / Y, as shown in FIG.
The image data variance SGM, which is the vertical variance with respect to the light source line in the chromaticity space represented by (BY) / Y, is calculated in the same manner as in the first embodiment.

On the other hand, the threshold value processing section 24 has a variance calculation section 23.
The image data variance SGM from is received and compared with the threshold value θ stored inside. When SGM <θ, J = GWA is established (OK) In other cases, J = GWA is not established (NO) (however, After standing up, at least once, SGM
Until <θ, in particular, J = OK), and the GWA determination signal J is output. The comprehensive determination unit 26 includes the light source estimation unit 25.
Primary light source estimation result S1 from G and G from the threshold processing unit 24
Upon receiving the WA determination signal J, when J = OK, S2 = S1 and when J = NO, S2 = determination is not possible, and the secondary light source estimation result S2 is output. The light source estimation result holding unit 27 receives the secondary light source estimation result S2 from the comprehensive determination unit 26, and when S2 ≠ determination is not possible S f = S2 S buf = S2 S2 = when determination is not possible S f = S buf S buf = S buf, the secondary light source estimation result is held in S buf, and the final light source estimation result S f is output.

As described above, according to the second embodiment,
G based on the vertical dispersion of the image data with respect to the light source line
By determining whether the WA is established, the light source determination when the GWA is not established, which is likely to make an error in the light source estimation, is discarded. Therefore, it is possible to realize a light source estimation device with few errors as a whole.

(Embodiment 3) Next, a third embodiment of the present invention will be described in which another embodiment of the image judging apparatus is used as a light source estimating apparatus. FIG. 3 is a block diagram showing the configuration of the light source estimation device in the third embodiment of the present invention. In FIG. 3, reference numeral 31 denotes an image determination device, which includes a sampling circuit 32 for obtaining image data suitable for image determination from color-separated image signals, an axis parameter calculation unit 33 that determines a dispersion axis direction from the image data, A dispersion calculator 34 that receives the image data and a signal relating to the direction of the blackbody radiation curve of FIG. 5 from the axis parameter calculator 33 and calculates the vertical dispersion of the color signals.
And a chromatic dispersion signal from the dispersion calculation unit 34, and compares the chromatic dispersion signal with a threshold value set internally. If the dispersion is smaller than the threshold value, GWA is established, and otherwise, a threshold processing unit 35 is output. It has and. Reference numeral 36 denotes a light source estimation unit that receives the image data and estimates the light source, and 37 receives the primary light source estimation result S1 and the GWA determination signal J from the light source estimation unit 36 and the image determination device 31, respectively, and outputs them as the GWA determination signal J. Reference numeral 38 is a comprehensive determination unit that processes the primary light source estimation result S1 and outputs a secondary light source estimation result S2, and 38 is a light source estimation result holding unit that retains the secondary light source estimation result S2 from the comprehensive determination unit 37. is there.

The operation of the light source estimation device having the above-described structure will be described below. First, the image signal output from the color separation circuit through an image pickup device such as a CCD is taken in by the sampling circuit 32 according to an appropriate sampling rule, and the light source estimation unit 36 and the axis parameter calculation unit 33 and the dispersion calculation unit 34 of the image determination device 31. Sent to.
The light source estimation unit 36 receives the input image data IS ((RG
B), (Y, RY, BY), etc.), the image data average IS ave is calculated, for example, while the data is evaluated depending on the case. The ave is compared, and the light source estimation result S1 is output with the closest light source as the estimation result. Further, the axis parameter calculation unit 33 of the image determination device 31 receives the image signal, determines the dispersion axis direction in the black body radiation curve based on the image data average value IS ave, and outputs the axis parameter. The variance calculator 34 receives the axis parameters from the axis parameter calculator 33 and the input image data IS ((RGB),
(Y, R-Y, B-Y, etc.), the image data variance SGM, which is the vertical variance with respect to the blackbody radiation curve in the chromaticity space of the data, is calculated while evaluating the data in some cases. .. The threshold value processing means 35 receives the image data variance SGM from the variance calculator 34 and compares it with the threshold value θ stored inside. When SGM <θ, J = GWA is established (OK), otherwise, J = GWA not established (NO) (However, at least once after starting up, SGM
Until <θ, in particular, J = OK), and the GWA determination signal J is output. The comprehensive determination unit 37 includes the light source estimation unit 36.
Light source estimation result S1 from GWA from the threshold processing unit 35
Upon receiving the determination signal J, when J = OK, S2 = S1 and when J = NO, S2 = determination is impossible, and the secondary light source estimation result S2 is output. The light source estimation result holding unit 38 receives the secondary light source estimation result S2 from the comprehensive determination unit 37, and when S2 ≠ determination is not possible S f = S2 S buf = S2 S2 = when determination is not possible S f = S buf S buf = S buf, the secondary light source estimation result is held in S buf, and the final light source estimation result S f is output.

As described above, according to the third embodiment,
Since the axis parameter calculation unit 33 obtains the dispersion axis direction in the black body radiation curve of the chromaticity space, the accuracy of calculation of the vertical fraction increases. Then, based on the vertical distribution of the image data, G
By determining whether the WA is established, the light source determination when the GWA is not established, which is likely to make an error in the light source estimation, is abandoned. Therefore, it is possible to realize a light source estimation apparatus with fewer errors as a whole.

(Embodiment 4) Next, a fourth embodiment of the present invention will be described in which another embodiment of the image judging apparatus is used as a light source estimating apparatus. FIG. 4 is a block diagram showing the configuration of the light source estimation device in the fourth embodiment of the present invention.
In FIG. 4, reference numeral 41 denotes an image determination device, which includes a sampling circuit 42 for obtaining image data suitable for image determination from color-separated image signals, and an average for receiving the image data and calculating an average IS ave of the image data. The direction of the black body radiation curve is calculated from the calculation unit 43, the axis parameter calculation unit 44 that receives the image data average IS ave from the average calculation unit 43 and determines the dispersion axis direction, and the sampled image data and the axis parameter calculation unit 44. And a threshold value set internally by receiving the chromatic dispersion signal from the dispersion calculating unit 45,
A threshold processing unit 46 that outputs GWA when the variance is smaller than the threshold and outputs otherwise when the variance is less than the threshold. Reference numeral 47 denotes an average light source estimation unit that receives the image data average IS ave of the average calculation unit 43 and estimates the light source. Reference numeral 48 denotes the primary light source estimation result S1 and the GWA determination signal from the average light source estimation unit 47 and the image determination device 41, respectively. J, and processes the primary light source estimation result S1 based on the GWA determination signal J
It is a comprehensive determination unit that outputs the next light source estimation result S2,
Is a light source estimation result holding unit that holds the secondary light source estimation result S2 from the comprehensive determination unit 48.

The operation of the light source estimation device configured as described above will be described below. First, the image signal output from the color separation circuit through an image pickup device such as a CCD is captured by the sampling circuit 42 according to an appropriate sampling rule, and sent to the average calculation unit 43. The average calculator 43 receives the input image data IS ((RGB),
(Y, RY, BY), etc.), the image data average IS a
Calculate ve. The average light source estimation unit 47 includes an average calculation unit 43.
Upon receiving the image data average IS ave from, the light source color stored internally is compared with IS ave, and the light source estimation result S1 is output with the closest light source as the estimation result. Further, the axis parameter calculation unit 44 of the image determination device 41 finds a point on the black body radiation curve closest to the image data average IS ave from the average calculation unit 43, and sets the normal direction of the point as the vertical dispersion axis. To output the axis parameters. Distributed calculation unit 4
Reference numeral 5 denotes the image data IS ((RGB), (Y, RY,
(B-Y), etc.), the image data dispersion S, which is the vertical dispersion with respect to the normal line of the blackbody radiation curve in the chromaticity space of the data, is evaluated while the data is evaluated.
Calculate GM. The subsequent processing is the same as in the third embodiment.

As described above, according to the fourth embodiment,
Since the axis parameter calculation unit 44 obtains the closest point on the black body radiation curve from the image data average IS ave and outputs the axis parameter with the normal direction of that point as the vertical dispersion axis, more accurate vertical dispersion data is obtained. Obtainable. By determining the establishment of GWA based on the vertical dispersion of the image data, the light source determination when the GWA is not established, which is easy to make an error in the light source estimation, is discarded. Therefore, it is possible to realize a light source estimation apparatus with fewer errors as a whole. You can

In the third and fourth embodiments, the processing of the axis parameter calculation units 33 and 44 has a considerably large calculation load, so the accuracy is lowered, but the chromaticity space is divided into appropriate regions. It is possible to adopt a simple means of allocating an axis parameter for each area and determining the axis parameter by calculating in which area the image data average falls.

[0047]

As described above, according to the present invention, the sampling means for sampling the color-separated image signal to obtain the image data suitable for the image determination, and the statistical quantity representing the characteristics of the distribution from the sampled image data. Since it is provided with a means for calculating and a means for determining the quality of the image based on the calculated statistical amount, the statistical processing of the image data can be performed correctly.

According to the present invention, by providing the variance calculating means as the means for calculating the statistic and the threshold processing means as the means for judging the quality of the image, it is possible to determine whether or not the GWA is established in the photographed image. It can be judged and the color balance can be adjusted correctly.

According to the present invention, the GWA determination can be performed more accurately by calculating the vertical dispersion for the light source line approximated to the black body radiation curve in the dispersion calculating means.

According to the present invention, the GWA determination can be performed more accurately by calculating the vertical dispersion with respect to the black body radiation curve itself in the dispersion calculating means.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image determination device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a light source estimation device using an image determination device according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing the configuration of a light source estimation device using another image determination device according to the third embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a light source estimation device using still another image determination device according to a fourth embodiment of the present invention.

FIG. 5 is a conceptual diagram showing a blackbody radiation curve and a light source line in a chromaticity space.

[Explanation of symbols]

 11 Sampling Circuit 12 Variance Calculating Section 13 Threshold Processing Section 21 Image Judgment Device 22 Sampling Circuit 23 Variance Calculating Section 24 Threshold Processing Section 25 Light Source Estimating Section 26 Total Judgment Section 27 Light Source Estimation Result Holding Section 31 Image Judging Device 32 Sampling Circuit 33 Axis Parameter Calculation unit 34 Variance calculation unit 35 Threshold processing unit 36 Light source estimation unit 37 Total determination unit 38 Light source estimation result storage unit 41 Image determination device 42 Sampling circuit 43 Average calculation unit 44 Axis parameter calculation unit 45 Variance calculation unit 46 Threshold processing unit 47 Average Light source estimation unit 48 Comprehensive determination unit 49 Light source estimation result storage unit

Claims (5)

[Claims] 1. A sampling means for sampling color-separated image signals to obtain image data suitable for image determination, a means for calculating a statistic representing characteristics of distribution of the sampled image data, and a calculated means. An image determination device comprising means for determining the quality of an image based on a statistic. 2. The means for calculating a statistic is a variance calculating means for calculating the variance of sampled image data, and the means for determining the quality of an image determines the quality of a threshold of the calculated statistic. The image determination device according to claim 1, which is a threshold value processing unit for performing. 3. The image determining apparatus according to claim 2, wherein the variance of the image data is a variance of the image data in the chromaticity space. 4. The image determination apparatus according to claim 3, wherein the dispersion in the chromaticity space is vertical dispersion with respect to the light source line approximated to the black body radiation curve. 5. The image determination device according to claim 3, wherein the dispersion in the chromaticity space is vertical dispersion with respect to the black body radiation curve.