1. Field of the Invention
The present invention generally relates to a technical field capable of adjusting image density. More specifically, the present invention relates to an image recording method, an image recording apparatus, and a calibration system of image recording apparatuses, in which after the image recording apparatus is calibrated by employing a test chart of calibration purposes, an image recording operation of a desirable image is carried out.
2. Description of the Related Art
In various sorts of image recording apparatus (printers) such as laser printers, thermal printers, copying apparatus, and ink jet printers, calibration operations of these apparatuses are carried out in order that while aging-effect changes, characteristic differences in recording media such as photosensitive materials with respect to each of manufacturing lots and the like are absorbed, images can be properly recorded in response to input image signals supplied to these apparatus.
In general, a calibration operation of this apparatus is carried out as follows. That is, while a calibration test chart image having a plurality of patch images (hereinafter simply referred to as patches) is employed, a converting condition applied to an input image signal or an exposure light amount signal is calculated in order that desirable image density may be represented from an input image signal representative of the test chart image.
First, an image recording apparatus outputs a test chart for calibration purposes on which patches made of three primary colors such as C(cyan), M(magenta), and Y(yellow) have been recorded in a predetermined format. Next, density of each of these primary color patches of this test chart is measured. Furthermore, in order that a proper image recording operation adapted to the input image signal or the exposure light amount signal may be carried out based upon both the measurement density values and target density data, a calculation is made on an image signal converting condition or an exposure light amount signal converting condition, which converts the input image signal or the exposure light amount signal into an output image signal so as to adjust the image signal converting condition or the exposure light amount signal converting condition.
On the other hand, an example of such a calibration method is described in Japanese Patent Application Laid-open No. 2000-33732. In this publication, in accordance with the image recording method for exposing/recording the image on the photosensitive material, the test chart image for the calibration purpose which is provided with a plurality of three-primary-color patches such as C, M, Y patches whose densities are different from each other is formed by applying a predetermined amount of exposure light to the photosensitive material. In other words, when the input image signal values of the test chart image are converted into the output image signal values, the input image signal values are converted to the exposure light amount signal values of the test chart image corresponding to the intermediate signal and the exposure light amount signal values are converted to the output image signal values by employing the exposure light amount signal converting condition representative of such a relationship between the exposure light amount signal and the output image signal. The respective patches of the test chart image are produced by employing the acquired output image signal values (test chart output image signal values). After the test chart image has been formed, the density measurement is carried out to acquire the measurement density values corresponding to the respective patches. Alternatively, the respective patches of the test chart image are produced by employing the previously-fixed output image signal values of the test chart image (test chart output image signal values), and then, the density measurements of the respective patches are carried out to acquire the measurement density values corresponding to the respective patches. In this test chart image, when a desirable measurement density values cannot be acquired, this exposure light amount signal converting condition must be adjusted.
The exposure light amount signal converting condition is adjusted as follows. That is, while a sample of plural sets of both the exposure light amount signal values corresponding to the sample data of the target gradation data and the image density values is fixed (as standard), a plurality of regions of the image density value are defined under such a condition that image density values located adjacent to each other while these plural fixed image density values are arranged in the order of the image density value are set as both an upper limit value and a lower limit value of each of the regions. Target exposure light amount signal values of the test chart corresponding to each of the image density values (target density values) by which these plural regions are defined are calculated by employing such a relationship between the measurement density values of the test chart image and the exposure light amount signal values of the test chart image. Then, the exposure light amount signal converting condition is calculated by employing the target exposure light amount signal values and the test chart output image signal values.
As a consequence, in order to improve the adjustment precision of the exposure light amount signal converting condition with employment of the test chart image, the target exposure light amount signal values must be calculated with high precision. These target exposure light amount signal values are required to be calculated with high precision by the following manner. That is, while a large number of the patches having the different densities from each other, which are owned by the test chart image, are prepared, the density measurement is carried out. Then, each of the image density values (target density values) of the target gradation data is interposed between a pair of density measurement values of the test chart image, and is internally interpolated so as to obtain the target exposure light amount signal value of the test chart. As a result, a total number of the data related to the measurement density values, which are measured by employing the test chart image, becomes necessarily larger than a total number of the data related to the above-explained image density values of the target gradation data (target density values). Therefore, there is a problem that the density measurement takes a lot of time. Also, since the total patch number is increased, the patch arrangement of the test chart image must be arranged in a two-dimensional manner. Thus, there is another problem in that the complex apparatus arrangement of the density measuring apparatus is needed by which the densities of the patches arranged in the two-dimensional manner are measured. Also, the amount of the photosensitive materials to be used for recording thereon the test chart image is necessarily increased. As a result, there is another problem in that the consumption of these photosensitive materials cannot be reduced, as well as the running cost cannot be lowered.