Optics: measuring and testing – By shade or color
Reexamination Certificate
2001-10-31
2004-04-06
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By shade or color
C356S404000, C356S073000
Reexamination Certificate
active
06717672
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color measurement method of determining colorimetric values of a measurement object color area on a printed form, typically color patches constituting a color chart on the printed form.
2. Description of the Related Art
Hitherto, it is performed that an input device, for example, a color scanner or an electronic still camera, is used to take an image (hereinafter, it is referred to as an original image) in to obtain image data, so that an reproduced image of the original image is obtained in accordance with the image data by a printing machine or a printer. In this case, there are determined a color reproduction characteristic (profile) associating a color on the original image with a color on the image data, according to the input device, and a color reproduction characteristic (profile) associating a color on the image data with a color on the reproduced image, according to the output device such as a printing machine and a printer, and image data obtained from the original image by the input device is converted into image data suitable for the output device in accordance with both the color reproduction characteristics, so that the reproduced image is outputted in accordance with the image data for the output device. This feature makes it possible to obtain the reproduced image coincident with the original image in color.
The same matter as the above will occur between output devices. Next, there will be explained an example.
Hitherto, when a printing machine is used to perform a color image printing, it is performed that prior to the printing, a color printer and the like is used to create a proof image which is intended to be similar in color to an image to be printed by the printing machine. When the printer creates the proof image, detected are a color reproduction characteristic (a printing profile) describing a relationship between image data and a color of the actual printed matter, associated with a printing machine of interest, and a color reproduction characteristic (a printer profile) describing a relationship between image data and a color of an image to be actually printed, associated with a printer. Image data for printing is converted into image data for printers in accordance with the printing profile and the printer profile, so that a proof image is created in accordance with the image data for printers thus converted. Thus, it is possible to create a proof image that is coincident with the actual printed matter in color.
In order to obtain a proof image that is coincident with the actual printed matter in color in the manner as mentioned above, there is a need to determine with great accuracy color reproduction characteristics (profiles) of the input device and the output device. When the color reproduction characteristics (profiles) are determined, for example, in case of the input device, a color chart, in which color patches are arranged, is read by the input device and then converted into image data, and coordinates (CYMK values, or RGB values) of color spaces (a device color space: for example, a CMYK color space consisting of four colors of cyan (C), magenta (M), yellow (Y) and black (K), or an RGB color space consisting of three colors of red (R), green (G) and blue (B))) on the image data are determined. And the same color chart is measure by a spectrocolorimeter to determine coordinates (L*a*b* values or XYZ values) of a colorimetry color space (for example, L*a*b* color spaces or XYZ color spaces), and the coordinates on the device color space are associated with the coordinates on the colorimetry color space. Thus, it is possible to determine the color reproduction characteristics (profile) of the input device.
When the color reproduction characteristics (profile) of the output device is determined, image data, which corresponds to a color chart wherein color patches are arranged, is created, the output device outputs the color chart in accordance with the image data thus created, the color chart is measured by the spectrocolorimeter, and the coordinates of the color space (the device color space) on the image data are associated with the coordinates of the colorimetry color space. Thus, it is possible to determine the color reproduction characteristics (profile) of the output device.
By the way, a printed form, which includes fluorescent brightening agent to enhance white so that an image looks more beautiful, comes onto the market. In the event that an original image is recorded on a printed form including the fluorescent brightening agent, or in the event that a printing image or a print image is outputted onto the printed form including the fluorescent brightening agent, when a measurement light source used in measurement for colorimetric values of color charts when a profile is produced is different from an observation light source for illuminating images such as an original image, a printing image and a print image when those images are observed, a difference between the measurement light source and the observation light source in emission quantity of the fluorescent brightening agent included in the printed form causes discrepancy in spectral reflectance. Thus, it happens that although there is obtained coincidence in value derived through a color measurement, there is obtained no association in color through the visual observation.
As a method of solving this problem, there is proposed a technology (cf. Japanese Patent Laid Open Gazette Hei. 10-176953) that at the time of color measurement, the color measurement is performed on each of color patches constituting a color chart in two ways according to one of which light of a shortwave is cut and another light of a shortwave is not cut, so that emission quantity of the fluorescent brightening agent is determined and the colorimetric value is correct to meet the observation light source. This method is expressed by formulas as follows.
X=X
0
+Eil
*(
X
1−
X
0)
Y=Y
0+
Eil
*(
Y
1−
Y
0)
Z=Z
0+
Eil
*(
Z
1−
Z
0) (1)
Where X0, Y0 and Z0 denote XYZ values measured using a measurement light source wherein a short wavelength side is cut, and X1, Y1 and Z1 denote XYZ values measured using a measurement light source wherein a short wavelength side is not cut. Eil denotes an index indicative of the influence by a fluorescent brightening agent, and is expressed by Eil=E
S
/E
L
, where E
L
denotes fluorescence excitation intensity on the measurement light source wherein a short wavelength side is not cut, and E
5
denotes fluorescence excitation intensity on the observation light source. This Eil is a value, which can be determined beforehand taking the observation light source and the like into consideration.
According to adoption of the above-mentioned former method, it is possible to correct XYZ values obtained through a color measurement to XYZ values obtained through an observation light source.
However, according to the above-mentioned former method, it is necessary to perform twice measurements on each of a plurality of color patches constituting a color chart using the measurement light source wherein a short wavelength side is cut and the measurement light source wherein a short wavelength side is not cut. It is usual that a color chart is constituted of hundreds of color patches arranged. It would take a long time to perform twice measurements on each of such a many color patches, and it is a problem in workability.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a color measurement method capable of determining colorimetric values corrected in the influence of the fluorescent brightening agent, which are involved in the actual observation, with excellent workability.
To achieve the above-mentioned object, the present invention provides a color measurement method of determining colorimetric values on a colorimetric object color area on a printed form, said color measurement meth
Font Frank G.
Lauchman Layla
Sughrue & Mion, PLLC
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