1. Field of the Invention
The present invention relates to an image-forming method, an image-forming apparatus, an ink set, and an ink. More specifically, the present invention relates to an image-forming method, an image-forming apparatus, an ink set, and an ink for allowing an image to be obtained on a recording medium, the image being vivid, the image having a high contrast, high transparency, and a high stereoscopic effect, and the image smoothly representing a change of color.
2. Related Background Art
Methods of forming a full-color image such as offset printing, gravure printing, electrophotographic printing, and an ink jet recording method have been conventionally and extensively used. Of those image-forming methods, the ink jet recording method has been extensively used for personal-use and office-use printers, facsimiles, copying machines, and the like. The reasons why the ink jet recording method is used include: that the method causes low noise; that a manufacturing cost of an apparatus used in the method is low; that the apparatus can be miniaturized; and that a full-color recorded image can be easily obtained.
In many of those image-forming methods, a full-color image is formed on the basis of subtractive color mixing. Therefore, color reproduction is performed by using three primary colors of printing: yellow, magenta, and cyan. In some of the image-forming methods, a black ink is used in addition to the inks of those three primary colors, while a UCR treatment is performed to improve contrast or to stably reproduce a neutral color. In the UCR treatment, a black component K is sampled form data Y, M, and C on the respective colors of yellow, magenta, and cyan to substitute for black, and the substituted color components of C, M, and Y are removed. With the above procedure, for example, an image of an orange to red region, an image of a green region, and an image of a blue to violet region can be formed by color mixing of yellow and magenta, color mixing of yellow and cyan, and color mixing of magenta and cyan, respectively. As a result, the entire region of hue can be represented.
In addition, a full-color printing technique requires a printing method having a wide color reproduction region for reproduction of a natural image or the like. Therefore, color materials with good color developability for use in recording agents for the basic three primary colors, yellow, magenta, and cyan, have been widely proposed. However, when one attempts to represent the entire region of hue with the three primary colors, even if color materials for the three primary colors with good color developability are used, the chroma saturation in a color region represented by color mixing of the three primary colors is not sufficient. Thus, a color reproduction region that can be represented is insufficient in some cases. In view of the above, there has been proposed a method of forming an image using, for example, recording agents for colors each having an intermediate hue angle in a hue space (hereinafter, referred to as particular colors) such as red, green, and blue in addition to the recording agents for yellow, magenta, and cyan.
For example, the pamphlet of WO 02/100959 A discloses an ink set containing inks of the basic three primary colors having specific hue angles and inks of red and blue. In addition, the ink of each of red and blue used has a lightness lower than that of the ink of each of magenta and cyan, whereby the gamut is enlarged, graininess is mitigated, and gloss is improved.
JP 2003-034765 A discloses an ink set containing: inks of the basic three primary colors using a magenta ink containing a specific dye; and an ink of any one of orange, green, and violet. Similarly to the above, the gamut is enlarged through the addition of a particular color.
JP 2002-241661 A discloses an ink jet printing method using inks of red, green, and blue in addition to inks of the three primary colors, yellow, magenta, and cyan, more specifically, a printing method using a vat dye for an ink of each color. In this patent document as well, the gamut is enlarged and, at the same time, an intermediate color is represented by using a basic color and a particular color close to each other in hue. As a result, graininess is reduced as compared to that in the case where an intermediate color is represented by using a basic color alone, and color gradation is improved.
However, the widespread of a recording system, in particular a recording system using an ink jet recording method, up to a personal user has been requesting a further improvement in image quality. The further improvement in image quality is ultimately nothing but an attempt to bring a color reproduction region of a printer near to a color range which man can visually recognize in the natural world. However, the improvement cannot be achieved merely by adding a particular color (for instance, red, orange, green, blue, or violet) having an angle in an intermediate region of the three primary colors of printing in the color space.
For example, in any of the above documents, an image-forming method in which an ink of a particular color (red or orange) in an intermediate region between yellow and magenta is merely added has an effect of enlarging a color reproduction region of an orange to red region on an a*b* plane of Commission Internationale de l'Eclairage (CIE)-L*a*b*, but is insufficient for representing the vividness, stereoscopic effect, and transparency of an image.
In addition, when image representation is performed by adding a particular color to the basic three primary colors as in the pamphlet of WO 02/100959 A, graininess is reduced. However, the occurrence of pseudocontour or the so-called “color skip” caused by an increase in times of switching of ink colors during a change of color in the image is insufficiently suppressed. Consequently, at present, it is impossible to form an image that has enlarged a color reproduction region while smoothly representing a natural image. In particular, for beautifully reproducing an image of a view of sunset, autumn leaves, or the like, not only a wide color reproduction region but also an image-forming method for improving the vividness, transparency, and contrast of an image in an orange to red region and for minimizing pseudocontour or color skip occurring when a color continuously changes in the image to smoothly represent a color with no discontinuity will be required. However, a satisfactory result has not been obtained yet.
In view of the above, the inventors of the present invention have recognized that selection or the like of a particular color recording agent having appropriate properties should be performed in relation to the basic three primary colors. In addition to the above, the inventors have found that an image formed on a positive film of a silver halide photograph will be a guideline to the selection or the like. Since the image is a transmission image in which light is allowed to transmit through the backside of the image formed on the positive film to act on the sense of sight of a human being, an image excellent in realism, vividness, transparency, contrast, and stereoscopic effect may be perceived. In addition, the inventors have thought that the realization of image quality comparable to that of a transmission image with a reflection image is effective in further improving image quality.
First of all, the inventors of the present invention compared an image formed on a positive film and an image formed with a printer with the widest color reproduction region at present for various images of scenes, plants, persons, computer graphics (CG), and the like. An example of the comparison is described below.
FIG. 1 shows gamuts of an ink jet recording system and a positive film plotted on the a*b* plane of CIE-L*a*b*. In the figure, the gamut of the ink jet printer is surrounded by a solid line and painted whereas the gamut of the positive film is indicated by points. As is apparent from the figure, the gamut of the positive film is larger than the gamut of the ink jet printer in the Y to R region, the G region, and the B region.
FIGS. 2A and 2B are each a diagram for explaining the mode of calculating the gamut data shown in FIG. 1. In FIG. 2A, the gamut data for the positive film is obtained by scanning a total of 84 positive films from 8 categories consisting of mountain photograph (sunset), scene (sea and mountain), flower, fish, bird, butterfly, ethnic costume, and CG. Here, a Nexscan F4200 manufactured by Heidelberg GmbH was used as the scanner, and the color space used was Wide Gamut RGB. In the Wide Gamut RGB, the chromaticity of a white point is D50 and the values for chromaticity coordinates of RGB three primary colors are (0.73, 0.27) for R, (0.12, 0.83) for G, and (0.16, 0.02) for B. Equations for converting the Wide Gamut RGB into XYZ are:X=0.7165×R+0.1010×G+0.1468×B;Y=0.2587×R+0.7247×G+0.0166×B; andX=0.0000×R+0.0512×G+0.7739×B.Equations for converting XYZ into L*a*b* used were those defined in CIE.
In addition, in the calculation of the gamut data for the ink-jet recording system shown in FIG. 2B, a color patch was printed on recording paper PR101 manufactured by Canon Inc. by using a PIXUS 950i manufactured by Canon Inc. as a recording system, and the paper was subjected to colorimetry on a Spectrolino manufactured by Gretag Macbeth Ltd. The printer used here is for forming an image by adding light cyan and light magenta to yellow, magenta, cyan, and black. The gamut of the printer is smaller than the gamut of a recorded product obtained from the positive film of the so-called silver halide photograph shown in FIG. 2A.