Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1994-05-16
1996-12-03
Vu, Kim Y.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358455, 358457, 382237, H04N 1405
Patent
active
055813720
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is directed to a method for generating and storing digitized density thresholds for rastering a half-tone original image, particularly in the form of a color separation (plans). Density thresholds of a portion of a raster are stored in at least one data memory as memory words dependent on a spot function. A plurality of spots (raster points) in the portion that respectively cover a plurality of memory words are periodically arranged next to one another and above one another, forming a multiple reference cell (super cell). A sorted sequence based on a measure of the spot function is calculated for the memory words of the data memory, and density thresholds are allocated to the memory words of the data memory dependent on the position of the memory word in the sorted sequence.
The raster can thereby be turned relative to a scan direction of a recording means that scans a recording carrier along scan lines.
Limiting lines of the portion of the raster proceed in the scan direction as well as at a right angle relative thereto.
It is known for the rastered recording of tonal value signals (image signals) that are required by scanning the half-tone original image to superimpose these tonal value signals with density threshold signals (raster signals) of a raster that is turned relative to a recording direction (German Patent 19 01 101). The density threshold signals or, respectively, raster signals generated for this purpose correspond to a density structure content of a portion taken from the selected, turned raster whose limiting lines lie in the recording direction and in a feed direction that is orthogonal thereto. The basic period of the structure of the turned raster with respect to each of the two orthogonal directions is contained once in the portion. The portion thereby comprises a plurality of raster points (spots) in scan direction as well as at a right angle thereto, these spots being periodically arranged next to one another and above one another. This portion can also be referred to as a multiple reference cell or super cell. As a consequence of the periodicity of the portion of the turned raster, the density threshold signals (raster signals) can be periodically repeated without further ado in order to be superimposed with the tonal value signals of larger image formats or, respectively, image portions. Over and above this, the raster portion can be resolved into so many sub-lines proceeding in the image recording direction that a plurality of such sub-lines devolve onto one image line width.
As a result of this subdivision of the raster portion, however, nothing regarding the size and periodicity thereof is changed. The condition that the raster portion seamlessly merges into itself in each of the two orthogonal directions (vertically and horizontally) is referred to as the wrap-around condition.
Data memories wherein the density thresholds of the raster portions are digitally stored are utilized for the implementation of the described, known method. The density thresholds stored therein, and imaged visually, can also be referred to as density hills or, respectively, threshold hills. The density thresholds are stored in the data memories in such a form that the required raster information are input by previous scanning of a model raster and quantizing as well as coding of the raster signals. The digital density thresholds thus contained in the data memories serve the purpose of being converted back into analog values with the tonal value signals scanned line-by-line from the original image and of being subsequently supplied into superimposition and threshold units. Typically, round, oval or rectangular point forms that grow proceeding from the middle are employed when scanning an optical original.
Digital recorders are also used in order to expose the individual color screen separations, a light source, particularly a laser beam, for exposing a light-sensitive surface therein being capable of being displaced with constant step size in two orthogonal direc
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patent: 5422742 (1995-06-01), Ostromoukhov et al.
patent: 5469516 (1995-11-01), Kerr
Patent Abstracts of Japan, vol. 10, No. 379 (E-465), 1986, "Picture Element Information Processing System", Tadao Shinya.
Linotype-Hell AG
Vu Kim Y.
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