Color tone control method for printing press

Printing – Processes – Condition responsive

Reexamination Certificate

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Details

C358S001900, C358S500000, C358S512000

Reexamination Certificate

active

06722281

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color tone control method that adjusts the amount of ink dispensed to a printing press that is controlled by the results of multispectral measurements on printed articles, in particular, it relates to determining a transfer function to calculate the amount of ink dispensed based upon multispectral measurements, wherein the deviation from the target color is taken as the deviation in the multispectral output, and then the aforementioned calculation with the transfer function is used to calculate a corrected amount of ink to dispense as a means to control the color tone for printing press.
2. Description of the Related Art
Since the color reproducibility of printing presses varies according to a number of factors, in order to achieve the desired color tone in a print, it is imperative to use a color tone measuring apparatus to measure a color print and then adjust the color tone by adjusting the ink key, which controls the amount of ink dispensed by the printing press.
For example, in color management systems, in order to match the color reproducibility in individual devices such as printing presses and plate makers, one must determine the percentage dot area for the printing press and the color, for example, something corresponding to the color model as defined by the Commission Internationale de l'Eclairage (CIE L*a*b*) such as the color data called the “profile” by the International Color Consortium (ICC) (hereinafter referred to as the “profile”). Then based upon these elements, digital data must be converted on the upstream side in order to achieve a printed article with measured values that approximate the desired colors to thereby achieve a match to obtain the color reproducibility in a number of devices.
However, even if prints are made using this profile, in order to obtain the color tones exactly as desired, it is necessary to maintain the exact conditions during actual printing that were in place when the printing press's profile was prepared. But sometimes conditions of color reproducibility changes for a printing press, and sometimes conditions under which characteristic data was obtained change during actual printing.
In other words, color reproducibility is affected by small changes in the swing roller pass that evenly applies ink to the ink roller, the movement of the water roller, the printing pressure applied by the rubber roller body, etc. Further there can be variations in the materials used in the inks and printing paper, differences among printing presses, differences in humidity, temperature and in the start time for the printing which can all affect reproducibility, and even if printed at standard concentrations, there are cases where halftones are incompatible.
Accordingly, even when a color management system such as described above is used to prepare printing plates appropriate to a printing profile, for example, as indicated in Japanese laid-open patent application 2001-47605, spectral reflection measurements are made on the color coordinate values (L*a*b*) on actually printed articles (for commercial printed articles), and the concentrations of the inks are calculated in order to control the dispensing of ink. The case is the same when color management systems are not used. Proof prints and test prints (OK sheets) are measured using spectro-reflectometers for commercially printed items and then computations of the ink density are used to control the amount of ink dispensed.
When the amount of ink dispensed is controlled using spectral reflections, and when the spectral reflections are made to a high degree of precision, it is possible to determine correspondingly accurate color coordinates. However, as the resolution becomes finer in order to obtain high precision measurements, it is necessary to increase the number of channels, and so doing causes each signal to be smaller, which intensifies the influence of noise. In addition, the multichannel processing requires a great deal of time, so much as to be difficult to implement on a commercial basis.
At this point, attention was focused upon the redundancy of the spectral reflection wave forms, and an approach involving the learning of these spectral wave forms and then predicting the wave form by using just a few measurements. To wit, the spectral reflection wave forms change smoothly, and by keeping the materials such as ink and printing paper constant, it is possible to learn the characteristics of the spectral reflections in advance, and then, using just a few channels, predict the wave forms and reproduce them to a high degree of precision. Examples of the use of such technology include U.S. Pat. No. 5,319,472, and Japanese laid-open patent application 1997-43058, 2000-333186, 2001-99710, etc.
To wit, in U.S. Pat. No. 5,319,472 discloses a correction method in which 4 or more narrow band filters are interchanged as a picture image signal is obtained by light receptor elements, and then with a black filter (light blocking filter) that is substituted for the foregoing narrow band filter, and using a white sheet in place of the image, the image signals read by each of the narrow band filters are corrected by the signals obtained using the black filter and white sheet, and then, a coefficient is applied to that output in order to obtain the original spectral reflection of the image.
Also, disclosed in Japanese laid-open patent application 1997-43058 is the use of a plurality of band pass filters when scanning original, with the resulting signal being analyzed by statistical methods to compute a classification spectrum for the colors used as a means of determining the classification of the original article.
The method disclosed in Japanese laid-open patent application 2000-333186, illuminates the article to be photographed (the original) with a specific light source, and then using a plurality of filters that transmit different wavelengths, produces output into a plurality of channels of differing spectral sensitivity, and then either a photograph is taken with black and white film, which has an approximately uniform spectral sensitivity in the visible light wavelength range, and the image is scanned, or an image signal is obtained for each filter using a CCD sensor at the imaging position to obtain a wavelength range signal. Then, from that information, a multichannel camera can be used to regenerate the spectral reflectance of the article that was photographed, which provides spectral wave forms for each pixel of the photographed image that can be converted into a control signal for various image reproduction methods.
Japanese laid-open patent application 2001-99710 discloses the photographing of a multi-band image using a variable wavelength filter, which is then used to estimate the spectral reflectance of the article that was photographed. Since the estimated spectral information takes place over a short period of time, the precision of the estimate is not degraded, and the reflectance for each channel of the multi-band image is converted in a pre-prepared table for the corresponding reflectance for brightness values obtained by photographing a known chart. Then the table is used to estimate, in a short period of time, the spectral reflectance of the object photographed based upon the brightness values.
However, with regard to U.S. Pat. No. 5,319,472, as well as with Japanese laid-open patent application 1997-43058, 2000-333186, and 2001-99710, the first, U.S. Pat. No. 5,319,472 relates to a correction method for the spectral reflectance, Japanese laid-open patent application 1997-43058 makes a color classification determination on the article being reproduced, Japanese laid-open patent application 2000-333186 photographs an image with a multichannel camera and then produces spectral wave forms for each pixel that can be converted into control signals for various image reproduction methods, and Japanese laid-open patent application 2001-99710, quickly estimates the spectral reflectance of an item, an

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