Distance measuring method

A distance measuring method for measuring a distance between a plurality of points in a main scanning direction based on waveform data of a black-and-white pattern on a distance correction chart read by an image reading device including pixels being light receivers arranged in the main scanning direction, the black-and-white pattern including black portions and white portions arranged at regular intervals in the main scanning direction, the distance correction chart being read with the light receivers arranged in the main scanning direction, the method comprising:

• a first step of converting the waveform data to a binary waveform binarized based on a predetermined threshold;
• a second step of comparing the binary waveform with the black-and-white pattern on the distance correction chart to convert, by removing noise from the binary waveform, the binary waveform to edge information including falling edges and rising edges;
• and
• a third step of comparing the edge information with physical lengths of the black-and-white pattern of the distance correction chart to derive a number of pixels being the light receivers corresponding to a physical interval between black portions of the distance correction chart adjacent to each other in the main scanning direction.