Color image reading apparatus with a plurality of line sensors in which a white balance operation is performed by determining amplifier gains while reading a white reference plate

A color image reading apparatus comprising:

• a plurality of linear sensor means for reading a color document, each of said linear sensor means photoelectrically reading a different portion of a line of the color document in a divided manner and generating a plurality of color component signals representing colors on the color document;
• a plurality of amplifying means each for amplifying said plurality of color component signals generated by a respective one of said plurality of linear sensor means;
• determining means for determining gains for said plurality of amplifying means to use in amplifying corresponding ones of said plurality of color component signals on the basis of a plurality of reference color component signals generated by reading a reference member having a reference density with said plurality of linear sensor means;
• and
• correcting means for causing each of said plurality of amplifying means to amplify said plurality of color component signals using the respective gains determined by said determining means, thereby correcting the level of each of said plurality of color component signals representing colors on the color document generated by each of said plurality of linear sensor means.