JP2001086354A - Image-processing method and image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire an image which is seen similarly as an image that is photographed under a desired light source, on the basis of a spectral image obtained from an image forming medium, even though an object actively emitting light every due to the illumination of light such as fluorescence is contained in the image-forming medium. SOLUTION: A detecting part 4 detects an image formed on an image-forming medium 1, while a light source part 3 capable of switching a plurality of light sources switches light sources whose spectral energy distribution is known. The part 4 changes transmission wavelength areas of light emitted from the medium 1, obtains a spectral image representing a plurality of images in each wavelength in every light source and further obtains the spectral reflectance of the spectral image. The spectral energy distribution of a desired light source is expressed by performing weighted addition of the spectral energy distributions of a plurality of light sources of the part 3, the spectral reflectance of the spectral image in each light source is subjected to weighted addition by the weight coefficient at this time, spectral reflectance under the desired light source is obtained, and an image which is seen similarly as an image that is photographed under the desired light source is obtained on the basis of the obtained spectral reflectance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image obtained by irradiating an image forming medium containing a substance such as fluorescent light with light, and to provide the same appearance as when photographed under a desired light source. The present invention relates to an image processing method and an apparatus for obtaining an image having the same.

[0002]

2. Description of the Related Art A plurality of spectral images representing color information of a subject for each wavelength are obtained by photographing the subject using a multi-band camera which performs photographing through, for example, eight types of filters having different transmission wavelength ranges. A technique for measuring the spectral reflectance of a subject from this image has been proposed. By using such a multi-band camera, the spectral reflectance of the subject can be measured with high accuracy. Therefore, even when the subject is photographed using many colors such as a painting, A highly accurate image can be obtained without impairing color reproducibility.

Here, in a spectral image obtained by a multi-band camera, the data value of each pixel is (spectral reflectance of subject) × (spectral energy of light source). Therefore, in order to obtain the spectral reflectance of the subject, shooting is performed by including an object such as a Macbeth chart having a known spectral reflectance in the scene together with the subject, and the data value corresponding to this object is calculated using the known spectral reflectance. Then, the spectral reflectance of the subject in the image can be obtained by calculating the spectral energy of the light source by dividing by the spectral power and by normalizing the data value of each pixel by the spectral energy corresponding to each wavelength. If the spectral energy distribution of the light source is known, the spectral reflectance of the subject can be obtained without using the Macbeth chart as described above.

If the spectral reflectance is obtained as described above,
It is also easy to obtain an image having the same appearance as when the image is captured under a desired light source different from the time of the image capturing. That is, if the spectral reflectance obtained for each pixel is multiplied by the spectral energy of the desired light source, the value becomes the same data value as when the image was captured under that light source. It is possible to obtain an image having the same appearance as when the image is taken under a light source.

Further, not only a multi-band camera,
Even in an image reading device such as a scanner, when reading an image from an image forming medium, a plurality of filters representing color information of an image for each wavelength is detected by detecting read light through a plurality of filters having different transmission wavelength ranges. A spectral image can be obtained, and the same appearance as when photographing is performed under a desired light source different from the light source when the image formed on the image forming medium is obtained in the same manner as described above. Images can be acquired.

[0006]

Incidentally, the image formed on the image forming medium containing a fluorescent substance and the image formed on the image forming medium with the fluorescent ink have different excitation states of the fluorescent light depending on the spectral energy distribution of the light source. Therefore, the data value of each pixel changes according to the spectral energy distribution of the light source. For this reason, as described above, even if a plurality of spectral images representing the color information of the image for each wavelength are obtained, if fluorescent light is contained in the image forming medium or the image, a desired light source different from that at the time of shooting may be used. It is not possible to obtain an image having the same appearance as when shooting.

The present invention has been made in view of the above circumstances. Even when a substance such as fluorescent light is contained in an image forming medium, the same effect as when photographing under a desired light source is obtained. It is an object of the present invention to provide an image processing method and apparatus capable of obtaining an image having a visible appearance.

[0008]

SUMMARY OF THE INVENTION An image processing method according to the present invention is directed to an image forming medium containing a substance which actively emits light energy upon irradiation with light, the light emitted from a plurality of light sources having different spectral energy distributions from each other. And irradiate
Light that carries an image formed on the image forming medium is generated from the image forming medium, the light is photoelectrically detected while switching a filter capable of changing a transmission wavelength range, and color information of the image is previously detected. Obtaining a plurality of spectral images for each of a plurality of predetermined wavelengths determined for each of the light sources, and obtaining spectral reflectances of all pixels of the spectral image for each of the light sources based on the plurality of spectral images. The spectral energy distribution corresponding to the plurality of predetermined wavelengths of the desired light source is calculated by weighting the spectral energy distribution of each light source by weighting and adding, and the weight coefficient is used to calculate each of the light sources. The spectral reflectance of all pixels of the spectral image is weighted and added for each corresponding pixel to obtain the spectral reflectance of the image under the desired light source. It is intended.

Here, as the "substance which actively emits light energy by irradiation of light", various substances such as a fluorescent substance which emits light excited by irradiation of light and a substance which emits heat by irradiation of light are employed. can do.

[0010] The "image forming medium containing a substance" means that not only an image is formed on the image forming medium by the above substance, but also a printing paper containing a fluorescent substance to make the color appear whiter. This also means that the substance is contained in the image forming medium itself.

The “plurality of light sources” is preferably three or more, and more preferably five or more. When five types of light sources are used, for example, it is preferable to specifically include ultraviolet light, near ultraviolet light, daylight of about 6500K, daylight of about 2800K, and a fluorescent lamp.

The "light carrying an image formed on the image forming medium" may be reflected light of light applied to the image forming medium, or transmitted light if the image forming medium is a light transmitting medium. It may be.

As the "filter capable of changing the transmission wavelength range", a plurality of filters having different transmission wavelength ranges are arranged on a disk, and by rotating the disk, different filters are provided on the optical path of the light carrying the image. , A liquid crystal tunable filter capable of arbitrarily changing a transmission wavelength range according to an applied voltage, or the like.

The term "plurality of spectral images" refers to spectral images obtained by photographing in six or more wavelength ranges.

In the image processing method according to the present invention, it is preferable that the plurality of light sources include a light source having substantially the same spectral energy distribution as the desired light source.

An image processing apparatus according to the present invention irradiates an image forming medium containing a substance which actively emits light energy by light irradiation with light emitted from a plurality of light sources having mutually different spectral energy distributions. Light that carries an image formed on the image forming medium is generated from the image forming medium, the light is photoelectrically detected while switching a filter capable of changing a transmission wavelength range, and color information of the image is determined in advance. Image acquisition means for acquiring, for each of the light sources, a plurality of spectral images represented for each of the plurality of predetermined wavelengths, based on the plurality of spectral images, and spectral reflectances at all pixels of the spectral image for each of the light sources Spectral reflectance obtaining means for obtaining the spectral energy distribution corresponding to the plurality of predetermined wavelengths of the desired light source, and weighting the spectral energy distribution of each light source. Weighting factor calculation means for calculating a weighting factor when representing by adding and subtracting, weighting and adding the spectral reflectance of all the pixels of each spectral image of each light source for each corresponding pixel by the weighting factor, Adding means for acquiring the spectral reflectance of the image under the desired light source.

In the image processing apparatus according to the present invention, it is preferable that the plurality of light sources include a light source having substantially the same spectral energy distribution as the desired light source.

[0018]

According to the present invention, a plurality of color information representing color information of an image formed on an image forming medium containing a substance which actively emits light energy by light irradiation is provided for each of a plurality of predetermined wavelengths. A spectral image is obtained for each light source, and based on the plurality of spectral images, spectral reflectances of all pixels of the spectral image for each light source are obtained. here,
Since the spectral energy distribution corresponding to a plurality of predetermined wavelengths of the desired light source can be represented by weighting and adding the spectral energy distribution of each light source, a weight coefficient for performing the weighting addition is calculated. Then, by adding the weighted coefficients to the spectral reflectances of all the pixels of each spectral image of each light source for each corresponding pixel, the spectral reflectance of the image formed on the image forming medium under the desired light source is obtained. Can be obtained. Therefore, by multiplying the spectral reflectance by the desired spectral energy distribution of the light source, a substance such as a fluorescent substance that actively emits light energy by light irradiation is included in the image forming medium. However, the pixel value represented by the substance under a desired light source can be estimated, and an image having the same appearance as that of the image captured under the desired light source can be obtained.

If a plurality of light sources include a light source having substantially the same spectral energy distribution as a desired light source, the weighting coefficient for performing the weighted addition becomes simple, so that the calculation is performed. Can be done at high speed.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic block diagram showing a configuration of a photographing apparatus to which an image processing apparatus according to an embodiment of the present invention is applied. As shown in FIG. 1, the photographing apparatus includes a holding unit 2 made of a transparent plate or the like for holding an image forming medium 1, and a holding unit 2.
Light source unit 3 for irradiating light to image forming medium 1 held in
A detecting unit 4 that photoelectrically detects light emitted from the light source unit 3 and reflected on the image forming medium 1 to obtain image data S0 representing an image formed on the image forming medium 1;
A calculation unit 5 that performs various calculations described below based on the image data S0 detected in step 1 and obtains image data S1 representing an image having the same appearance as that obtained when photographed under a desired light source. A scanning unit (not shown) for moving the light source unit 3 and the detection unit 4 in the direction of the arrow Y with respect to the holding unit 2 to scan light emitted from the light source unit 3 over the entire surface of the image forming medium 1; Is provided. In the present embodiment, the detection unit 4 is considered as a multi-band camera.

An image is formed on the image forming medium 1, and this image is partially or entirely drawn with fluorescent ink. The fluorescent substance contained in the fluorescent ink is shown in FIG.
By absorbing light in the wavelength range shown in FIGS.
It is possible to use one that generates fluorescence in the wavelength range shown in FIGS. Note that FIGS. 2 and 3 show the characteristics of nine types of fluorescent substances.

In the present embodiment, the light source unit 3 switches the eight types of light sources L1 to L8, and irradiates the light emitted from each of the light sources L1 to L8 to the image forming medium 1 held in the holding unit 2. . As the light sources L1 to L8, those including a light source that emits ultraviolet light, near ultraviolet light, daylight of about 6500K, daylight of about 2800K, and light of a fluorescent lamp are used. Further, it is assumed that the spectral energy distribution of light emitted from the light sources L1 to L8 is known.

As shown in FIG. 4, the detecting unit 4 as a multi-band camera is formed on the image forming medium 1 with a spectral filter 11 capable of changing the transmission wavelength range of light reflected on the image forming medium 1. An imaging device 12 such as a CCD camera that photoelectrically converts light carrying an image to obtain an electric signal representing the image; a conversion unit 13 that converts the electric signal obtained by the imaging device 12 into digital image data S0; , A spectral filter 11, an imaging device 12, and a control unit 14 for controlling the driving of the conversion unit 13. In the present embodiment, a liquid crystal tunable filter capable of arbitrarily changing a transmission wavelength range in a wavelength range of 400 to 720 nm is used as the spectral filter 11. In this embodiment, eight light sources L1 are used.
To L8 while changing the transmission wavelength range at intervals of 20 nm in the wavelength range of 410 to 710 nm, for example.
It is assumed that imaging is performed in six wavelength ranges, and image data S0 representing a total of 128 spectral images, 16 for each light source, is obtained. Further, the control unit 14 may have the function of the calculation unit 5.

Here, as the spectral filter 11, for example, a Varispec Tunable Filter manufactured by CRI can be used, and as the imaging device 12, for example, DALSA
CA-D4-1024A (pixel number 1024 × 1024, pixel size 12 × 12 microns, with PCI interface, monochrome) manufactured by Co., Ltd. can be used. When taking an image, an imaging lens (for example, Nikomart (f = 50 mm, F1.4)) and 40 mm
It is preferable to use a filter that cuts ultraviolet light of 0 nm or less and infrared light of 730 nm or more.

The calculation section 5 performs the calculation as follows. Here, the spectral energy distribution at the wavelength λs of the eight types of light sources L1 to L8 is S (k, λs) (where k = 1 to 8), and 1 obtained by the k-th light source.
Rij is the spectral reflectance of each pixel in the spectral image of FIG.
(K, λol) (where ij: pixel position, k = 1 to 8, λ
o: wavelength, l = 1 to 16; corresponding to a spectrum image). Here, the spectral energy distribution S of the light sources L1 to L8
The wavelength λs of (k, λs) is made to correspond to the wavelength of the spectrum image, and is hereinafter referred to as a spectral energy distribution S (k, λol) at the wavelength λol. The data value of each pixel in the spectral image is (spectral reflectance of each pixel) × (spectral energy distribution of the light source). Since the spectral energy distribution of the light source is known, the data value of each pixel is Is divided by the spectral energy distribution of the light source.

First, the spectral energy distribution So (λol) of the desired light source at the wavelength λol is calculated by dividing the spectral energy distribution S (k, λol) of the eight light sources L1 to L8 as shown in the following equation (1). Expressed by the sum of the loads. In addition,
It is assumed that the spectral energy distribution So (λol) and the spectral energy distribution S (k, λs) are normalized by the integrated value of energy as shown in the following equation (2).
By normalizing in this way, the weighting factor Ak in equation (1) can be set to a value smaller than 1.

[0028] _{So (λol) = Σ k Ak} · S (k, λol) (1) However, Ak: the weighting factor (k = 1~8, Ak ≧ 0 ) Σ k So (λol) = Σ k S (k , Λs) (2) In general, the relationship of the above equation (1) is not strictly established, and therefore the following equations (3) and (4) are minimum values min,
The weighting factor Ak is optimized and determined so as to be the maximum value max.

[0029] _{{Σ k So (λol) -Σ} k (Ak · S (k, λol)) 2} (3) Σ k (Ak) 2 (4) In addition, the spectral energy distribution So (λol) and spectral energy distribution Since S (k, λs) is normalized by the integrated value of energy as shown in the above equation (2), the value of equation (4) is obtained by converting the spectral energy distribution S (k, λs) into the spectral energy distribution So ( λol), it becomes 1 at the maximum. Further, the expression (4) is set to the maximum value max because the spectral energy distribution So (λ
ol), the spectral energy distribution So should be
Spectral energy distribution S having a value close to (λol)
This is because (k, λs) is used. Here, assuming that the equations (3) and (4) are to be simultaneously optimized, the weighting coefficient Ak is obtained by the simplex method so that the following equation (5) is set to the minimum value min.

｛Σ _k So (λol) −Σ _k (Ak · S (k, λol)) ² + ρ (1- _{k (Ak) ² )} (5) where ρ: a constant where the simplex method and Is a method for finding the minimum of a function having two or more independent variables, and using a simplex (geometric figure) to change the shape of a figure while using the vertices of the figure as independent variables. This is a method to find the minimum of the function. For the simplex method,
"Numerical Recipes in C [Japanese], WHPress
Translator Okumura et al., Technology Review Co., Ltd., August 2, 1994
5th, pp295-299).

The weighting factor A obtained as described above
k, the spectral reflectance of each pixel is weighted and added as shown in the following equation (6), and the spectral reflectance Roij (λ) of the image formed on the image forming medium 1 under a desired light source is obtained.
ol) is obtained for each wavelength corresponding to the spectral image.

Roij (λol) = ΣAk · Rij (k, λol) (6) As described above, when the spectral reflectance Roij (λol) of each pixel in the spectral image corresponding to each wavelength region is obtained, this spectral reflection is obtained. The ratio Roij (λol) is multiplied by the desired spectral energy distribution of the light source to obtain the pixel value of each pixel,
With this pixel value, it is possible to obtain image data S1 representing an image having the same appearance as when the image is captured under the desired light source.

Next, the operation of this embodiment will be described. FIG. 5 is a flowchart showing the operation of the present embodiment. First, the image forming medium 1 held by the holding unit 2 is irradiated with light while switching the light source of the light source unit 3.
The photoelectric conversion is performed on the light carrying the image formed on the image forming medium 1 while changing the transmission wavelength of the spectral filter 11 to obtain image data S0 representing the image (step S).
1). The image data S0 is input to the arithmetic unit 5, where
As described above, the weight coefficient Ak is calculated (step S
2), the spectral reflectance Roij (λol) is calculated (step S3). Then, the spectral reflectance Roij (λol)
Is multiplied by the desired spectral energy distribution of the light sources L1 to L8 to obtain image data S1 representing an image having the same appearance as when photographing under the desired light source (step S4). finish.

As described above, in the present embodiment, even when the image formed on the image forming medium 1 and the image is drawn with the fluorescent ink, the spectral reflectance represented by the above substance under a desired light source can be improved. Then, an image having the same appearance as an image obtained under a desired light source can be obtained based on the spectral reflectance.

In the above embodiment, the image formed on the image forming medium 1 is described as being drawn with fluorescent ink. However, even when the image forming medium 1 itself contains a fluorescent substance, The present invention can be applied in the same manner as described above.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram illustrating a configuration of a photographing apparatus to which an image processing apparatus according to an embodiment of the present invention is applied.

FIG. 2 is a graph showing a wavelength range of light absorbed by a fluorescent substance.

3 is a graph showing a spectral distribution of fluorescence emitted from the fluorescent ink shown in FIG.

FIG. 4 is a block diagram illustrating a configuration of a detection unit.

FIG. 5 is a flowchart showing the operation of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming medium 2 Holding part 3 Light source part 4 Detection part 5 Operation part

Continued on front page F term (reference) 5B047 AA30 AB02 BA01 BB10 BC07 BC11 CA17 CA19 CB04 CB05 CB22 5C077 MM03 MM30 MP01 NP01 NP07 PP43 PQ08 PQ18 SS03 SS04 TT09 5C079 JA16 JA17 JA23 LA01 LA31 MA11

Claims (4)

[Claims] An image forming medium including a substance that actively emits light energy by light irradiation is irradiated with light emitted from a plurality of light sources having different spectral energy distributions from each other to form an image formed on the image forming medium. Generating light carrying the image from the image forming medium, photoelectrically detecting the light while switching a filter capable of changing a transmission wavelength range,
Acquiring a plurality of spectral images representing the color information of the image for each of a plurality of predetermined wavelengths for each of the light sources, based on the plurality of spectral images, all pixels of the spectral image for each of the light sources And calculating a weighting factor for expressing the spectral energy distribution corresponding to the plurality of predetermined wavelengths of the desired light source by weighting and adding the spectral energy distribution of each light source. A weighted addition of the spectral reflectances of all the pixels of each of the spectral images for each light source for each corresponding pixel to obtain the spectral reflectance of the image under the desired light source. Processing method. 2. The image processing method according to claim 1, wherein the plurality of light sources include a light source having substantially the same spectral energy distribution as the desired light source. 3. An image forming medium including a substance that actively emits light energy by light irradiation is irradiated with light emitted from a plurality of light sources having different spectral energy distributions from each other to form an image on the image forming medium. Generating light carrying the image from the image forming medium, photoelectrically detecting the light while switching a filter capable of changing a transmission wavelength range,
An image acquisition unit configured to acquire, for each of the light sources, a plurality of spectral images representing color information of the image for each of a plurality of predetermined wavelengths, based on the plurality of spectral images, the spectrum for each of the light sources; A spectral reflectance acquisition unit configured to acquire spectral reflectances of all pixels of an image; and a spectral energy distribution corresponding to the plurality of predetermined wavelengths of a desired light source. Weighting factor calculating means for calculating the weighting factor of the spectral weights of all the pixels of each of the spectral images for each of the light sources for each of the corresponding pixels by weighting and adding the weighted spectral reflectances to each of the corresponding pixels to obtain the desired image. An image processing apparatus comprising: an addition unit that acquires a spectral reflectance under a light source. 4. The image processing apparatus according to claim 3, wherein the plurality of light sources include a light source having substantially the same spectral energy distribution as the desired light source.