Image processing method, image processing apparatus, and storage medium

• US 7,446,899 B2
• Filed: 07/12/2001
• Issued: 11/04/2008
• Est. Priority Date: 07/14/2000
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Matsuoka, Hirochika
• Primary Examiner(s): Coles; Edward L
• Assistant Examiner(s): Thompson; James A
• Application Number:
  US09/902,760
• Publication Number:
  US 20020054307A1
• Time in Patent Office: 2,672 Days
• Field of Search: 358/1.9, 358/448, 358/504, 358/505, 358/515, 358/518, 382/162, 382/167, 345/590
• US Class Current: 358/1.9
• CPC Class Codes: G06T 11/001 Texturing; Colouring; Generation of texture or colour inpainting G06T5/77
• CPC Class Codes: H04N 1/6058 Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut

Abstract

Mapping conversion to absorb differences of shapes of color reproduction gamuts and also preserve gradation is provided. In this image processing method, a color signal located within a first color reproduction gamut represented by a first color system is subjected to mapping conversion into a color signal located within a second color reproduction gamut represented by the first color system, where a locus of a change of color in the first color reproduction gamut is represented by a curve, mapping is performed to the curve, and the mapping conversion is performed on the basis of relation of the curves before and after the mapping.

Claims

1. An image processing method which maps a first color gamut into a second color gamut, comprising the steps of:

setting first sample points on a surface of the first color gamut, and second sample points in the first color gamut;

obtaining third sample points by mapping the first sample points into the second color gamut, and obtaining fourth sample points by mapping the second sample points into the second color gamut;

setting a plurality of independent surface gradation lines based on the first sample points and a plurality of independent internal gradation lines based on the second sample points, one of the surface gradation lines being defined by a function indicating a continuous locus linking the plurality of sample points in the first sample points, and one of the internal gradation lines being defined by a function indicating a continuous locus linking the plurality of sample points in the second sample points;

mapping the plurality of independent surface gradation lines based on the third sample points, and mapping the plurality of independent internal gradation lines based on the fourth sample points;

calculating a relative position of an input color to the surface gradation lines or the internal gradation lines; and

calculating an output color from the plurality of independent mapped surface gradation lines or the plurality of independent mapped internal gradation lines, based on the relative position,

wherein the surface gradation lines and the internal gradation lines each indicate a locus of color change in the first color gamut, and the plurality of independent mapped surface gradation lines and the plurality of independent mapped internal gradation lines each indicate a locus of color change in the second color gamut.

2. A method according to claim 1, wherein the surface, internal, mapped surface and mapped internal gradation lines are obtained by using at least one of a B-spline curve, a rational B-spline curve, a Bé

zier curve, and a one- or more-dimensional spline curve.

3. A method according to claim 1, wherein the first sample points are located on six faces of an R (red) face, a G (green) face, a B (blue) face, a C (cyan) face, an M (magenta) face and a Y (yellow) face in the first color gamut.

4. A method according to claim 1, wherein the mapping of the surface and internal gradation lines to the second color gamut includes two-dimensional mapping on a lightness-chroma plane according to the first color gamut and the second color gamut, and adjustment of a hue component.

5. An image processing method according to claim 1, wherein the relative position is defined by a ratio of internal division.

6. An image processing method according to claim 1, wherein the relative position is defined by an angle ratio.

7. An image processing apparatus which maps a first color gamut into a second color gamut, comprising:

a first sample point setting unit adapted to set first sample points on a surface of the first color gamut and second sample points in the first color gamut;

an obtaining unit adapted to obtain third sample points by mapping the first sample points into the second color gamut, and obtaining fourth sample points by mapping the second sample points into the second color gamut;

a gradation line setting unit adapted to set a plurality of independent surface gradation lines based on the first sample points and a plurality of independent internal gradation lines based on the second sample points, one of the surface gradation lines being defined by a function indicating a continuous locus linking the plurality of sample points in the first sample points, and one of the internal gradation lines being defined by a function indicating a continuous locus linking the plurality of sample points in the second sample points;

a gradation line mapping unit adapted to map the plurality of independent surface gradation lines based on the third sample points, and mapping the plurality of independent internal gradation lines based on the fourth sample points;

a calculating unit, for calculating a relative position of an input color to the surface gradation lines or the internal gradation lines; and

a calculating unit, for calculating an output color from the plurality of independent mapped surface gradation lines or the plurality of independent mapped internal gradation lines, based on the relative position,

wherein the surface gradation lines and the internal gradation lines each indicate a locus of color change in the first color gamut, and the plurality of independent mapped surface gradation lines and the plurality of independent mapped internal gradation lines each indicate a locus of color change in the second color gamut.

8. A computer-readable storage medium which computer-readably stores a program to cause a computer to execute an image processing method which maps a first color gamut into a second color gamut, said method comprising the steps of:

setting first sample points on a surface of the first color gamut, and second sample points in the first color gamut;

obtaining third sample points by mapping the first sample points into the second color gamut, and obtaining fourth sample points by mapping the second sample points into the second color gamut;

setting a plurality of independent surface gradation lines based on the first sample points and a plurality of independent internal gradation lines based on the second sample points, one of the surface gradation lines being defined by a function indicating a continuous locus linking the plurality of sample points in the first sample points, and one of the internal gradation lines being defined by a function indicating a continuous locus linking the plurality of sample points in the second sample points;

mapping the plurality of independent surface gradation lines based on the third sample points, and mapping the plurality of independent internal gradation lines based on the fourth sample points;

calculating a relative position of an input color to the surface gradation lines or the internal gradation lines; and

calculating an output color from the plurality of independent mapped surface gradation lines or the plurality of independent mapped internal gradation lines, based on the relative position,

wherein the surface gradation lines and the internal gradation lines each indicate a locus of color change in the first color gamut, and the plurality of independent mapped surface gradation lines and the plurality of independent mapped internal gradation lines each indicate a locus of color change in the second color gamut. aa

9. An image processing method which maps a first color gamut into a second color gamut, the first color gamut having a surface and having an interior contained entirely within the surface, and the second color gamut having a surface and having an interior contained entirely within the surface of the second color gamut, said method comprising the steps of:

setting a set consisting of a first predetermined number of first sample points on the surface of the first color gamut, and a set consisting of a second predetermined number of second sample points in the interior of the first color gamut, where the second predetermined number may be either equal to or different from the first predetermined number;

obtaining third sample points corresponding to respective ones of the first sample points, and fourth sample points corresponding to respective ones of the second sample points, wherein the third sample points and the fourth sample points are in the second color gamut, and the fourth sample points are in the interior of the second color gamut;

setting a plurality of independent first surface gradation lines based on the first sample points and a plurality of independent first internal gradation lines based on the second sample points, the plurality of independent first surface gradation lines each lying entirely on the surface of the first color gamut and the plurality of independent first internal gradation lines each containing points in the interior of the first color gamut, wherein the plurality of independent first surface gradation lines and the plurality of independent first internal gradation lines each indicate a respective locus of color change in the first color gamut, one of the surface gradation lines being defined by a function indicating a continuous locus linking the plurality of sample points in the first sample points, and one of the internal gradation lines being defined by a function indicating a continuous locus linking the plurality of sample points in the second sample points;

mapping the plurality of independent first surface gradation lines to a plurality of independent second surface gradation lines that are based on the third sample points, and mapping the plurality of independent first internal gradation lines to a plurality of independent second internal gradation lines that are based on the fourth sample points and that lie in the interior of the second color gamut, wherein the plurality of independent second surface gradation lines and the plurality of independent second internal gradation lines each indicate a respective locus of color change in the second color gamut; and

mapping an input color into an output color in the second color gamut by using the plurality of independent second surface gradation lines and the plurality of independent second internal gradation lines,

wherein said step of mapping the input color into the output color in the second gamut includes calculating the output color from the plurality of independent second surface gradation lines and the plurality of independent second internal gradation lines, based on the input color and its location in the first color gamut relative to at least one gradation line from among the plurality of independent first surface gradation lines and the plurality of independent first internal gradation lines.