Image forming method and apparatus using rotated screen with pulse width modulation
AssigneeMatsushita Electric Industrial Co., Ltd.
InventorKazuyuki Murata
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Abstract
Image forming apparatus and method for forming half tone images by pulse width modulating multi-valued image signals comprises first and second pattern signal generators which generate pattern signals each having the same period and a phase shifted from each other, first and second pulse width modulators for pulse width modulating said image signals using the first and second pattern signals, respectively, a selector for selecting either of the first and second pulse width modulated signals and a controller for controlling the selector to obtain a screen angle of 45.degree.. Further, image forming apparatus and method which realizes a screen angle .theta. wherein tan .theta. is represented by a rational number.
Claims12
An image forming apparatus for forming half tone images by pulse width modulating multi-valued image signals, comprising:
- a first pattern signal generator for generating a first pattern signal having a period other than periods represented by twice a pitch of a scanning line multiplied with an integer,
- a second pattern signal generator for generating a second pattern signal with a frequency equal to a frequency of said generated first pattern signal and a phase shifted 180.degree. from a phase of said generated first pattern signal,
- a first pulse width modulation means for outputting a first pulse width modulation signal by pulse width modulating an image signal based on said generated first pattern signal,
- a second pulse width modulation means for outputting a second pulse width modulation signal by pulse width modulating the image signal based on said generated second pattern signal,
- a selector for selecting one of said first pulse width modulation signal and said second pulse width modulation signal, and
- a selector control means for controlling selection operation of said selector for every scan line whereby half tone images are formed with a right angled screen of which pitch is equal to an inverse of a square root of a period of said one of said first pulse width modulation signal and said second pulse width modulation signal selected by said selector and of which pseudo-screen angle is equal to 45.degree..
An image forming apparatus for forming images by pulse width modulating multi-valued image signals, comprising:
- a clock signal generator for generating a first clock signal having a period other than periods represented by twice a pitch of a scanning line multiplied with an integer and a second clock signal with a frequency equal to a frequency of said generated first clock signal and a phase shifted 180.degree. therefrom,
- a selector for selecting and outputting one of said generated first clock signal and said generated second clock signal,
- a pattern signal generator for generating a pattern signal based on said one of said generated first and second clock signals output from said selector,
- a pulse width modulation means for pulse width modulating an image signal based on the pattern signal generated by said pattern signal generator and outputting a pulse width modulation signal, and
- a selector control means for controlling selection operation of said selector for every scan line whereby half tone images are formed with a right angled screen of which pitch is equal to an inverse of a square root of a period of said one of said generated first clock signal and said Generated second clock signal and of which pseudo-screen angle is equal to 45.degree..
An image forming method for forming half tone images by pulse width modulating multi-valued image signals, comprising steps of:
- generating a first pattern signal having a period other than periods represented by twice a pitch of a scan line multiplied with an integer and a second pattern signal with a period equal to said period of said first pattern signal but a phase shifted 180.degree. from the phase of the first pattern signal,
- generating first and second pulse width modulated signals by pulse width modulating said image signals with said first pattern signal and said second pattern signal, and
- controlling selection of said first and second pulse width modulated signals for every scan line whereby half tone images are formed with a right angled screen of which pitch is equal to an inverse of a square root of a period of one of said first pattern signal and said second pattern signal selected and of which pseudo-screen angle of is equal to 45.degree..
Dependencies are inferred from the claim text.