Image reading device and image reading method

Abstract

A technology capable of preventing generation of a problem due to saturation of an output value in an image pick-up section caused by a variation of illumination light from a light source. An image reading device includes a plurality of light sources each of which illuminates a document surface as a target for reading with illuminating light of a color different from the other light sources, an image pick-up section for imaging light radiated from the plurality of the light sources and reflected on the document surface, a controlling unit for making the plurality of the light sources emit light with any one of the plurality of the light sources as a reference light source, and an adjusting unit for lowering a current value of a power source which makes the reference light source emit light when an amount of light imaged in the image pick-up section exceeds a threshold value as a predetermined upper limit value.

1 . An image reading device comprising:
 a conveying unit that conveys a document to a document reading position;   a first light emitting element that is disposed at an upstream side of the document reading position in a direction in which the document is conveyed, and emits light to the document at the document reading position;   a second light emitting element that is disposed at a downstream side of the document reading position in the document conveying direction, and emits light different in color from the light emitted by the first light emitting element to the document at the document reading position;   a photoelectric transducer; and   an optical member that guides light reflected from the document at the document reading position to the photoelectric transducer.   
   
   
       2 . The image reading device according to  claim 1 , wherein the first and second light emitting elements are disposed at locations symmetric to each other with respect to the document reading position. 
   
   
       3 . The image reading device according to  claim 1 , wherein the first light emitting element comprises a red LED, a green LED, and a blue LED. 
   
   
       4 . The image reading device according to  claim 1 , wherein the second light emitting element comprises a yellowish-green LED. 
   
   
       5 . The image reading device according to  claim 1 , wherein the first light emitting element comprises a yellowish-green LED. 
   
   
       6 . The image reading device according to  claim 1 , wherein the second light emitting element comprises a red LED, a green LED, and a blue LED. 
   
   
       7 . The image reading device according to  claim 1 , wherein the optical member comprises a Selfoc lens. 
   
   
       8 . An image reading device comprising:
 an exposure unit that has a plurality of light sources and is movable in a first direction;   a first light emitting element that is disposed at an upstream side of a document reading position in the first direction, and emits light to the document at the document reading position;   a second light emitting element that is disposed at a downstream side of the document reading position in the first direction, and emits light different in color from the light emitted by the first light emitting element to the document at the document reading position;   a photoelectric transducer; and   an optical member that guides light reflected from the document at the document reading position to the photoelectric transducer.   
   
   
       9 . The image reading device according to  claim 8 , wherein the first and second light emitting elements are disposed at locations symmetric to each other with respect to the document reading position. 
   
   
       10 . The image reading device according to  claim 8 , wherein the first light emitting element comprises a red LED, a green LED, and a blue LED. 
   
   
       11 . The image reading device according to  claim 8 , wherein the second light emitting element comprises a yellowish-green LED. 
   
   
       12 . The image reading device according to  claim 8 , wherein the first light emitting element comprises a yellowish-green LED. 
   
   
       13 . The image reading device according to  claim 8 , wherein the second light emitting element comprises a red LED, a green LED, and a blue LED. 
   
   
       14 . The image reading device according to  claim 8 , wherein the optical member comprises a Selfoc lens.