Facsimile and static presentation processing – Natural color facsimile – Measuring – testing – and calibrating
Reexamination Certificate
1998-12-05
2003-03-18
Lee, Thomas D. (Department: 2724)
Facsimile and static presentation processing
Natural color facsimile
Measuring, testing, and calibrating
C358S406000
Reexamination Certificate
active
06535307
ABSTRACT:
TECHNICAL FIELD
This invention relates to digital imagesetting and, more particularly, to visual sensors for detecting imaging parameters.
BACKGROUND INFORMATION
Printing presses use plates to print ink onto paper and other media. One method used for creating plates is to expose photosensitive film with the matter to be printed. When the film is developed, the matter imaged on the film may be imaged onto a photosensitive plate, sometimes referred to as “burning” a plate. After processing, the plate can be used on a press to print the matter onto a medium. Part of the plate, usually the part defining the image to be printed, retains ink, while the other part of the plate does not. When the plate is introduced to ink and then to paper or other medium, the image is printed on the medium.
In a black and white printing job, there is usually one plate that is used to print black ink. In a color printing job, a different plate may be used for each color ink. A color job may use three colors of ink, usually cyan, magenta, and yellow, which in combination can be used to make other colors. A plate is usually produced for each color ink. Often, in addition to cyan, magenta, and yellow, black ink is also used. An additional plate is then required to print the black ink. Occasionally, one or more colors will be printed separately as well, referred to as a “spot color.” That color will also have its own plate.
Electronic prepress systems have used an imagesetter to receive raster data associated with a plate and to image the raster data onto photosensitive film. In this context, a raster may specify an image by pixels in columns and rows, at a predefined resolution. The film is then used to create a plate. The imagesetter exposes the photosensitive film pixel by pixel. One way that imagesetters image the raster data is to scan a laser across and down a piece of film. Electronics control the laser to expose, or refrain from exposing, each pixel in the raster data. The imagesetter images the pixels on the film in a manner that is precise and repeatable. Recently, platesetters also have been used to create plates directly from raster data without the use of intermediate film. Imagesetters, platesetters and like print engines, including proofers, are also referred to generally as output devices and writing engines.
Modem output devices may write or record images on various media used in image reproduction, including but not limited to photo or thermal sensitive paper or polymer films, photo or thermal sensitive coatings, erasable imaging materials or ink receptive media mounted onto an image recording surface, polymer film or aluminum based printing plate materials. Such media are mounted onto a recording surface which may be planar or curved.
Conventional digital imagesetters include a raster image processor (RIP) which receives signals representing an image to be recorded on the applicable media and converts the signals into instructions to a scanner which scans the recording media to produce the desired image. It is the function of the RIP to process the received signals representing the image into a corresponding instruction set that can be understood by the scanner.
In an article entitled “How to Calibrate and Linearize an Imagesetter Using the Digital UGRA/FOGRA Wedge” by Franz Sigg and David Romano, published in the Society for Imaging Science and Technology Proceeding of the Fourth Technical Symposium on Prepress Proofing and Printing, October 1995, pp. 88-92, which was co-authored by David Romano who is also a co-inventor of the invention described herein, the need for imagesetter predictability and repeatability is discussed. As noted in the article, most modem imagesetters require adjustment so that a pre-specified solid density associated with the media to be imaged is produced. In most cases, it is required that the imagesetter be adjusted until a solid density is obtained on the medium being recorded. A densitometer can be utilized to measure the density of a recorded image to ensure correspondence with the pre-specified density. A densitometer measure within the range 1.0-4.0 or more is generally considered a solid density.
In practice, there are many imaging parameters, including scanner intensity that can be adjusted to change the density of a recorded image. However, because the intensity adjustment does not guarantee that desired dot areas will actually be recorded on the medium, it has been proposed that linearization curves be utilized to further adjust the imagesetter to offset the dot gain on the medium recorded by the imagesetter which is typically experienced as the intensity of the scanner is increased. In this way, the size or number of dots within an image are modified so that the desired dot areas will actually be recorded on the imaged medium. However, utilizing linearization curves does not ensure proper exposure. Although the use of linearization curves, may result in proper dot areas, the adjustments made to obtain the desired density may also result in undesirable dot fringe or fog between the dots on the recorded medium.
In the above-referenced Sigg and Romano article, it is proposed that half-tone patterns formed of one-by-one, two-by-two and four-by-four pixel checkerboards be compared with a 50% half-tone patch to calibrate the imagesetter. More particularly, it was disclosed that the proper imagesetter exposure occurs when the three checkerboards and a 50% half-tone patch have the same darkness or tint and hence the same visual density.
In non-digital platemaking, its is well known to form continuous gray tone wedges with a plurality of continuous tone density patches on a separate sheet of medium to compare with a test or registration patch formed on the recorded medium to initially set the exposure of the platemaker and/or to confirm that teach individual sheet of recorded medium includes a test patch which matches the selected patch on the wedge. Such a wedge is depicted in prior art FIG.
1
.
As shown in
FIG. 1
, the wedge
10
includes various continuous tone density patches
20
which are numbered
1
-
13
on the wedge. The densities of the respective patches vary from 0.15 D-0.195 D in steps of 0.15 D where D represents optical density. Other fields, which are not relevant for purposes of the present disclosure, are also included on the wedge
10
. The patches
20
are formed on a medium
30
which is preferably of a material substantially similar to the medium to be production imaged and on which the test patch is to be recorded. The platemaker operator is instructed which of the particular step(s) on the wedge
10
, and therefore which of the specific patch or patches within the continuous tone density patches
20
the test patch recorded on each piece of production medium must correspond to in order to be acceptable.
In a typical operational setting, a range of steps, e.g.,
4
,
5
and
6
, might be designed for use in initially establishing the exposure setting for the platemaker or in monitoring the acceptability of recorded media and hence the repeatability of the platemaker. The wedge
10
provides a simple way in which to initially set the recorded media in non-digital platemakers. Although providing a rough indicator for initially establishing an acceptable platemaker exposure setting and for monitoring platemaker repeatability by ensuring that all recorded media is exposed at approximately the same level, the wedge
10
cannot ensure that the recorded test patch actually corresponds to a desired density. In any event, may of the operators now operating digital platesetters and imagesetters were trained on non-digital platemakers and are familiar with the use of the
FIG. 1
wedge for quality control.
Density is an example of one imaging quality parameter. An output device may have several imaging parameters, including, but not limited to, focus, spot size, spot side lobe size, addressability, and pulse width modulation. Depending on the design of a writing engine, it may be possible to adjust imaging parameter settings with software con
Allen Roy D.
Hinds Stephen C.
Romano David J.
Agfa Corporation
Beloborodov Mark L.
Heffan Ira V.
Lee Thomas D.
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