Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-07-01
2001-04-24
Rogers, Scott (Department: 2724)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S451000
Reexamination Certificate
active
06222640
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of making a copy of an original document in accordance with an adjustable reproduction characteristic.
BACKGROUND OF THE INVENTION
Generally, the reproduction characteristic of a copying apparatus has a three-part form, namely a first part which without distinction maps low optical densities on the original to the color white on the copy, a second part which with distinction maps grey tints to optical densities between white and black, and a third part which without distinction maps high optical densities, i.e., dark grey tints, on the original to the color black on the copy. The color black corresponds to the maximum optical density that can be supplied by the printing system.
Documents may differ considerably in the number of grey tints present, and it is frequently desirable to be able to optimize the reproduction of the grey tints by a copying apparatus for the type of document that has to be copied at any particular time. This can generally be achieved by using an adapted reproduction characteristic. In analogue copy apparatus (which makes a copy by charging a photoconductive medium, exposing imagewise with a projection of the document for copying, and developing the residual charge image with toner powder), it is possible to adapt the reproduction characteristic by adjusting the quantity of light used to make the projection. The reproduction characteristic shifts as a result and specific grey tints on the document which are reproduced without distinction under normal exposure, e.g. the dark tints, are now separately visible. This is usually at the expense of the distinctive reproduction of other grey tints, the lighter ones in this example.
With the advent of the digital copying machine it has become possible to treat grey tints as digital data and process them as such, with much less dependence on other grey tints. The present invention is aimed at this area of the art.
A method and apparatus having an adjustable mapping of optical densities are known from Paul M. Butterfield, “User-Oriented approach to control of tone reproduction for electronic reprographic systems”, SPIE Vol. 1670, Color Hard Copy and Graphic Arts (1992), p.512-520. This document describes how a reproduction characteristic in the optical density domain can be adjusted by an operator. The reproduction characteristic is a graph indicating the relationship between input optical density ODin (on the X-axis) and output optical density ODout (on the Y-axis). According to Butterfield, a value on the Y-axis, i.e. an ODout value, can be adjusted by an operator at five approximately equidistant points on the X-axis. These ODout values are interconnected by straight lines and thus determine the reproduction characteristic. By determining five points an operator can define a complicated reproduction characteristic and hence very accurately control the reproduction of a document having a large number of grey tints.
The known method offers an operator very great freedom for programming the reproduction characteristic, but consequently requires a large number of adjustment operations, the effect of which cannot always be completely seen.
SUMMARY OF THE INVENTION
The invention, in part, reflects a recognition that an operator is usually only interested in satisfactory, moderate, or non-reproduction of specific dark or light tints. This can be achieved by influencing the location of the transitions between the above-mentioned first, second and third parts of the reproduction characteristic. The invention, also in part, also reflects a recognition that an adjustment of the form of the second part has hardly any influence on the result. With the known method according to Butterfield, it is possible to change the location of the transitions only indirectly, and then only with little accuracy.
An object of the invention is to provide a method and apparatus wherein simple and readily visible procedures enable a copy to be made with an adjustable reproduction characteristic. The invention provides, among other steps, the step of determining a reproduction characteristic.
A reproduction characteristic comprises a first part, which maps on white, a second part, which maps on density values between white and black, and a third part, which maps on black. The parts merge into one another in a first and second shoulder point respectively (A, B). An input optical density ODin value for at least one shoulder point is selected on the basis of specification by an operator.
According to the invention, therefore, only two adjustment points, namely the shoulder points, are offered to the operator for adjustment, and they can be shifted over the X-axis (ODin). These two points are necessary and sufficient to achieve the required result of an adjustable gradation when they are shifted over the X-axis.
According to one embodiment of the method according to the invention, the step of processing the first digital image data and the generation of second digital image data in so doing is performed using a predetermined transfer function, which has a form such that ODin values are mapped on ODout values in accordance with the reproduction characteristic as determined, wherein the method also comprises calculating a transfer function in accordance with the reproduction characteristic specified by an operator.
The values of the two shoulder points to be set by the operator can be specified as absolute values or as a change of an automatically set default. In the latter embodiment, the step of determining a reproduction characteristic on the basis of specification by an operator comprises: first determining a default reproduction characteristic on the basis of the first digital image data and determining a final reproduction characteristic on the basis of a change of the ODin value of at least one of the shoulder points as specified by the operator. Having a default can facilitate the operator's work, because it is then possible to assume that there is a setting that has already been optimized, and to which then changes, usually minor changes, need be applied.
The present invention is not limited to black-and-white copying, but can also very well be used for changing the contrast in color copying. It would, however, not be practical to have the operator adjust the individual color channels for red, green and blue, or cyan, magenta and yellow, because there would be a chance that the color tone would be affected, which is of course not intended. Rather, it is preferable to use the luminance comprised in the digital image data generated by the scanner, as the parameter for adjusting the reproduction characteristic.
The luminance, as defined in the L-a-b or the L-C-H coordinate systems, both widely known, is a perceptual parameter defining the light/dark character of an image, and is therefore a good choice for an adjustment parameter. Moreover, it has, just like the optical density in black-and-white copying, a more or less logarithmic course, so that the reproduction characteristic in L is also linear. Therefore, the theory applied to the optical density OD in the black-and-white case, also applies to the luminance in color copying, with no substantial differences.
The foregoing and other objectives of the present invention will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 3893166 (1975-07-01), Pugsley
patent: 4402015 (1983-08-01), Yamada
patent: 5745263 (1998-04-01), Oryo et al.
patent: 5838455 (1998-11-01), Imaizumi et al.
patent: 5867169 (1999-02-01), Prater et al.
patent: 5966503 (1999-10-01), van Vliembergen et al.
patent: 1236377 (1971-06-01), None
patent: 20-415722 (1991-03-01), None
patent:
Cornelissen Petrus A. M.
Ophelders Cornelis A. W.
Peulen Jacobus H. M.
Van Strijp Romeo M.
Oce--Technologies B.V.
Rogers Scott
LandOfFree
Copying apparatus having adjustable gradation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Copying apparatus having adjustable gradation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Copying apparatus having adjustable gradation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2546683