Image forming apparatus and method of controlling the apparatus

An image forming apparatus comprising:

• a scanning means for reading a document image and outputting image data representing the density of the read image for each pixel;
• a pulse width modulating means for taking in as input the image data output from said scanning means and performing a pulse width modulating operation of generating and outputting a drive signal synchronized for one or more than one pixel of the image data and having a pulse width corresponding to the density of the one or more than one pixel, whichever appropriate;
• a laser unit configured to be turned on and off according to the drive signal output from said pulse width modulating means and emit a laser beam during each on period;
• a photosensitive drum;
• a scanning means for linearly scanning the surface of said photosensitive drum with the laser beam emitted from said laser unit along the axial direction of the photosensitive drum and repeating the linear scanning operation successively in synchronism with the rotation of said photosensitive drum;
• a control means for shifting the number of pixels to be used for the pulse width modulating operation of said pulse width modulating means for each linear scanning operation of said scanning means;
• and
• a correcting means for correcting the image data output from said scanning means and input to said pulse width modulating means according to the input/output characteristics of the pulse width modulating means.

A method of controlling an image forming apparatus, the image forming apparatus having:

• a scanning section which reads a document image and outputting image data representing the density of the read image for each pixel;
• a pulse width modulating section which takes in as input the image data output from said scanning section and performing a pulse width modulating operation of generating and outputting a drive signal synchronized for one or more than one pixel of the image data and having a pulse width corresponding to the density of the one or more than one pixel, whichever appropriate;
• a laser unit configured to be turned on and off according to the drive signal output from said pulse width modulating section and emit a laser beam during each on period;
• a photosensitive drum;
• and
• a scanning section which linearly scans the surface of said photosensitive drum with the laser beam emitted from said laser unit along the axial direction of the photosensitive drum and repeating the linear scanning operation successively in synchronism with the rotation of said photosensitive drum;
• said method comprising:
• shifting the number of pixels to be used for the pulse width modulating operation of said pulse width modulating section for each linear scanning operation of said scanning section;
• and
• correcting the image data output from said scanning section and input to said pulse width modulating section according to the input/output characteristics of the pulse width modulating section.