Patent ID: 7050199
Filing Date: 2006-05-23
Classification: H04N

Abstract:
1. An image forming apparatus comprising: a scanning section which reads a document image and outputs 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 performs 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; 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 repeats the linear scanning operation successively in synchronism with the rotation of said photosensitive drum; a control section which shifts 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 a correcting section which corrects 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, where in said scanning section comprises: a document table configured to set a document; an exposure unit configured to expose the document set on said document table to light; a photoelectric conversion element configured to receive the image formed by the light reflected from the document table and output an image signal showing a voltage level corresponding to the density of the red image, an image signal showing a voltage level corresponding to the density of the green image and an image signal showing a voltage level corresponding to the density of the blue image out of the received image formed by the reflected light; an A/D conversion unit configured to perform A/D conversion on each of the image signals output from said photoelectric conversion element and output image data R showing the density of the red image, image data G showing the density of the green image and image data B showing the density of the blue image; and an image processing section configured to process the image data R, G, B output from said A/D conversion unit and output image data Y showing the density of the yellow image, image data M showing the density of the magenta image, image data C showing the density of the cyan image and image data K showing the density of the black image, wherein said pulse width modulating section selectively performs a pulse width modulating operation of generating and outputting a drive signal with a pulse width corresponding to the density of a single pixel in synchronism with each of the pixels of the input image data, a pulse width modulating operation of generating and outputting a drive signal with a pulse width corresponding to the density of two pixels in synchronism with every two of the pixels of the input image data, or a pulse width modulating operation of generating and outputting a drive signal with a pulse width corresponding to the density of three or more than three pixels in synchronism with every three or more than three, whichever appropriate, of the pixels of the input image data, wherein said control section selects two of the pulse width modulating operation for a single pixel, the pulse width modulating operation for two pixels, and the pulse width modulating operation for three or more than three pixels, in accordance with which one of the image data Y, M, C, K has been output from said image processing section and for causing the pulse width modulating section to carry out the selected two pulse width modulating operations alternately on a line-by-line basis for the linear scanning operation of said scanning section.