Method for obtaining full reflectance spectrum of a surface and apparatus therefor

Patent metadata

Field	Value
Publication number	US-9778109-B2
Application number	US-201414894302-A
Country	US
Kind code	B2
Filing date	May 12, 2014
Priority date	May 28, 2013
Publication date	Oct 3, 2017
Grant date	Oct 3, 2017

Abstract

Disclosed are a method for obtaining a full reflectance spectrum of a surface and an apparatus therefor. The method for obtaining a full reflectance spectrum of a surface, comprises the steps of: (a) calculating a combination value of spectral characteristics of a light source and response characteristics of a camera for an image of a reference object, the full reflectance spectrum of a surface of which is known, by utilizing the known full reflectance spectrum of a surface; (b) obtaining an image by photographing an object irradiated with light according to a predetermined lighting environment; and (c) obtaining a full reflectance spectrum of a surface for the object by utilizing the combination value of the spectral characteristics of the light source and the response characteristics of the camera for the image.

First claim

What is claimed is:

1. A full reflectance spectrum of a surface obtainment method comprising:
(a) calculating a light source spectrum characteristic and camera response characteristic combination value from a photographed image of a reference object having a known full reflectance spectrum of a surface by using the known full reflectance spectrum of a surface;
(b) obtaining an image by photographing an object irradiated with light according to a predetermined lighting environment; and
(c) obtaining a full reflectance spectrum of a surface for the object by using the light source spectrum characteristic and camera response characteristic combination value.

2. The full reflectance spectrum of a surface obtainment method of claim 1 , wherein the light source spectrum characteristic and camera response characteristic combination value is a result of multiplying a camera response characteristic value and a spectrum characteristic value of a light source.

3. The full reflectance spectrum of a surface obtainment method of claim 1 , wherein said step (a) comprises:
calculating a weight for a known basis function for the known full reflectance spectrum of a surface by using the known full reflectance spectrum of a surface and the known basis function; and
obtaining the light source spectrum characteristic and camera response characteristic combination value by using the weight for the known basis function.

4. The full reflectance spectrum of a surface obtainment method of claim 3 , wherein the weight for the basis function is calculated by using an equation shown below:
σ k =∫s (λ) b k (λ) d λ, for k= 1, . . . , K s

where K s is a number of basis functions, s(λ) represents the full reflectance spectrum of a surface of the object, and b k (λ) represents a basis function of the full reflectance spectrum of a surface of the object.

5. The full reflectance spectrum of a surface obtainment method of claim 1 , wherein camera conditions for a camera photographing the image and lighting conditions are the same in said step (a) and said step (b), and
the camera conditions entail the same camera and lens.

6. A calibration apparatus for obtaining a full reflectance spectrum of a surface, the calibration apparatus comprising:
an image obtainment unit having a lighting device and a camera mounted therein; and
a calibration unit having an insertion hole formed therein for inserting the image obtainment unit, the calibration unit having a reference-object securing unit therein, the reference-object securing unit having a reference object with a known full reflectance spectrum of a surface secured thereto,
wherein the calibration unit is closed at all sides when the image obtainment unit is inserted, and
the image obtainment unit obtains a plurality of images with at least one of an illuminance and a color of the lighting device changed.

7. The calibration apparatus of claim 6 , wherein the reference-object securing unit is attachable and detachable with respect to the calibration unit.

8. The calibration apparatus of claim 6 , wherein a light source spectrum characteristic and camera response characteristic combination value is calculated using the plurality of images obtained at the image obtainment unit.

9. A method of obtaining images in a calibration apparatus, the calibration apparatus comprising an image obtainment unit having a lighting device and a camera mounted therein and a calibration unit having a reference object with a known full reflectance spectrum of a surface mounted therein, the method comprising:
closing off an inside of the calibration unit where the reference object is adhered by coupling the image obtainment unit with the calibration unit; and
obtaining a plurality of images of the reference object by altering the lighting device.

10. The method of claim 9 , wherein a light source spectrum characteristic and camera response characteristic combination value is calculated using the plurality of images, and
an image of a target object is obtained using the camera of the image obtainment unit while the calibration unit is in a detached state, and a full reflectance spectrum of a surface of the target object is computed by using the image of the target object and the light source spectrum characteristic and camera response characteristic combination value.

11. The method of claim 10 , further comprising:
obtaining an image of the target object while the lighting device is off,
wherein a difference image is derived between the image obtained of the target object while the lighting device is off and an image obtained of the target object with the lighting device altered, the full reflectance spectrum of a surface of the target object is computed by using the difference image and the light source spectrum characteristic and camera response characteristic combination value.

Assignees

• Industry-Univ Coop Found Hanyang Univ
• Industry-Unuiversity Coop Found Hanyang Univ

Inventors

• Park Jong-Il
• Lee Moon-Hyun
• Seo Byung-Kuk

Classifications

• G01J3/2823 Primary

  Imaging spectrometer · CPC title

• G01J3/12

  Generating the spectrum; Monochromators · CPC title

• G03B43/00

  Testing correct operation of photographic apparatus or parts thereof · CPC title

• G01J3/0275

  making use of sensor-related data, e.g. for identification of sensor parts or optical elements · CPC title

• G01J2003/2806

  Array and filter array · CPC title