Image analysis – Image transformation or preprocessing – Changing the image coordinates
Reexamination Certificate
2000-05-30
2004-12-28
Patel, Kanjibhai (Department: 2625)
Image analysis
Image transformation or preprocessing
Changing the image coordinates
C358S001200, C345S660000
Reexamination Certificate
active
06836571
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is directed to a method for converting digital source data in the raster of a first resolution into digital target data having a second resolution according to the preamble of patent claim
1
.
2. Description of the Related Art
In digital data processing, it is often necessary to convert digital image data that are present in the raster of a first resolution into target data having a second resolution. Each picture element, i.e. a point in the raster allocated to the digital value, is thereby referred to as pixel. Without gray levels, thus, a pixel corresponds to one bit. The topical resolution is thereby indicated in picture elements per inch (dots per inch, dpi). As known, one inch corresponds to 25.4 mm. The second resolution (target resolution) is usually higher than the first (source resolution). The target image in the second resolution can also contain more gray scale values per pixel than the source image instead of or in addition to the higher topical resolution.
For example, it often occurs in digital printing technology that image data are supplied by a computer in a first raster, for example in a 240 dpi raster, but are to be reproduced by a printer in a different raster, for example in a 600 dpi raster. Particularly when expanding an existing EDP system by a modern printer, it occurs that print jobs that were produced earlier comprise, for example, only masters in 240 dpi resolution. When the user wishes to use a new printer with, for example, a resolution of 600 dpi, then the print data must be correspondingly converted. The conversion should thereby ensue automatically without requiring inputs by the user.
Since half the pixels cannot be represented in playback units having discrete presentation levels such as LCD picture screens or digital printers, specific rules must be erected for conversions by factors of the resolution that are not whole-numbered.
The conversion can then ensue such that each value of the first raster is multiplied by a scaling factor SF that is prescribed by the ratio of the two resolution values of the rasters, that, thus, for example, the SF-fold set of identical values in the second raster is generated from a value in the first raster, whereby the following applies:
S
F
i
=
resolution
of
the
second
raster
in
direction
i
resolution
of
the
first
raster
in
direction
i
(
Equation
1
)
Although the data are transformed into the target raster with such a scaling procedure, the playback quality is thereby not improved.
On the other hand, the conversion of data into a raster having higher resolution in fact enables the improvement of the playback quality in that, for example, contours are more finely drawn. It is usually necessary to smooth the data for such a conversion. In known smoothing methods, smoothing parameters usually enter into the smoothing process in the form of a matrix or, respectively, of a window, whereby the weighting of neighboring picture elements of a point to be smoothed is prescribed by the values of the matrix. Given SF
x
=SF
y
, such windows are 3×3 windows or 5×5 windows.
A method for scaling and smoothing image data is disclosed by German Patent Document DE 195 06 792 A1. In this method, a plurality of sets of pixel patterns or, respectively, Boolean calculating operations allocated to them are provided, with reference whereto the conversion ensues. For conversion, a matrix of source image data having, for example, 7×7 picture elements is subjected to the basic calculating operations and the target image data are acquired therefrom. When scaling the image data “up” (SF>1), a respective group of target pixels is allocated to a group of source pixels. The calculating operations are configured such that the same number of high-resolution pixels are removed as added on average in the conversion. What is thereby achieved is that the degree of blackening of an overall image is essentially preserved.
What is disadvantageous about this method is that the conversion ensues only in groups with respect to the source pixels. Given, in particular, a scaling factor that is not whole-numbered (a broken scaling factor), one of the target pixels (&PHgr;) can then only be optionally allocated to a cluster of neighboring target pixels, i.e. relatively unmotivated, and cannot be unambiguously allocated to a source pixel. In addition, the allocation must be defined in advance in corresponding method rules.
A method for converting digital image data from a first raster into a second raster that is suitable for non-whole-numbered scaling factors is also disclosed by German Patent Application 197 13 079.8. This method likewise works region-oriented. A target region is thereby allocated to each source region, whereby the two regions having the same position in the overall image. Boolean calculating rules are prescribed within the target region, the conversion ensuing in conformity with these rules.
Another procedure for scaling and smoothing image data is disclosed by European Patent Document EP 506 379 B1 as well as by U.S. Pat. No. 5,270,836. Two steps for scaling and smoothing are provided in this procedure. As schematically shown in
FIG. 1
, a source image
1
that is present in a source raster is scaled in a first step
2
given this procedure, as a result whereof an intermediate image
3
arises in the target raster. The smoothing in the target raster is implemented on the basis of this intermediate image in the second step
4
, as a result whereof the target
5
arises.
What is disadvantageous about the above-described procedure is that a plurality of data in the target raster must be respectively taken into consideration for the smoothing. Due to the relatively great number of memory accesses and calculating operations that are thereby required, the outlay connected therewith is relatively high and is therefore hardly suited for applications such as high-performance printing systems wherein the speed of the conversion is crucial. A realization of the method on the basis of software thus likewise seems hardly possible.
A scaling and smoothing of transmission data can also be necessary in the field of telefax transmission when the data, for example, are received in a first resolution but are stored, forwarded or are to be printed out in a different resolution. A corresponding method for this application is disclosed, for example, by U.S. Pat. No. 5,394,485 A.
Another method for converting image data is disclosed by German Patent Document DE 42 06 277 A1. Only a raster conversion but no smoothing of the image data ensues given this method. European Patent Document EP 708 415 A2 likewise discloses a method for converting image data that, however, is only suitable for whole-numbered scaling factors. European Patent Document EP 0 006 351 A1 discloses an image processing system that works with look-up tables. U.S. Pat. No. 5,657,430 A discloses a method for converting vector fonts onto gray scale bit maps.
U.S. Pat. No. 5,646,741 discloses a method and an apparatus wherein image signals are scaled and smoothed. A check according to predetermined criteria is thereby carried out in the source region to see whether a smoothing should be implemented and the source image signals potentially smoothed. The smoothed image signals are smoothed thereafter.
PCT Published International Application WO-A-96/16380 discloses a system and a method for the interpolation of image signals. A rule is thereby respectively selected from a plurality of interpolation rules. The source image signals are then processed in a plurality of successive steps. In a first step, the image signals are interpolated line-by-line on the basis of a selected, line-related rule. In a second step, the image signals are then interpolated colum
Oce Printing Systems GmbH
Patel Kanjibhai
Schiff & Hardin LLP
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