Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1997-07-22
2001-06-19
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S015000
Reexamination Certificate
active
06247780
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a recording apparatus, and particularly a recording apparatus in which shading correction processing can be performed.
2. Description of the Prior Art
In the widespread use of computers and communication apparatus, recording apparatus outputting information of these apparatus by enabling recording heads to form digitized dots has been generally used. In addition, such digitized recording apparatus is generally applied into copy machines. In a recording apparatus using recording heads, in order to increase the recording speed, it is a general habit to use a multi-head including a plurality of recording elements. However, it is rather difficult to fabricate a plurality of recording elements in an individual multi-head in a uniform quality and hence, the characteristic of fabricated recording elements may not be stabilized. As a result, shading or density shading (density ununiformity of an image which is recorded on a recording medium by the reading head which has a plurality of recording elements) occurs in the recorded image which causes the reduction of the image quality. By repetitive use of recording elements, recording elements suffer from aged deterioration which also causes characteristic instability and shading.
In order to solve above problems, what is proposed is a method for correcting characteristic of recording elements by means that a specific read-out part for reading out shading at an arbitrary time is placed in the recording apparatus and shading correction data are generated according to the read-out data.
FIG. 1
shows a diagrammatic picture illustrating an example of such a method for reading out shading as described above.
In
FIG. 1
, a reference numeral
121
is a recording sheet,
122
a recording head,
123
a recording element placed in the recording head
122
,
124
a read-out head composed of CCD,
125
a read-out element installed in the read-out head
124
, and
126
a test pattern obtained by scanning in the X direction the recording head
122
including recording elements
123
which are arranged in the Y direction relative to the recording sheet in order to record one line pattern. The number of the read-out elements in the read-out head
124
is equivalent to that of the recording elements of the recording head
122
. By scanning the read out head
124
in the direction of an arrow B in
FIG. 1
, the density of the pattern
126
is read out. In this configuration shown in
FIG. 1
, the number of density data read-out by each read-out element
125
in a single scanning operation is equal to the number of the recording elements
123
of the recording head
122
, and the average of these density data is used as an ideal density to be realized by individual recording elements.
Even if input signals to all the recording elements
123
of the recording head
122
are identical to one another, in case that the read out density has shading property, the input signals should be corrected. For example, with respect to the recording element giving lower density, the input signal is corrected so as to be larger, and with respect to the recording element giving higher density, the input signal is corrected so as to be smaller. So far, the density defined by individual recording elements can be corrected to be uniform. In case that shading occurs as the recording apparatus is used, further shading correction is performed in order to establish uniform density. The modification of input signal values described above is performed by referring conversion tables.
By referring to
FIGS. 2 and 3
, an outline process of the shading correction processing is described below.
Now assume that the relationship between the input (driving) signal to a certain recording element n and the density of the recorded (outputted) image or dot is one shown in FIG.
2
. It can be stated that the recording element n recording an image with the density OD
n
with respect to the input signal S. If the average density over all the recording elements with respect to the driving signal S is assumed to be {overscore (OD)}, in other words, the correction density is assumed to be {overscore (OD)}, the recording element n records an image with higher density. In order to correct the density of the recording element n from OD
n
to {overscore (OD)}, the intensity of the input signal to the recording element n is modified from S to S′ by referring to the conversion table.
FIG. 3
is a graph illustrating a content of the conversion table. The table shown in
FIG. 3
contains 64 correction curves or straight lines, each of which corresponds to a couple of an input signal S and its corresponding output signal, each signal formed in 255 gray level data. In
FIG. 3
, only two out of 64 lines, A and B, are shown. Information about which correction curve is selected to an individual recording element are separately stored and referred in responsive to the read-out density data in order to select a desirable correction curve. When the input signal S is inputted with respect to one recording element, this element giving the density according to the correction curve or line selected. For example, with respect to the recording element accepting the input signal S and outputting the density OD
n
, correction line B is selected and input signal is modified to S′ so that the density recorded by that recording element is {overscore (OD)}.
The density distribution established in the configuration defined as in
FIG. 1
is generally found to be one shown in
FIG. 4
, where the horizontal axis represents the position of recording elements in the recording head, and the vertical axis represents the recording density defined by individual recording elements. One problem in this situation is that the density by the recording elements at the end parts of the array of recording elements is different from the density by the recording elements at the rest part of the array. That is, a pixel recorded by the recording elements at the rest part of the array involves recorded parts by the adjacent recording elements, on the other hand, the pixel recorded by the recording elements of the end parts of the array involves a part of ground of the recording sheet. Therefore, in the case that the sheet color is white, as shown in
FIG. 4
, the density at the edge parts is formed n a gradually increasing or decreasing curve in which the measured density is estimated to be less than the actual density. If the density correction is performed in such a situation, the density at the connection parts between the recording lines repetitively developed by multiple scanning operations of the recording head may be modified to be greater than the actual density.
In order to solve the above problem, as described in U.S. Ser. No. 07/593,765 (filed on Oct. 4, 1990) and U.S. Ser. No. 07/711,648 (filed on Jun. 11, 1991), there is a correction method in which three lines (three time scan operations) are recorded and only the central line data are used for correction calculations. In the case of recording three lines, recording elements at the both end parts of the array of recording elements form pixels so as to be adjacent to each other so that the above described problem may be solved.
In either method for density shading correction, it is known that several problems specific to text-pattern read-out procedures still exist.
(1) The first problem relates to the density shading correction in recording images by using a multi-head, for example, in reduction recording in copy machines.
As for a method for reduction recording, what is well known is a method that, by selecting input signals defined to individual recording elements, recording is performed not by all the recording elements but by partial recording elements. This method is further categorized into two methods. Examples on these methods applied to reduction recording in the recording apparatus shown in
FIG. 5
are described below.
FIG. 5
is an isometric view of the main part of the reco
Koitabashi Noribumi
Matsubara Miyuki
Matsuo Takayuki
Sugishima Kiyohisa
Suzuki Akio
Barlow John
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hallacher Craig A.
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