Method of converting colorimetric values, and color image output apparatus

• US 6,522,778 B1
• Filed: 03/08/1999
• Issued: 02/18/2003
• Est. Priority Date: 03/11/1998
• Status: Expired due to Term

• Current Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Original Assignee: Fuji Photo Film Co Limited (Fujifilm Holdings Corporation)
• Inventors: Tamagawa, Kiyomi
• Primary Examiner(s): Wu, Jingge
• Application Number:
  US09/264,033
• Time in Patent Office: 1,443 Days
• Field of Search: 382/162, 382/167, 358/501, 358/504, 358/515, 358/518-523, 345/431, 345/589-604
• US Class Current: 382/167
• CPC Class Codes: H04N 1/4078 using gradational references, e.g. grey-scale test pattern analysis
• CPC Class Codes: H04N 1/60 Colour correction or control H04N1/54 takes precedence
• CPC Class Codes: H04N 1/6033 using test pattern analysis H04N1/6055 takes precedence

Abstract

In a color image output apparatus for producing a color proof, even when target gradations corresponding to printing conditions (inks, sheets, and printing press conditions) to be simulated are changed, colorimetric values measured by a first colorimeter for correcting gradation correcting one-dimensional LUTs for the hues R, G, B are converted into desired colorimetric values to enable the color image output apparatus to output desired colors. For using a three-dimensional CM LUT generated by a second colorimeter in order to generate corrective values for the one-dimensional LUTs, there is provided a colorimetric value correcting table for converting output data from the first colorimeter into desired colorimetric values on the second colorimeter.

Claims

1. A method of converting colorimetric values, comprising the steps of:

measuring a gray chart having equal gradations of hues of image data with a first colorimeter to obtain a measure reflectivity Rλ

1;

measuring a gray chart having one or more gray patches and having a constant reflectivity irrespective of the wavelength within a visible wavelength range at predeterimined wavelength intervals dλ

, with a second colorimeter and said first colorimeter to obtain a reflectivity at each of the wavelength intervals;

determining colorimetric values X, Y, Z according to the equations;

2. A method according to claim 1, wherein hues of said image data comprise R, G, B.

3. A color image output apparatus for supplying imputted device-dependent image data to an expose recording unit through gradation converting means for converting gradations of the image data depending on printing conditions of a given printing press, and outputting a color print for use as a color proof from said exposure recording unit, comprising:

color converting means for outputting a color chart having a plurality of color patches which represent spaced values of said image data, from said exposure recording unit, and converting colorimetric values measured of said color chart by a second colorimeter into device-dependent image data;

a first colorimeter for measuring colorimeteric values of said color chart to obtain an association between measured colorimetric values and colorimetric values corresponding to said device-dependent image data;

colorimetric value correcting means for converting colorimetric values measured by said first colorimeter into colorimetric values on said second colorimeter, in order to equalize the colorimetric values measured by said first colorimeter with the colorimetric values on said second colorimeter; and

means for supplying output data from said colorimetric value correcting means to said color converting means and correcting gradation converting characteristics of said gradation converting means with output data from said color converting means;

wherein said means comprises;

first means for outputting a gray chart having equal gradations of hues of the inputted image data of said gradation converting means from said exposure recording means;

second means for measuring colorimetric values of said gray chart with said first colorimeter, and producing measured colorimetric values L*, a*, b* by correcting the measured colorimetric values with said colorimetric value correction means; and

third means for inputting said measured colorimetric values L*, a*, b* and target colorimetric values L*0, a*0, b*0 to said color converting means, and adding differences Δ

R, Δ

G, Δ

B between image data R0, G0, B0 of the hues corresponding to said target colorimetric values L*0, a*0, b*0 and image data R1, G1, B1 of the hues corresponding to said measured colorimetric values L*, a*, b*, to output data of the hues from said gradation converting means thereby to correct said gradation converting characteristics.

4. A color image output apparatus according to claim 3, wherein said second means comprises:

means for measuring a gray chart having one or more gray patches having a constant reflectivity irrespective of the wavelength within a visible wavelength range at predetermined wavelength intervals dλ

, with a second colorimeter and said first colorimeter to obtain a reflectivity Rλ

1 at each of the wavelength intervals, determining colorimetric values X, Y, Z according to the equations;

5. A color image output apparatus according to claim 3, wherein said first colorimeter is an external colorimeter connected on-line to the color image output apparatus.

6. A color image output apparatus according to claim 3, wherein said first colorimeter is a built-in colorimeter incorporated in the color image output apparatus.

7. A color image output apparatus according to claim 4, wherein said first colorimeter is a built-in colorimeter incorporated in the color image output apparatus.

8. A color image output apparatus according to claim 4, wherein said first colorimeter is an external colorimeter connected on-line to the color image output apparatus.

9. A color image output apparatus for supplying inputted device-dependent image data to an exposure recording unit through gradation converting means for converting gradations of the image data depending on printing conditions of a given printing press, and outputting a color print for use as a color proof from said exposure recording unit, comprising:

color converting means for outputting a color chart having a plurality of color patches which represent spaced values of said image data, from said exposure recording unit, and converting colorimetric values measured of said color chart by a second colorimeter into device-dependent image data;

colorimetric value correcting means for converting colorimetric values outputted by a first colorimeter into inputted colorimetric values of said color converting means; and

means for measuring a gray chart having one or more gray patches having a constant reflectivity irrespective of the wavelength within a visible wavelength range at predetermined wavelength intervals dλ

, with said second colorimeter and said first colorimeter to obtain a reflectivity Rλ

1 at each of the wave length intervals, determining xolorimetric values X, Y, Z according to the equations;

10. A color image output apparatus according to claim 9, wherein said device-dependent image data comprise image data R, G, B.

11. A color image output apparatus according to claim 9, wherein said first colorimeter is an external colorimeter connected on-line to the color image output apparatus.

12. A color image output apparatus according to claim 9, wherein said first colorimeter is a built-in colorimeter incorporated in the color image output apparatus.

13. A color image output apparatus for supplying inputted device-dependent image data to an exposure recording unit through gradation converting means for converting gradations of the image data depending on printing conditions of a given printing press, and outputting a color print for use as a color proof from said exposure recording unit, comprising:

color converting means for outputting a color chart having a plurality of color patches which represent spaced values of said image data, from said exposure recording unit, and converting colorimetric values measured of said color chart by a second colorimeter into device-dependent image data;

a first colorimeter for measuring colorimeteric values of said color chart to obtain an association between measured colorimetric values and colorimetric values corresponding to said device-dependent image data;

colorimetric value correcting means for converting colorimetric values measured by said first colorimeter into colorimetric values on said second colorimeter, in order to equalize the colorimetric values measured by said first colorimeter with the colorimetric values on said second colorimeter; and

means for supplying output data from said colorimetric value correcting means to said color converting means and correcting gradation converting characteristics of said gradation converting means with output data from said color converting means;

wherein said means comprises;

first means for outputting a gray chart having equal gradations of hues of the inputted image data of said gradation converting means from said exposure recording means; and

second means for measuring colorimetric values of said gray chart with said first colorimeter, and producing measured colorimetric values L*, a*, b* by correcting the measured colorimetric values with said colorimetric value correcting means.