Image reading apparatus and control method therefor

• US 6,785,026 B1
• Filed: 04/08/1999
• Issued: 08/31/2004
• Est. Priority Date: 04/10/1998
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Terajima, Hisao, Ono, Takashi, Shinada, Yasuyuki
• Primary Examiner(s): Lee, Cheukfan
• Application Number:
  US09/288,445
• Time in Patent Office: 1,972 Days
• Field of Search: 358/474, 358/509, 358/475, 358/505, 358/506, 358/487, 358/445, 358/514, 358/513, 358/512, 358/483, 358/482, 358/461, 358/504, 358/406, 250/208.1, 250/234-236, 250/205, 382/312, 382/313, 382/318, 382/319, 382/317, 382/274, 362/800, 348/96-98
• US Class Current: 358/509
• CPC Class Codes: H04N 1/484 with sequential colour illumination of the original

Abstract

An image reading apparatus individually reads a predetermined white reference plate by flickering light sources of the respective colors before an original image is read by sequentially turning on the light sources during one line sync period. The flickering duty ratio of the light source obtained when the white reference plate is read is set for each color so as to maximize the output value from an A/D converter within its predetermined conversion range. When an original is read, the image reading apparatus changes the emission color by switching the light source to be flickered every line sync period, and turns on the light sources of the respective colors in accordance with different duty ratios set for these colors.

Claims

1. An image reading apparatus which reads an original image by sequentially irradiating the original image with a plurality of emission colors and detecting light of each color from the original image by an image sensor, comprising:

a light source capable of sequentially generating the plurality of emission colors in accordance with an emission control signal; and

control unit adapted to supply the emission control signal so as to change the emission color of said light source every predetermined charge accumulation period of the image sensor, and turn on-and-off of said light source a plurality number of times uniformly during the charge accumulation period in accordance with a duty ratio set for each emission color.

2. The apparatus according to claim 1, wherein when a reference white background is irradiated by turning on-and-off of said light source with one of the plurality of emission colors, and an output value from the image sensor is smaller than a predetermined value and comes nearest to the predetermined value, said control unit sets a duty ratio at this time as an optimum duty ratio for the emission color, said control unit repeating the duty ratio setting operation for each of the plurality of emission colors.

3. The apparatus according to claim 2, wherein said control unit performs the duty ratio setting operation for each emission color before the original image is read.

4. The apparatus according to claim 1, wherein said control unit reads an entire original image by repeating turning on-and-off of said light source and change of the emission color at a predetermined pitch a plurality of number of times.

5. The apparatus according to claim 1, further comprising light sources for the plurality of emission colors.

6. A method of controlling an image reading apparatus which reads an original image by sequentially irradiating the original image with a plurality of emission colors and detecting light of each color from the original image by an image sensor, comprising:

supplying an emission control signal to change the emission color of a light source every predetermined charge accumulation period of the image sensor, the light source capable of sequentially generating the plurality of emission colors in accordance with the emission control signal, and turning on-and-off of the light source a plurality number of times uniformly during the charge accumulation period in accordance with a duty ratio set for each emission color.

7. The method according to claim 6, further comprising, when a reference white background is irradiated by turning on-and-off of the light source with one of the plurality of emission colors, and an output value from the image sensor is smaller than a predetermined value and comes nearest to the predetermined value, setting a duty ratio at this time as an optimum duty ratio for the emission color, the duty ratio setting operation being repeated for each of the plurality of emission colors.

8. An image reading apparatus which reads an original image by detecting, by an image sensor, light from the original image irradiated by a light source, comprising:

a control unit adapted to control a single light source for irradiating the original image to flicker a plurality of number of times uniformly during every predetermined charge accumulation time of the image sensor when the original image is read,

wherein said control unit adjusts a flickering duty ratio of the light source for reading the original image based on an output value from the image sensor when the image sensor reads a reference background irradiated by flickering the light source a plurality of number of times.

9. The apparatus according to claim 8, wherein when the reference background is irradiated by flickering the light source a plurality of number of times, and an output value from the image sensor is smaller than a predetermined value and comes nearest to the predetermined value, said control unit selects the flickering duty ratio of the light source at this time as an optimum duty ratio for reading the original image.

10. The apparatus according to claim 9, wherein said control unit performs the duty ratio adjustment operation before the original image is read.

11. A method of controlling an image reading apparatus which reads an original image by detecting, by an image sensor, light from the original image irradiated by a light source, comprising:

controlling a single light source for irradiating the original image to flicker a plurality of number of times uniformly during every predetermined charge accumulation time of the image sensor when the original image is read,

wherein the step of controlling adjusts a flickering duty ratio of the light source for reading the original image based on an output value from the image sensor when the image sensor reads a reference background irradiated by flickering the light source a plurality of number of times.

12. The method according to claim 11, further comprising the step of, when the reference background is irradiated by flickering the light source a plurality of number of times, and an output value from the image sensor is smaller than a predetermined value and comes nearest to the predetermined value, selecting the flickering duty ratio of the light source at this time as an optimum duty ratio for reading the original image.

13. The method according to claim 12, wherein the step of controlling adjusts the duty ratio before the original image is read.

14. An image reading apparatus which reads an original image by sequentially irradiating the original image with a plurality of emission colors and detecting light of each color from the original image by an image sensor, comprising:

a light source capable of sequentially generating the plurality of emission colors in accordance with an emission control signal; and

control unit adapted to supply the emission control signal so as to change the emission color of said light source every charge accumulation period, and repeat, in the charge accumulation period, turning on-and-off of said light source with a first emission color of the plurality of emission colors a plurality of number of times,

wherein the number of times of turning on-and-off of said light source with the first emission color is different from a number of times of turning on-and-off of said light source with a second emission color different from the first emission color of the plurality of emission colors.

15. The apparatus according to claim 14, wherein said control unit sets a duty ratio of another emission color using, as a reference, a total ON time of one of the plurality of emission colors in the predetermined charge accumulation period of the image sensor.

16. The apparatus according to claim 15, wherein said control unit calculates the duty ratio of said light source for each emission color, calculates a product of the calculated duty ratio and the predetermined charge accumulation period of the image sensor to calculate the total ON time for each color, and selects a product of an emission color having the largest calculated value as the reference total ON time.

17. The apparatus according to claim 16, wherein when a reference white background is irradiated by repeating on-and-off of said light source with one of the plurality of emission colors, and an output value from the image sensor is smaller than a predetermined value and comes nearest to the predetermined value, said control unit sets the duty ratio at this time as an optimum duty ratio for the emission color, said control unit repeating the duty ratio setting operation for each of the plurality of emission colors.

18. The apparatus according to claim 15, wherein said control unit selects, as a reference, a total ON time of an emission color having the smallest light quantity selected in advance from the plurality of emission colors.

19. The apparatus according to claim 15, wherein said control unit holds an ON state over the total ON time by setting the duty ratio of the emission color selected as the reference of the total ON time from the plurality of emission colors to 100%.

20. The apparatus according to claim 14, wherein said control unit performs the duty ratio setting operation for each emission color before the original image is read.

21. The apparatus according to claim 14, wherein said control unit reads an entire original image by repeating on-and-off of said light source and change of the emission color at a predetermined pitch a plurality of number of times.

22. The apparatus according to claim 14, wherein said image reading apparatus comprises light sources for the plurality of emission colors.

23. A method of controlling an image reading apparatus which reads an original image by sequentially irradiating the original image with a plurality of emission colors and detecting light of each color from the original image by an image sensor, comprising:

supplying an emission control signal to change the emission color of a light source every charge accumulation period, the light source capable of sequentially generating the plurality of emission colors in accordance with the emission control signal, and repeating, in the charge accumulation period, turning on-and-off of said light source with a first emission color of the plurality of emission colors a plurality of number of times,

wherein the number of times of turning on-and-off of said light source with the first emission color is different from a number of times of turning on-and-off of said light source with a second emission color different from the first emission color of the plurality of emission colors.