Patent ID: 8395830

Claim:
An image reading apparatus, comprising: a color linear image sensor which optically reads color image information of a document, converts the read color image information into electric signals corresponding to three primary colors, and outputs the electric signals as analog image signals; and an image reading signal processing IC to which the analog image signals are input; wherein the image reading signal processing IC includes three circuits which independently process the input analog image signals of the corresponding three primary colors; each of the three circuits includes a sample-hold circuit which samples the analog image signals and holds the values of the sampled analog image signals; a VGA which amplifies the analog image signals held by and output from the sample-hold circuit; an ADC which converts the amplified analog image signals into digital image data; an LVDS processing circuit which outputs the digital image data in a low voltage differential signaling level; a test pattern generating circuit connected between the ADC and the LVDS processing circuit for generating digital data of a test pattern; and a line delaying circuit which cancels differences in positions of light receiving sections of respective colors of the color linear image sensor by delaying a start line of the digital data of the test pattern generated by the test pattern generating circuit by a predetermined number of lines, according to a control signal that is input separately for the corresponding color of the three primary colors, the image reading signal processing IC further includes an operational mode determination information input unit which inputs operational mode determination information to the test pattern generating circuit; a switching unit which switches one of the digital data of the test patterns to any one or more of main scanning direction gradation pattern data and sub scanning direction gradation pattern data; and a designation unit that designates the following parameters when the test pattern generating circuit generates the digital data of the test pattern, the parameters are a first line start level, a number of output pixels having a same level, a change level between gradations for the main scanning direction gradation pattern data, and a first line start level, a number of output lines having a same level, a change level between gradations for the sub scanning direction gradation pattern data, and an operational mode of each of the test pattern generating circuits is switched between a normal mode which outputs digital image data output from the ADC and a test pattern output mode which outputs the digital data of the test pattern generated by the test pattern generating circuit corresponding to the operational mode determination information input from the operational mode determination information input unit.