An image signal processing device in an image reading apparatus, the image signal processing device configured to extract line image data points from an image signal in synchronization with input of horizontal synchronization pulses,
- the image reading apparatus comprising:
- an image reading portion configured to sequentially read single line images, each serving as an image of a single line extending in a main scanning direction, from a document sheet and to output the image signal that sequentially transmits the line image data points that represent the single line images;
- and
- a synchronization signal generating portion configured to generate and output a horizontal synchronization signal that sequentially transmits the horizontal synchronization pulses synchronized with timing of reading the single line images,
- the image signal processing device comprising:
- a reference signal generating portion configured to generate and output a reference signal that sequentially transmits reference pulses shifted from the horizontal synchronization pulses by a shift time set in advance;
- a determination portion configured to determine whether the horizontal synchronization pulses are normal by comparing time differences between an input of the horizontal synchronization pulses and input of the reference pulses with the shift time;
- and
- an extraction portion configured to extract the line image data points from the image signal in synchronization with the input of the horizontal synchronization pulses that have been determined as normal.