1. Field of the Invention
The present invention generally relates to image processing apparatus, image processing method, and computer-readable recording medium storing image processing program for generating color tone correction parameter, and more particularly to the image processing apparatus, the image processing method, and the computer-readable recording medium storing image processing program for generating color tone correction parameter which are used for correcting color tone value of an image data, wherein patches of the same color, which indicate gradual changes of color tones of an uniform color, are arranged in a predetermined direction.
2. Description of the Related Art
Since a temporal change is occurred in a component or an assembled portion of the component of an image forming portion, the same print may not be obtained from the same image forming apparatus by using the same image data after a certain period of time. For example, two prints obtained from the same image data may be different from each other in a manner that color strength of the two prints differ from each other. An image forming apparatus, for example disclosed in patent document 1, has been proposed which scans a patch which constitutes an image data for correcting the color strength and is printed on a sheet, and executes a process for generating a color tone correction parameter based on the patch, in order to correct the different color strength. The image forming apparatus, disclosed in patent document 1, generates a color tone correction parameter based on four patches, each of which including a plurality of color tones and corresponding to each toner color of C, M, Y and K, and based on a patch formed by stacking three toner colors C, M and Y, in order to correct a specific characteristics of each toner.
The image forming apparatus may print a sheet with nonuniformity of color strength even if an image data, used for printing the sheet, includes uniform color strength for all of the pixels. In a xerographic image forming apparatus, the nonuniformity of color strength may be caused by assembling accuracy or quality of components such as, for example, eccentricity of a photo conductor and a transfer roller, variability of a distance between the photo conductor and a developer sleeve in the direction of rotational direction of the photo conductor.
An image forming apparatus, for example disclosed in patent documents 2 and 3, generates a color tone correction parameter used for reducing the nonuniformity of color strength in the direction of rotational axis of the photo conductor or the like (hereinafter referred to simply as a “main scanning direction”), or in the rotational direction of the photo conductor (hereinafter referred to simply as a “sub-scanning direction”), and for correcting the temporal change of the component or the like.
The image forming apparatus, disclosed in patent document 2, generates color tone correction parameter for reducing the nonuniformity of color strength in the main scanning direction, and for correcting the temporal change of the component or the like by measuring the color strength of patches of the same color and the same color tone which are disposed on the surface of the photo conductor, and each of which is disposed in a different position in the main scanning direction.
As disclosed in patent document 2, the image forming apparatus reduces the nonuniformity of color strength in the main scanning direction by averaging procedure of color strength of the patches of the same color and the same color tone. However, as will be apparent below, two patches of the same color and the same color tone is not always enough to reduce the nonuniformity of color strength.
As disclosed in patent document 3, the image forming apparatus further generates color tone correction parameter for reducing the nonuniformity of color strength and for correcting the temporal change of the component or the like in the sub-scanning direction by using patches, each of which are disposed in a different position in the sub-scanning direction.
Since the image forming apparatus disclosed in patent document 3 uses the patches of the same color and different color tone, each of which are disposed in a different position in the sub-scanning direction, an irrelevance color tone correction parameter which are caused by nonuniformity of color strength in the sub-scanning direction may be generated. As will be apparent below, a color tone image data for figuring out a temporal change of the color strength is printed by distorted color tone characteristics which are caused by color strength in the sub-scanning direction.
A printed sheet, printed by utilizing a color tone correction parameter based on the distorted color tone characteristics, is recognized as a sheet which includes the distorted color tone characteristics such as the color tone skip.
The image forming apparatus disclosed in patent document 3 generates the color tone correction parameter in an image forming apparatus. The image forming apparatus disclosed in patent document 3 includes two sensors which are arranged in the main scanning direction. Thus, it is not easy to retain space for the sensors, because space in the image forming apparatus is limited. Further, it is not easy to arrange a number of sensors in order to sense color tone values of the patches of the same color arranged in the main scanning direction. Thus, it is not easy to generate the color tone correction parameter based on the color values sensed by the number of sensors.
[Patent Document 1] Japanese Patent No. 3241986
[Patent Document 2] Japanese Patent Laid-Open Publication No. 2007-264371
[Patent Document 3] Japanese Patent Laid-Open Publication No. 2007-264364