Electrophotography – Diagnostics – By inspection of copied image
Reexamination Certificate
2001-10-17
2003-04-29
Ngo, Hoang (Department: 2852)
Electrophotography
Diagnostics
By inspection of copied image
C347S240000, C347S251000, C347S254000, C399S039000, C399S049000, C399S072000
Reexamination Certificate
active
06556793
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to image forming apparatuses and, more particularly, to an image forming apparatus, such as a copying machine, a printer or a facsimile, which creates an adjustment sheet used for concentration adjustment (&ggr;-correction) of reference colors which constitute a color printing output image.
2. Description of the Related Art
In an image forming apparatus, such as a color printer, a color concentration of printing may shift from a reference value due to change with passage of time, and, thus, it is required to make a color correction. Conventional image forming apparatuses adopt various color correction methods.
For example, there is a method of determining an amount of correction of concentration by comparing a color sample sheet enclosed in a package of a printer with a print of a test pattern, which is stored in the printer. Moreover, there is a method of correcting a concentration curve by reading concentration of a figure printed on a print paper by a scanner or a concentration measurement apparatus and calculating a difference between a color of the drawn figure and an actual color. Furthermore, there is a method of correcting a concentration curve by selecting a concentration, which is equal to a reference concentration printed on a previously prepared template, the selection being made by printing all selectable concentrations on a print paper by a printer of which concentration curve is to be corrected.
A concentration value of print data sent from a host apparatus to an image forming apparatuses such as a printer is normally specified by one of numerical values of 0 to 255 expressed by 8 bits per one color. A process called &ggr;-conversion is performed so that the concentration in a printing result matches a desired concentration with respect to each concentration value. The &ggr;-conversion is a process that obtains, when a concentration is expressed by 8 bits, output values 0-255 with respect to input values 0-255 using a conversion table stored in a memory of a controller.
In a graph having horizontal and vertical axes of the same scale, if an input value is assigned to the horizontal axis and an output value is assigned to the vertical axis, the input value becomes equal to the output value and the &ggr;-conversion process is unnecessary when the input-and-output characteristic of a printer engine is expressed by a straight line having an inclination of 45 degrees. However, the input-and-output characteristic of a printer engine does not have linearity, and the &ggr;-conversion process is indispensable so as to obtain a proper image by the printer.
Moreover, even if printer engines are of the same model, generally the input-and-output characteristic varies according to individual differences. The input-and-output characteristic varies also with passage of time and further the environment where the printer is placed. Therefore, it is necessary to rewrite the contents of the conversion table in accordance with a change in the input-and-output characteristic.
If the contents of &ggr;-conversion table are expressed by a graph in which an input value and an output value are assigned to the horizontal axis and the vertical axis, respectively, the &ggr;-conversion table is indicated as a curve. For this reason, the process to rewrite the contents of &ggr;-conversion table may be referred to as a “gamma curve correction”. Moreover, the contents of &ggr;-conversion table after correction may be referred to as “corrected &ggr;” or “corrected &ggr;-curve”.
FIG. 1
is an illustration showing a structure of a conventional printer system. The printer system shown in
FIG. 1
comprises a host computer
1
and a printer engine
2
. A printer controller
3
is provided in the printer engine
2
. The data to be printed is specified by the host computer
1
. The printer controller
3
creates image data according to instructions of the host computer
1
so as to perform a printing operation. After being developed on the frame memory according to the specified concentration, the image data to be printed is sent to the printer engine
2
, and the printing operation is completed.
As shown in
FIG. 2
, the printer engine
2
comprises a central processing unit (CPU)
31
, a random access memory (RAM)
32
, a program read only memory (ROM)
33
, a font ROM
34
, a host interface (I/F)
35
and an engine I/F
36
, and these parts are mutually connected through a bus. The CPU
31
controls the entire printer controller
3
based on programs stored in the program ROM
33
, mode instructions from a panel apparatus and commands from the host computer
1
. As mentioned above, a control program of the printer controller
3
is stored in the program ROM
33
, and pattern data of a font etc. is stored in the font ROM
34
.
The RAM
32
functions as a work memory of the CPU
31
, and is used as an input buffer of input data, a page buffer of print data, a memory for download fonts, etc. The engine I/F
36
performs communication with the printer engine
2
so as to exchange commands and status and print data. The host I/F
35
is an interface which communicates with the host computer
1
, and is usually Centronics I/F or RS232C I/F. The printer engine
2
may be connected with the host computer
1
through networks such as Ether Net or Local Talk.
Here, a concentration of an image printed by the printer engine may differ from a concentration which the printer controller intends to print due to a change in the surrounding environment or a change with passage of time. In such as case, in the printer controller provided with a reading apparatus such as a scanner, the printed paper output from the printer engine is read by the scanner. Then, the concentration value (output result), which is the result of reading, is compared with the concentration value (expected output value) which the printer controller intends to print. If there is a difference, the concentration value used for drawing is corrected (the above-mentioned &ggr;-correction) so as to absorb the difference. Then, a printed matter can be obtained which the printer controller intends to, that is, which the host computer intends to.
In an image forming apparatus which is not provided with a reading apparatus such as a scanner, the same effect can be obtained by inputting the input data to the printer controller
3
by determining, as shown in
FIG. 3
, whether the printed result output from the printer engine
2
has a higher concentration or a lower concentration by a visual check of a human
4
without using a reading apparatus such as a scanner. In this case, since it is difficult to determine the concentration by human eyes unlike reading apparatuses such as a scanner, a sheet referred to as an adjustment sheet
5
is used so as to help the visual check so that the determination can easily made even by the human eyes.
In the adjustment sheet
5
, when an adjustment is performed with respect a particular concentration, reference concentration patterns (B of
FIG. 4
) used as a reference and test concentration patterns (A of
FIG. 4
) which indicates concentrations near the particular concentration including the particular concentration are arranged in an alternative sequence. By comparing the concentration patterns and selecting a number at which the concentration of the test concentration pattern matches the concentration of the reference concentration pattern, the &ggr;-correction value is obtained based on the concentration value (output result) indicated by the number attached to the selected test concentration pattern and the concentration values (expected output value) which the controller intends to represent. Thus, a desired concentration can be obtained by reflecting the thus-obtained &ggr;-correction in the printing process. It should be noted that an example of such a process is disclosed in Japanese Patent Application No. 11-314395 filed by the present inventor. As for the reference concentration pattern, a pattern, which is hardly
Dickstein , Shapiro, Morin & Oshinsky, LLP
Ngo Hoang
Ricoh & Company, Ltd.
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