High definition image generating system for image processing apparatus

A high definition image generating system for an image processing apparatus for forming an image by converting multi-level data into dot impact output data of font patterns. The system comprises a block forming circuit for averaging multi-level data by a (2.times.2) block, an edge-direction detecting circuit for detecting an edge direction to output an edge-direction detection signal, an edge detecting circuit for detecting an edge to output an edge detection signal, and a switching circuit for switching a font pattern to be outputted to another pattern according to the edge detection signal and the edge-direction detection signal.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a high definition image generating system 
for an image processing apparatus which converts multi-level data into dot 
impact output data of font patterns. 
2. Description of the Prior Art 
A digital copying machine reads an image on an original document, converts 
the resultant analog signal into a multi-level data, performs 
image-quality adjustment processings, such as the adjustments of granular, 
tone, and definition, and reproduces the original image in the form of a 
mesh-dot image. In the digital copying machine, the multi-level data as 
digital data is used for the data processing to generate a high definition 
image. Because of this, various types of edits can be done using the 
digital data and a memory. 
FIG. 11 is a block diagram showing an arrangement of a digital copying 
machine. 
In FIG. 11 , an IIT (image input terminal) 100 reads an image on a color 
original document in the form of separated three primary colors, B (blue), 
G (green), and R (red) by using a CCD line sensor, and converts the 
separated three color signals into digital image data. An IOT (image 
output terminal) 115 performs the exposure by a laser beam, and the 
development, and reproduces the original color image. Various processing 
units ranging from an END converter 101 to an IOT interface 110, which are 
located between the IIT 100 and the IOT 115, make up a system for editing 
image data, i.e., an image processing system (IPS). In the edit processing 
system, the image data of B, G and R are converted into toner color data 
of Y (yellow), M (magenta), and C (cyan), and K (black or India ink), and 
every developing cycle produces a toner signal corresponding to the 
developing color. When the separated color signals (B, G, and R signals) 
are converted into toner signals (Y, M, C, and K signals), the following 
items become problematic; how to adjust color balance, how to reproduce 
the colors in conformity with the read characteristic of the IIT and the 
output characteristic of the IOT, how to adjust the balance between 
density and contrast, and how to adjust edge emphasis, blur and Moire, and 
the like. 
The IIT reads the original image, by using a CCD line sensor, with the size 
of 16 dots/mm for each pixel for the respective colors B, G and R, and 
outputs the data of 24 bits (3 colors.times.8 bits; 256 gray levels). The 
CCD line sensor is coupled with color filters of B, G, and R, and has a 
length of 300 mm at a density of 16 dots/mm, and makes a scan of 16 
lines/mm at a process speed of 190.5 mm/sec. Therefore, it produces read 
data at a speed of approximately 15M pixels/sec. for each color. In the 
IIT, the analog data of B, G and R pixels is subjected to the logarithmic 
conversion. As the result of the conversion, the reflectivity information 
is transformed into density information, and further to digital data. 
The IPS receives the separated color signals of B, G and R from the ITT, 
and executes various data processings to improve color reproduction, tone 
reproduction, definition reproduction, and the like, converts the toner 
signals of the developing process colors into on/off signals, and outputs 
them to the IOT. the IPS is made up of various types of modules; an END 
(equivalent neutral density) conversion module 101 for adjusting 
(converting) the color signals to a gray-balanced color signals, a color 
masking module 102 for converting the color signals B, G and R into toner 
quantity signals of Y, M and C by matrix-calculating the signals of B, G 
and R, a document-size detecting module 103 for detecting the document 
size in a prescan mode and erasing (frame-erasing) a platen color in a 
scan mode, a color conversion module 104 for converting a color in a 
designated area into another color according to an area signal that is 
applied from an area image control module, a UCR (under color removal) & 
black generating module 105 which generates black K of such a proper 
quantity as to prevent impure color, equally reduces colors of Y, M, C 
according to the quantity of K, removes the under color of the K, and Y, 
M, and C according to signals of the monocolor mode and 4-pass full color 
mode, a spatial filter 106 capable of removing blur and Moire, a TRC (tone 
reproduction control) for density adjustment, contrast adjustment, 
negative/positive inversion, color balance, and the like in order to 
improve the reproduction performance, a screen generator 109 for 
converting the tone toner signals of the process colors into on/off or 
2-level toner signal, an IOT interface module 110, the area image control 
module 111 including an area generating circuit and a switch matrix, and 
an edit control module including an area command memory 112, a color 
palette video switch circuit 113, and font buffer 114, and the like. 
For the separated color signals of B, G, and R from the IIT, 8-bit data 
(256 gray levels) is inputted to the END conversion module 101 where those 
are converted into toner signals of Y, M, C and K. The toner signal X of 
the process color is selected and converted into 2-level signal. It is 
outputted as on/off data of the toner signal of the process color, from 
the IOT interface module 110 to the IOT. In the case of the full color 
(4-pass full color), through the prescan, a document size, an edit area 
and other document information are first collected. Then, a copy cycle is 
first executed with the toner signal X whose developing color is Y, for 
example. Another copy cycle is next executed with the toner signal X whose 
developing color is M. Subsequently, similar copy cycles are repeated for 
the four image readings. 
In the copying machine as mentioned above, since the removal of mesh dots 
results in blur, a nonlinear spatial filter to emphasize the edge and a 
screen generator are combined to generate a high definition image. Use of 
the combination leads to increase of the hardware scale. Excessive 
emphasis of the edge brings about unnatural emphasis of the edge. This 
appears as discontinuity in the reproduced image. That is, the edge 
portion in the image is unnaturally emphasized or the details in the image 
are blurred. The image quality of the reproduced image is deteriorated. In 
such a case, when the generation copy is progressively repeated, the image 
quality deterioration is amplified and enlarged. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a copy of high image 
quality with a small scale hardware. 
Another object of the invention is to remarkably improve details 
reproduction, and reproduction of the generation copy. 
A further object of the invention is to enable data compression without 
deteriorating the original image. 
According to the present invention, there is provided a high definition 
image generating system for an image processing apparatus which converts 
multi-level data into dot impact output data of font patterns, and outputs 
the converted one, the high definition image generating system as shown in 
FIG. 1 comprising: block-forming means 1 for averaging multi-level data by 
(2.times.2)-black data; edge- direction detecting means 1 for detecting 
the vertical and horizontal edge directions on the basis of density 
distribution patterns; edge detect means 2 for detecting an edge on the 
basis of a density difference between a marked pixel and pixels around the 
marked pixel; and a font pattern to control font output means and to be 
outputted being switched to another pattern on the basis of the edge 
detect signal and the edge-direction detect signal. With such an 
arrangement, when an edge is detected, a font pattern to be outputted 
corresponds to the edge direction. Accordingly, there is eliminated the 
unnatural edge emphasis and a high definition image can be reproduced. 
Further, the high definition image generating system detects the edge 
direction on the basis of a density distribution of 2.times.2, which is to 
be converted into block data or as shown in FIG. 3, further comprises 
smoothing means 33 for smoothing the block data by the pixels around a 
marked pixel, when an edge is not detected, the smoothing means producing 
smoothed data. In the image generating system, font patterns corresponding 
to edge-direction patterns are provided for font output means, and the 
font pattern is selectively switched one from another according to the 
edge and edge-direction detect signals. Additionally, the font output 
means 5 contains error data owing to a gradation difference between input 
data and output data, the error data is fed back to the input data. 
The high definition image generating system thus arranged can detect the 
edge and edge-directions with high precision. When the edge is not 
detected, the smoothed image data may be used. Even if there is a 
gradation difference between input data and output data, the tone 
reproduction performance can be improved by the error data of the error 
data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Some specific embodiments of the invention will be described with reference 
to the accompanying drawings. 
FIG. 1 is a block diagram showing an embodiment of a high definition image 
generating system for an image processing apparatus according to the 
present invention. FIGS. 2 and 3 are block diagrams showing other 
embodiments of the high definition image generating system. 
In FIG. 1, a (2.times.2)-block forming/edge-direction detector 1 converts 
image data at 400 spi into blocks of image data at 200 spi each consisting 
of 4 pixels (=2.times.2), and averages multi-level data, and detects the 
direction of an edge by using the four (4) pixels. An edge detector 2 
detects an edge by using the 200 spi block image data. A font output 
circuit 5, which contains output font pattern data, is addressed by the 
output signal of a multiplexer 4, and converts multi-level data that is 
outputted from an adder 3, into font data. Specifically, in the font 
output circuit 5, the multi-level data of 8 bits and 256 gray- levels is 
converted into the font data of 8.times.4 bits. An error filter 6 is 
provided for feeding an error contained in the font data back to the adder 
3 to correct the next data. The error correction prevents a gradation of 
the image from being deteriorated. When the edge detector 2 detects an 
edge, the multiplexer 4 outputs the edge-direction data, which is detected 
by the (2.times.2)-block forming/edge- direction detector 1, to the font 
output circuit 5. In this case, the edge-direction data is used as address 
data for the font output circuit 5. When the edge is not detected, the 
multiplexer 4 produces fixed parameter P as the address for the font 
output circuit 5. Accordingly, a font pattern outputted from the font 
output circuit 5 when the edge is detected is different from that when the 
edge is not detected, even if the output data of the adder 3 applied to 
the font output circuit 5 remains unchanged at 8-bit and 256 gray-levels. 
Also when the edge is detected, the font pattern outputted from the font 
output circuit changes depending on the direction of the edge detected. 
Since the edge direction is detected by the block data of 2.times.2 
pixels, it may be classified into one side and the other side of each of 
the vertical, horizontal, and oblique lines, which are applied to the data 
block. The font pattern data outputted from the font output circuit 5 
correspond to those items classified. 
In the instance as mentioned above, the image data is converted into block 
data of 2.times.2 pixels, and the edge is also detected. Another circuit 
arrangement is presented in FIG. 2, in which the block image data is used 
for detecting the edge-direction as for the edge detection. In this 
instance, a (2.times.2)-block data averaging circuit 11 averages the four 
pixels into multi-level data. The edge-direction detector 12 detects the 
edge by using the multi-level, and the edge direction as well. When the 
edge is detected, the edge-direction detector 12 produces data of 3 to 4 
bits. When not detected, it produces the fixed parameter P as a font 
select signal, and serves as address data to the font output circuit 14. 
An additional circuit arrangement is presented in FIG. 3, in which the edge 
is detected and smoothed data is generated, and when no edge is detected, 
the data is smoothed. In FIG. 3, a (2.times.2)-block/edge-direction 
detector 21 is the same as that shown in FIG. 1. An edge detect/smoothing 
circuit 22 detects the edge by using block data and outputs an edge detect 
signal and a smoothed signal. A multiplexer 23 selects either of the block 
data and smoothed data resulting from smoothing the block data in response 
to the edge detect signal. When the edge is detected, it allows the block 
data to straightforwardly go to an adder 24. When the edge is not 
detected, it allows the smoothed data generated by the edge 
detect/smoothing circuit 22 to go to the adder 24. 
The algorithms for detecting the edge-direction and the edge, and the 
circuit arrangements implementing them will be described. 
FIG. 4 shows diagrams useful in explaining the definition of the 
edge-direction detection. FIG. 5 is a block diagram showing a circuit 
arrangement of the edge- direction detector. 
Where the data block consisting of 2.times.2 pixels is used as a detect 
unit for detecting the edge direction, the edge direction may be defined 
by nine types of patterns as shown in FIG. 4; a pattern No. 1 having no 
edge, patterns Nos. 2 and 3 having edges vertically extending, patterns 
Nos. 4 and 5 horizontally extending, and patterns Nos. 6 to 9 having edges 
that are located on both sides of an oblique line and extends along the 
oblique line. An arrangement of a circuit capable of recognizing those 
patterns is shown in FIG. 5(a). 
In FIG. 5, reference numeral 31 designates a (2.times.2)-block forming 
circuit. Comparators 32A to 32D compare respectively the values of pixels 
A to D in the (2.times.2) data block with a mean value m (=(A+B+C+D)/4) 
that is calculated by the (2.times.2)-block forming circuit 31. A LUT 
(look-up table) 33 is a ROM (read only memory) which receives 4-bit edge 
pattern signals outputted from the comparators 32A to 32D as address 
signals, and edge pattern signals. It is assumed that the 4-bit output 
data of the comparators 32A to 32D is arranged such that the pixel A is 
allocated to the least significant bit 0, the pixel B to bit 1, the pixel 
C to bit 2, and the pixel D to the most significant bit 3, and further 
that when the value of the pixel is larger than the mean value "m", each 
of those comparators 32A to 32D produces data of "1". On the assumption, 
4-bit edge pattern signals "0000" to "1111" can be produced, which 
correspond to the position of the pixel whose value is above the mean 
value "m", as shown in FIG. 5(b). When the LUT 33 is addressed by any of 
those edge patterns signals, the LUT 33 produces the corresponding one of 
the edge-direction data No. 1 to No. 9 defined in FIG. 4. 
FIG. 6 shows arrangements of the comparators 32A to 32D in the 
edge-direction detector shown in FIG. 5(a). Those comparators are arranged 
such that the pixel values A to D are each compared with the mean value 
"m", and the edge direction is detected on the basis of the position of 
the pixel whose value is larger than the mean value. When it is the mean 
value "m", for example, where a character is present above a half-tone 
image and a density in the background of the character changes, the 
portion in the image, which is not the character, provides the edge- 
direction data. To cope with the problem, the comparators of FIG. 6 use 
maximum-value (max-value) selectors 34 for selecting a value to be 
compared with the pixel values A to D. In the circuit of FIG. 6(a), a 
fixed value Bth, which is empirically determined, is applied as a 
threshold value for comparison to the max-value selector 34, which also 
receives the mean value "m". The selector selects one of those values, 
which is the larger. In the circuit of FIG. 6(b), the selector 34 receives 
the fixed value Bth and a value as the result of subtraction of a fixed 
value "k" from the maximum value of each of the pixel values A to D, and 
selects either of them, which is the larger. In the circuit of FIG. 6(c), 
the selector 34 receives a value as the sum of a fixed value "k" and the 
means value "m", and the fixed value Bth, and selected either of them, 
which is the larger of the two. 
The edge detector 2, the edge-direction detector 12, and the edge 
detect/smoothing circuit 22 shown in FIGS. 1 to 3 will be described. 
FIG. 7 shows diagrams for explaining an algorithm to detect the edge. FIG. 
8 shows diagrams for explaining an algorithm for the smoothing circuit. 
The edge detector 2 shown in FIG. 1 is arranged as shown in FIG. 7, for 
example. For the edge detection, a 3.times.3 window of the data blocks is 
used as shown in FIG. 7. In the figure, blocks A to I are each a pixel of 
200.times.200 spi, which results from the averaging of the data block. Let 
a pixel E be a marked pixel, and us define densities in the window as 
follows: 
##EQU1## 
Then, the edge is given by 
EQU Edge=max (E.sub.1, E.sub.2, E.sub.3, E.sub.4) 
where E.sub.1 =.vertline.e.sub.1-e.sub.2 .vertline. (absolute of the 
difference between the densities of the upper and lower rows), E.sub.2 
=.vertline.e.sub.3 -e.sub.4 .vertline. (absolute of the difference between 
the densities of the right and left columns), E.sub.3 =.vertline.e.sub.5 
-e.sub.6 .vertline. (absolute of the difference between the densities of 
the left upper corner and the right lower corner), and E.sub.4 
=.vertline.e.sub.7 -e.sub.8 .vertline. (absolute of the difference between 
the densities of the right upper corner and the left lower corner). The 
edge value is compared with a threshold value "th". When the former is 
larger than the latter, control determines that it is in an edge area. In 
the reverse case, control determines that it is in the non-edge area. In 
FIG. 7(b) showing an arrangement of the detector, an edge detecting 
portion 41 detects an edge by using the 9-pixel data of 200.times.200 spi. 
A comparator portion 42 compares the detected edge with the threshold 
value "th" to determine whether the marked pixel is in the area or 
non-edge area. 
The edge-direction detector 12 in the embodiment shown in FIG. 2 detects 
the edge as just mentioned and its direction as well. The edge direction 
is determined by finding the maximum edge of those E1 to E4, and its sign, 
positive or negative. For example, when the maximum edge is El and its 
sign is positive, the edge pattern No. 4 is selected for the edge 
direction. If the sign is negative, the pattern No. 5 is selected. When 
the maximum edge is E2, the edge pattern No. 2 is selected for the 
positive sign, and the edge No. 3 for the negative sign. When the maximum 
edge is E3, the edge pattern No. 8 is selected for the positive sign, and 
the edge No. 9 for the negative sign. When the maximum edge is E4, the 
edge pattern No. 6 is selected for the positive sign, and the edge pattern 
No. 7 for the negative sign. When no edge is present, the edge pattern No. 
1 is selected. 
In this way, the edge detect/smoothing circuit 22 shown in FIG. 3 detects 
the edge, and produces a smoothed signal "f". The simplest expression of 
the smoothed signal "f" is 
EQU f=(A+B+C+D+E+F+G+H+I)/9. 
It is very difficult to realize the expression in a hardware manner, 
however. One of the feasible methods is to weight pixel values as shown in 
FIG. 8, and to average them. In the case of FIG. 8(a), the marked pixel 
value is four times the original pixel value; the values of the pixels on 
the right and left sides of the marked pixel, and above and below the 
same, are two times the original pixel value; and the values of the pixels 
at the four corners are each equal to the original one. The pixel values 
thus weighted are added together and divided by 16. The result of the 
dividing calculation forms the smoothed signal. Accordingly, the following 
calculation suffices for this case. 
EQU f=0.0625(A+C+G+I)+0.125(B+D+F+H) +0.25E. 
In hardware, this can be realized by shifting A, C, G, and I by 4 bits to 
the right, B, D, F, and H by 3 bits to the right, and E by 2 bits to the 
right, and adding them together. 
In the case of FIG. 8(b), the value of only the marked pixel is set to be 
four times the original pixel value. The pixels values of those pixels are 
added together, and the result of the addition is divided by eight (8), 
thereby to provide the smoothed signal. In this case, the smoothed signal 
"f" is 
EQU f=0.5E+0.125(B+D+F+H). 
In hardware, B, D, F, and H are shifted by 3 bits to the right, and E is 
shifted by 2 bits to the right, and those are added together. 
The font output circuit will be described. 
FIG. 9 shows diagrams for explaining the font output circuit. 
It is assumed that the data resolution is set at 3200 spi in the main scan 
direction, and is at 400 spi in the vertical scan direction, as shown in 
FIG. 9(a). Then, the font produced by the font output circuit is basically 
the called ten-thousands lines type font of 200 lines. In this instance, 
the font is switched from one font to another on the edge, thereby to 
improving a definition (sharpness) of the image. Since the font type is 
used in the present invention, an error occurring between the input and 
output can be obtained without calculation, and the error may be prestored 
in an LUT 43, as shown in FIG. 9(b). In this instance, address data to 
address the LUT 43 is the combination of edge-direction data of 3 to 4 
bits and input image data (200 spi) of 8 bits, and accordingly its data 
width is 11 to 12 bits. With the address data, font pattern data and error 
data are read out of the LUT 43. Accordingly, no time to calculate the 
error is taken. The feedback loops of the error filters 6, 15, and 27 can 
be operated more quickly. Where the data preset in the LUT has the 
resolution of 3200 spi.times.400 spi, for example, the number of output 
dots is 32 dots. If the input data is 200, the number of the output dots 
is 25 dots, and the error is 200-25.times.(255/32).perspectiveto.1. 
FIG. 10 is a diagram showing relationships between the edge numbers and 
output font patterns. 
As shown, in the font pattern for the edge No. 1, the dot grows from the 
center of the pattern. In the font pattern for No. 2, it grows from the 
left end of the pattern. For No. 3, it grows from the right end. For No 4, 
it grows from the center of the upper row. For No. 5, it grows from the 
center of the lower row. For No. 6, it grows from the right upper corner. 
For No. 7, it grows from the left lower end. For No. 8, it grows from the 
left upper corner. For No. 9, it grows from the right lower corner. 
It should be understood that the present invention is not limited to the 
embodiments as mentioned above, but may variously be changed and modified 
within the scope of the appended claims. In the embodiment as mentioned 
above, the image data having the resolution of 400 spi is converted into 
block data at 200 spi. It is evident that if required, it may be converted 
into block data of another resolution. In the embodiment, the image data 
is converted into block data, the edge-direction in the data is detected, 
and then is outputted as font data. Alternatively, a memory may be 
provided preceding to the font output circuit. The edge direction data of 
3 to 4 bits and 8-bit (2.times.2)-block averaged data are stored as image 
data into the memory. When comparing with the case where the image data is 
stored as intact in the memory, a required memory capacity of the memory 
can be saved, because the image data is compressed into the data of (3 to 
4 bits+8 bits), with one block of (8 bits.times.4 pixels). Thus, the data 
is reduced to approximately 1/3. 
As seen from the foregoing description, the present invention realizes the 
functions of forming the (2.times.2)- block data, edge-direction 
detection, font generation, and the feedback system including the error 
filter in simple hardware. Accordingly, the cost to construct the hardware 
is more reduced and the circuit construction is simpler than in the 
hardware using the digital filter and the screen generator. Further, the 
invention detects the edge and its direction, while guaranteeing the 
average value resulting from averaging the (2.times.2) block, and switches 
a font to another depending on them. Therefore, the dot attracting effect 
operates to minimize formation of unnatural edges. A high definition image 
can be reproduced, which is excellent in granular and tone reproduction 
characteristics, and in image quality. Hence, the present invention 
provides an image processing apparatus which exhibits an excellent 
performance for the generation copy. Even when the data resolution is 
converted from 400 spi.times.400 spi to 200 spi.times.200 spi, the edge 
component information reflects on the font switchover. Accordingly, the 
amount of image information can be reduced to 1/3 without deteriorating 
the image quality. With the reduction of the data amount, the image 
processing apparatus can cope with the increasing of the processing speed.