1. Technical Field
The present invention relates to technology for adjusting image formation conditions of an image forming device.
2. Related Art
In image forming devices such as copiers or printers, recording methods such as electrophotography, thermal printing, inkjet printing or the like are used. Image forming devices have been subjected to various improvements in accordance with the characteristics of these recording methods, in order to fulfill such user demands as high-speed, and high-quality image formation.
For example, image forming devices employing electrophotography utilize the electrostatic effect of toner, which is made of microscopic particles, and therefore the image quality tends to drop due to fluctuations in the image darkness that occur when the toner is affected by environmental or temporal changes in temperature or humidity, or due to tiny variations in the structural components of the image forming device. Accordingly, electrophotographic image forming devices are commonly provided with a function for adjusting image darkness, in order to sustain a stable image quality.
Image darkness adjustment means the forming of a standard image, such as a pattern image or patch image or the like, on a recording material (paper or the like) or image-carrying member (photosensitive member, intermediate transfer belt or the like), based on a target darkness that has been stored beforehand, and if the darkness of the formed standard image does not match the target darkness, adjusting the conditions relating to the image formation (hereinafter referred to as “image formation conditions”), such as the exposure potential during exposure or the amount of toner that is discharged during development or the like, such that the darkness of the formed standard image becomes the target darkness. By performing such an image darkness adjustment, images having a constant quality can be formed over a long period of time.
Generally, there are two kinds of image darkness adjustment, namely “automatic darkness adjustment” in which the image forming device itself performs the image darkness adjustment automatically when the power is turned on, when the apparatus is idle, or at predetermined time intervals; and “user calibration” in which the user instructs the image forming device to perform an image darkness adjustment, for example, when the user feels that the image quality has dropped. In these two kinds of image darkness adjustment, the specific methods for adjusting the image darkness may be the same, or they may be different.
Further, in addition to these two kinds of image darkness adjustment, image forming devices are normally also provided with a function by which the user can operate an operation section or the like of the image forming device to change the image formation conditions (hereinafter referred to as “manual darkness adjustment”). This manual darkness adjustment is often performed when the formed image does not have a level of image darkness or a color hue that is desired by the user. That is to say, the above-described automatic darkness adjustment and user calibration are adjustments for attaining a standard image quality, whereas the manual darkness adjustment is enables a user to select an image quality.
The automatic darkness adjustment and the user calibration are both adjustments for attaining a standard image quality. Therefore, after either an automatic darkness adjustment or a user calibration has been carried out, the image formation conditions should be the same, and if an identical image is output, then the image quality should be the same.
However, if the method for adjusting the image darkness differs between the automatic darkness adjustment and the user calibration, then the image formation conditions do not necessarily match after the respective image darkness adjustments have been carried out, so there is a risk that the output results will be different. A technology has been developed with an object of addressing this problem by generating correction data from print output characteristic information, that corresponds respectively to a “device calibration”, which is equivalent to the automatic darkness adjustment, and a “software calibration”, which is equivalent to the user calibration.
However, in these conventional technologies, the result of carrying out both the automatic darkness adjustment and the manual darkness adjustment, or both the user calibration and the manual darkness adjustment, is not taken into consideration.
As an example, a case will be explained where the image formation conditions are adjusted to a user's liking; that is, the image formation conditions after a manual darkness adjustment has been carried out are “lighter” than the image formation conditions after an automatic darkness adjustment has been carried out, that is, the standard image formation conditions. When the manual darkness adjustment is carried out, and a first automatic darkness adjustment is started in a state in which the image formation conditions are “lighter” than the standard image formation conditions, then the image forming device will form a standard image that is “lighter” than standard. Thus, a correction is performed to form a “darker” image, for example a correction is performed by which the look-up table is overwritten in a manner resulting in a larger output for a given input signal (see FIG. 12). After this automatic darkness adjustment, the image formation conditions approach the standard conditions, but in this situation, the user's preferences are not reflected, and the user again has to perform a manual darkness adjustment in order to set image formation conditions that are “lighter” than the standard image formation conditions. Thus, when the automatic darkness adjustment is performed for a second time, a correction is performed such that an image is formed which is even “darker” than the previous image. When such an adjustment is carried out repeatedly, the manual darkness adjustment and the automatic darkness adjustment will make repeated corrections in opposite directions. As a result, the second correction will be larger than the first and the third will be larger than the second, and the correction amount will continue to increase.
Furthermore, when a large correction is performed as described above, the image forming device is not able to form an image using the original number of gradations, resulting in a problem that, for example, tone jumps brought about by the reduction of the number of gradations occur, and the reproducibility of the original image is compromised.