Image processing apparatus

An image processing apparatus comprising a detector for reading out image information on an original placed on an original glass plate and detecting an area of the original, and a microcomputer for detecting a concentration level regarding the main-scan line of the image information in the original area read out by the detector and operating a threshold value for a binary coding process regarding the main-scan line of the image information on the basis of the concentration level. By changing the threshold level, the background noise eliminating process can be performed even if the background level varies. Thus, even if an original is unevenly placed on the original glass plate, the background noise eliminating process can be executed in the whole area of the original image.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an image processing apparatus which can 
perform a process of an image on an original. 
2. Description of the Prior Art 
Conventionally, in the case of performing a process to remove the 
background noise of an original image, there has been adopted a method of 
performing the process to eliminate the background noise in an arbitrary 
area on a predetermined original readout surface on the basis of the size 
of the original which is selected by the operator. However, this method 
has the drawback that with respect to a small original or an original 
which was preliminarily irregularly placed on the original readout surface 
without being designated, it is impossible to perform the process to 
eliminate the background noise in the whole area of the original image. 
In this invention, the process to eliminate the background noise denotes a 
series of processes such that, upon recording of an image, the portion 
other than the image information such as characters, figures or the like 
on an original, namely, the background portion on the original, is not 
recorded at the gradient level which was actually detected in that 
background portion but is recorded at a predetermined level such as white 
or the like. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to eliminate the above-mentioned 
drawback. 
Another object of the invention is to improve an image processing 
apparatus. 
Another object of the invention is to provide an image processing apparatus 
which can perform the process to eliminate the background noises in the 
whole original image even with respect to an original which was placed 
irregularly on an original mounting plate by detecting a range of 
original. 
Another object of the invention is to provide an image processing apparatus 
which can perform the background noise eliminating process even when a 
background level varies by changing a threshold level. 
Other objects and features of the present invention will be apparent from 
the following detailed description in conjunction with the accompanying 
drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described in detail hereinbelow with 
reference to the drawings. 
FIG. 1 shows an example of an arrangement of an image processing apparatus 
according to the present invention. In the diagram, an original 101 may be 
placed upside down on an original glass 102 and pressed on the original 
glass 102 by an original cover 103. The original 101 is illuminated by a 
light source 104 and the reflected light from the original 101 forms an 
optical path L so as to be formed as an image on a photo sensitive surface 
of an image pickup device 109 such as, for example, a CCD image sensor 
through mirrors 105, 106 and 107 and a lens 108. 
The light source 104 and mirror 105 and the mirrors 106 and 107 constitute 
an optical unit R which moves at a relative velocity of 2:1. This optical 
unit R moves from the left to the right at a constant velocity while 
performing the PLL control by a DC servo motor 110. The moving velocity of 
the optical unit R is variable from 90 to 360 mm/sec in the forward path 
in accordance with copy magnification, while it is always a constant 
velocity of 630 mm/sec in the backward path. The optical unit R is 
forwardly moved from the left end to the right end by the DC servo motor 
110 while reading out an image in the moving direction of the optical unit 
R, namely, in a main-scan direction X perpendicular to a sub-scan 
direction Y by the image pickup device 109 with a resolution power of 16 
pel/mm. Thereafter, the optical unit R is again moved backward to the left 
end by the DC servo motor 110, thereby finishing the single readout scan. 
Next, a method of detecting the position of the original 101 will be 
explained with reference to FIG. 2. 
FIG. 2 shows the state in that the original 101 is placed on the original 
glass 102. Although the original 101 is generally placed in a manner such 
that the corner of the original 101 is aligned with reference coordinates 
SP on the original glass 102, it may be obliquely placed as shown in the 
diagram. In this case, an original range from X.sub.jt to X.sub.je on the 
Y.sub.j -th main-scan line (where it is assumed that the main-scan 
direction is X and the sub-scan direction is Y) from the reference 
coordinates SP is detected by, for instance, pre-scanning the optical unit 
R during the preliminary operation of the apparatus. This makes it 
possible to detect the image range of the original 101 and to determine 
the size and position of the original from the detection result. It is 
also possible to determine the scan stroke of the recording apparatus and 
to select a desired paper size. The original cover 103 (refer to FIG. 1) 
is mirror processed so that the image data which is obtained out of the 
area where the original 101 is placed becomes black data. Therefore, the 
range of the original can be detected on the basis of the difference of 
the image data obtained due to the reflection. In the pre-scan by the 
optical unit R prior to recording an image, the main-scan and sub-scan are 
performed with respect to the whole surafce area of the original glass 102 
to detect the range of original, thereafter the scan for recording the 
image which will be explained later is executed subsequently. The pre-scan 
velocity is set to be faster than the scan velocity when the image is 
recorded. 
Next, FIG. 3 shows an example of an arrangement of an original position 
detecting circuit to detect the foregoing original range. 
An image signal VIDEO which was read out by the image pickup device 109 
during to the pre-scan by the optical unit R and was binary coded is 
inputted to a shift register 201 which can input it as, for instance, 
eight-bit data. The shift register 201 is made operative in response to a 
clock pulse CLK. Upon completion on of the input of the data of eight 
bits, the shift register 201 sends the 8-bit data to gate circuits 202 and 
204. The gate circuit 202 checks the 8-bit data to see if all of them are 
"0" (white image) or not. When all of the 8-bit data indicate white image, 
the gate circuit 202 outputs "1" onto a signal line 203. Likewise, the 
gate circuit 204 detects whether all of the 8-bit data are "1" (black 
image) or not and outputs "1" onto a signal line 205 when all of the 8-bit 
data represent the black image. 
A flip flop 206 is set in response to the output "1" of when gate circuit 
202, namely, the data of eight bits indicative of white image first 
appears after the scan of the original is started. This flip flop 206 has 
been preliminarily reset in response to an image head signal VSYNC. 
When the flip flop 206 is once set in response to the output "1" from the 
gate circuit 202, the set state is maintained until the next image head 
signal VSYNC is inputted. The output signal is supplied to a latch circuit 
207 when the flip flop 206 is set, so that a value of a sub-scan counter 
208 for counting the sub-scan lines by the optical unit R is transferred 
to the latch circuit 207. The numerical value stored in the latch circuit 
207 becomes a coordinate value Y.sub.t in FIG. 2. This coordinate value 
Y.sub.t is held until the next image head signal VSYNC is inputted. 
Since the output of the gate circuit 204 becomes "1" whenever the 
above-mentioned eight bits change from the state whereby at least one bit 
among them indicates white image to the state whereby all of the eight 
bits represent black image, the value of the sub-scan counter 208 at this 
time is transferred to a latch circuit 209. In other words, the value of 
the sub-scan counter 208 is latched whenever the output of the gate 
circuit 204 changes from "0" to "1". Therefore, in the sub-scan direction 
Y, all of the data having a unit of eight bits after a coordinate value 
Y.sub.e shown in FIG. 2 continuously indicate black image, that is, the 
output of the gate circuit 204 is held to be "1", so that this value 
Y.sub.e is maintained in the latch circuit 209. 
When the 8-bit white image data first appears for every main-scan line, a 
flip flop 210 is set in response to the output "1" from the gate circuit 
202. This flip flop 210 has been reset in response to a horizontal sync 
signal HSYNC which is given when the optical unit R scans. The flip flop 
210 is set by the 8-bit white image data which first appears and this set 
state is maintained until the next horizontal sync signal HSYNC is 
generated. Since output signal is supplied to a latch circuit 212 when the 
flip flop 210 is set, a value of a main-scan counter 211 for counting the 
line in the main-scan direction is transferred to the latch circuit 212. 
The value stored in the latch circuit 212 becomes the coordinate value 
X.sub.jt in FIG. 2. 
The output of the gate circuit 204 becomes "1" whenever the eight bits 
change from the state whereby at least one bit indicates the white image 
to the state whereby all of the eight bits represent the black image, so 
that a value of the main-scan counter 211 at this time is transferred to a 
latch circuit 213. Thus, in the main-scan direction X, all of the 
eight-bit data after the coordinate value X.sub.je in FIG. 2 continuously 
indicate black image; therefore, this value is held. 
Each data which is stored in the latch circuits 207, 209, 212, and 213 is 
supplied through a bus BUS to a central processing unit (hereinafter 
referred to as a CPU)307 of, for instance, the microprocessor type shown 
in FIG. 4. 
In this way, due to the single scan of the original, it is possible to read 
out the coordinate values Y.sub.t and Y.sub.e in the sub-scan direction Y 
and the coordinate values X.sub.jt and X.sub.je in each main-scan 
direction X from the start of scan position to the end of scan position in 
the sub-scan direction with respect to the main-scan direction X, 
respectively. Therefore, the range of original on the readout surface 102 
of the original 101 can be detected. According to this method, the 
original range can be accurately detected irrespective of the arrangement 
of the original or the shape of image area, for example, rectangle, 
triangle, circle, or the like. 
Then, FIG. 4 shows an example of an arrangement of an image signal 
processing circuit for processing the image signal which is obtained from 
the image pickup device 109 shown in FIG. 1. 
An A/D converter 301 A/D converts an image signal (analog signal) A-VIDEO 
which was read out by the image pickup device 109 to a six-bit digital 
signal. The digital signal converted by the A/D converter 301 is once 
stored in a latch circuit 302 which operates synchronously with the 
sampling clock CLK. The signal stored in the latch circuit 302 is 
respectively transferred to a latch circuit 303, a comparator 304 and a 
latch circuit 305 synchronously with the next clock CLK. 
The comparator 304 compares the output levels of the 6-bit image signal 
transferred from the latch circuit 302 and of the 6-bit image signal sent 
from the latch circuit 303 which is one clock before. When the level of 
the new image signal transferred from the latch circuit 302 has a smaller 
value, a comparison output is sent to an AND gate 306. The AND gate 306 
sends the comparison output from the comparator 304 to the latch circuit 
305 synchronously with the sampling clock CLK. When the latch circuit 305 
receives the comparison output, it sends the image signal transferred from 
the latch circuit 302 to the CPU 307. In addition to the output from the 
comparator 304 and the sampling clock CLK, an enable signal ENABLE 
indicative of the effective interval of the original image is inputted to 
the AND gate 306. 
This signal ENABLE is made enable only in the original range obtained by 
the foregoing circuit shown in FIG. 3, that is, in the range from the 
coordinate values Y.sub.t to Y.sub.e which are stored in the latch circuit 
207 and 209 in the sub-scan direction Y and in the range from the 
coordinate values X.sub.jt to X.sub.je which are stored in the latch 
circuit 212 and 213 in the main-scan direction X in the above-mentioned 
interval from the coordinate values Y.sub.t to Y.sub.e. The result of 
comparison in level of the image signal of two clocks in this interval is 
sent from the latch circuit 305 to the CPU 307. In the CPU 307, the lowest 
concentration level of each main-scan line, i.e., the concentration of the 
background of the original (hereinafter referred to as the background 
level), can be detected by receiving the image signal from the latch 
circuit 305 synchronously with a main-scan line sync signal MLS. 
Next, the CPU 307 determines the binary coded threshold value for every 
main-scan line due to the algorithm mentioned later on the basis of the 
background level which was detected as described above and sends this 
threshold value to a comparator 308 synchronously with the main-scan line 
sync signal MLS. The comparator 308 compares the image signal from the 
latch circuit 303 with the threshold value from the CPU 307 and produces a 
binary coded signal. Since the level of each pixel after the A/D 
conversion by the A/D converter 301 is constituted by six bits, the most 
black portion is expressed by 3F.sub.(HEX) (hereinafter, referred to as 
3F.sub.H) and the most white portion is expressed by 0. The threshold 
value and background level for every main-scan line are also expressed by 
0 to 3F.sub.H. 
Referring now to FIG. 5, there will then be explained the algorithm to 
predict the background level and determine the threshold value regarding 
the main-scan line which should be scanned from the background level of 
each of the N lines immediately before the main-scan line that is to be 
scanned at present. In the drawing, W.sub.i-1 denotes a background level 
detected with regard to the (i-1)th main-scan line; W is a prediction 
value of the background level of the i-th main-scan line which is 
predicted due to an algorithm mentioned later on the basis of the N data 
from a background level W.sub.i-N of the (i-N)th main-scan line to a 
background level W.sub.i-1 of the (i-1)th main-scan line; and S.sub.i is a 
threshold value regarding the i-th main-scan line which is determined from 
the prediction value W due to an algorithm mentioned later. 
Practically speaking, after completion of the scan of the (i-1)th line, the 
prediction value W.sub.i of the background level of the i-th line is 
derived from the N background levels W.sub.i-k (where, k=1, . . . , N) 
which were detected with regard to the N lines from the (i-N)th line to 
the (i-1)th line before the scan of the i-th line is started. Then, the 
threshold value S.sub.i regarding the i-th line is obtained from the 
prediction value W.sub.i. When the scan of the i-th line is started, the 
binary coding process is performed on the basis of the threshold value 
S.sub.i, and at the same time the actual background level of the i-th line 
is also derived. 
Next, an example of the control operation of the CPU 307 will be explained 
with reference to FIG. 6. 
First, as shown in FIG. 7, the optical unit R starts the forward movement 
from its home position point A (step S1), then initialization of each 
circuit is executed (steps S2 and S3) until the optical unit R reaches a 
head point B of the image (step S4). In step S2, an initialization is made 
with respect to memory areas BUF.sub.1 to BUF.sub.N (not shown) in an 
N-byte random access memory in which the N background levels of the N 
lines immediately before the line that should be scanned at present are 
always stored. In step S3, W.sub.0 is set to 0 in order to obtain a 
prediction value w.sub.1 of the background level of the first main-scan 
line. 
Subsequently, it is determined by means of a sensor (not shown) that the 
optical unit R has reached point B (step S4). Thereafter, whenever the 
main-scan line sync signal is generated, the background level of the 
previous line is fetched (steps S5 and S6); the oldest background level 
data stored in the memory area BUF.sub.1 is erased; the content of the 
memory area BUF.sub.j is transferred to the memory area BUF.sub.j-1 ; and 
the fetched latest data is stored in the memory area BUF.sub.N. Thus, the 
newest N background level data are always stored in the memory areas 
BUF.sub.1 -BUF.sub.N (step S7). 
Next, as shown in step S8, in order to eliminate the peculiar data from the 
N background level data, the maximum and minimum values in the N data are 
eliminated and the mean value of the remaining N-2 data is adopted as the 
prediction value W.sub.i of the background level of the line that should 
be scanned. Namely, the prediction value W.sub.i becomes 
##EQU1## 
Further, in the case where the prediction value W.sub.i is smaller than a 
predetermined value P, the threshold value S.sub.i is determined by 
EQU S.sub.i =(3F.sub.H -W.sub.i).times..alpha.+W.sub.i 
so that the background level W.sub.i which is predicted indicates the white 
image (steps S9 and S10). On the other hand, when the prediction value 
W.sub.i is equal to or greater than the predetermined value P in step S9, 
step S11 follows and the threshold value S.sub.i is set to 
EQU S.sub.i =3F.sub.H .times..alpha. 
.alpha. is a coefficient to set an interior division point of a 
predetermined ratio between the black level 3F.sub.H and the background 
level W.sub.i to a threshold value and satisfies the relation of 
0&lt;.alpha.&lt;1. This coefficient .alpha. is determined from experience and is 
set to, e.g., .alpha.=1/2. FIGS. 8A and 8B show the situations in 
determination of the threshold values in the cases where W.sub.i .gtoreq.P 
and where Wi&lt;P when .alpha.=1/2. The coefficient .alpha. may be set to any 
value of, e.g., 1/10, 2/10, . . . , 9/10, etc., in accordance with the 
proper set concentration which is set by the operator by use of a 
concentration lever (not shown). 
The threshold values S.sub.i which was determined as mentioned above is 
outputted (step S12) and the processes in steps S5 to S14 are repeatedly 
performed until the optical unit R reaches a reversing position point C of 
the optical unit shown in FIG. 7. When it is detected by a sensor (not 
shown) that the optical unit R has reached begin point C, the optical unit 
R is reversed, to the backward movement (step S15). Further, when the 
optical unit R has reached the home position point A, the operation of the 
optical unit R is stopped (steps S16 and S17). 
After the (N+1)th line, the actual detection data is always stored in the 
memory area BUF.sub.i. However, with respect to the first to N-th lines, 
upon initialization in steps S2 and S3, the virtual N lines of which the 
detection value of the background level is 0 are assumed before the first 
line and the threshold value is calculated and the binary coding process 
is performed. 
For example, assuming that N=16, the binary coding process is carried out 
on the basis of the virtual data with respect to the first 16 lines. 
However, the resolution power of 16 pel equivalently corresponds to 1 mm 
and the head portion of 1 mm in the actual original is generally the 
background portion without information; therefore, there will be no 
problem if it is assumed that the head portion has the background level of 
0. 
According to the above-mentioned method, with regard to an original such 
that the background level W largely varies as shown in FIG. 9(A), a 
threshold value A cannot adequately follow in correspondence to this 
change; therefore, it is binary coded as shown in FIG. 9(B) and the 
background portion and information portion could not be sufficiently 
separated. However, in this embodiment, a threshold value B follows the 
change of the background level as shown in FIG. 9(A), so that the 
background portion certainly becomes white and can be separated from the 
information portion as shown in FIG. 9(C). Consequently, in the 
embodiment, the pre-scan and memory for storage of the image signal are 
not needed in particular for determining or binary coding the threshold 
value, but the threshold value can be determined at a real-time. In FIG. 
9(A), VIDEO denotes the image signal. 
In the foregoing method, the threshold value can be obviously determined on 
the basis of the main-scan line of N=1, that is, immediately before the 
line that should be scanned. 
Although the background level is detected in the embodiment, it is also 
possible to detect the concentration peak values of both white and black 
images, namely, the lowest concentration level and the highest 
concentration level and to determine the threshold value to perform the 
binary coding process by use of those levels. 
As described above, according to the embodiment, the original range can be 
automatically detected and the background noise eliminating process can be 
performed with respect to only the image area. However, it is apparent 
that the area where the background noise eliminating process is performed 
can be manually decided by scanning on a scan panel (not shown). 
As described above, a range of original is preliminarily detected and the 
background noise eliminating process is executed with respect to only this 
detected area of the original. Consequently, even with regard to an 
original placed at any position on the original plate, it is possible to 
perform the background noise eliminating process with respect to the whole 
original area. 
The present invention is not limited to the above-described embodiment, but 
many modifications and variations are possible within the spirit and scope 
of the appended claims.