Image forming apparatus with security feature which prevents copying of specific types of documents

In a digital copier, facsimile machine, scanner, image filing apparatus or similar apparatus, an image processing device is provided with a capability of surely identifying confidential or secrecy documents which should be protected from unauthorized persons. The confidential or inhibited documents are provided with inhibition patterns by printing or copying over the entire surfaces thereof. The device prevents image data representative of this kind of documents from being improperly copied, transferred, stored or input.

BACKGROUND OF THE INVENTION 
The present invention relates to an image processing device for use in a 
digital copier, facsimile machine, scanner, image filing apparatus or 
similar apparatus and, more particularly, to an image processing device 
capable of preventing unauthorized persons from copying inhibited 
documents. 
Recent progress in image processing and image forming technologies has made 
it possible to produce even copies of bills as finely as true bills with a 
digital color copier. Today, a digital color copier capable of identifying 
special documents prohibited from being reproduced, e.g., bills and 
securities and preventing them from being copied illegally is available. 
To identify special documents of the kind described, image data input to 
the copier may be compared with a particular registered mark (pattern 
data) by a pattern matching scheme. If the image data includes the 
particular mark, the document is determined to be a special document. 
Alternatively, the identification may rely on the comparison of the 
configuration of a histogram based on a hue distribution, as taught in 
Japanese Patent Laid-Open Publication No. 4-54681. 
In offices, for example, even ordinary documents other than bills, 
securities and other special documents are often inhibited from being 
copied for a secrecy purpose. Let this kind of documents be referred to as 
inhibited documents for simplicity hereinafter. Usually, inhibited 
documents dealt with in offices are marked with "TOP SECRET", "NO COPYING" 
or similar indication and distinguished from other documents which can be 
copied. However, such a mark is not a substantial implementation for 
preventing inhibited copies from being copied. Specifically, the 
precondition for the inhibition is that a person, noticed the mark, sees 
that the document is an inhibited document and surely observes the 
inhibition. It is likely that a person copies an inhibited document by a 
copier, sends it by a facsimile machine, or inputs it in an image filing 
apparatus. 
The conventional method for identifying bills, securities and other special 
documents may also be used to implement an apparatus for distinguishing 
inhibited documents from other documents. For example, the apparatus may 
be constructed to identify the label "TOP SECRET" or "NO COPYING" on a 
document and inhibit the document from being copied. However, even such an 
apparatus will fail to identify the inhibited document if a person covers 
the label with, for example, a paper. 
The identification using the configuration of a histogram based on a hue 
distribution is not applicable to an apparatus handling images in the form 
of bilevel data, i.e., black and white data. Moreover, the problem with 
this kind of scheme is that the identification of inhibited documents 
itself is not satisfactory since numerous kinds of inhibited documents are 
dealt with in office transactions and since their histograms do not always 
have a common configuration. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the present invention to provide an image 
processing device capable of surely identifying inhibited documents and 
preventing them from being copied, transferred, stored or input. 
In accordance with the present invention, an image processing device for 
executing various kinds of image processing, including filtering, 
magnification change and gamma correction, with input image data comprises 
a pattern detecting section for determining, pixel data by pixel data, 
whether or not pixel data constituting the input image data are part of a 
predetermined inhibition pattern, and a document deciding section for 
determining, based on the number of pixel data determined to be part of 
the predetermined inhibition pattern by the pattern detecting section, 
whether or not the input image data are representative of an inhibited 
document inhibited from being copied. The inhibited document comprises a 
sheet on which the inhibition pattern is printed or copied over the entire 
area thereof. 
Also, in accordance with the present invention, an image processing device 
for executing various kinds of image processing, including filtering, 
magnification change and gamma correction, with input image data comprises 
a black peak detecting section for determining, on the basis of individual 
pixel data constituting the input image data, whether or not pixel data 
under observation is a black peak by referencing the pixel data and pixel 
data adjoining it, a black peak density deciding section for determining, 
based on the output of the black peak detecting section, whether or not a 
predetermined area centering around the pixel data under observation has a 
black peak density coincident with the black peak density of a 
predetermined inhibition pattern, and a document deciding section for 
determining, based on the number of the pixel data determined to be 
coincident by the black peak density deciding section, whether or not the 
input image data are representative of an inhibited document inhibited 
from being copied. The the inhibited document comprises a sheet on which 
the inhibition pattern is printed or copied over the entire area thereof. 
Also, in accordance with the present invention, an image processing device 
for executing various kinds of image Processing, including filtering, 
magnification change and gamma correction, with input image data comprises 
a black peak detecting section for determining, on the basis of individual 
pixel data constituting the input image data, whether or not pixel data 
under observation is a black peak by referencing the pixel data and pixel 
data adjoining it, a black peak density deciding section for determining, 
based on the output of the black peak detecting section, whether or not a 
predetermined area centering around the pixel data under observation has a 
black peak density coincident with the black peak density of a 
predetermined inhibition pattern, a white ground detecting section for 
detecting a white ground out of the input image data, a surrounding white 
ground deciding section for determining, based on the outputs of the black 
peak detecting section and white ground detecting section, whether or not 
a white ground of predetermined size is present around and at a 
predetermined distance from the pixel data under observation which has 
been determined to be a black peak, an observed pixel data deciding 
section for determining, based on the outputs of the black peak density 
deciding section and surrounding white ground deciding section, whether or 
not the pixel data under observation is part of the inhibition pattern, 
and a document deciding section for determining, based on the number of 
the pixel data determined to be part of the inhibition pattern by the 
observed pixel data deciding section, whether or not the input image data 
are representative of an inhibited document inhibited from being copied. 
The inhibited document comprises a sheet on which the inhibition pattern 
is printed or copied over the entire area thereof. 
Also, in accordance with the present invention, an image processing device 
for executing various kinds of image processing, including filtering, 
magnification change and gamma correction, with input image data comprises 
a pattern detecting section for determining, pixel data by pixel data, 
whether or not pixel data constituting the input image data are part of a 
predetermined inhibition pattern, a document deciding section for 
determining, based on the number of pixel data determined to be part of 
the predetermined inhibition pattern by the pattern detecting section, 
whether or not the input image data are representative of an inhibited 
document inhibited from being copied, and an inhibiting section for 
inhibiting the input image data from being output when the image data are 
representative of the inhibited document as determined by the document 
deciding means. The inhibited document comprises a sheet on which the 
inhibition pattern is printed or copied over the entire area thereof. 
Also, in accordance with the present invention, an image processing device 
for executing various kinds of image processing, including filtering, 
magnification change and gamma correction, with input image data has a 
pattern detecting section for determining, pixel data by pixel data, 
whether or not pixel data constituting the input image data are part of a 
predetermined inhibition pattern. The pattern detecting section has 
variable detection accuracy. A document deciding section determines, based 
on the number of pixel data determined to be part of the predetermined 
inhibition pattern by the pattern detecting means, whether or not the 
input image data are representative of an inhibited document inhibited 
from being copied. The document deciding section has variable decision 
accuracy. A changing section changes the detection accuracy of the pattern 
detecting section and the decision accuracy of the document deciding 
section. The inhibited document comprises a sheet on which the inhibition 
pattern is printed or copied over the entire area thereof. 
Also, in accordance with the present invention, an image processing device 
for executing various kinds of image processing, including filtering, 
magnification change and gamma correction, with input image data comprises 
a pattern detecting section for determining, pixel data by pixel data, 
whether or not pixel data constituting the input image data are part of a 
predetermined inhibition pattern, a document deciding section for 
determining, based on the number of pixel data determined to be part of 
the predetermined inhibition pattern by the pattern detecting section, 
whether or not the input image data are representative of an inhibited 
document inhibited from being copied, and a warning section for producing 
a warning when the input image data are representative of the inhibited 
document as determined by the document deciding section. The inhibited 
document comprises a sheet on which the inhibition pattern is printed or 
copied over the entire area thereof. 
Further, in accordance with the present invention, an image processing 
device for executing various kinds of image processing, including 
filtering, magnification change and gamma correction, with input image 
data comprises a pattern detecting section for determining, pixel data by 
pixel data, whether or not pixel data constituting the input image data 
are part of a predetermined inhibition pattern, a document deciding 
section for determining, based on the number of pixel data determined to 
be part of the predetermined inhibition pattern by the pattern detecting 
section, whether or not the input image data are representative of an 
inhibited document inhibited from being copied, an inhibiting section for 
inhibiting the input image data from being output when the input image 
data are representative of the inhibited document as determined by the 
document deciding section, and a cancelling section for invalidating the 
inhibition set by the inhibiting section. The inhibited document comprises 
a sheet on which the inhibition pattern is printed or copied over the 
entire area thereof. 
Further, in accordance with the present invention, an image processing 
device for executing various kinds of image processing, including shading 
correction, filtering, magnification change, gamma correction and tone 
conversion comprises a pattern detecting section for determining, pixel 
data by pixel data, whether or not pixel data constituting the input image 
data, subjected to the shading correction but not to the other processing, 
are part of a predetermined inhibition pattern, and a document deciding 
section for determining, based on the number of pixel data determined to 
be part of the predetermined inhibition pattern by the pattern detecting 
section, whether or not the input image data are representative of an 
inhibited document inhibited from being copied. The inhibited document 
comprises a sheet on which the inhibition pattern is printed or copied 
over the entire area thereof. 
Furthermore, in accordance with the present invention, an image processing 
device for executing various kinds of image processing, including shading 
correction, filtering, magnification change and gamma correction and tone 
conversion, with input image data comprises a black peak detecting section 
for determining, on the basis of individual pixel data constituting the 
input image data, whether or not pixel data under observation is a black 
peak by referencing the pixel data and pixel data adjoining it, a black 
peak density deciding section for determining, based on the output of the 
black peak detecting section, whether or not a predetermined area 
centering around the pixel data under observation has a black peak density 
coincident with the black peak density of a predetermined inhibition 
pattern, a white ground detecting section for detecting a white ground out 
of the input image data, an edge detecting section for detecting an edge 
region in response to the input image data, a surrounding white ground 
deciding section for determining, based on the outputs of the black peak 
detecting section and white ground detecting section, whether or not a 
white ground of predetermined size is present around and at a 
predetermined distance from the pixel data under observation which has 
been determined to be coincident with the black peak density of the 
inhibition pattern, a mesh graph/mesh character deciding section for 
determining, based on the outputs of the black peak density deciding 
section and edge detecting section, whether or not the pixel data under 
observation which has been determined to be coincident with the black peak 
density of the inhibition pattern lies in either a mesh graph or a mesh 
character, an observed pixel data deciding section for determining, based 
on the outputs of the black peak density deciding section, surrounding 
white ground deciding section and mesh graph/mesh character deciding 
section, whether or not the pixel data under observation is part of the 
inhibition pattern, and a document deciding section for determining, based 
on the number of the pixel data determined to be part of the inhibition 
pattern by the observed pixel data deciding section, whether or not the 
input image data are representative of an inhibited document inhibited 
from being copied. The inhibited document comprises a sheet on which the 
inhibition pattern is printed or copied over the entire area thereof. 
Moreover, in accordance with the present invention, an image processing 
device for executing various kinds of image processing, including shading 
correction, filtering, magnification change and gamma correction and tone 
conversion, with input image data comprises a black peak detecting section 
for determining, on the basis of individual pixel data constituting the 
input on the basis of individual pixel data under observation is a black 
peak by referencing the pixel data and pixel data adjoining it, a black 
peak density deciding section for determining, based on the output of the 
black peak detecting section, whether or not a predeterminedarea centering 
around the pixel data under observation has a black peak density 
coincident with a black peak density of a predetermined inhibition 
pattern, a white ground detecting section for detecting a white ground out 
of the input image data, an edge detecting section for detecting an edge 
region in response to the input image data, a surrounding white ground 
deciding section for determining, based on the outputs of the black peak 
detecting section and white ground detecting section, whether or not a 
white ground of predetermined size is present around and at a 
predetermined distance from the pixel data under observation which has 
been determined to be coincident with the black peak density of the 
inhibition pattern, a mesh graph/mesh character deciding section for 
determining, based on the outputs of the black peak density deciding means 
and edge detecting section, whether or not the pixel data under 
observation which has been determined to be coincident with the black peak 
density of the inhibition pattern lies in either a mesh graph or a mesh 
character, an observed pixel data deciding section for determining, based 
on the outputs of the black peak density deciding section, surrounding 
white ground deciding section and mesh graph/mesh character deciding 
section, whether or not the pixel data under observation is part of the 
inhibition pattern, a document deciding section for determining, based on 
the number of the pixel data determined to be part of the inhibition 
pattern by the observed pixel data deciding section, whether or not the 
input image data are representative of an inhibited document inhibited 
from being copied, and an inhibiting section for inhibiting the input 
image data from being output when the input image data are representative 
of the inhibited document as determined by the document deciding section. 
The inhibited document comprises a sheet on which the inhibition pattern 
is printed or copied over the entire area thereof. 
In addition, in accordance with the present invention, an image processing 
device for executing various kinds of image processing, including shading 
correction, filtering, magnification change, gamma correction and tone 
conversion, with input image data of the present invention comprises a 
pattern detecting section for determining, pixel data by pixel data, 
whether or not pixel data constituting the input image data, subjected to 
the shading correction but not to the other processing, are part of a 
predetermined inhibition pattern, a document deciding section for 
determining, based on the number of pixel data determined to be part of 
the predetermined inhibition pattern by the pattern detecting section, 
whether or not the input image data are representative of an inhibited 
document inhibited from being copied, and a pattern printing section for 
printing the inhibited pattern indicative of an inhibited document 
inhibited from being copied. The inhibited document comprises a sheet on 
which the inhibition pattern is printed or copied over the entire area 
thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the image processing device in accordance with the 
present invention will be described with reference to the accompanying 
drawings and in relation to a digital copier by way of example. 
1st Embodiment 
Briefly, this embodiment determines, pixel by pixel, whether pixel data 
representative of an image form part of a predetermined inhibition pattern 
and then determines, based on the number of pixel data found to form of 
the inhibition pattern, whether or not the image data represent an 
inhibited document. As a result, inhibited documents are surely 
distinguished from ordinary documents which are allowed to be copied. This 
can be done if the inhibited documents are implemented as sheets on which 
an inhibition pattern or patterns are printed or copied beforehand. 
The embodiment will be described under the following items: (I) General 
Construction of Digital Copier, (II) Inhibition Pattern, (III) Detecting 
Section, (IV) Decision Section, and (V) Decision Routine. 
(I) General Construction of Digital Copier 
Referring to FIG. 1, the general construction of a digital copier 
implemented with the illustrative embodiment is schematically shown. As 
shown, the copier has a scanner 101 for reading a document and converting 
the resulting analog image data to digital image data or signal. An image 
processing section, generally 102, receives the digital image data from 
the scanner 101 and executes therewith various kinds of image processing 
and a decision routine of the present invention, which will be described. 
A plotter 103 prints out the processed image data on a sheet. An operation 
and display panel 104 allows various kinds of modes to be input thereon 
and displays necessary messages. A system controller 105 controls the 
sections 101-104. 
In the image processing section 102, a filter 106 has a shading correction 
filter, smoothing filter, edge enhancing filter and other conventional 
filters for filtering the input image data in various ways. A 
magnification change 107 changes the magnification of the image data. A 
gamma (.gamma.) correction 108 executes gamma correction with the image 
data. A tone conversion 109 converts the image data to predetermined 
multilevel data. A pattern detection 110 determines, on a pixel basis, 
whether the image data form part of a preselected inhibition pattern, 
pixel by pixel. A document decision 111 determines, based on the number of 
pixel data determined to form part of the inhibition pattern, whether or 
not the image data represents a an inhibited document. A white data 
generation 112 generates image data in the form of white data. A selector 
113 selects, according to the output of the document decision 111, either 
the image data from the tone conversion 109 or the image data, or white 
data, from the white data generation 112. The image data from the selector 
113 is applied to the plotter 103. 
(II) Inhibition Pattern 
A reference will be made to FIGS. 2A and 2B for describing the inhibition 
pattern indicating whether or not the document represented by the image 
data is an inhibited document. In the illustrative embodiment, a document 
with the inhibition pattern is determined to be an inhibited document. It 
is, therefore, assumed that the inhibition pattern or patterns are printed 
or copied on the entire surface of an inhibited document beforehand. For 
example, as shown in FIG. 2A, inhibition patterns 201 may be printed or 
copied on the entire surface of a fresh sheet. Such a sheet will turn out 
a secrecy or inhibited document when information is recorded therein. In 
this embodiment, the inhibition patterns 201 are implemented by a 
conventional secrecy numbering function available with a digital copier, 
although such an implementation is only illustrative. As shown in FIG. 2B 
in an enlarged scale, the inhibition patterns 201 are each configured by a 
mesh of about 65 lines (numeral "1" in the figure). When the patterns 201 
are distributed over the entire surface of a document, as shown in FIG. 
2A, the embodiment determines it to be an inhibited document and prevents 
it from being copied, as will be described in detail later. For the other 
documents, the embodiment performs an ordinary copying operation. 
(III) Detecting Section 
FIG. 3 shows the pattern detection 110 specifically. As shown, the pattern 
detection 110 includes a black peak detection 301 which determines, pixel 
by pixel, whether or not pixel data being observed is a black peak on the 
basis of a relation between it and surrounding pixel data. A black peak 
density decision 302 determines, in response to the outputs of the black 
peak detection 301, whether or not the black peak density of a 
predetermined area having the pixel data under observation at the center 
is coincident with that of the predetermined inhibition pattern. A white 
ground detection 303 receives the image data so as to detect a white 
ground. A surrounding white ground decision 304 determines, in response to 
the outputs of the black peak detection 301 and white ground detection 
303, whether or not a white area of predetermined size exists around and 
at a predetermined distance from the pixel data determined to be a black 
peak. An observed pixel data decision 305 determines whether or not the 
pixel data under observation is part of the inhibition pattern in response 
to the outputs of the black peak density decision 303 and surrounding 
white ground decision. 
FIG. 4 shows a specific 3 by 3 pixel matrix applicable to the black peak 
detection 301. In the pixel matrix, a pixel E is assumed to be the center 
pixel being observed. If the center pixel E is higher in density than the 
other pixels of the matrix and has a density higher than a predetermined 
threshold (referred to as a black peak threshold hereinafter), the 
detection 301 determines that the pixel data under observation is a black 
peak pixel. 
The black peak density decision 302 determines a black peak density in a 
predetermined area centering around the pixel data under observation 
(e.g., 11 by 11 matrix), and then whether or not the density is equal to 
the peak density of the mesh of about 65 lines particular to the 
inhibition pattern 201, FIGS. 2A and 2B. 
Likewise, the white ground detection 303 determines whether or not a white 
ground exists in a predetermined area. Specifically, the detection 303 
binarizes pixels constituting an M by M matrix (e.g., 11.times.11 matrix) 
by use of a preselected threshold (referred to as a white ground threshold 
hereinafter) and determines, if all the pixels in the matrix are white, 
the matrix to be a white ground. 
The surrounding white ground decision 304 is responsive to the outputs of 
the white ground detection 303 and black peak detection 301 for 
determining whether or not a white ground exists at positions a 
predetermined distance apart from the pixel determined to be a black 
pixel. For example, as shown in FIG. 5A, assume that a white ground exists 
at each of positions 502, 503, 504 and 505 which are a predetermined 
distance d apart from the pixel 501 under observation. Then, the decision 
304 determines that the pixel 501 is surrounded by a white ground. If 
desired, the four positions, i.e., upper, lower, left and right positions 
502-505 may be replaced with eight positions 502-509 shown in FIG. 5B in 
order to enhance accuracy. The eight positions 502-509 are an upper, 
lower, left, right, upper left, upper right, lower right and lower left 
positions. Furthermore, only the two positions 502 and 503 of FIG. 5A may 
be used for the purpose of simplifying the hardware architecture. 
The observed pixel data decision 305 receives the outputs of the black peak 
density decision 302 and surrounding white ground decision 304. Only if 
the black peak pixel, or pixel under observation, has a black peak density 
particular to the inhibition pattern and is surrounded by a white ground 
at a predetermined distance, the decision 305 determines that the pixel 
data under observation forms part of the inhibition pattern. Then, the 
decision 305 outputs the result of decision. 
(IV) Decision Section 
Referring to FIG. 6, the document decision 111 includes a line decision 601 
which receives the results of pixel-by-pixel decision from the observed 
pixel data decision 305 of the pattern detection 110. The line decision 
601 counts the pixel data on one line in the main scanning direction which 
have been determined to be part of the inhibition pattern. If the number 
of such pixels is greater than a predetermined first threshold TH1, the 
line decision 601 determines that the line is an inhibition pattern line. 
A line count 602 holds the results of decision of the line decision 601 
over N lines and counts inhibition pattern lines on the N lines (count M). 
A decision 603 determines, if the count M of the line count 602 (M 
.ltoreq.N) is greater than a predetermined second threshold TH2, that the 
image data represent an inhibited document and causes a white data select 
signal to go high. 
(V) Decision Routine 
A reference will be made to FIGS. 7A, 7B and 8 for describing the decision 
procedure for identifying an inhibited document more specifically. Assume 
that a person sets a desired document at a predetermined position of the 
scanner 101 and then presses a copy start key, not shown, provided on the 
operation and display panel 104. Then, the scanner 101 reads the document 
and sends the resulting digital image signal, or image data, to the image 
processing section 102. This section 102 delivers the input image data to 
both the filter 106 and the pattern detection 110. The image data applied 
to the filter 106 are sequentially processed by the filter 106, 
magnification change 107, gamma correction 108 and tone conversion 109, as 
stated earlier, and then transferred to the selector 113. On the other 
hand, the pattern detection 110 determines, pixel by pixel, whether or not 
the input pixel data representing the document image are part of the 
predetermined inhibition pattern. 
FIG. 7A demonstrates the operations of the white ground detection 303 and 
surrounding white ground decision 304 included in the pattern detection 
110. FIG. 7B shows the operations of the black peak detection 301, black 
peak density decision 302 and observed pixel data decision 305. The 
procedures shown in these figurers are executed in parallel at the same 
time. 
As shown in FIG. 7A, the white ground detection 303 determines whether or 
not a white ground exists in a predetermined area (step S701). 
Subsequently, the surrounding white ground decision 304 determines, based 
on the output of the black peak detection 301, whether or not the pixel 
data under observation is a black peak (step S702). If the pixel data 
under observation is a black peak (Yes, step S702), the surrounding white 
ground decision 304 determines whether or not a white ground is present in 
a zone which is a predetermined distance apart from the pixel determined 
to be a black peak pixel (step S703). The result of decision in the step 
S703 is fed to the observed pixel data decision 305. On the other hand, if 
the pixel data under observation is not a black peak (No, step S702), the 
program returns to the step S701, ending the processing on the observed 
pixel data. 
As shown in FIG. 7B, the black peak detection 301 determined whether or not 
the pixel data under observation is a black peak (steps S704 and S705). If 
it is not a black peak (No, step S705), the observed pixel data decision 
305 determines that the pixel data under observation is not part of the 
inhibition pattern (step S710). If the pixel data is a black pixel (Yes, 
step S705), the black peak density decision 302 calculates a density of 
black peaks (step S706) and determines whether or not the density is 
coincident with the black peak density of the inhibition pattern (step 
S707). If the determined black peak density is not coincident with the 
black peak density of the inhibition pattern (No, step S707), the observed 
pixel data decision 305 determines that the pixel data under observation 
is not part of the inhibition pattern (step S710). If the answer of the 
step S707 is positive, Yes, the decision 305 determines whether or not a 
surrounding white ground exists on the basis of the output of the 
surrounding white ground decision 304 (step S708). If a surrounding white 
ground exists (Yes, step S708), the decision 305 determines that the pixel 
data under observation is part of the inhibition pattern (step S709). If 
the answer of the step S708 is negative, No, the decision 305 determines 
that the pixel data is not part of the inhibition pattern (step S710). 
It is to be noted that the steps S701-S710 described above are executed 
with each of the pixel data representative of the document image and then 
with the entire document image. 
FIG. 8 shows the operation of the document decision 111. To begin with, the 
results of pixel-by-pixel decision relating to the inhibition pattern are 
applied to the line decision 601. The line decision 601 counts the pixel 
data on one line in the main scanning direction which have been determined 
to be part of the inhibition pattern (step S801). Then, the decision 601 
compares the resulting count with the first threshold TH1 to see if the 
former is greater than or equal to the latter (step S802). If the answer 
of the step S802 is positive, Yes, the decision 601 determines that the 
line is an inhibition pattern line (step S803); if otherwise, it 
determines that the line is an ordinary line as distinguished from an 
inhibition pattern line (S804). Subsequently, the line count 602 holds the 
results of decision of the decision 601 over N consecutive lines and 
counts the inhibition pattern lines included in the N lines. (count M) 
(step S805). Thereafter, the decision 603 compares the count M with the 
second threshold TH2 (S806) and, if the former is greater than or equal to 
the latter (Yes, step S806), causes the previously mentioned white data 
select signal to go high (step S807). If the answer of the step S806 is 
negative, No, the decision 603 causes the white data select signal to go 
low (S808). The selector 113 receives image data from both the tone 
conversion 109 and the white data generation 112, as stated previously. If 
the white data select signal from the decision 111 is in a high level, the 
selector 113 selectively applies the white data from the white data 
generation 112 to the plotter 103. If the signal is in a low level, the 
selector 113 selectively delivers the image data from the tone conversion 
109 to the plotter 103. 
By the above procedure, when the desired document is determined to be an 
inhibited document on the basis of the inhibition patterns, the image data 
are replaced with white data and, therefore, not output to the plotter 
103. Stated another way, the selector 113 inhibits the image data 
representative of the inhibited document from being copied. 
As stated above, the embodiment determines that the pixel data under 
observation is part of the inhibition pattern when the black peak pixels 
(observed pixels) have a density particular to the inhibition pattern and 
a white ground exists at a predetermined distance. Hence, the embodiment 
can detect the inhibition pattern surely and easily. 
Further, the embodiment examines each line to see if it is an inhibition 
pattern line and determines, when the number M of such inhibition pattern 
lines exceeds a predetermined value in N lines, that the document is an 
inhibited document. This successfully identifies an inhibited document 
without errors. In addition, the white data generation 112 and selector 
113 allow a portion of a document, which is determined to be an inhibited 
document, to be surely erased even from the middle. 
While the embodiment has been shown and described in relation to a digital 
copier, it is similarly applicable to a facsimile machine for the purpose 
of preventing data representing an inhibited document from being sent. 
When the embodiment is applied to an image filing apparatus, it will 
prevent inhibited documents from being filed. Further, when the embodiment 
is applied to a scanner, it will prevent inhibited documents from being 
read. 
The white data, selectively replacing the image data in the embodiment, may 
be replaced with black data or even with data representative of a 
predetermined pattern. 
2nd Embodiment 
This embodiment allows the detection accuracy of the pattern detection 110 
and the decision accuracy of the document decision 111 to be changed on 
the operation and display panel 104 so as to implement more strict 
decision. This scheme is desirable when the probability that image data 
representative of inhibited documents are input on the copier is high. The 
following description will concentrate on the differences of the second 
embodiment from the first embodiment. 
As shown in FIG. 9, the system controller 105 includes a ROM(Read Only 
Memory) 901 storing parameters for changing the detection accuracy of the 
pattern detection 110 and parameters for changing the decision accuracy of 
the document decision 111. The parameters relating to the pattern 
detection 110 may include the black peak threshold of the black peak 
detection 301, the white peak threshold of the white ground detection 303, 
and the number of directions to be observed, FIGS. 5A and 5B. The 
parameters associated with the document decision 111 may include the first 
threshold TH1 of the line decision 601 and the second threshold TH2 of the 
decision 603. 
In operation, when a particular identification (ID) number is entered on 
the operation and display panel 104, particular parameters matching the ID 
number are transferred from the ROM 901 to the pattern detection 110 and 
decision 111. When the parameters are of the kind enhancing strict 
decision, an inhibited document will be identified with higher accuracy. 
With the embodiment allowing the decision accuracy to be changed, the user 
can strictly prevent inhibited documents from being copied, depending on 
the conditions and environment of use and so forth. When the chance that 
inhibited documents is copied is little, the decision accuracy may be 
reduced to minimize an occurrence that an ordinary document is mistaken 
for an inhibited document. 
3rd Embodiment 
This embodiment allows the pattern on accuracy of the pattern detector 110 
and the decision accuracy of the decision 111 to be automatically changed 
via a timer. With this embodiment, it is possible to effect more strict 
decision in a time zone in which the entry of image data representing 
inhibited documents is quite probable. This embodiment is essentially 
similar to the second embodiment except for the following. 
As shown in FIG. 10, the system controller 105 includes the ROM 901 storing 
parameters for changing the detection accuracy of the pattern detection 
110 and parameters for changing the decision accuracy of the document 
decision 111. A timer 1001 is connected to the system controller 105. 
Assume that a desired period of time is set on the operation and display 
panel 104. Then, when a preset time is reached, the system controller 105 
controls the ROM 901 t o automatically set particular parameters in the 
pattern detection 110 and document decision 111. With the timer 1001, it 
is possible to set parameters for more strict decision during nighttime or 
on holidays when the improper copying of confidential papers is apt to 
occur and to loosen them during daytime of weekdays in order to reduce 
erroneous decision. 
The embodiment allows the user to set desired parameters in the pattern 
detection 110 and document decision 111 on the basis of time and, 
therefore, to change the strictness of decision during desired hours. 
4th Embodiment 
When the document to be copied is an inhibited document, this embodiment 
produces a warning via the operation and display panel 104. This 
embodiment essentially similar to the first embodiment except for the 
following. 
FIG. 11 is a block diagram schematically showing the fourth embodiment. 
Assume that the document decision 111 causes the white data decision 
signal coupled to the system controller 105 to go high. Then, the system 
controller 105 determines that an inhibited document has been copied and 
shows on the display (e.g., liquid crystal display) of the display and 
operation panel 104 a message, e.g., "Inhibited document was copied" or 
"This document is inhibited" for warning the operator. 
By displaying the warning message on the operation and display panel 104, 
this embodiment checks persons tending to copy confidential documents 
improperly, while achieving the advantages of the first embodiment at the 
same time. 
5th Embodiment 
When the document to be copied is an inhibited document, this embodiment 
produces a warning via a buzzer, loudspeaker or similar audible output 
means. This embodiment is also essentially similar to the first embodiment 
except for the following. 
FIG. 12 is a block diagram schematically showing the fifth embodiment. 
Assume that the document decision 111 causes the white data decision 
signal coupled to the system controller 105 to go high. Then, the system 
controller 105 determines that an inhibited document has been copied and 
generates a tone for warning via a buzzer 1201. Of course, the buzzer 1201 
may be replaced with a loudspeaker for producing an audible message 
registered at the copier beforehand. 
With the buzzer 1201, this embodiment checks persons tending to copy 
confidential documents improperly and, at the same time, alerts persons 
around the copier to the improper reproduction, while achieving the 
advantages of the first embodiment. 
6th Embodiment 
This embodiment allows the inhibition to be cancelled, i.e., allows an 
inhibited document to be copied by an authorized person, as needed. This 
embodiment is essentially similar to the first embodiment except for the 
following. 
FIG. 13 is a block diagram schematically showing the sixth embodiment. As 
shown, the embodiment includes an AND gate 1301. When a particular 
identification number is entered on the operation and display panel 104, 
the result of decision from the document decision 111 is invalidated with 
the result that an ordinary copy mode is set up. Specifically, the white 
data select signal is coupled to the AND gate 1301 and goes high in the 
case of an inhibited document or goes low in the case of an ordinary 
document. On the other hand, an inhibition signal is coupled from the 
system controller 105 to the AND gate 1301 and usually remains in a high 
level for validating the inhibition. In this configuration, when the white 
data select signal goes high, the AND gate 1301 delivers the high level 
white data select signal to the selector 113 as a result of ANDing. 
When a particular identification number is entered on the operation and 
display panel 104, the system controller causes the inhibition signal to 
go low in order to cancel or invalidate the inhibition. In response, the 
AND gate 1301 feeds a low level white data select signal to the selector 
as a result of ANDing without regard to the output of the decision 111. 
Stated another way, the identification number entered on the panel 104 
invalidates the result of decision of the decision 111, thereby setting up 
an ordinary copy mode. 
As stated above, this embodiment is capable of invalidating the output of 
the decision 111, i.e., cancelling the inhibition in response to an 
identification number entered on the operation and display panel 104. This 
allows only an authorized person to copy inhibited documents, as needed. 
In the embodiments described so far, the pattern detection 110 consists of 
the black peak detection 301, black peak density detection 302, white 
ground detection 303, surrounding white ground detection 304, and observed 
pixel data decision 305, as shown in FIG. 3. FIG. 14 shows an alternative 
pattern detection 110 which is made up of a black peak detection 301, a 
black peak density decision 302, and an observed pixel data decision 305. 
The black peak detection 301 determines whether or not pixel data under 
observation is a black peak. The black peak density decision 302 
determines, based on the output of the black peak detection 301, whether 
or not the black peak density of a predetermined area centering around the 
pixel data under observation is coincident with a predetermined black peak 
density particular to the inhibition pattern. In this configuration, when 
the result of decision of the black peak density decision 302 indicates 
the predetermined black peak density, the observed pixel data decision 305 
determines that the pixel data being observed is part of the inhibition 
pattern. Such an alternative arrangement is comparable with the foregoing 
embodiments in respect of advantages. 
7th Embodiment 
This embodiment, like the first embodiment, determines whether or not pixel 
data are part of the inhibition pattern pixel by pixel, counts the pixel 
data determined to be part of the inhibition pattern, and determines 
whether or not the document is an inhibited document on the basis of the 
resulting count. Again, use is made of a sheet over which the inhibition 
patterns are printed or copied beforehand. The following description will 
concentrate on the differences of the seventh embodiment from the first 
embodiment. 
FIG. 15 shows the seventh embodiment in a schematic block diagram. As 
shown, an inhibition pattern combining section 115 is connected between 
the image processing section 102 and the plotter 103 in order to combine 
the inhibition patterns with the image data output from the image 
processing section 102. A shading correction 114 is included in the image 
processing section 102 for executing shading correction with the image 
data output from the scanner 101. In this configuration, when a 
confidential original document is copied, the inhibition patterns may be 
printed on a copy by the combining section 115, thereby producing an 
inhibited document. 
FIG. 16 shows the pattern detection 110 in a schematic block diagram. This 
pattern detection 110 differs from the pattern detection 110 of FIG. 3 in 
that it additionally includes an edge detection 306, and a mesh graph/mesh 
character decision 307. The edge detection 306 detects an edge portion on 
receiving the image data. The mesh graph/mesh character decision 307 
determines, on receiving the results of decision from the black peak 
density decision 302 and edge detection 306, whether or not the pixel data 
under observation and determined to be a pixel coincident with the black 
peak density of the inhibition pattern lies in a mesh graph portion or a 
mesh character portion. 
Specifically, the edge detection 306 determines whether or not a pixel lies 
in an edge portion. While the edge pixel identification is based on an N 
by N reference matrix, the embodiment uses a 5 by 5 matrix by way of 
example. For the elements of the reference matrix, there are set values 
produced by binarizing individual pixels by a threshold for edge pixel 
identification. FIG. 17 demonstrates an edge detection identification 
procedure. As shown, projections xs[] and ys[] of the 5 by 5 pixel matrix 
are produced in the x and y directions, respectively. 
For example, the element xs[0] is expressed by the following Eq. (1) and 
schematically shown in FIG. 18. Let each element of the 5.times.5 matrix 
be represented by dxy. 
EQU xs[0]=d00.linevert split..linevert split.d01.linevert split..linevert 
split.d02.linevert split..linevert split.d03.linevert split..linevert 
split.d04 Eq. (1) 
The Eq. (1) means that a group of meshed pixels shown in FIG. 18 are ORed. 
In the same manner, the elements xs[] and ys[] are calculated. 
Subsequently, the projections in the x and y directions are determined as 
to continuity by use of the calculated xs[] and ys[] and Eq. (2) shown 
below: 
##EQU1## 
The results xs and ys of decision on continuity are each an AND of the 
associated elements, as seen from the above Eq. (2). 
Thereafter, whether or not the center pixel X of FIG. 17 is an edge pixel 
is determined. Specifically, the results of decision on continuity xs and 
ys are ORed, as expressed as: 
EQU x=xs.linevert split..linevert split.ys Eq. (3) 
FIG. 19 shows the mesh graph/mesh character decision 307 specifically. As 
shown, the decision 307 is made up of an in-image edge detection 801, a 
left edge detection 802, a right edge detection 803, a mesh character 
decision 804, a mesh graph decision 805, and an OR gate 806. Among them, 
the in-image edge detection 801, left edge detection 802 and right edge 
detection 803 respectively detects edge pixels existing in a mesh image, 
edge pixels existing at the left edge of a mesh image, and edge pixels 
existing as the right edge of a mesh image, as shown in FIGS. 20A-20C. 
Assume that a pixel under observation is an edge pixel. Then, whether or 
not a pixel is present which lies in a predetermined area centering around 
pixel data under observation within WDTH widths in the main scanning or 
right-and-left direction and determined to have a black peak density 
coincident with that of the inhibition pattern is determined, where WDTH 
is a width. If such a pixel is present at the right and left of the pixel 
of interest, the pixel is determined to be an edge pixel in a mesh image. 
If the former is present only at the right of the latter, the latter is 
determined to be a left edge pixel; if the former is present only at the 
left of the latter, the latter is determined to be a right edge pixel. 
Subsequently, the mesh character decision 804 determines whether or not the 
pixel under observation lies in the above-mentioned particular area and 
adjoins an in-image edge pixel. If these conditions are satisfied, the 
decision 804 determines that the pixel under observation is a pixel lying 
in a mesh character portion. Further, the mesh graph decision 805 
determines that a pixel under observation lies in a mesh graph portion on 
condition that it lies in the above-mentioned particular area, that a mesh 
image left edge pixel is positioned nearest thereto in the left LNGTH 
range, and that a mesh image right edge pixel is present nearest thereto 
in the right LNGTH range, where both of the LNGTHs are lengths. 
Finally, the OR gate 806 ORs the result of decision on the mesh character 
portion and that on the mesh graph portion pixel by pixel. With such a 
procedure, it is possible to identify a mesh character portion and a mesh 
graph portion having a feature similar to that of the black peak of the 
inhibition pattern. 
Assume that the observed pixel data decision 305, FIG. 16, determines, 
based on the outputs of the black peak density decision 302, surrounding 
white ground decision 304 and mesh graph/mesh character decision 307, that 
the pixel under observation has a black peak density coincident with that 
of the inhibition pattern, that it is a surrounding white ground pixel, 
and that it is not a mesh graph/mesh character pixel. Then, the decision 
305 determines that the pixel data under observation is an inhibition 
pattern pixel. 
FIGS. 21A-21C show a specific operation of the pattern detection 110. 
Specifically, FIG. 21A demonstrates the operations of the white ground 
detection 303 and surrounding white ground decision 304. FIG. 21B 
represents the operations of the edge detection 306 and mesh graph/mesh 
character decision 307. FIG. 21C shows the operations of the black peak 
detection 301, black peak density decision 302, and observed pixel data 
decision 305. The flows shown in these figures occur in parallel at the 
same time. 
As shown in FIG. 21A, the white ground detection 303 determined whether or 
not a white ground exists in a predetermined region (step S1101). 
Subsequently, the surrounding white ground decision 304 determines a black 
peak density on the basis of the output of the black peak decision 302 
(step S1102). If the answer of the step S1102 is positive, Yes, the 
decision 304 determines whether or not a white ground is present in a 
portion a predetermined distance apart from the pixel determined to be a 
black peak density coincidence pixel, feeding the result of decision to t 
h e observed pixel data decision 305 (step S1103). If the answer of the 
step S1102 is negative, No, the program returns to the step S1101, ending 
the processing on the pixel data under observation. 
As shown in FIG. 21B, the edge detection 306 detects an edge portion by 
producing the projections of the reference matrix in the x and y 
directions (step S1104). Then, whether or not a pixel is an edge pixel is 
determined (step S1105). If it is at, edge pixel (Yes, step S1105), the 
result of decision on black peak density is examined in the right-and-left 
WDTH (step S1106). If a portion whose black peak density is coincident 
with that of the inhibition pattern is present at the right and/or the 
left, whether the edge pixel of interest is an in-image edge, right edge 
or left edge of a mesh image is determined (steps S1107 and S1108). 
Subsequently, whether the portion is a mesh graph/mesh character portion 
is determined, and the result of decision is fed to the observed pixel 
data decision 305 (step S1109). If the pixel is not an edge pixel or if a 
black peak density coincidence pixel is absent, the program returns to the 
step S1104, ending the processing on the pixel data under observation. 
As shown in FIG. 21C, the black peak detection 301 determines whether or 
not a black peak pixel is present (step S1110), and then the black density 
decision 302 determines a black peak density (step S1111). Subsequently, 
whether the black peak density is coincident with that of the inhibition 
pattern is determined (step S1112). If the answer of the step S1112 is 
negative, No, it is determined that the pixel under observation is not 
part of the inhibition pattern (step S1116). If the answer of the step 
S1112 is positive, Yes, whether or not surrounding white ground pixels are 
present is determined (S1113). If the answer of the step S1113 is 
negative, No, it is determined that the pixel is not part of the 
inhibition pattern (S1116). If the answer of the step S1113 is positive, 
Yes, whether or not the pixel lies in a mesh graph/mesh character portion 
is determined (S1114). If the answer of the step S1114 is positive, Yes, 
it is determined that the pixel is not part of the inhibition pattern 
(S1116). If the answer of the step S1111 is negative, No, it is determined 
that the pixel is part of the inhibition pattern (S1115). 
It is to be noted that the steps S1110-S1116 are executed with each pixel 
data and then with the entire input image. 
How the pattern combining section 115 is operated for forming the 
inhibition patterns on a sheet, i.e., producing an inhibited document is 
as follows. To begin with, a predetermined key on the operation and 
display panel 104 is pressed to enter an inhibition pattern generation 
command. In response, the system controller 105 sends a combine signal to 
the pattern combining section 115. On receiving the combine signal, the 
pattern combining section 115 combines the inhibition patterns shown in 
FIGS. 2A and 2B with the image signal output from the selector 113 and 
sends the resulting composite image signal to the plotter 103. As a 
result, the plotter 103 produces a sheet on which the inhibition patterns 
are printed, i.e., an inhibited document. 
As stated above, the illustrative embodiment causes the pattern combining 
section 115 to combine the inhibition patterns with the image data and 
outputs an inhibition pattern via the plotter 103. This embodiment is, 
therefore, comparable with the previous embodiments in respect of 
advantages. 
8th Embodiment 
This embodiment is essentially similar to the seventh embodiment except 
that it determines whether or not to thin, or reduce, lines in the 
subscanning direction, and that it changes the parameters of the pattern 
detection 110 so as to ensure the identification of an inhibited document 
even when the magnification is changed. The following description will 
concentrate only on the difference of this embodiment from the seventh 
embodiment. 
FIG. 22 shows the pattern detection 110 including a line thinning section 
1302 in addition to the constituents of the seventh embodiment. The line 
thinning section 1302 thins lines in the subscanning direction in matching 
relation to a magnification change ratio and generates a line synchronous 
signal meant for the pattern detection 110 and document decision 111. 
When the magnification change ratio is 200%, for example, the line thinning 
section 1302 sends to the pattern detection 110 a signal in which every 
other line is omitted. At this instant, the line thinning section 1302 
generates a line synchronous signal twice as great as the line synchronous 
signal of the image data input to the section 1302. Specifically, FIG. 23A 
shows the line synchronous signal of the image data input to the line 
thinning section 1302 while FIG. 23B shows the line synchronous signal 
output from the section 1302. The signal shown in FIG. 23B is used by the 
pattern detection 110 and document decision 111. FIG. 23C shows the lines 
of the image data input to the line thinning section 1302. Assuming the 
magnification change ratio of 200%, the lines shown in FIG. 23C are 
thinned every other line. As a result, the line thinning section 1302 
outputs lines shown in FIG. 23D. 
The pattern detection 110 changes the matrix of the black peak detection 
301 and that of the edge detection 306 on the basis of the magnification 
change ratio. Specifically, when the line thinning section 1302 does not 
thin the lines in an enlargement mode, the black peak detection 301 uses a 
3 by 5 matrix shown in FIG. 24 in place of the 3 by 3 matrix shown in FIG. 
4. When the section 1302 thins the lines, the detection 301 uses the 3 by 
3 matrix of FIG. 4. The procedure is identical with that of the seventh 
embodiment except for the positions of pixels other than a pixel E. 
Regarding the edge detection 306, while edge pixel decision is executed by 
use of an N by N pixel reference matrix, the embodiment uses a 5 by 5 
matrix. The individual pixels are binarized by an edge pixel decision 
threshold beforehand, and the resulting values are set as the elements of 
the reference matrix. FIG. 25 demonstrates an edge pixel decision 
procedure. For edge decision, the projections of the 5 by 5 matrix in the 
x and y directions are produced and respectively labeled xs[] and ys[]. 
For the projection xs[], the embodiment operates in the same manner as the 
seventh embodiment. For the projection ys[], the embodiment selects A, B 
or C shown in FIG. 25 in matching relation to the magnification change 
ratio. Equations for the decision are the same as those of the seventh 
embodiment except for their size. For example, in a 50% reduction mode, A 
of FIG. 25 is used. Specifically, in such a mode, since the scanner reads 
an image at a variable speed, the length per pixel over which the document 
is read in the subscanning direction is shorter than in the case of a x1 
mode. This can be compensated for only if A of FIG. 25 is used. 
When the line thinning section 1302 thins the lines in an enlargement mode, 
the above procedure is executed since the pattern detection 1301 will, in 
an apparent sense, receive image data reduced in scale. 
In summary, it will be seen that the present invention provides an image 
processing device having various unprecedented advantages, as enumerated 
below. 
(1 ) The device surely identifies an inhibited document on which inhibition 
patterns are printed or copied over the entire area. Hence, inhibited 
documents are surely prevented from being copied, transferred, stored, or 
input. 
(2) In the case of an inhibited document, the device, for example, masks 
image data with another image signal for thereby invalidating the image 
data. This prevents such image data from being output. 
(3) When the probability that image data representative of inhibited 
documents are input is high, the device executes more strict decision. 
(4) The device checks an unauthorized person tending to copy an inhibited 
document and, in addition, informs persons around copier of the improper 
copying. 
(5) Since the inhibition can be invalidated, only an authorized person is 
allowed to copy even an inhibited document, as needed. 
(6) The device can produce an inhibited document and identify it as an 
inhibited document. Specifically, the device is provided with pattern 
printing means so as to produce and identify inhibition documents with 
ease. 
(7) Even in a magnification change mode, the device can detect inhibition 
patterns and identify an inhibited document with accuracy. 
Various modifications will become possible for those skilled in the art 
after receiving the teachings of the present disclosure without departing 
from the scope thereof.