WO1992005659A1

WO1992005659A1 - Pseudo-halftone picture processing equipment

Info

Publication number: WO1992005659A1
Application number: PCT/JP1991/001274
Authority: WO
Inventors: Masahiro Suzuki
Original assignee: Seiko Instruments Inc.
Priority date: 1990-09-26
Filing date: 1991-09-25
Publication date: 1992-04-02

Abstract

Pseudo-halftone picture processing equipment which has a means (5b) for storing a plurality of reference values for calculating errors or reference value classes for calculating errors, a means (5d) for calculating and storing a plurality of thresholds or threshold classes and a means (3) for comparing modified input picture data with the plurality of thresholds, and performs the processing according to the method of minimum average error. The modified value of the input picture data is compared with the plurality of thresholds. The nearest reference value for calculating errors to that modified value is outputted and the difference between both the values is calculated. The calculated difference is used to modify the next input picture data. Also, by making the output value of a means (4) for outputting multivalued data different from the reference value for calculating errors, the gradation characteristic of the result of the pseudo-halftone processing can be changed.

Description

Pseudo halftone image processing device

Technical field

The present invention relates to a pseudo-halftone image processing apparatus for converting _m- value image data into n-valued (m>η> 2, mn is an integer) pseudo-halftone image data and a device utilizing the same. Light

Background art

Conventionally, a half-tone image or a pseudo half-tone image is written in a binary image.

In order to more quasi-grayscale representation, Οpseudo halftone image processing device is known.

This device is a display or output device or a binary display or output, that is, a pixel can be represented only as ON or OFF2, but the original image data is multi-valued. If it is a 間 halftone or a pseudo halftone consisting of タ data, such as (C 1) or (0,: 55) する To convert to binary data:;: _c used

At this time, if a force image is considered with the binarized image data, for example, even if a color image is represented by three colors of R (red), G (green), and B (blue), the pixel is At the level, the number of colors that can be represented is usually 2 ^s = 8 colors.For multivalued image data, simply assigning a specific value to the binary value I and assigning it to the difference O In particular, it is often the case that only unnatural images can be obtained for natural images. For this reason, pseudo halftone processing has been performed so that a pseudo halftone color can be visually sensed.

As the pseudo-halftone processing method, the average error method ']' is known. The above-mentioned average error method uses the same average luminance level between the input image and the output image. To express pseudo-halftones-Attention pixel On the other hand, the difference between the input value and the output value when binarizing is stored as an error, and correction is performed using the error when binarizing the pixel of interest. The above-mentioned average error minimizing method has a feature that gradation characteristics are good. .

FIG. 2 is a block diagram showing a configuration of a pseudo halftone image processing apparatus A ′ that performs the conventional average error minimization method. Here, it is assumed that the input image data is gradation data of 0 to R (R is an integer), and the output data is either 0 or R.

Image data is input from the input means 1 to the image data to be subjected to pseudo halftone processing

The multi-valued pixel te input from the input means 1 is added to the correction value obtained by the correction value calculation means 7 described later and the correction value calculation means. The O-added value is output from the corrected value calculating means 2 as a corrected value.

The correction value is compared with a specific value by the singular threshold comparing means 8. c The value is, for example, an intermediate value R / 2 of the input image data. The above-mentioned correction value is used to determine the magnitude of σ at the boundary, and is classified into one of them.

The binary data output means 9 outputs binary data corresponding to either 0 or R based on the comparison result of the single orchid value comparison means 8.

The error calculating means 5 calculates a difference between the correction value and the output value as an error. The calculated error is stored in the error storage means 6. The error storage means 6 has a liner 'and stores at least an error of one line. That is, each error is stored here for a predetermined number of pixels input immediately before the target pixel to be subjected to the binarization processing.

Next, the correction value calculation means 7 will be described. The correction value calculation means 7 is located in the vicinity of the pixel of interest and is stored in the error storage means 6. With reference to the elementary errors, the above errors are weighted by means that have been roughly determined, and the errors are averaged: the calculated average value is the correction value c

FIG. 9 is a diagram showing the pixels and the original image. The above processing is performed on the original image in the rightward direction in FIG. 9 for each pixel in the main scanning direction, or the like, and is performed while shifting it by one line in the subscanning direction.

Figure 3 shows an example of weighting factors for calculating the correction value. It is natural that the error storage means 6 has a reference range of the error 誤差 a capacity for storing the error. .

Conventional pseudo-tank ί¾ 'image processing device A' Ο Let the maximum output value be 2 δ 5 '. = 2 δ 6) P All-steel image data is on the second floor, namely: 0 Or, an example of conversion to 255 O image data will be described.

FIG. 5 is an explanatory diagram showing the relationship between the output value and the threshold value i in this case. First, binary data output means 9 © output value · _0 and 255 G2 value. The threshold value of the singular value comparison means 8 is., Above: the median value of the two output values 1 2 —, and the singular threshold value comparing means S. Half of the force in the area between and

Binary data output means 9, single-value comparison means 8 G) Receives the result and outputs one of the binary output values.In other words, the corrected value is less than 127, that is, area A in FIG. , 0 is output, and if it is 1 2 7 or more (area A ₂ ), 255 is output.

As described above, the error is a difference between the output value corresponding to the comparison result of the singular threshold value comparing means S and the correction value. If the correction value is less than 127 (the difference between Q and Q in the case of region A, or the correction value is more than ₂₇ (the difference between 255 and 0 if the region A _£ : 'is the error) The above-mentioned error is stored in the above-mentioned error storage means 6 as described above, and is used by the correction value calculating means Ί to calculate a correction value. As is apparent from the above description, the pseudo halftone processing device cannot obtain a pseudo halftone image having three or more values.

In other words, by changing the size of the dot, it is possible to express a multi-gradation (for example, 4 gradations, 16 gradations, etc.) at the dot level by using a mature transfer type color printer, When trying to perform display or output on a liquid crystal display device or the like that can express multi-gradation such as 4-gradation or 16-gradation, naturally multi-gradation data such as 256-gradation is required. Display and output cannot be performed, and even with the pseudo-halftone image processing device that outputs the C binary data described above, the performance with the display or output device of 4 gradations or 16 gradations can be sufficiently exhibited. Not coming. Also, the pseudo-intermediate processing device cannot convert pseudo-tone characteristics of an image subjected to pseudo-halftone processing by itself.

The present invention solves the above-described drawbacks of the prior art, and provides a pseudo-halftone image processing device that can sufficiently exhibit the performance of a 4-gradation, 16-gradation display or output device. Both aim to provide a display or output device using this. Disclosure of the invention

According to the present invention, in a pseudo halftone processing apparatus that performs processing of the average error minimum method, an error calculation reference value storage unit, a threshold value calculation storage unit, and an error calculation unit are provided, and a plurality or a plurality of sets of reference values are set and stored. The threshold value comparing means compares the corrected value with a plurality of threshold values, and outputs a multi-value output value based on the result.

By the Conoco, also good halftone image gradation characteristics can be obtained, and can be the this to change the gradation characteristic 'is _c BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram showing a preferred embodiment of the present invention, FIG. 2 is a block diagram showing a conventional technique, and FIG. 3 is a diagram showing storage contents of an error storage means. Yes, FIG. 4 is a diagram showing an example of a weighting coefficient, FIG. 5 is an explanatory diagram showing a relationship between an output value and a threshold with respect to a conventional example, and FIG. 6 is a diagram showing an output in the first embodiment of the present invention. FIG. 7 is an explanatory diagram showing the relationship between the output value, the 闞 value, and the error calculation reference value when a = 1.δ in Example 2 of the present invention. FIG. 8 is an explanatory diagram showing the relationship between the output value, the threshold value, and the error calculation reference value O in the case of a-D.5 © in the second embodiment of the present invention. Is a diagram showing an arrangement of G pixels of an original image, and FIG. 10 is a pseudo halftone image processing device of the present invention. FIG. 11 is a block diagram schematically showing a printing apparatus used. FIG. 11 is a block diagram showing an example in which the pseudo halftone image processing apparatus of the present invention is applied to a color printer for printing three colors simultaneously. FIG. 12 is a block diagram schematically showing a color display device using the pseudo halftone image processing apparatus of the present invention, and FIG. 13 is a pseudo halftone image processing apparatus of the present invention. share each color in the image processing apparatus, it is if O force over the display device C 'Bed π click H showing an example of displaying _c

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 is a pseudo halftone image processing apparatus A0 block diagram of the present invention, which has a function of converting m-value multi-gradation image data into n-value gradation image data and outputting it. (M:>n> 2, m and η are integers). Reference numeral 1 denotes an input means including an image storage means, and the output is multi-tone Ο-valued pixel data. The pixel data is sequentially read from the original image in the main scanning direction for each pixel in the right direction in Fig. 9 and processed, and this is processed one line at a time in the sub-scanning direction. The processing is performed sequentially. Reference numeral 2 denotes a correction value calculating means, which receives as input the correction value output of the correction value calculating means 7 described later and the multi-gradation m-value image data output from the input means 1 and adds them to obtain the correction value. Is output as. Numeral 3 is a multi-value comparing means having a plurality of (n-1) thresholds, and comparing these with the above-mentioned correction values, and inputting the correction values to the n regions divided by this threshold. It is determined to which one it belongs. Then, output the result.

Numeral 4 denotes multi-value data output means, in which output values corresponding to the above-mentioned n areas are specified, respectively, and based on the comparison result of the plural threshold comparing means 3, the corrected value is obtained. Outputs the output value for the area to which it belongs IS j ""? .

5c is an error calculation reference value setting means for setting an error calculation reference value corresponding to the output value of the multi-level data output means 4.

5b is an error calculation reference value storage means for storing an error calculation reference value set by the error calculation reference value setting means 5c and corresponding to the output value of the multi-value data output means 4.

5d is a 閬 value calculation storage means. Based on the error calculation reference value set by the error calculation reference value setting means 5c, the I value used by the multiple threshold value comparison means 3 is calculated and stored.

5a is an error calculation means, an error calculation reference value stored in the error calculation reference value storage means 5b and corresponding to the comparison result of the multiple threshold value comparison means 3, and an output value of the correction value calculation means 2 Is calculated and output as an error value.

Numeral 6 is an error storage means having a line buffer for storing an error of at least one line.

FIG. 3 shows an example of the storage contents of the error storage means 6. .. £ are the error values stored in the error storage means 6, and * is the position where the error value of the pixel of interest is stored. Reference numeral 7 denotes a correction value calculating means, which is described in the above-mentioned error storage means 6 for the vicinity of the target pixel Ο, and refers to each pixel Ο error, and weights each error by a predetermined means. Is averaged over row t. The calculated average value is input to the correction value calculation means 2 as a correction value.

FIG. 4 shows an example of a weighting coefficient for calculating a correction value. The correction value calculation by the correction value calculation means 7 is performed by the following calculation.

Correction value-(a 1/4 8)-(b X 3/4 8 Ϊ--

One (1: X5, 4S '~'(> ノ 48J this ^-;:, 1, ...-40c-4 、, ..., ', evil. Weighting in each pixel Coefficient _c

〔Example 】〕

First, an example of how to determine the output and output values

First, the case where the error calculation reference value is equal to the multi-value data output means 4 Ο Output value is described as an example.- Multi-value data output means C The output value type is pseudo-halftone processed. It is common practice to match the number of gradations in the device that displays or outputs the image. O: Input image data The range of density gradation is 0 to R. At equal intervals, and set the partition value as the output value of the multi-value data output means 4. At this time, the output value is

i R (n-1) where i = 0 to η — 1 (1). The same applies to the error calculation reference value in the present embodiment. This error calculation reference value is stored in the error calculation reference value storage means 5b. The threshold value is an intermediate value between the above error calculation reference values.

(2 j-1) R / 2 (n-1) where j = '~ n-2 (2:'. The threshold is calculated by the threshold calculation and storage means 5 d. It is calculated from the error error reference value and stored.

Now, the maximum output value of the pseudo halftone image processing device AG of the present invention is set to 255 As an example, an example will be described in which image data of m (= 256) gradation is converted to image data of n (= 4 :) gradation.

FIG. 6 is an explanatory diagram illustrating a relationship among an output value, a threshold value, and an error calculation reference value in the case of the first embodiment. First, the output value of the multi-level data output means 4 and the error calculation reference value are 0, = 0 (= 255 x 0/3) and 0 z = 85, as is clear from equation (1). = 2 5 δ 1/3) , O s = 1 7 0 (= 2 5 δ χ 2 ./ 3). a four values of _{0 4 = 2 5 5 (=} 2 5 5 x 3/3).

The threshold value of the multi-threshold comparing means 3 depends on the above four output values, and as is clear from the expression), T i −4 ′ = 2 5 5/6) and T 2 = 1 2 7

(= 2 5 5... '2 no, T ₂ ' = 2 1! = 5 '2 δ δ, 6) を取 Takes 3 values, and the multiple-value comparison means 3 takes the orchid value and the corrected value. By comparing the correction value with the correction value from the calculation means 2, it is determined which area the correction value is between.

The multi-value data output means 4 receives the result of the multiple threshold value comparison means 3 and outputs one of the four output values.

In other words, the corrected value should not be dropped by 4 2; ρ Fig. 6 0 If the area A is 0, the corrected value is 4 2 or more 1 2 7 The area A ₂ .. value 1 0 if 1 2 7 more than 1 2 Not潢(Ryo璩a _3), and outputs a 2 5 5 if 2 1 2 or more (area a _4).

Next, how to calculate the error will be described. The error takes a difference between the error calculation reference value corresponding to the comparison result of the multiple threshold value comparing means 3 and the corrected value, as in the case of the front ridge. Here, since the error calculation reference value is equal to the output value of the multi-value data output means 4, the correction value is less than 42.

If it is (Area A), the difference between 0 and the corrected value is not less than 4 2 and not more than 1 2 7 If it is (Area A ₂ ), the difference from 85 and the corrected value is 1 27 or more 2 less than the error of the difference between (realm a ₃₎ a long Invite 1 7 0, to 2 1 2 or more error the difference between the 2 [delta] 5 if (area a ₄₎ is the error in the Hare by above Record The correction value is stored in the storage means 6 and is used for calculating the correction value in the correction value calculation means 7.

In the above description, if the above processing is applied to one plane of image data, two monochromatic images can be obtained. For example, for each of the R, G, and BG planes,

Five

Of course, if it is applied to image data, it can also process color images. a

R

(Example 2

X

Next, the error calculation reference value differs from the output value of 2 multi-level data output means 4.

Five

The case will be described. Here, 5 also assumes that the maximum output value of the pseudo halftone image processing device A of the present invention is 255, and that the image data of m (= 256) gradations is n (−4) tone. As an example, since the output value is determined by the display device or the output device as described above, the following equation (1) is used as in the first embodiment. It is assumed that

The error calculation reference value is, for example, 'as can be expressed by the following equation.

0 n one 1 (3) n 1

This error calculation reference value is set 5 by the error calculation reference value setting means 5c, and the threshold value stored in the error calculation reference value writing means 5b is 5

To take. This is calculated and stored by the threshold calculation storage unit 5d, where a is a constant value. When the error calculation reference value is different from the output value of the multi-value data output means 4 as described above, a pseudo halftone image in which the error calculation reference value is an output value is obtained once, and is multiplied. This is equivalent to converting to the output value of value 4 output means 4. Now, assuming that a == l.5, the error reference value is 0, 49, 13 39, 25 5 and the threshold value is 25, 9 _4-19 7 _c FIG. 7 is an explanatory diagram showing a relationship among an output value, an end value, and an error calculation reference value when a = 1.5 in the second embodiment. As a result, when the pseudo halftone processing according to the present method is performed, a result in which the brightness is reduced as compared with the case of the first embodiment is obtained. Similarly, when a = 0.5, the error calculation reference values are 0,〗 47, 207, 255, and the threshold values are 74, 178, 232.

FIG. 8 is an explanatory diagram showing the relationship among the output value, the threshold value, and the error calculation reference value when a = 0.5 in the second embodiment. As a result, when the pseudo halftone processing according to the present method is performed, a result in which the brightness is improved as compared with the case of the first embodiment can be obtained. It is also possible to correct the nonlinearity of the input / output relationship of the display or output device.

As described above, the gradation characteristics of the pseudo halftone processing result can be changed depending on the value of a.

(Example 3)

In the present invention, in the error calculation reference value storage means 5b, the error calculation reference value setting means 5c, the end value calculation storage means 5d and the error calculation means 5a, a plurality of sets of reference values are set, stored and stored. By enabling the error calculation using the color characteristic, the color image is switched for each primary color, for example, for each of the R, G, and B planes, so that the gradation characteristic plane shown in the second embodiment can be obtained. It can be changed every time. As a result, the power balance of the pseudo halftone processing result can be changed.

In the above description, each threshold value is described as being an intermediate value between the output values. However, the same effect can be achieved without necessarily setting the intermediate value.

Further, the weighting coefficient of the pixel near the target pixel is not limited to the example described above, and the range of the error to be referred to is not limited to the example described above.

FIG. 10 shows a printing apparatus using the pseudo halftone image processing apparatus of the present invention. FIG. The print section 4 may be any device capable of printing an image of n gradations, and examples thereof include a monochromic printer and a force lap printer that prints in a line-sequential or line-sequential manner. Can be done.

The m-value multi-gradation image data is temporarily stored in the image data storage means 11 via the input means 21, and is stored in the pseudo halftone image processing apparatus 20 according to the present invention by the stored data read means 12. Is entered.

The pseudo-halftone image processing device 20 converts the m-value gradation image data into an n-value pseudo-halftone image data according to the above-described method, and sends it to the print control means 13. Output _c : Control means: 3 is for converting the converted value O gradation pseudo halftone image data for printing! 314 to print section 14 Output. In response to the output, the print unit 14 prints out pseudo halftone image data of η gradation.

FIG. 11 is a block diagram showing an example in which the pseudo halftone image processing device 20 of the present invention is applied to a color printer that prints three colors simultaneously.

The m-gradation image data input to the image data-recording means 11 by the image data input means 21 is stored once. The storage data reading means 12 and the image data writing means ii have m-valued floors.

(R, G, E), and output them to the pseudo halftone image processing devices 20R, 20G, and 20B, respectively, which handle the R, G., and B O colors, respectively. The pseudo halftone image processing devices 20F 20G and 20B convert the input m-value gradation image data into pseudo halftone image data having R, G, and B n-value gradations, respectively, and pre-convert them. Output to the point control means 13. The print control unit 13 further converts the image data of R, G, and B converted to the n-valued gradation for the print unit 14, and outputs the image data to the cyan magenta and the yellow. , And outputs it to the print unit 14, which prints pseudo-halftone image data of n gradations.

In the above explanation, input the image data of, GB and The same applies if the complementary color conversion is performed by the print control means 13 or the image data of yellow —., Magenta, cyan is directly input and the complementary color conversion is not performed by the print control means 13. Has the effect. The same effect can be obtained even if the complementary color conversion is performed by the input means 21 or the storage data reading means 12.

FIG. 12 is a block diagram schematically showing the color display device of the present invention. The m-value multi-gradation image data is temporarily stored in the image data storage means 11 via the input means 21 and is input from the storage data reading means 12 to the pseudo halftone image processing device 20 according to the present invention. .

The pseudo halftone image processing device 20 converts the m-value gradation image data into n-value pseudo halftone image data and outputs it to the display control means 15 by the above-described configuration. The display control means 15 further converts the converted pseudo halftone image data of n-valued gradation for the display unit 16 and outputs the data to the display unit 16. In response to the output, the display unit 16 displays the pseudo halftone image data of n gradations. ―

As the display unit 16, various display devices such as a liquid crystal display device and a CRT can be applied.

FIG. 13 is a block diagram showing an example of a case where display is performed by the pseudo-Φ halftone image processing devices 20R, 20G, and 20B of the present invention, which are assigned to each color.

The m-value / gradation image data separated for each of the colors R, G, and B is supplied to each of the input means 21R, 21G, and 21B. , 20B is entered. The pseudo halftone image processing devices 20R, 20G, and 20B convert the input m-value gradation image data into pseudo halftones of R, G, and B n-value gradations, respectively, and display them. Output to control means 15. The display control means 15 further converts the R, G, and B image data converted to the n-valued gradation for the display unit 16 and outputs the converted data. Outputs the toned image data to the screen. Industrial applicability

As described above, the pseudo-halftone image processing apparatus according to the present invention converts an image represented by m-value image data into a pseudo-halftone image having n values (m> n> 2, m and η are integers). It is converted to data, and is used for image data on display devices such as color printers, color printers, liquid crystal display devices, and CR II.

-It is useful as a data processor.

Claims

An input means for inputting pixel data of a pixel of interest;

Correction value calculating means for calculating a correction value by adding the pixel data and the correction value output from the correction value calculating means;

A plurality of orchid value comparing means for comparing the corrected value with a plurality of orchid values; an output means for outputting an output value corresponding to a comparison result of the plurality of orchid value comparing means;

An error calculation reference value storage means for storing an error calculation reference value corresponding to the output value and used for calculating an error with the correction value;

A threshold calculation storage unit that calculates and stores a value used by the multiple threshold comparison unit based on the error calculation reference value;

Error calculating means for calculating a difference between the corrected value and the error reference value as an error,

An error storage means HV for storing the error calculated by the error calculation means,

A pseudo-halftone image processing apparatus, comprising: the correction value calculating means for calculating a correction value based on an error of the error storage means.

The error calculation reference value storage means, the threshold value calculation storage means and the error calculation means of the pseudo halftone image processing apparatus according to claim 1, wherein a plurality of sets of reference values are set and stored, and a pseudo error capable of calculating an error using them is provided. Halftone image processing device.

A printing apparatus, characterized in that a printing section is connected to the output means of the pseudo halftone image processing apparatus according to claim 1.

A display device, wherein a display unit is connected to the output means of the pseudo halftone image processing device according to claim 1.