Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
2000-12-18
2004-02-24
Lee, Thomas D. (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S003060
Reexamination Certificate
active
06697170
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to devices and methods for offset and similar printing systems.
More particularly, the present invention relates to devices and methods for screening information from a continuous tone original to produce a halftone image on a photosensitive layer.
In particular, the invention relates to a novel screen, photomechanically or electronically generated, for the preparation of offset or similar printing plates to be used in offset or similar printing of halftone copies of continuous tone originals.
There exists a wide variety of photomechanical screens. Their purpose is to break up the continuous tone information of the original into discrete dots, whose size is related to the optical density of the original. The resultant film, upon processing, produces a “dot” image of the original.
In the prior art systems all the dots, which are small enough for the reconstruct into a coherent image are of equal opaque optical density while their relative sizes produce the impression of various grey values. The practical resolution of these screens, and those generated electronically (e.g. via an Electronic Dot Generator Scanner) is usually about 100-200 dots/inch.
In the past, the standard screen utilised an array of symmetrical round or square dots. The details of the original reproduced through such a screen are determined by the arbitrary geometrical centres of the dots in the screen. Further, in the resulting halftone, until 50% dot density one has black dots on a transparent background. An abrupt jump in the tonal scale occurs at 50%, where the four corners of the square dot join at 50%. This discontinuity prevents smooth midtone transitions.
To overcome the latter limitation, an elliptical, diamond, multi-dot or star-like dot pattern is mainly used in modern offset printing. These dot shapes allow a smoother tonal gradation than the square dot, in the 50% area, Two opposite corners of e.g., the diamond shaped dot, join the adjacent dots first at about 40%, while the other two remaining corners join adjacent dots, near 60%. Since the dots join in two steps, a smoother tonal transformation is achieved, This strategy, of having adjacent dots join in multiple steps, is used, for example, in the Double Dot Policrom Screen and the Triplet Dot HRS Beta Screen. The result is smoother, but far from ideal, as the abrupt jump in tonal scales is only attenuated to some degree. Aside from these jumps the image remains discontinuous in the X and Y direction because of the spacing between the dots in both directions which becomes more apparent with a lower screen ruling.
In U.S. Pat. No. 4,768,101 there is disclosed a method of generating a half-tone representation of an image from digital data defining the colour content of pixels arranged in a series of substantially parallel input scan lines.
U.S. Pat. No. 4,700,235 discloses a method and apparatus for producing half-tone printing forms with screens having arbitrary screen angles and screen width.
U.S. Pat. No. 4,833,546 discloses a photomechanical apparatus adapted to print a half-tone picture corresponding to an original continuous tone picture on the basis of tonal information signals obtained by photoelectrically scanning the original continuous tone picture.
U.S. Pat. No. 4,547,812 discloses a method and apparatus for forming high resolution half-tone images.
U.S. Pat. No. 4,543,613 discloses a method for producing half-tone dots in a half-tone plate recording apparatus.
As will be realised none of said patents teach or suggest the device and method of the present invention.
SUMMARY OF THE INVENTION
In contradistinction to said prior art photomechanical screens and methods, using the same or involving electronically generating an effective electronic equivalent thereof, the present invention now provides a device for offset and similar printing methods from a continuous tone original to produce a halftone image on a photosensitive layer comprising means for screening said information via a first array of parallely extending lines of effective minimum optical density and a second array of parallely extending lines of effective maximum optical density, said arrays being interposed to form a composite array of substantially parallel, spaced-apart, alternating lines of maximum and minimum optical density, said lines delimiting therebetween zones of effective graduated optical density, the gradient inside each zone progressively varying from low optical density adjacent lines of said first array to high optical density adjacent lines of said second array, the spacing of lines of said first array being between about 100 and 400 lines per inch and wherein the resulting thickness of each reproduced line on a resulting developed photosensitive layer, generated by screening said information via said array, continuously varies as a function of the density of each information point of the original.
In a preferred embodiment of the present invention there is now provided a photomechanical screen for offset and similar printing methods by screening information from a continuous tone original to produce a halftone image on a photosensitive layer, said screen comprising a first array of parallely extending lines of minimum optical density and a second array of parallely extending lines of maximum optical density, said arrays being interposed to form a composite array of substantially parallel spaced-apart, alternating lines of maximum and minimum optical density, said lines delimiting therebetween zones of graduated optical density, the gradient inside each zone progressively varying from low optical density adjacent lines of said first array to high optical density adjacent lines of said second array, the spacing of lines of said first array being between about 100 and 400 lines per inch and wherein the resulting thickness of each reproduced line on a resulting developed photosensitive layer, generated by screening said information via said array, continuously varies as a function of the density of each information point of the original.
The invention also provides a method for generating a halftone image from a continuous tone original comprising exposing a commercial lith or line film to a continuous tone original via a device as hereinbefore defined wherein the resulting thickness of each resulting line generated on said developed lith or line film continuously varies as a function of the density of each information point of the original.
A preferred embodiment of the present method comprises electronically outputting the information of the original onto an unexposed scanner type film, in an electronic output simulating a screen formats defined above, the pattern of this screen being lines spaced 100-400 lines/inch without this film being in contact with a standard photomechanical screen.
In another aspect of the present invention there is also provided a method for generating a halftone image from a continuous tone original comprising outputting the information of the original onto an unexposed scanner-type film, in an electronic output simulating a screen format, the pattern of this screen in a screen format, the pattern of this screen being a first array of parallels extending lines of effective minimum optical density and a second array of parallels extending lines of effective maximum optical density, said arrays being interposed to form a composite array of substantially parallel, spaced apart, alternating lines of effective maximum and minimum optical density, said lines delimiting therebetween zones of effective graduated optical density, the gradient inside each zone progressively varying from low optical density adjacent lines of said first array to high optical density adjacent lines of said second array, the spacing of lines of said first array being between about 400-600 lines per inch and developing in a lith developer containing a hydroquinone developing agent in combination with carbonate, bicarbonate and halide salt together with sodium formaldehyde sulfoxylate and formal
Hoffman Arnold
Netz Yoel
Brinich Stephen
Friedman Mark M.
Hoffman Arnold
Lee Thomas D.
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