Electronic halftone generator

• US 4,196,451 A
• Filed: 07/28/1978
• Issued: 04/01/1980
• Est. Priority Date: 05/21/1976
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Pellar, Ronald J.
• Primary Examiner(s): Martin, John C.
• Application Number:
  US05/928,652
• Time in Patent Office: 613 Days
• Field of Search: 358/75.80, 358/283, 358/298, 358/299
• US Class Current: 358/534
• CPC Class Codes: H04N 1/4058 with details for producing a halftone screen at an oblique angle H04N1/4056 takes precedence
• CPC Class Codes: H04N 1/52 Circuits or arrangements for halftone screening

Abstract

Method and apparatus for scanning a document original, either black and white or color, and reproducing a corresponding halftone reproduction thereof either locally or at a remote location. A halftone signal is generated by pulse width modulating or comparing the scanned, or video, signal with a periodic signal having two frequencies and phases to create a dot pattern output which is a function of the frequency and phase of the two combined modulating signals. The halftone reproduction generated has variable dot configurations that are controllable to enable both rotation of the dot pattern (screen angle) and geometric modifications of the dot pattern. If the document original is in color, light of three different colors is caused to scan the document, each resultant video signal being processed in a manner as set forth hereinabove. In a preferred embodiment, different screen angles are utilized for each color that comprises the reproduction.

Claims

1. Apparatus for converting an electrical analog input signal representing an image into a corresponding output signal in the form of a dot pattern corresponding to said image comprising:

means for generating a time-varying electrical function which is a function of first and second signals of first and second frequencies, respectively, said first and second frequencies being separately adjustable,

means for accepting said analog signal as a series of successive scan lines during the generation of each dot which will form said dot pattern, said analog signal being produced by scanning said image in first and second directions,

means coupled to said generating means and said accepting means for comparing said successive scans with said function and generating a comparison signal when said function differs from said successive scans,

means responsive to said difference signal for providing an output signal, and

means for generating said dot pattern by scanning said output signal in directions corresponding to said first and second directions, the direction of alignment of the dots relative to said first direction of scan being determined by the selection of said first and second frequencies.

2. The apparatus as defined in claim 1 wherein said first and second signals have first and second amplitudes associated therewith, said first and second amplitudes being separately adjustable in a manner wherein the shape of each dot in said dot pattern can be controlled.

3. The apparatus as defined in claim 2 wherein said first and second amplitudes further control the direction of chaining of each dot in said dot pattern in a manner such that the chaining direction may be different than said alignment direction.

4. The apparatus as defined in claim 1 wherein said first and second frequencies are selected such that the alignment direction is different from said first and second directions of scan.

6. The method as defined in claim 2 wherein said first and second signals have first and second amplitudes associated therewith, said first and second amplitudes being separately adjustable in a manner wherein the shape of each dot in said dot pattern can be controlled.

7. The method as defined in claim 6 wherein said first and second amplitudes further control the direction of chaining of each dot in said dot pattern in a manner such that the chaining direction may be different than said alignment direction.

5. A method for converting an electrical analog input signal representing an image into a corresponding output signal in the form of a dot pattern corresponding to said image comprising the steps of:

generating a time-varying electrical function which is a function of first and second signals of first and second frequencies, respectively, said first and second frequencies being separately adjustable,

accepting said analog signal as a series of successive scans during the generation of each dot which will form said dot pattern, said analog signal being produced by scanning said image in first and second directions,

comparing said successive scans with said function and generating a comparison signal when said function differs from said successive scans, and

providing an output signal, said dot pattern being generated by scanning said output signal in directions corresponding to said first and second directions, the direction of alignment of the dots relative to said first direction of scan being determined by the selection of said first and second frequencies.

8. The method as defined in claim 5 wherein said first and second frequencies are selected such that the alignment direction is different from said first and second directions of scan.