Image reading apparatus, image forming apparatus, and image forming method

• US 20070291331A1
• Filed: 06/14/2006
• Published: 12/20/2007
• Est. Priority Date: 06/14/2006
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation), Toshiba Tec Corporation (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation), Toshiba Tec Corporation (Toshiba Corporation)
• Inventors: Sekizawa, Hidekazu, Hashizume, Yusuke, Someya, Akihiko
• Granted Patent: US 7,616,359 B2
• Time in Patent Office: Days
• US Class Current: 358/509
• CPC Class Codes: H04N 1/46 Colour picture communication systems
• CPC Class Codes: H04N 1/48 Picture signal generators for halftone screening H04N1/52

Abstract

In an image reading apparatus for reading a color document as a monochrome image, an image forming apparatus of the invention includes a composite light source that irradiates the color document and includes plural light sources different in spectral distribution, a sensor to detect the intensity of a reflected light from the color document, a light emission ratio setting unit to changeably set light emission ratios different for the respective light sources, and a light source control unit to control effective light amounts of the plural light sources with the set light emission ratios. According to the image forming apparatus of the invention, when the color document is monochromatically read, the reading is performed with the brightness close to the human visual sensitivity, the user can changeably set color sensitivity, and uneven density can be reduced.

Claims

1. An image reading apparatus for reading a color document as a monochrome image, comprising:

a composite light source that irradiates the color document and includes plural light sources different in spectral distribution;

a sensor configured to detect an intensity of a reflected light from the color document;

a light emission ratio setting unit configured to changeably set light emission ratios different for the respective light sources; and

a light source control unit to control effective light amounts of the plural light sources with the set light emission ratios.

2. The image reading apparatus according to claim 1, wherein,

the light emission ratio setting unit includes a storage unit, and

the light emission ratio setting unit sets standard light emission ratios stored in the storage unit into the light source control unit.

3. The image reading apparatus according to claim 2, wherein,

the standard light emission ratios are calculated such that

a product of a composite spectral distribution obtained by combining spectral distributions of the plural light sources with specified light emission ratios, spectral distributions of standard color charts, and a spectral distribution of a sensitivity of the sensor is integrated with respect to wavelengths to obtain first lightnesses for the standard color charts,

a product of a spectral distribution of a standard light source, the spectral distributions of the standard color charts, and a spectral distribution of a visibility characteristic is integrated with respect to wavelengths to obtain second lightnesses for the standard color charts, and

a square sum of errors between the first lightnesses and the second lightnesses with respect to the plural standard color charts different in color becomes a minimum.

4. The image reading apparatus according to claim 3, wherein,

the visibility characteristic is a color matching function y(λ

) in a CIE standard colorimetric system, and the standard light source is a xenon light source.

5. The image reading apparatus according to claim 3, wherein,

the visibility characteristic is a color matching function y(λ

) in a CIE standard colorimetric system, and the standard light source is a CIE standard illuminant or a CIE supplementary illuminant.

6. The image reading apparatus according to claim 1, wherein,

the light emission ratio setting unit includes a storage unit configured to store standard lightnesses set for plural standard color charts, and standard light emission ratios determined by a determination sequence,

in the determination sequence,

measurement lightnesses for the plural respective standard color charts obtained from the sensor when the plural standard color charts are irradiated by the plural light sources with specified light emission ratios are inputted,

a square sum of errors between the standard lightnesses and the measurement lightnesses for the plural standard color charts is obtained,

a change of the light emission ratios and setting of the changed light emission ratios into the light source control unit are repeated to decrease the square sum of the errors by a hill-climbing method, and

the light emission ratios at a time when the square sum of the errors becomes a specified threshold or less are determined to be the standard light emission ratios, and

the light emission ratio setting unit sets the standard light emission ratios into the light source control unit.

7. The image reading apparatus according to claim 6, further comprising a display operation unit, wherein,

the storage unit further stores quasi-standard lightnesses set for the plural respective standard color charts and quasi-standard light emission ratios determined by a second determination sequence,

in the second determination sequence,

measurement lightnesses for the plural respective standard color charts obtained from the sensor when the plural standard color charts are irradiated by the plural light sources with specified light emission ratios are inputted,

a square sum of errors between the standard lightnesses and the measurement lightnesses for the plural standard color charts is obtained,

a change of the light emission ratios and setting of the changed light emission ratios into the light source control unit are repeated to decrease the square sum of the errors by the hill-climbing method, and

the light emission ratios at a time when the square sum of the error becomes a specified threshold or less are determined to be the standard light emission ratios,

in the display operation unit,

the standard light emission ratios and the quasi-light emission ratios are selectable, and

the light emission ratio setting unit sets selected ones of the standard light emission ratios and the quasi-standard light emission ratios into the light source control unit.

8. The image reading apparatus according to claim 6, further comprising a display operation unit, wherein,

the display operation unit includes

display means for displaying the standard lightnesses for the plural respective standard color charts, and

desired lightness generation means for generating desired lightnesses by increasing/decreasing the standard lightnesses for the plural respective standard color charts,

the storage unit further stores desired lightnesses generated for the plural respective standard color charts and desired light emission ratios determined by a third determination sequence,

in the third determination sequence,

measurement lightnesses for the plural respective standard color charts obtained from the sensor when the plural standard color charts are irradiated by the plural light sources with specified light emission ratios are inputted,

a square sum of errors between the desired lightnesses and the measurement lightnesses for the plural standard color charts is obtained,

a change of the light emission ratios and setting of the changed light emission ratios into the light source control unit are repeated to decrease the square sum of the errors by the hill-climbing method, and

the light emission ratios at a time when the square sum of the errors becomes a specified threshold or less are determined to be the desired light emission ratios,

in the display operation unit,

the standard light emission ratios and the desired light emission ratios are selectable, and

the light emission ratio setting unit sets selected ones of the standard light emission ratios and the desired light emission ratios into the light source control unit.

9. The image reading apparatus according to claim 1, wherein,

the composite light source is an array-shaped composite light source in which plural LED elements of plural colors are arranged, and

diffusion means for diffusing emitted light is provided at an emission side of the LED elements.

10. The image reading apparatus according to claim 9, wherein the diffusion means is a Fresnel lens.

11. An image forming apparatus for reading a color document as a monochrome image and forming the monochrome image, the image forming apparatus comprising:

a composite light source that irradiates the color document and includes plural light sources different in spectral distribution;

a sensor configured to detect an intensity of a reflected light from the color document;

a light emission ratio setting unit configured to changeably set light emission ratios different for the respective light sources;

a light source control unit configured to control effective light amounts of the plural light sources with the set light emission ratios; and

an image forming unit configured to form the monochrome image from an output of the sensor.

12. The image forming apparatus according to claim 11, wherein,

the light emission ratio setting unit includes a storage unit, and

the light emission ratio setting unit sets standard light emission ratios stored in the storage unit into the light source control unit.

13. The image forming apparatus according to claim 12, wherein,

the standard light emission ratios are calculated such that

a product of a composite spectral distribution obtained by combining spectral distributions of the plural light sources with specified light emission ratios, spectral distributions of standard color charts, and a spectral distribution of the a sensitivity of the sensor is integrated with respect to wavelengths to obtain first lightnesses for the standard color charts,

a product of a spectral distribution of a standard light source, the spectral distributions of the standard color charts, and a spectral distribution of a visibility characteristic is integrated with respect to wavelengths to obtain second lightnesses for the standard color charts, and

a square sum of errors between the first lightnesses and the second lightnesses for the plural standard color charts different in color becomes a minimum.

14. The image forming apparatus according to claim 13, wherein,

the visibility characteristic is a color matching function y(λ

) in a CIE standard colorimetric system, and the standard light source is a xenon light source.

15. The image forming apparatus according to claim 13, Wherein,

the visibility characteristic is a color matching function y(λ

) in a CIE standard colorimetric system, and the standard light source is a CIE standard illuminant or a CIE supplementary illuminant.

16. The image forming apparatus according to claim 11, wherein,

the light emission ratio setting unit includes a storage unit configured to store standard lightnesses set for plural standard color charts, and standard light emission ratios determined by a determination sequence,

in the second determination sequence,

measurement lightnesses for the plural respective standard color charts obtained from the sensor when the plural standard color charts are irradiated by the plural light sources with specified light emission ratios are inputted,

a square sum of errors between the standard lightnesses and the measurement lightnesses for the plural standard color charts is obtained,

a change of the light emission ratios and setting of the changed light emission ratios into the light source control unit are repeated to decrease the square sum of the errors by a hill-climbing method, and

the light emission ratios at a time when the square sum of the errors becomes a specified threshold or less are determined to be the standard light emission ratios, and

the light emission ratio setting unit sets the standard light emission ratios into the light source control unit.

17. The image forming apparatus according to claim 16, further comprising a display operation unit, wherein,

the storage unit further stores quasi-standard lightnesses set for the plural respective standard color charts and quasi-standard light emission ratios determined by a second determination sequence,

in the second determination sequence,

measurement lightnesses for the plural respective standard color charts obtained from the sensor when the plural standard color charts are irradiated by the plural light sources with specified light emission ratios are inputted,

a square sum of errors between the standard lightnesses and the measurement lightnesses for the plural standard color charts is obtained,

a change of the light emission ratios and setting of the changed light emission ratios into the light source control unit are repeated to decrease the square sum of the errors by the hill-climbing method, and

the light emission ratios at a time when the square sum of the errors becomes a specified threshold or less are determined to be the quasi-standard light emission ratios,

in the display operation unit,

the standard light emission ratios and the quasi-light emission ratios are selectable, and

the light emission ratio setting unit sets selected ones of the standard light emission ratios and the quasi-standard light emission ratios into the light source control unit.

18. The image forming apparatus according to claim 16, further comprising a display operation unit, wherein,

the display operation unit includes

display means for displaying the standard lightnesses for the plural respective standard color charts, and

desired lightness generation means for generating desired lightnesses by increasing/decreasing the standard lightnesses for the plural respective standard color charts,

the storage unit further stores desired lightnesses generated for the plural respective standard color charts and desired light emission ratios determined by a third determination sequence,

in the third determination sequence,

measurement lightnesses for the plural respective standard color charts obtained from the sensor when the plural standard color charts are irradiated by the plural light sources with specified light emission ratios are inputted,

a square sum of errors between the desired lightnesses and the measurement lightnesses for the plural standard color charts is obtained,

a change of the light emission ratios and setting of the changed light emission ratios into the light source control unit are repeated to decrease the square sum of the errors by the hill-climbing method, and

the light emission ratios at a time when the square sum of the errors becomes a specified threshold or less are determined to be the desired light emission ratios,

in the display operation unit,

the standard light emission ratios and the desired light emission ratios are selectable, and

the light emission ratio setting unit sets selected ones of the standard light emission ratios and the desired light emission ratios into the light source control unit.

19. The image forming apparatus according to claim 11, wherein,

the composite light source is an array-shaped composite light source in which plural LED elements of plural colors are arranged, and

diffusion means for diffusing emitted light is provided at an emission side of the LED elements.

20. The image forming apparatus according to claim 19, wherein the diffusion means is a Fresnel lens.

21. An image forming method for reading a color document as a monochrome image and forming the monochrome image, characterized by comprising:

a step of irradiating the color document by a composite light source including plural light sources different in spectral distribution;

a detection step of detecting an intensity of a reflected light from the color document by a sensor;

a light emission ratio setting step of changeably setting light emission ratios different for the respective light sources;

a light source control step of controlling effective light amounts of the plural light sources with the set light emission ratios; and

an image formation step of forming the monochrome image from an output of the sensor.

22. The image forming method according to claim 21, wherein,

at the light emission setting step, previously stored standard light emission ratios are set.

23. The image forming method according to claim 22, wherein,

the standard light emission ratio is calculated such that

a product of a composite spectral distribution obtained by combining spectral distributions of the plural light sources with specified light emission ratios, spectral distributions of standard color charts, and a spectral distribution of a sensitivity of the sensor is integrated with respect to wavelengths to obtain first lightnesses for the standard color charts,

a product of a spectral distribution of a standard light source, the spectral distributions of the standard color charts, and a spectral distribution of a visibility characteristic is integrated with respect to wavelengths to obtain second lightnesses of the standard color charts, and

a square sum of errors between the first lightnesses and the second lightnesses for the plural standard color charts different in color becomes a minimum.

24. The image forming method according to claim 23, wherein,

the visibility characteristic is a color matching function y(λ

) in a CIE standard colorimetric system, and the standard light source is a xenon light source.

25. The image forming method according to claim 23, wherein,

the visibility characteristic is a color matching function y(λ

) in a CIE standard colorimetric system, and the standard light source is a CIE standard illuminant or a CIE supplementary illuminant.

26. The image forming method according to claim 21, wherein,

the light emission ratio setting step comprises:

a step of storing standard lightnesses set for plural respective standard color charts;

a step of inputting measurement lightnesses for the plural standard color charts obtained from the sensor when the plural standard color charts are irradiated by the plural light sources with specified light emission ratios;

a step of obtaining a square sum of errors between the standard lightnesses and the measurement lightnesses for the plural standard color charts;

a step of repeating a change of the light emission ratios and setting of the changed light emission ratios into the light source control unit to decrease the square sum of the errors by a hill-climbing method;

a step of determining the light emission ratios at a time when the square sum of the errors becomes a specified threshold or less to be the standard light emission ratios;

a step of storing the determined standard light emission ratios; and

a step of setting the stored standard light emission ratios.

27. The image forming method according to claim 26, wherein,

the light emission ratio setting step further comprises:

a step of storing quasi-standard lightnesses set for the plural standard color charts;

a step of inputting measurement lightnesses for the plural respective standard color charts obtained from the sensor when the plural standard color charts are irradiated by the plural light sources with specified light emission ratios;

a step of obtaining a square sum of errors between the standard lightnesses and the measurement lightnesses for the plural standard color charts;

a step of repeating a change of the light emission ratios and setting of the changed light emission ratios to decrease the square sum of the errors by the hill-climbing method;

a step of determining the light emission ratios at a time when the square sum of the errors becomes a specified threshold or less to be the quasi-standard light emission ratios;

a step of storing the determined quasi-standard light emission ratios;

a step of selecting the standard light emission ratios and the quasi-standard light emission ratios; and

a step of setting selected ones of the standard light emission ratios and the quasi-standard light emission ratios.

28. The image forming method according to claim 26, wherein,

the light emission ratio setting step further comprises:

a step of displaying the standard lightnesses for the plural respective standard color charts;

a desired lightness generation step of generating desired lightnesses by increasing/decreasing the standard lightnesses for the plural respective standard color charts;

a step of storing the desired lightnesses generated for the plural respective standard color charts;

a step of inputting measurement lightnesses for the plural standard color charts obtained from the sensor when the plural standard color charts are irradiated by the plural light sources with specified light emission ratios;

a step of obtaining a square sum of errors between the desired lightnesses and the measurement lightnesses for the plural standard color charts;

a step of repeating a change of the light emission ratios and setting of the changed light emission ratios to decrease the square sum of the errors by the hill-climbing method;

a step of determining the light emission ratios at a time when the square sum of the errors becomes a specified threshold or less to be the desired light emission ratios;

a step of storing the determined desired light emission ratios;

a step of selecting the standard light emission ratios and the desired emission ratios; and

a step of setting selected ones of the standard light emission ratios and the desired light emission ratios.

29. The image forming method according to claim 21, wherein,

the composite light source is an array-shaped composite light source in which plural LED elements of plural colors are arranged, and

emitted light is diffused to an emission side of the LED elements and is irradiated to the color document.

30. The image forming method according to claim 29, wherein the emitted light is diffused by using a Fresnel lens.