JP2004088602A - Method and apparatus for determining fluorescent lamp light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine whether a light source which illuminates an object is a fluorescent lamp or not. <P>SOLUTION: In the fluorescent lamp light source determining method, when photographing the object while illuminating it with an illumination light source, an image photographed by absorbing light in a predetermined bright line area out of light from the object and an image photographed without absorbing the light of the predetermined bright line area are acquired, an exposure difference is calculated for each pixel of each image and by using the exposure difference for each pixel, it is determined whether the illumination source is a fluorescent lamp or not. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to the technical field of a light source type discrimination method for discriminating the type of a light source illuminating a subject, and particularly relates to a fluorescent lamp light source determination method and apparatus for determining whether a light source is a fluorescent lamp.
[0002]
[Prior art]
In color reproduction of photographs and video images, the color of the light source illuminating the subject has a great influence on the color reproduction of the reproduced image. For example, the light coming from a subject illuminated with a tungsten lamp contains a lot of redness, and an image of the subject illuminated with a tungsten lamp is reproduced in the same way as an image taken under normal daylight. In this case, the image becomes very reddish. In other words, even if the light coming from the subject has actually changed, if the light quality of the illumination light source is reproduced at a constant level, the color of the illumination light source is directly reflected in the reproduced image, which is inconvenient for the human eye. It looks natural.
[0003]
Thus, when a subject is photographed with a camera or the like under a certain illumination light source, the color information of the acquired image may differ greatly depending on what light source the subject is illuminated with. Of course, when the color temperature of the illumination light source is different, even when the color temperature of the illumination light source is almost the same, shooting under normal daylight when a certain type of fluorescent lamp and a specific silver halide photosensitive material are combined The color balance may be different from the case where it is done.
[0004]
For this reason, when photographing a subject, knowing in advance what light source the subject is illuminated with may be very useful in the subsequent color balance adjustment. From such a viewpoint, various methods for estimating the color of the illumination light source have been proposed.
[0005]
[Problems to be solved by the invention]
However, many of the conventional methods for estimating the color of the illumination light source estimate the color temperature of the illumination light source, and this has the problem that the illumination type cannot be determined when the color temperatures are equal. It was.
On the other hand, fluorescent lamps, in particular, have a spectral distribution characteristic that is significantly different from that of so-called daylight, and they are obtained in different colors when combined with some silver salt photosensitive materials and CCD sensors. There has been a strong desire to separate light sources other than lamps.
[0006]
The present invention has been made in view of the above-described conventional problems, and provides a fluorescent lamp light source determination method and apparatus capable of determining whether a light source illuminating a subject is a fluorescent lamp or not. This is the issue.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problem, the first aspect of the present invention is that when photographing a subject by illuminating the subject with an illumination light source, the light from the subject is photographed by absorbing light in a predetermined bright line region. An image and an image captured without absorbing the light in the predetermined bright line area are obtained, an exposure amount difference for each pixel of each image is calculated, and the exposure amount difference for each pixel is used. A fluorescent lamp light source determination method is provided that determines whether or not the illumination light source is a fluorescent lamp.
[0008]
Further, when the average value of the exposure amount difference for each pixel exceeds a predetermined threshold value, it is determined that the illumination light source is a fluorescent lamp, and the average value of the exposure amount difference for each pixel is a predetermined value. If the threshold is not exceeded, it is preferable to determine that the illumination light source is not a fluorescent lamp.
[0009]
Similarly, in order to solve the above-described problem, the second aspect of the present invention absorbs light in a predetermined bright line region out of light from the subject when the subject is illuminated with an illumination light source. Means for obtaining an image photographed without absorbing light in the predetermined bright line region, means for calculating an exposure amount difference for each pixel of each image, and the exposure amount difference And a light source determination unit that determines whether or not the illumination light source is a fluorescent lamp.
[0010]
In addition, the light source determination unit includes a unit that calculates an average value of the exposure amount difference for each pixel and a unit that compares the average value with a predetermined threshold value, and the average value exceeds the threshold value. Preferably, it is determined that the illumination light source is a fluorescent lamp, and if the average value does not exceed the threshold value, the illumination light source is not a fluorescent lamp.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a fluorescent lamp light source determination method and apparatus according to the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
[0012]
FIG. 1 is a block diagram showing a schematic configuration of a fluorescent lamp light source determination apparatus that executes a fluorescent lamp light source determination method according to the present invention.
As shown in FIG. 1, the fluorescent lamp light source determination device 10 determines a light source type of the illumination light source 2 from image data obtained by imaging the subject 4 illuminated by the illumination light source 2 by the imaging means 6. And comprises an exposure amount calculation means 12, an exposure amount difference calculation means 14, and a light source type determination means 16.
The light source type determination unit 16 includes an average exposure amount difference calculation unit 18 and a comparison unit 20.
[0013]
As the illumination light source 2, the fluorescent light source determination device 10 of the present invention determines the type of the light source (particularly, whether or not it is a fluorescent lamp). As will be described later, various fluorescent lamps and tungsten lamps are used. Or various light sources other than fluorescent lights, such as a daylight, are used.
The subject 4 is also not particularly limited, but it is preferable to use a color chart or the like with a clear color for determining the light source type.
[0014]
Before describing each means constituting the photographing means 6 and the fluorescent light source determination device 10, the principle of the fluorescent light source determination method of the present invention will be described.
FIG. 2 shows the spectral distribution of a general fluorescent lamp, and FIG. 3 shows the spectral distribution of a three-wavelength fluorescent lamp. As can be seen from FIGS. 2 and 3, both the general fluorescent lamp and the three-wavelength fluorescent lamp have bright lines in the same region where the wavelength is around 430 or 545. FIG. 4 shows the waveform of the first principal component obtained as a result of applying principal component analysis to the spectral distribution of daylight and fluorescent lamp.
[0015]
Comparing FIG. 4 with FIGS. 2 and 3, it can be seen that the concave portion of the waveform of the first main component shown in FIG. 4 corresponds to the bright line portion of the fluorescent lamp.
From this, it can be said that it is a feature of the fluorescent lamp to have such a dent of the waveform of FIG. 4 or a peak of the waveform of FIG. 2 (or FIG. 3). Therefore, the method of the present invention is to determine whether or not the lamp is a fluorescent lamp based on whether or not there is a mountain corresponding to the bright line peculiar to the spectral distribution waveform of the fluorescent lamp.
[0016]
That is, according to the method of the present invention, among the light from the subject, the image captured by absorbing the light in the region where the fluorescent lamp has the bright line (with the light after the absorption), and the fluorescent lamp displays the bright line. To obtain a photographed image without absorbing the light of the area it has (with the light containing the light of the wavelength area), and determine the presence of a mountain corresponding to the bright line portion from the exposure amount difference of each image Thus, it is determined whether or not the illumination light source is a fluorescent lamp.
[0017]
For this reason, for example, when trying to detect a bright line portion having a wavelength of around 545, a filter having absorption in this wavelength region is photographed while being mounted in front of the camera, and this filter is not mounted (or Two images may be taken by attaching a filter having no absorption in this wavelength region. As a result, an image captured by absorbing light in the bright line region near the wavelength 545 and an image captured without absorption can be obtained.
[0018]
In addition, when there is no filter having absorption only in a specific wavelength region as described above, for example, as shown in FIG. 5, a filter that absorbs (cuts) light having a wavelength of about 550 or less indicated by a broken line, Images may be taken using a shifted filter that absorbs light having a wavelength of about 530 or less as indicated by a solid line, and each exposure amount may be calculated in the obtained image to take the difference.
[0019]
Alternatively, two filters as shown in FIG. 5 may be combined and used as one filter.
Further, if there is one filter having absorption in each of the three bright line portions of the three-wavelength fluorescent lamp as shown in FIG. 3, it is possible to simultaneously detect the three bright line portions.
[0020]
As described above, the imaging unit 6 absorbs the image of the light from the subject 4 that is captured by absorbing the light in the region where the fluorescent lamp has the bright line and the light in the region where the fluorescent lamp has the bright line. It is necessary to be able to obtain a photographed image without using it.
For example, the imaging means 6 is preferably exemplified by a filter in which a filter having absorption in the bright line region of a fluorescent lamp is attached in front of a CCD camera, and a filter having a filter having no absorption in this bright line region. This filter can be removed and replaced with a different type of filter, or if the filter can be removed and taken without a filter, multiple images can be taken with a single camera. it can.
In addition, a plurality of CCD sensors having sensitivity in different wavelength regions may be used as the imaging unit 6 without using such a filter.
[0021]
The exposure amount calculation means 12 receives from the imaging means 6 an image captured by absorbing light in a region where the fluorescent lamp has a bright line out of light from the subject 4, and light in a region where the fluorescent lamp has a bright line. An image captured without absorption is received, and an exposure amount is calculated from the value of each pixel of each image.
Further, the exposure amount difference calculating means 14 calculates a difference in exposure amount for each pixel of each image.
[0022]
Further, the average exposure amount difference calculating unit 18 constituting the light source type determining unit 16 adds the exposure amount difference for each pixel, which has been stopped as described above, with respect to all the pixels of the image, and calculates the sum of the exposure amount differences. This is divided by the total number of pixels to calculate the average exposure amount difference.
Moreover, the comparison means 20 which comprises the light source kind determination means 16 compares the average exposure amount difference calculated above with a predetermined threshold value. As a result of this comparison, when the average exposure amount difference exceeds the threshold value, In this case, it is determined that the illumination light source 2 is a fluorescent lamp. If the threshold value is not exceeded, it is determined that the illumination light source 2 is not a fluorescent lamp.
[0023]
Hereinafter, the operation of the present embodiment will be described along the flowchart of FIG.
First, in step 100 of FIG. 6, the subject 4 is illuminated with the illumination light source 2, and an image is taken by the imaging means 6 with a filter having absorption in a specific bright line area (fluorescent lamp bright line area). An image is photographed by an imaging means 6 such as a CCD camera equipped with a filter having no absorption in the region (or not fitted with a filter), and two types of images are acquired. The image photographed by the imaging means 6 is sent to the exposure amount calculation means 12 of the fluorescent lamp light source determination device 10.
[0024]
Next, in step 110, the exposure amount calculation means 12 calculates the exposure amount for each pixel from the value of each pixel for each image.
Next, in step 120, the exposure amount difference calculating means 14 calculates an exposure amount difference for each pixel.
[0025]
Next, in step 130, the average exposure amount difference calculating means 18 adds the exposure amount differences for each pixel for all the pixels constituting the image, calculates the sum, and divides it by the total number of pixels to obtain one pixel. The average exposure amount difference per unit is calculated.
Next, in step 140, the comparison unit 20 compares the average exposure amount difference per pixel obtained above with a predetermined threshold value.
As a result of comparison, if the average exposure amount difference exceeds the threshold value, it is determined in step 150 that the illumination light source 2 is a fluorescent lamp, and if the average exposure amount difference does not exceed the threshold value. In step 160, it is determined that the illumination light source 2 is not a fluorescent lamp.
[0026]
As described above, according to the present embodiment, it is possible to determine whether the illumination light source is a fluorescent lamp based on, for example, image data captured using a filter having absorption in a certain bright line region. It becomes. In addition, by transmitting information on the light source type to a subsequent image processing unit, it is possible to perform appropriate color processing on the image thereafter.
[0027]
Hereinafter, more specific examples will be described.
(Example)
As the imaging means 6, a monochrome CCD camera (DALSA, CA-DA-1024A) and Kodak's Latin filter No. 16 or No. 21 was used, and the subject 4 was a color checker manufactured by GretagMacbeth, and photographed under various illumination sources as described later.
The spectral distribution of the Latin filter is as shown in FIG. 16 and the broken line graph is No. 16. 21.
[0028]
The exposure amount when using each filter was adjusted in advance so that the same exposure amount was obtained under daylight with a color temperature of 5500K.
Each image signal G (8-bit signal from 0 to 255) of the photographed image was converted into an exposure amount g by the following equation (1).
g = [{(G / 255.0) +0.099} /1.099] ^{1 / 0.45} (1)
[0029]
After that, the Latin filter No. 16 and a Latin filter No. 21 is used to calculate the difference value of the exposure amount g of each pixel of the image photographed using 21 and add it for all the pixels and divide by the total number of pixels to obtain an average value per pixel, which is Δgm It was.
Using the nine types of fluorescent lamps A to I and four types of non-fluorescent lamps (tungsten lamp, sun, bright shade, strobe) as the illumination light source, the above Δgm was determined.
[0030]
The result is shown in FIG. As can be seen from FIG. 7, Δgm is a positive value for fluorescent lamps A to I, but Δgm is a negative value for non-fluorescent lamps. There is a difference between non-fluorescent lamps.
Therefore, in this case, it was possible to determine whether or not the lamp is a fluorescent lamp by taking 0 as a threshold value.
[0031]
As mentioned above, although the fluorescent lamp light source determination method and apparatus of the present invention have been described in detail, the present invention is not limited to the above embodiment, and various improvements and modifications can be made without departing from the gist of the present invention. Of course, changes may be made.
[0032]
【The invention's effect】
As described above, according to the present invention, of the light from the subject illuminated by the illumination light source, the image captured by absorbing the light in the region where the fluorescent lamp has the bright line, and the fluorescent lamp displays the bright line. It is possible to determine whether the illumination light source is a fluorescent lamp based on the exposure amount difference based on the image data of an image taken without absorbing the light of the area it has.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a fluorescent lamp light source determination apparatus that executes a fluorescent lamp light source determination method according to the present invention.
FIG. 2 is a diagram showing a spectral distribution of a general fluorescent lamp.
FIG. 3 is a diagram showing a spectral distribution of a three-wavelength fluorescent lamp.
FIG. 4 is a diagram showing a first principal component obtained by applying principal component analysis to spectral distributions of daylight and fluorescent lamp.
FIG. 5 is a diagram showing spectral transmittances of filters having different absorption wavelength bands.
FIG. 6 is a flowchart showing the operation of the present embodiment.
FIG. 7 is an explanatory diagram showing an average exposure amount difference for various light sources calculated in a specific embodiment of the present invention.
[Explanation of symbols]
2 Illumination light source 4 Subject 6 Imaging means 10 Fluorescent lamp light source determination device 12 Exposure amount calculation means 14 Exposure amount difference calculation means 16 Light source type determination means 18 Average exposure amount difference calculation means 20 Comparison means

Claims (4)

When illuminating a subject with an illumination light source and taking a picture, the image taken by absorbing the light in the predetermined bright line area out of the light from the subject and the picture taken without absorbing the light in the predetermined bright line area Get images and
Calculate the exposure amount difference for each pixel of each image,
A fluorescent lamp light source determination method, comprising: determining whether or not the illumination light source is a fluorescent lamp using an exposure amount difference for each pixel. When the average value of the exposure amount difference for each pixel exceeds a predetermined threshold value, it is determined that the illumination light source is a fluorescent lamp, and the average value of the exposure amount difference for each pixel exceeds the predetermined threshold value. The fluorescent lamp light source determination method according to claim 1, wherein if it does not exceed, the illumination light source is determined not to be a fluorescent lamp. When photographing an object with an illumination light source, an image photographed by absorbing light in a predetermined bright line region out of light from the subject and photographed without absorbing light in the predetermined bright line region Means for acquiring images;
Means for calculating an exposure amount difference for each pixel of each image;
A fluorescent light source determination device, comprising: a light source determination unit configured to determine whether the illumination light source is a fluorescent lamp from the exposure amount difference. The light source determination means includes means for calculating an average value of the exposure amount difference for each pixel, and means for comparing the average value with a predetermined threshold, and when the average value exceeds the threshold, The fluorescent light source determination device according to claim 3, wherein the illumination light source is determined to be a fluorescent lamp, and if the average value does not exceed the threshold value, the illumination light source is determined not to be a fluorescent lamp.

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