Color conversion apparatus, non-transitory recording medium storing color conversion program and color conversion method

Patent metadata

Field	Value
Publication number	US-10129438-B2
Application number	US-201715642562-A
Country	US
Kind code	B2
Filing date	Jul 6, 2017
Priority date	Jul 11, 2016
Publication date	Nov 13, 2018
Grant date	Nov 13, 2018

Abstract

A color conversion apparatus includes a hardware processor that obtains a scanner profile created on the basis of measured RGB values and corresponding measured colorimetric values of patches in a first color chart, and creates a table including correction amounts of RGB values, each according to the level of flare estimated for a patch and each associated with an RGB-value difference and a patch-size difference, on the basis of RGB values of patches in the first color chart and RGB values of patches in a specific chart. The specific chart is created by using a part of the patches in the first color chart with the RGB value or patch size being changed. The hardware processor further corrects measured RGB values of patches in a second color chart with the table, and convers the corrected RGB values into colorimetric values with the scanner profile.

First claim

The invention claimed is:

1. A color conversion apparatus for converting measured RGB values given by measurement of a color chart printed by a printer, into colorimetric values being L*a*b* values or XYZ values, the color conversion apparatus comprising:
a storage unit; and
a hardware processor that performs:
obtaining a scanner profile in which measured RGB values and corresponding measured colorimetric values given by measurement of patches in a first color chart printed by the printer are associated with each other;
creating a table on a basis of RGB values of patches in the first color chart and RGB values of patches in a specific chart created by using a part of the patches in the first color chart with an RGB value or patch size being changed, wherein the table includes correction amounts of RGB values, each according to a level of flare estimated for a patch and each associated with an RGB-value difference and a patch-size difference;
storing the table in the storage unit;
correcting, by using the table, measured RGB values given by measurement of patches in a second color chart which is different from the first color chart in RGB values or patch size of at least a part of patches, to obtain corrected RGB values; and
converting the corrected RGB values into colorimetric values by using the scanner profile.

2. The color conversion apparatus of claim 1 ,
wherein the color conversion apparatus is communicably connected with a scanner and a colorimeter,
the hardware processor further performs:
obtaining, from the scanner, measured RGB values given by measurement of the patches in the first color chart with the scanner and measured RGB values given by measurement of the patches in the second color chart with the scanner;
obtaining, from the colorimeter, measured colorimetric values given by measurement of the patches in the first color chart with the colorimeter; and
in the obtaining the scanner profile, associating the measured RGB values of the patches in the first color chart obtained from the scanner, with the corresponding measured colorimetric values of the patches in the first color chart obtained from the colorimeter, to create the scanner profile.

3. The color conversion apparatus of claim 1 ,
wherein the hardware processor further performs, in the creating the table:
choosing a reference patch group being a group of a certain number of patches, from the first color chart;
creating a first plurality of patch groups by changing an RGB value of a patch located at a certain position in the reference patch group and creating a second plurality of patch groups by changing patch size of the reference patch group;
causing the printer to print the specific chart in which the first plurality of patch groups and the second plurality of patch groups are arranged;
obtaining measured RGB values given by measurement of patches in the specific chart with the scanner;
calculating RGB-value differences of set RGB values of patches in the specific chart from a mean RGB value of the first color chart, the patches in the specific chart being patches in the first plurality of patch groups in the specific chart and having been changed in RGB values in creating the first plurality of patch groups, the mean RGB value being given by averaging set RGB values of all of the patches in the first color chart;
calculating patch-size differences of patch sizes of the second plurality of patch groups in the specific chart from patch size of the first color chart;
calculating a first value by subtracting a set RGB value of a patch located at a center of each of the first and second plurality of patch groups in the specific chart, from the measured RGB value of the patch located at the center of each of the first and second plurality of patch groups in the specific chart;
calculating a second value by subtracting the mean RGB value of the first color chart, from the measured RGB value of a patch located at a center of the reference patch group in the first color chart;
subtracting the first value calculated for the patch located at the center of each of the first and second plurality of patch groups, from the second value, to obtain the correction amounts of RGB values; and
associating the correction amounts of RGB values with the corresponding RGB-value differences and the corresponding patch-size differences, to create the table.

4. The color conversion apparatus of claim 3 ,
wherein the hardware processor further performs, in the creating the table:
creating a first table by changing the RGB value of the patch located at the center of the reference patch group to RGB values, in the creating the first plurality of patch groups; and
creating a second table by changing an RGB value of each of patches surrounding the patch located at the center of the reference patch group to RGB values, in the creating the first plurality of patch groups, and

wherein the hardware processor further performs, in the correcting the RGB values:
comparing set RGB values of the patches in the second color chart with the mean RGB value of the first color chart and further comparing sizes of the patches in the second color chart with the patch size of the first color chart, to calculate RGB-value differences and patch-size differences for the patches in the second color chart; and
correcting the measured RGB values given by measurement of patches in the second color chart with the scanner, by
using the first table to obtain the correction amount of an RGB value of each of the patches in the second color chart, associated with the RGB-value difference and the patch-size difference under a condition that the patch located at the center of the reference patch group is changed to the each of the patches in the second color chart,
using the second table to obtain the correction amounts of an RGB value of each of the patches in the second color chart, associated with the RGB-value differences and the patch-size differences under a condition that each of the patches surrounding the patch located at the center in the reference patch group is changed to a corresponding one of patches surrounding each of the patches in the second color chart, and
correcting the measured RGB value of each of the patches in the second color chart, by using the correction amounts obtained with the first table and the second table for the each of the patches in the second color chart.

5. The color conversion apparatus of claim 4 ,
wherein the reference patch group is composed of a matrix of nine patches, having three rows and three columns, in the first color chart, and
the hardware processor further performs, in the correcting the RGB values:
using the first table to obtain the correction amount of an RGB value of each of the patches in the second color chart, under a condition that an RGB value of the patch located at the center of the reference patch group is changed to the RGB value of the each of the patches in the second color chart;
using the second table to obtain the correction amounts of the RGB value of each of the patches in the second color chart, under a condition that an RGB value of each of eight patches surrounding the patch located at the center of the reference patch group is changed to an RGB value of a corresponding one of eight patches surrounding the each of the patches in the second color chart; and
correcting the measured RGB value of each of the patches in the second color chart, by using a total correction amount calculated by adding up the correction amounts obtained by using the first table and the second table for the each of the patches in the second color chart.

6. The color conversion apparatus of claim 1 ,
wherein the patches in the first color chart are arranged so that a level of flare est

Assignees

• Konica Minolta Inc

Inventors

• Yamaguchi Takeshi

Classifications

• H04N2201/0094

  Multifunctional device, i.e. a device capable of all of reading, reproducing, copying, facsimile transception, file transception · CPC title

• H04N1/047

  Detection, control or error compensation of scanning velocity or position ({H04N1/0402 and } H04N1/17 take precedence) · CPC title

• G06T2207/20224

  Image subtraction · CPC title

• H04N1/6055

  using test pattern analysis · CPC title

• H04N1/6008 Primary

  with primary colour signals, e.g. RGB or CMY(K) · CPC title