Inkjet proofing with matched color and screen resolution

Incremental printing of symbolic information – Ink jet – Controller

Reexamination Certificate

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Details

C347S043000

Reexamination Certificate

active

06786565

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to apparatus and methods for creating proofs of documents to be printed on printing presses.
BACKGROUND OF THE INVENTION
Conventional halftoning is an amplitude modulated process in which continuous shading is simulated by varying the size of equally-spaced printed dots. The resolution at which the dots are placed is called the line screen ruling. The dots are typically oriented at an angle with respect to the print substrate, and this angle is called the screen angle. In grayscale images, the screen angle is typically 45°, which makes the resulting halftone pattern less noticeable to the human eye. For color images, each of the primary colors (usually cyan, magenta, yellow, and black—CMYK) are printed at different screen angles in order to minimize color shifts due to misregistration during the printing process. The angles are carefully selected for each color in order to minimize the occurrence of interference patterns called Moire (typical screen angles are C=15°, M=75°, Y=0°, K=45°).
Proofing is the process of generating a sample print, which represents the output that can be expected from a printing press. Proofing printers (“proofers”) are relatively inexpensive printers that strive to accurately represent the press output, including its color and quality. Color management for proofing devices is very important, because such devices generally use different color inks or donors than do the printing presses (proofer CMYK≠press CMYK). And even if a proofing device were to use the same color primaries as a particular press, such a device may not be usable with other presses. This is because not all of them use primary inks with the same hues, with American and European presses exhibiting significant differences in this area. Proofers may also need to match specialty or “spot” colors, which are essentially 5
th
or 6
th
colors used by the press for colors that the press's primary colors cannot reproduce well or at all.
In order to produce a color match on the proofer, the image data is typically color corrected before halftone processing. This process results in different data sets being halftone processed for the proofer and the press. Even if the same halftoning technique is used for both machines, the resulting halftone pattern for the two devices will be slightly different in order to make up for the color mismatch.
Some proofing devices focus on matching the color of the press, but appear not to be completely accepted because they use different halftoning techniques than the press. The feeling is that proofs from these devices cannot be used to predict the Moiré that can be expected on the press. Other proofing devices focus on matching the halftoning technique of the press as exactly as possible, but tend not to produce a good color match.
SUMMARY OF THE INVENTION
One general aspect of the invention provides for creating half-tone ink-jet proofs on print-enhanced sheets based on an effective image cell pitch of at least about 2400 image cells per inch that substantially matches a cell pitch used to create press plates. This approach has apparently never been tried by the engineers, technicians, and executives employed in the 15 year history of the dedicated digital inkjet contract proofing industry, despite the active participation of around 15 companies, including several large multinational corporations. This manner of thinking appears to result at least in part from a consistent and longstanding focus in the industry on the use of a single ink color set to match different press color sets and spot colors.
In preferred embodiments, print process variables can be adjusted for the ink-jet proofing printer based on received color matching information. These adjustments can define preprint ink mixing ratios that allow at least some image cells to be printed with ink mixtures. Or they can define sub-area printing values that allow at least some dots to be printed with areas of different inks.
Systems according to the invention can exhibit substantial advantages over other existing proofing techniques, including analog proofing techniques, press-specific proofing techniques, and laser deposition proofing techniques. Specifically, while analog proofs can be of high quality, they are cumbersome and expensive to produce. They are also incompatible with the increasingly common all-digital, direct-to-plate approach that the industry is steadily adopting.
Systems according to the invention also exhibit advantages over press-specific proofing techniques because press-specific proofers tend to be expensive and lack versatility. While proofers that match the exact process used on the press can produce high quality proofs, the process they are matching is typically optimized for large-scale printing. Press-specific proofers therefore tend to be more complex and more costly to run on a sheet-by-sheet basis. They also cannot generally be used to produce accurate proofs for presses that use other processes. And “dual-use” presses that include proofing capabilities generally cannot produce proofs without tying up their expensive high volume press capabilities, and cannot produce them at all during their long, high-volume runs.
Systems according to the invention exhibit advantages over laser deposition techniques because such techniques employ expensive proofers and rely on donor sheets that are bulky, expensive, and can be cumbersome to load, ship, and store. In addition, only a relatively small number of colors of donor sheets are currently available, even though this technique has been around for some time. And while print shops could produce their own sheets for particular requirements, this adds further complexity and expense to an already relatively cumbersome and expensive technique.
Generally, this aspect of the invention provides for a method of printing an inkjet proof of a document to be printed with a half-tone reference printer that uses one of four or more different inks with each of a number of different plates produced by a setter based an effective horizontal image cell pitch of at least about 2400 image cells per inch and an effective vertical image cell pitch of at least about 2400 image cells per inch. The method includes receiving print data that describes half-tone dots having a predetermined perimeter using image cells at substantially the same horizontal image cell pitch and substantially the same vertical image cell pitch that is used by the setter to create the plates for the reference printer for the four or more colors. A proofing sheet is received including a first rectangular deposited ink drop printable face having a periphery defined by an ordered series of first, second, third, and fourth edges of the proofing sheet, and including a second face opposite the first face and also having a periphery being defined by the first, second, third, and fourth edges of the imposition proofing print sheet, with at least the first face having properties resulting from a deposited ink drop print-enhancing treatment. A half-tone proof is made for the four or more colors with an inkjet proofer on at least the first face of the proofing sheet at substantially the same horizontal cell pitch as the effective horizontal cell pitch of the data received in the step of receiving and at substantially the same vertical cell pitch as the effective vertical cell pitch of the data received in the step of receiving.
In preferred embodiments, color matching information can be received for the ink set to be used by the reference printer to print the document, print process variables can be adjusted for the inkjet proofing printer based on the color matching information received in the step of receiving, and printing can occur according to these process variables. The step of adjusting can define preprint ink mixing ratios, with the step of printing printing at least some of the image cells with ink mixtures. The step of adjusting can define sub-area printing values, with the step of printing printing at l

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