Image sensor

An image sensor comprising:

• a light transmissive member, which includes a conveying region where a document is conveyed, and which extends in a direction orthogonal to a direction of conveying the document;
• a first reference portion and a second reference portion, which are respectively provided outside the conveying region at opposing ends of the light transmissive member with respect to the orthogonal direction, so that the first and second references portions are spaced from respective end portions of the conveying region by a same or different distances in the orthogonal direction, and the first and second reference portions having a transmittance lower than a transmittance of the conveying region of the light transmissive member;
• a light source unit that irradiates light to the conveying region, the first reference portion and the second reference portion;
• a rod lens array, which is arranged to be opposed to the light source unit, which is extending in a direction orthogonal to the direction of conveying, and which converges a light irradiated from the light source unit that is transmitted through the document conveyed in the conveying region and a light irradiated from the light source unit that is transmitted through the first reference portion and the second reference portion;
• a light receiving unit that receives the transmitted light corresponding to the conveying region and the transmitted light corresponding to the first reference portion and the second reference portion, through the rod lens array, and outputs electric signals corresponding to the conveying region, the first reference portion and the second reference portion;
• an A/D converting unit that converts the electric signals of the light receiving unit into respective digital signals;
• an amplifying unit that amplifies the digital signals based on an amplification factor signal and outputs an image data signal of the document based on the digital signal corresponding to the conveying region;
• and
• a controlling unit including:
• a collating unit that collates a first digital signal and a second digital signal respectively corresponding to the first and second reference portions with each other and outputs a difference value of the first digital signal and the second digital signal;
• and
• a determining unit that sets a plurality of data, determines data level to which the difference value data of the collating unit belongs, and outputs an amplification factor signal corresponding to the data level to which the difference value data belongs, thereby increasing or reducing the image data signal of the document of the amplifying unit, corresponding to the amplification factor signal.