Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
2000-04-14
2004-02-10
Rogers, Scott (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S003060, C358S504000, C358S521000, C358S525000, C358S534000, C358S406000
Reexamination Certificate
active
06690490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image processor for use in digital color image forming apparatuses such as a digital color copier and more specifically to a gradation correcting process.
2. Description of Prior Art
There is disclosed a prior art related to a gradation correction process in Japanese Unexamined Patent Publication JP-A 4-180354 (1992). A digital copier provided with a density correcting unit of JP-A 4-180354 comprises an electrophotographic printer. In the printer, a photosensitive film is exposed to a modulated light beam which is controlled by an optically modulated signal. The density correcting unit carries out a gradation correcting process while converting an image signal of an object to be processed into the optically modulated signal. To that end, the density correcting unit stores preset desired characteristics of the digital copier and a preset reference conversion table. The desired characteristic indicates changes of density of recording density to a density value of an image signal. The reference conversion table is a reference correction curve indicative of predetermined changes of a value of the optically modulated signal with respect to the density value within the image signal.
The density correcting unit carries out the following procedure to create a signal conversion table which is a correction curve actually used in processing the image signal. The density correcting unit generates a plurality of reference image signals whose density values are different from each other, converts the respective reference image signals into the optically modulated signals, respectively, based on the reference conversion table and supplies them to the printer. The printer prints a recorded image corresponding to the respective reference image signals by modulating the light beams based on the respective optically modulated signals, by exposing the photosensitive film by using the light beam and by developing the photosensitive film after the exposure. The density correcting unit measures the density of the respective printed recorded images and finds a density value of the desired characteristics to each density.
Next, the density correcting unit calculates a deviation between a value of the optically modulated signal on the reference conversion table to the density value of the desired characteristics to the density of the respective recorded images and a value of the optically modulated signal on the reference conversion table to the density value of the reference image signal corresponding to the respective recorded images. Then, the density correcting unit carries out an interpolation process using the deviation of the density values of the reference image signal to obtain a deviation of a density value other than the density value of the reference image signal to set the deviation of the density value as continuous data. The interpolation process is a publicly known interpolation and is realized by a combination of spline interpolation, linear interpolation and smoothing or by n-order function approximation.
Finally, the density correcting unit corrects the reference conversion table to obtain a value on the signal conversion table. A value of an optically modulated signal on the reference correction curve to the density value of the reference image signal corresponding to the respective recorded images is substituted into the correction value on the signal conversion table with respect to the density value on the desired characteristics to the density of the respective recorded images. A correction value on the signal conversion table with respect to a density value other than the density value on the desired characteristics to the density of the respective recorded images may be obtained by correcting the reference conversion table based on the data of the continuous deviation. The signal conversion table obtained as the result of the above-mentioned process is actually used in the density correcting unit.
The density correcting unit in the above-mentioned JP-A 4-180354 carries out the interpolation in order to obtain the data of deviation of the continuous density values as described above. The interpolation is realized by the combination of spline interpolation, linear interpolation and smoothing or by the n-order function approximation. When these known interpolations are used, no reference is made to the reference conversion table in the interpolation of the deviation. Thus, the output characteristics of the signal conversion table is liable to lack the reliability.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an image processor capable of improving the reliability of the output characteristics of the correction curve actually used in the gradation correcting process.
In a first aspect of the invention, an image processor comprises image inputting means for inputting an image, gradation correction processing means for performing a gradation correcting process using a correction curve to the inputted image and image outputting means for outputting the image for which the gradation correcting process has been performed, the image inputting means supplying input density values of pixels composing the image, to the gradation correction processing means, the gradation correction processing means supplying correction values on the correction curve to the input density values, to the image outputting means, the image processor further comprising:
reference correction curve storing means for storing a reference correction curve indicative of predetermined changes of the correction values to the input density values; and
correction amount storing means for storing correction amounts w
i
and w
i+1
which are preset based on the reference correction curve and correspond to a plurality of specified density values XP
i
and XP
i+1
, respectively, which are input density values specified at intervals from each other within the range of the input density values,
wherein the correction amount w
i
corresponding to the specified density value XP
i
is a difference between a correction value YB(XP
i
) on the reference correction curve to the specified density value XP
i
and a correction value YP(XP
i
) to the specified density value on the correction curve,
the gradation correction processing means, in order to create the correction curve to be used for the gradation correcting process,
(a) calculates the correction values YP(XP
i
) and YP(XP
i+1
) to the specified density values XP
i
and XP
i+1
on the correction curve, by adding the correction values to the specified density values XP
i
and XP
i+1
on the reference correction curve and the correction amounts w
i
and w
i+1
corresponding to the specified density values XP
i
and XP
i+1
, and
(b) calculates the correction value to the input density value other than the specified density value by means of interpolation operation for causing a shape of a part of the correction curve within a first section &Dgr;XP
i
having the specified density values XP
i
and XP
i+1
as both ends thereof, to coincide with a shape obtained by expanding or compressing in the direction X parallel to the axis of density value, a part of the reference correction curve within a second section &Dgr;YB
i
having the correction values YP(XP
i
) and YP(XP
i+1
) to the specified density values as both ends thereof.
According to the first aspect of the invention, the gradation correction processing means in the image processor can create the correction curve smoother than those created by using an interpolation operation linear interpolation quickly by easier calculation than the case of using spline interpolation or n-order function approximation. The output characteristics of the correction curve per first section having the both ends of the specified density values is analogous to the output characteristics of the reference correction curve in the second section having the both ends of the correction values to th
Conlin David G.
Edwards & Angell LLP
Rogers Scott
Tucker David A.
LandOfFree
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