JPH02312358A - Halftone image estimating device - Google Patents

Abstract

PURPOSE:To reduce the number of counter circuits by counting the number of white picture elements in plural scan apertures with a common counter circuit. CONSTITUTION:The device is comprised of an image reader 1, a halftone image estimating means 2, an image processing means 3, a binarization means 4, a recorder 5, and an image memory unit 6. And by dividing the picture element area of the half of the maximum aperture area out of the scan apertures into the units of 2<n> picture elements and 2<n+1> picture elements, and counting the number of white picture elements or black picture elements in respective unit, and also, counting the number of white picture elements or black picture elements in each area corresponding to a remaining half area with a timing of (n+1) clock, the number of white picture elements or black picture elements in the plural scan apertures having the aperture area of the half of the maximum aperture area can be calculated from the area by using the above counted values. Thereby, it is possible to reduce the number of counter circuits to count the number of white picture elements or black picture elements in the scan aperture.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a halftone image estimating device that can accurately estimate an original halftone image from a binary image displayed in halftones, and in particular, The number of counting means used for counting the number of white pixels or black pixels within the scanning aperture can be reduced.

[Background of the Invention] Many output devices such as display values and printing devices that are currently in practical use can only be expressed in binary values of white and black.

The dize method, which is a type of area gradation method, is known as a method for expressing a halftone image in a pseudo manner using such an output device.

As shown in Figure 11, the dither method uses a predetermined threshold value and size (approximately 8 x 8 pixels) as shown in Figure 11 (B) for the original halftone image (Figure 1A). The image is binarized using a threshold matrix (in this example, a Bayer dither matrix) to create a dithered image that is a pseudo halftone image as shown in (c) of the same figure. .

If it is possible to estimate the original halftone image from such a dithered image, it is possible to perform various data processing based on the estimated halftone image, and it is possible to have a degree of freedom in image conversion, which is convenient. Good.

To estimate a halftone image from a dithered image, a matrix of a predetermined size (hereinafter referred to as a scanning aperture) is prepared, and the number of white or black pixels existing within this scanning aperture and a predetermined requirement (described later) are determined. Under the condition that the condition is satisfied, the halftone level of the pixel of interest is estimated, and this is sequentially executed for each pixel.

At this time, estimation is performed by moving the scanning aperture pixel by pixel in the row and column directions, and this is executed up to the last pixel to estimate a pseudo halftone image relative to the original halftone image.

When estimating a halftone image using a scanning aperture in this way, rather than using scanning apertures with the same area, it is better to prepare multiple scanning apertures with different aperture areas in advance and adjust the frequency characteristics of the original dithered image. It is possible to estimate a halftone image closer to the original halftone image by selecting the scanning aperture with the most suitable aperture area and estimating the halftone image (halftone level) of that pixel.

This has a high pixel level gradation discrimination ability in the low spatial frequency region (region with few pixel level changes), but only a low pixel level gradation discrimination ability in the high spatial frequency region (region with many pixel level changes). The scanning aperture is selected such that a large scanning aperture is used in the low spatial frequency region and a small scanning aperture is used in the high spatial frequency region.

A specific example of estimating a halftone image based on such a principle has already been proposed by the applicant (for example, Japanese Patent Laid-Open No. 63-267571), so a detailed explanation thereof will be omitted. As the scanning apertures, scanning apertures A to G and Z having eight different aperture areas as shown in FIG. 12 are used.

The black circles shown in each scanning aperture of A-Z are as shown in Fig. 11 (c).
This is the center of movement when moving on the dithered image. Although the scanning aperture Z is selected at the upper left pixel with respect to the center of movement, it may be selected at any position at the lower left, upper right, or lower right. By specifying the position of the scanning aperture in this manner, the estimated pixel position is also specified.

When a halftone image is estimated from the dithered image of FIG. 11(C) using such a scanning aperture, a halftone image as shown in FIG. 13(B) is obtained. This is very close to the original halftone image shown in FIG. 11(a).

The scanning aperture for each pixel used when estimating the halftone image in FIG. 13(A) is shown in FIG. 13(B). The pixel in the 1st row and 1st column uses the scanning aperture D, the pixel in the 1st row and 2nd column uses the scanning aperture, and the pixel in the 1st row and 3rd column uses the scanning aperture C.

To estimate the original halftone image, it is necessary to count the number of white pixels (or the number of black pixels) existing within the scanning aperture. Since the maximum scanning aperture has an aperture area of 8×8, for example, to count the number of white pixels within the scanning aperture G,
A counting circuit 50g as shown in FIG. 14 is used.

In the figure, the shift register 40 is composed of eight human-powered latch circuits, which are connected in cascade over nine stages. This shift register 40 uses nine stages of latch circuits.
This is because it is commonly used as a shift register for all white pixel number counting circuits.

Since the scanning aperture G has an area of 8 rows x 8 columns, in order to count the total number of pixels within this scanning aperture, the latch outputs of the first and final stage latch circuits 41 and 49 are used as shown in the figure. be done.

Therefore, the latch output of the first stage latch circuit 41 is supplied to the first counting ROM 51, and the latch output of the final stage latch circuit 49 is supplied to the second counting ROM 5'2.
The number of white pixels in the binary data latched by each latch circuit is counted.

Each count output r, is supplied to the 'g calculator 53, k−r
calculations are performed. Then, when k>r, a subtraction output such as "o" and when k<r, "i" is obtained.

Each counting output r, is roughly supplied to a comparator 54 and compared in magnitude. In this example, when k>r, a comparison output such as ``l'' is obtained when 0°0° and k<r.

The subtraction output and the comparison output are supplied to the first and second latch circuits 55 and 56 and latched, and the output of the latch circuit 55 is supplied to the adder/subtractor 58 and the third latch circuit 57.
is supplied with the latch output. The second latch output described above can then be supplied to the adder/subtractor 58 as its control signal. In this example, when k>r, the subtraction operation is performed, and when k<r, the addition operation is performed.

The latch output of the third latch circuit 57 provided at the final stage is output as data indicating the number of white pixels in the scanning aperture G.

To count the number of white pixels in the scanning aperture, a counting circuit 5od configured as shown in FIG. 15 is used. 59 is an adder.

[Problems to be Solved by the Invention] As described above, conventionally, in order to count the number of white pixels in each scan interval A to G, the shift register 40 can be used in common; You just have to prepare a few.

Therefore, there was a drawback that the configuration of the counting circuit became complicated.

Therefore, the present invention attempts to simplify the configuration by sharing the counting circuit as much as possible.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention selects a plurality of scanning apertures with different aperture areas and estimates an original halftone image from a binary image such as a dithered image. In a halftone image estimation device, a pixel area of half the maximum aperture area of the scanning aperture is divided into units of 2n pixels and 2n + 1 pixels (n is an integer), and the number of white pixels or black pixels in each unit is The number of pixels is counted, and at the timing of the n+1 pixel clock, the number of white pixels or black pixels of each unit in the pixel area corresponding to the remaining half area is counted, and using these counted values, the maximum aperture area is calculated. The present invention is characterized in that the number of white pixels or the number of black pixels within a plurality of scanning apertures having half the aperture area is calculated.

[Action J If the maximum opening area is 8X8 (=23X23), the second
As shown in the figure, 2II (n is an integer, in this example 3
) pixel unit Bi (i is 1 to 4) and 2n+1 (=
24) The number of white pixels is counted separately for pixel units Da and Db.

After 3 clocks, the state shown in Fig. 2 (Ill') is reached, and since the unit Da (=Db) is equal to the aperture area of the scanning aperture, if you count the number of white pixels in the unit Da at this timing, this will be the scanning aperture. This means counting the number of white pixels within the aperture.

Furthermore, if the number of white pixels in the unit B 1.82°Da is added at the same timing, the value will be equivalent to counting the number of white pixels in the scanning aperture F. This means that the number of white pixels within an area that is half the maximum aperture area has been counted.

Similarly, the number of white pixels within the remaining half area is counted at the n+1 clock timing. Therefore, in state (V), by adding the units Da and Db, the number of white pixels of the scanning aperture E is obtained, and the units Bl, B2 .
B3. B4. By adding up both D a and D b , the number of white pixels of the scanning aperture G is determined.

According to this configuration, the same counting circuit SOx shown in FIG.
At least the number of white pixels of the scanning aperture, E, F, and G can be counted. The counting circuit shown in FIG. 15 is used for scanning apertures A-C.

[Example] Hereinafter, a halftone image estimation device according to the present invention will be described in detail with reference to FIG. 1 and subsequent figures.

FIG. 7 shows a specific example of a halftone image estimation device.

In the figure, an image reading device 1 reads an original image and converts it into binary data.

The original image is read using a photoelectric conversion element such as a CCD and converted into an electrical signal. The converted Denki No. 48 is converted into digital data, and after applying shading correction (correction for equalizing CCD output) to this digital data, it is converted into binary data (forming a dithered image) as shown in Figure 11 (C). A series of data processing is performed to convert the data into binary data.

The digitized binary data can be supplied to the halftone image estimating means 2 and, if necessary, to the image memory unit 6. The halftone image estimating means 2 is a means used when reprocessing binary data that has already been binarized, and in the case of binary data from the image reading device RA1, it is used to reprocess binary data that has already been digitized. Since it is halftone data, it is output to the subsequent stage without any particular processing. In addition to the binary data, the halftone image estimating means 2 is supplied with timing signals necessary for estimation processing.

The halftone image (No. 8) is supplied to the image processing means 3 together with the timing signal, and image processing corresponding to the specified processing mode, such as enlargement/reduction and filtering processing, is executed.

The image-processed halftone image signal is supplied to the binarization means 4, where it is re-binarized using the threshold selected by the threshold selection signal. The threshold selection signal is designated from a control terminal, keyboard, or the like.

Reference numeral 5 denotes a recording device such as a laser printer, which reproduces an image based on binary data output from the binarization means 4 or the image memory unit 6.

The image memory unit 6 is configured to be able to store the binary data itself obtained from the image reading device 1.

FIG. 8 shows an example of the configuration of FIG. 7 as an image processing system.

The image reading means 1, the halftone image estimating means 2, the image processing means 3, the z-value converting means 4 and the recording device 5 can be connected to the control terminal 13 via first and second interfaces 11, 12, respectively. Further, the image memory unit 6 is configured to be connected to the first interface 11 via the system bus 14. 15 indicates an external device.

FIG. 9 shows an example of the halftone image estimation means 2.

Since a part of the configuration disclosed in the above-mentioned publication can also be used in this case, a detailed explanation of the part to be used will be omitted.

Binary data from the image reading device 1 is supplied to the terminal 2a, and this binary data can be supplied to the line memory section 22 via the first selector 21.

The line memory section 22 is for receiving the binary data sent from the first selector 21 and storing the binary data for each line. Consists of line memory. Then, the second selector 23 sequentially selects and stores binary data corresponding to each gain in each of these nine line memories L1 to L9.

The line memory for 9 lines is prepared here because the maximum number of lines of the scanning aperture G to be used is 8 lines, and one more line memory is required for real-time processing. be.

Therefore, the second selector 23 selects eight line memories necessary for the current image processing among the nine line memories.

When using eight line memories, it is sufficient to combine them with one latch circuit. At this time, the input binary data is supplied to the latch circuit.

In this case, eight lines of binary data can be obtained using the output of the latch circuit and the outputs of the remaining seven line memories excluding the line memory currently being written.

The binary data of each of the eight selected line memories is supplied to the halftone image estimating section 30, and based on this binary data, a unique scanning aperture is selected from among the plurality of types of scanning apertures.

Data indicative of the selected scan aperture is provided to selection circuit 24 to estimate the value of the halftone image determined by the pixel level and gain within that scan aperture. Here, the gain corresponds to the area ratio of the scanning aperture, and the gain corresponds to the area ratio of the scanning aperture G.
When the gain of is 1, the scanning σMOE, F is the gain of 2
, inter-scan QD has a gain of 4, scan apertures B and C have a gain of 8,
Scan aperture A has a gain of 16 and scan aperture Z has a gain of 6.
It becomes 4.

The various timing signals obtained from the timing generation circuit 25 are supplied to the above-mentioned selectors 21 and 23, as well as the line memory section 22, halftone image estimation section 30, and selection circuit 24, so that the data can be input at the required timing. Selection and address sending are controlled.

FIG. 10 shows a specific example of the halftone image estimation section 30.

As mentioned above, the means 40 consisting of eight shift registers (for eight pixels) is provided for setting a plurality of scanning apertures.

Reference numeral 50 denotes a counting circuit, and counting circuits 50a to 50c, 50 are for scanning amounts A-C, Z smaller than the standard scanning aperture.
In addition to z (see FIG. 15), a shared counting circuit 50x is provided for counting the number of white pixels of a scanning aperture greater than or equal to the reference scanning aperture.

The outputs of the counting circuits 50a to 50c are supplied to the density pattern discriminating circuit 60, and two images created based on the counted values and two original images (11th
Figure (c)) is compared.

The counting output regarding the scanning apertures D to G obtained from the shared counting circuit 50x is supplied to the conditional expression determination circuit 70. The conditional expression is as disclosed in the publication cited above. The output of the coefficient circuit 50z is supplied to the register 32.

The same number of conditional expression determination circuits 70 as the scanning apertures D-G are provided,
The determination output from each and the determination output from the density pattern determination circuit 600 are supplied to a scanning aperture determination path 80, and a unique scanning aperture is selected.

31 is a circuit that outputs position information of the density pattern.

The register 32 is for holding the counted number of white pixels, and its output is supplied to a multiplier 33, where the counted number of white pixels is multiplied by the gain of each scanning aperture. The number of white pixels, which is the result of the multiplication, is used as the estimated value of the halftone image at the target pixel of interest.

Data indicating the estimated value of the halftone image is supplied to the selection circuit 24, and the estimated value of the halftone image is selected based on the scanning aperture selection signal output from the aperture determination circuit 80. For example, when a scanning aperture is selected, a halftone image estimated value (=4d) is selected, which is obtained by multiplying the number d of white pixels within this scanning aperture by a gain (=4).

FIG. 1 is an example of the shared counting circuit 50x, and similarly to FIG. 14, it counts the number of white pixels between RO and 91.92.94.95
are provided with corresponding units Bi, Da+, respectively.
Black and white z value data related to the number of white pixels in Db is input.

The outputs of the counting ROMs 91 and 92 are supplied to an adder 93, and the total number of self-pixels of the units Da and Db each composed of 24 pixels is determined. The calculated number of white pixels is supplied to an adder 99 through six latch circuits 97a to 97f that are continuously connected as shown in the figure.

The adder 99 adds the output of the latch circuit 1197f and the output of the latch circuit 97b. The addition output is again the latch circuit 97g
is latched at and guided to the output terminal 100e.

Similarly, the output of the latch circuit 97d is output to the latch circuit 98.
The signal is latched at and output to the output terminal 100d.

The output of the counting ROM 94.95 is also supplied to the adder 96, and the unit B1. The total number of self-pixels of B2 is determined. The calculated number of white pixels is latch, circuit 1
After being latched once in step 02a, it is added to the number of white pixels of unit Da in adder 103. Thereafter, the signal is supplied to the adder 105 through five latch circuits 102b to 102f connected in cascade as shown in the figure. The adder 105 adds the output of the latch circuit 102f and the output of the latch circuit 102b. The addition output is latched again by the latch circuit 102g and guided to the output terminal 100g.

Further, the output of the latch circuit 102d is similarly set to the latch circuit 1.
04 and output to the output terminal 100f. It is assumed that a common pixel clock is supplied to the plurality of latch circuits described above, and count data is sequentially shifted. The time points attached to each latch circuit indicate clock timing.

The counting operation when the shared counting circuit 50x is configured in this way will be explained with reference to FIGS. 2 to 6.

First, FIG. 2 shows the size of the scanning aperture G, and the counting operation shifts from left to right. When the shift position reaches exactly half the aperture area, that pixel area is converted into a unit Bl of 20 pixels (n is an integer).

B2 and 2′″+1+1 pixels Da (=D1+D
2) (state (I)).

n is determined by the maximum opening area and is 23 as described above.
In the case of a scanning aperture G having a size of X23, n=3, and the units B1 and B2 are 1/2 of Da.

The above-mentioned total i(ROM 91 counts the number of white pixels in the unit DI, and the counting ROM 92 counts the number of self-pixels in the unit D2.

When the state (I) is sequentially shifted by the pixel clock, states (11) to (V) are obtained. Therefore, the state (I
Since the position of the unit Da in ll) is the position of the scanning aperture, the number of white pixels of the unit Da at this time can be used as the number of white pixels of the scanning aperture. For similar reasons,
The total number of white pixels Fa of the units Bl, B2, and Da is used as the number of white pixels of the scanning aperture F.

Moreover, when the state (V) is reached, six units 81 to B4
．． Since all of Da and Db fall within the pixel area of the scanning aperture G, the total number of pixels of the units Da and Db is first used as the number of white pixels of the scanning aperture E. and,
The sum of all the numbers of white pixels is used as the number of white pixels of the scanning aperture G.

Therefore, for convenience of explanation, the top ○ shown in Figure 1 is replaced with the third point.
If the time point is matched with the shift time point in the eighth column in the figure and the time point is calculated backward based on this point, the time point t4 coincides with the time point when the unit) Da reaches the shaded area in FIG. Therefore, if the number of white pixels in the unit Da is latched at this time point L4, the number of white pixels in the scanning aperture is output from the terminal 100d.

Similarly, since the number of white pixels of unit Db is latched to the latch circuit 97b at time t2 as shown in FIG. 4, this number of white pixels and the number of white pixels of unit Da latched by the latch circuit 97f Addition result of the number of white pixels at time t7
If latched at , the number of white pixels related to the scanning aperture E will be output from the terminal 100e.

Furthermore, the latch circuit 102d at time t4 has a unit B.
l, B2. Since the addition result Fa of D a is latched, if this is latched at time t7, the terminal 100f
From this, the number of white pixels corresponding to the scanning aperture F has been determined. Similarly, the latch circuit 102f at time 0 has units Bl, 'B2. The enrichment result Fa of D a is latched, and the latch circuit 102b at t2 is connected to unit B3.
．． B4. Since the addition result Fb of Db is latched, if the addition result (=Fa+Fb) is latched at time 7, the number of white pixels of the scanning aperture G is obtained at the terminal 100F.

[Effects of the Invention] As explained above, in the present invention, the pixel area of half the maximum aperture area of the scanning aperture is divided into 2''' pixels and 2 ni1
Separate into pixel units, count the number of white pixels or black pixels in each unit, and count the number of white pixels or black pixels in each unit in the pixel area corresponding to the remaining half area at the timing of n+1 clocks. if,
Using these counted values, it is possible to calculate the number of white pixels or the number of black pixels within a plurality of scanning apertures having an aperture area that is half of the maximum aperture area.

When configured in this way, the number of white pixels within multiple scanning apertures can be counted by a common counting circuit, so it has the feature that the number of circuits can be significantly reduced compared to conventional methods. There is a real benefit in achieving significant cost reductions.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of a shared counting circuit used in the halftone image estimating device according to the present invention, FIGS. 2 to 6 are explanatory diagrams of counting operations, and FIGS. 7 and 8 are intermediate A system diagram showing an example of a tone image estimation device, FIG. 9 is a system diagram of a halftone image estimation means, FIG. 10 is a system diagram of a halftone image estimation section, and FIG.
Figure 1 is an explanatory diagram when creating a dithered image from an original halftone image, Figure 12 is a diagram showing an example of the scanning aperture used, and Figure 13 is an illustration of the estimated halftone image obtained when the scanning aperture is selected. 14 and 1S are block diagrams of conventional counting circuits. 1... Image reading device 2... Halftone image estimation means 3... Image processing means 4... 261 converting means 5... Recording device 22... Line memory section 24... Selection circuit 30...Halftone image estimation units 50a to 50c*50z...Counting circuit 50x...Shared counting circuit 91, 92. 94. 95...Counting ROM 93, 96. 99. 103. 106... Adders 97a to 97g, 98° 102a to 102g, 104... Latch circuit 70... Conditional expression judgment circuit Patent applicant Konica Co., Ltd. Agent Patent attorney Kunio Yamaguchi 1) (II) (rV)
(m) CV> Figure 2 pl) va4) t5 t6 t7 Pixel at a time) (a) Original intermediate image (b) 602852 threshold matrix 33511 633155: Part (c) Dizu ■36 1448 83g Figure 11 Example of traveling opening Figure 12 (a) (b) DDCBCBBCC DDCA, CCZAA BBAACBAZZ CAZCCFCCC CBBCCCBEE EEDDCBEE EEEECZCFE E F CB B B C'G
CFEBCGGEGB Figure 13

Claims (1)

[Claims] (1) In a halftone image estimation device that selects multiple scanning apertures with different aperture areas and estimates an original halftone image from a binary image such as a dithered image, a pixel area that is half of the maximum aperture area among the scanning apertures is used. , 2^n pixels and 2^n^
Divided into units of +^1 pixels (n is an integer), the number of white pixels or black pixels in each unit is counted, and each pixel area corresponding to the remaining half area is counted at the timing of the n+1 pixel clock. The number of white pixels or the number of black pixels of the unit is counted, and using these counted values, the number of white pixels or the number of black pixels within a plurality of scanning apertures having an aperture area half of the maximum aperture area is calculated. A halftone image estimation device characterized by: