Image processing apparatus and method, and profile generating method

• US 6,542,634 B1
• Filed: 07/22/1999
• Issued: 04/01/2003
• Est. Priority Date: 07/24/1998
• Status: Expired due to Term

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Ohga, Manabu
• Primary Examiner(s): Mancuso, Joseph
• Assistant Examiner(s): BHATNAGAR, ANAND P
• Application Number:
  US09/358,410
• Time in Patent Office: 1,349 Days
• Field of Search: 382/162, 382/167, 358/518, 358/519, 358/520, 358/521, 358/523, 358/1.9
• US Class Current: 382/167
• CPC Class Codes: H04N 1/6058 Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut
• CPC Class Codes: H04N 1/6086 by scene illuminant, i.e. conditions at the time of picture capture, e.g. flash, optical filter used, evening, cloud, daylight, artificial lighting, white point measurement, colour temperature
• CPC Class Codes: H04N 1/6088 by viewing conditions, i.e. conditions at picture output

Abstract

If gamut mapping (hue restoration) defined by one Lab color space is applied in color matching under different reference white points, the human vision perceives the hue as inconsistent. In view of this, input data which is dependent on a color space of an input device is converted by the conversion LUT 11 to color space data which is independent of any devices, based on a viewing condition at the time of viewing an input original. The data is converted to data in the human color perception space by the forward converter 12, then subjected to gamut mapping, and converted back to data in the color space independent of any devices by the inverse converter 15, based on a viewing condition at the time of viewing an output original. Then, the data is converted to output data in a color space which is dependent on an output device by the conversion LUT 16.

Claims

1. An image processing apparatus for performing color matching process, comprising:

a first converter, arranged to convert input image data in a color space dependent on an input device to first data, in accordance with a viewing condition at the time of viewing an input original in an independent color space which is independent of any device;

a second converter, arranged to convert the first data to second data in a human color perception space;

a third converter, arranged to convert the second data to third data in accordance with a viewing condition at the time of viewing an output original in the independent color space; and

a fourth converter, arranged to convert the third data to image data to be outputted to an output device in a color space dependent on the output device.

2. The apparatus according to claim 1, wherein said first converter uses a conversion characteristic to convert the input image data to the first data, and obtains the converting characteristic by:

obtaining relation data, which indicates a relationship between color target data in the independent color space and color target data in the color space dependent on the input device, from a profile corresponding to the input device;

converting the color target data in the independent color space included in the relation data to data in the human color perception space based on a condition for measuring the color target data in the independent color space; and

converting the data in the human color perception space to data in the independent color space based on the viewing condition at the time of viewing the input original.

3. The apparatus according to claim 1, wherein said fourth converter uses a conversion characteristic to convert the third data to the image data to be outputted, and obtains the converting characteristic by:

obtaining relation data, which indicates a relationship between color target data in the independent color space and color target data in the color space dependent on the output device, from a profile corresponding to the output device;

converting the color target data in the independent color space included in the relation data to data in the human color perception space based on a condition for measuring the color target data in the independent color space; and

converting the data in the human color perception space to data in the independent color space based on the viewing condition at the time of viewing the output original.

4. The apparatus according to claim 1, further comprising a color space compressor, arranged to perform gamut mapping on the second data, wherein the gamut mapping is the basis of a color gamut of the output device.

5. The apparatus according to claim 4, wherein the color gamut is obtained by:

obtaining conversion data from a profile corresponding to the output device, where the conversion data is used to convert data in the independent color space to data in the color space dependent on the output device;

converting data in the independent color space, which is included in the converting data, to data in the human color perception space based on a condition for measuring the data in the independent color space; and

converting the data in the human color perception space to data in the independent color space based on the viewing condition at the time of viewing the output original.

6. The apparatus according to claim 1, wherein JCH color space which is a color perception space relative to a reference white point of an ambient light, or QMH color space which is an absolute color perception space whose size is changed in accordance with an illumination level, is used as the human color perception space.

7. The apparatus according to claim 6, wherein the QMH color space is used for performing absolute color matching while the JCH color space is used for performing relative color matching.

8. The apparatus according to claim 1, wherein at least one of a digital still camera, digital video camera, image scanner, or film scanner serves as the input device.

9. The apparatus according to claim 1, wherein at least one of a monitor, printer, or film recorder serves as the output device.

10. An image processing method for performing color matching process, comprising:

a first converting step of converting input image data in a color space dependent on an input device to first data, in accordance with a viewing condition at the time of viewing an input original in an independent color space which is independent of any device;

a second converting step of converting the first data to second data in a human color perception space;

a third converting step of converting the second data to third data in accordance with a viewing condition at the time of viewing an output original in the independent color space; and

a fourth converting step of converting the third data to image data to be outputted to an output device in a color space dependent on the output device.

11. A computer program product comprising a computer readable medium having computer program codes, for an image processing method of performing color matching process, said product comprising:

process procedure code for converting input image data in a color space dependent on an input device to first data, in accordance with a viewing condition at the time of viewing an input original in an independent color space which is independent of any device;

second conversion process procedure code for converting the first data to second data in a human color perception space;

third conversion process procedure code for converting the second data to third data in accordance with a viewing condition at the time of viewing an output original in the independent color space; and

fourth conversion process procedure code for converting the third data to image data to be outputted to an output device in a color space dependent on the output device.

12. A profile generating method for generating a profile dependent on a viewing condition, comprising the steps of:

obtaining relation data from a profile where the relation data indicates relationship between color target data which has been measured under a standard illuminant and is independent of any device, and color target data dependent on an input device;

converting the color target data in the independent color space, which is included in the relation data, to data in a human color perception space based on a condition for measuring the color target data in the independent color space; and

converting the data in the human color perception space to data in the independent color space based on the viewing condition so as to generate a converting characteristic to convert data dependent on a device to data which is independent of any device as the profile.

13. A computer program product comprising a computer readable medium having computer program codes, for generating a profile dependent on a viewing condition, said product comprising:

obtaining process procedure code for obtaining relation data from a profile where the relation data indicates relationship between color target data which has been measured under a standard illuminant and is independent of any device, and color target data dependent on an input device;

first conversion process procedure code for converting the color target data in the independent color space, which is included in the relation data, to data in a human color perception space based on a condition for measuring the color target data in the independent color space; and

second conversion process procedure code converting the data in the human color perception space to data in the independent color space based on the viewing condition so as to generate a converting characteristic to convert data dependent on a device to data which is independent of any device as the profile.

14. A computer readable medium recording a converting characteristic in accordance with a viewing condition at the time of viewing an input original for converting data dependent on a device to data which is independent of any device, the converting characteristic generated by:

obtaining relation data from a profile where the relation data indicates relationship between color target data which has been measured under a standard illuminant and is independent of any device, and color target data dependent on an input device;

converting the color target data in the independent color space, which is included in the relation data, to data in a human color perception space based on a condition for measuring the color target data in the independent color space; and

converting the data in the human color perception space to data in the independent color space based on the viewing condition so as to generate a converting characteristic to convert data dependent on a device to data which is independent of any device as the profile.

15. An image processing method of performing color matching process, comprising the steps of:

converting input data in an input color space depended on an input device into first data in an independent color space which is independent of any device, based on an input viewing condition at the time of viewing an input original, by using a conversion characteristic;

calculating second data in a human color perception space by performing a forward conversion of a color appearance model, which corresponds to the input viewing condition, on the first data;

calculating third data in the human color perception space by performing gamut mapping, which corresponds to a color reproduction range of an output device, on the second data;

calculating fourth data in the independent color space by performing an inverse conversion of the color appearance model, which corresponds to an output viewing condition at the time of viewing an output original, on the third data; and

converting the fourth data into output data in an output color space depended on the output device,

wherein generation of the conversion characteristic comprising the steps of;

obtaining relational data which indicates relationship between target data of color targets in the independent color space, and read data in the input color space obtained by which the input device reads color of the color targets;

converting the target data included in the relational data into converted target data in the human color perception space based on a measuring condition for the target data; and

converting the converted target data into data in the independent color space as the conversion characteristic, based on the input viewing condition.

16. An image processing method of performing color matching process, comprising the steps of:

converting input data in an input color space depended on an input device into first data, based on an input viewing condition at the time of viewing an input original;

calculating second data in a human color perception space by performing a forward conversion of a color appearance model, which correspond to the input viewing condition, on the first data;

calculating third data in the human color perception space by performing gamut mapping, which corresponds to a color reproduction range of an output device, on the second data;

calculating fourth data in the independent color space by performing an inverse conversion of the color appearance model, which corresponds to an output viewing condition at the time of viewing an output original, on the third data; and

converting the fourth data into output data in an output color space depended on the output device by using a conversion characteristic,

wherein generation of the conversion characteristic comprising the steps of;

obtaining relational data which indicates relationship between first target data of color targets in the independent color space, and second target data in the output color space obtained by which the output device outputs the color targets;

converting the first target data included in the relational data into converted target data in the human color perception space based on a measuring condition for the first target data; and

converting the converted target data into data in the independent color space as the conversion characteristic, based on the output viewing condition.

17. A computer program product comprising a computer readable medium having computer program codes, for an image processing method of performing color matching process, said product comprising process procedure codes for:

converting input data in an input color space depended on an input device into first data in an independent color space which is independent of any device, based on an input viewing condition at the time of viewing an input original, by using a conversion characteristic;

calculating second data in a human color perception space by performing a forward conversion of a color appearance model, which corresponds to the input viewing condition, on the first data;

calculating third data in the human color perception space by performing gamut mapping, which corresponds to a color reproduction range of an output device, on the second data;

calculating fourth data in the independent color space by performing an inverse conversion of the color appearance model, which corresponds to an output viewing condition at the time of viewing an output original, on the third data; and

converting the fourth data into output data in an output color space depended on the output device,

wherein generation of the conversion characteristic comprising the process procedure codes for;

obtaining relational data which indicates relationship between target data of color targets in the independent color space, and read data in the input color space obtained by which the input device reads color of the color targets;

converting the target data included in the relational data into converted target data in the human color perception space based on a measuring condition for the target data; and

converting the converted target data into data in the independent color space as the conversion characteristic, based on the input viewing condition.

18. A computer program product comprising a computer readable medium having computer program codes, for an image processing method of performing color matching process, said product comprising process procedure codes for:

converting input data in an input color space depended on an input device into first data, based on an input viewing condition at the time of viewing an input original;

calculating second data in a human color perception space by performing a forward conversion of a color appearance model, which corresponds to the input viewing condition, on the first data;

calculating third data in the human color perception space by performing gamut mapping, which corresponds to a color reproduction range of an output device, on the second data;

calculating fourth data in the independent color space by performing an inverse conversion of the color appearance model, which corresponds to an output viewing condition at the time of viewing an output original, on the third data; and

converting the fourth data into output data in an output color space depended on the output device by using a conversion characteristic,

wherein generation of the conversion characteristic comprising process procedure codes for;

obtaining relational data which indicates relationship between first target data of color targets in the independent color space, and second target data in the output color space obtained by which the output device outputs the color targets;

converting the first target data included in the relational data into converted target data in the human color perception space based on a measuring condition for the first target data; and

converting the converted target data into data in the independent color space as the conversion characteristic, based on the output viewing condition.