JPH0792829B2 - Method and apparatus for generating image data for continuous tone image recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention, when recording an image in which gradation changes continuously by a pixel array having discrete gradation, discontinues gradation. Change (hereinafter referred to as "tone jump")
The present invention relates to a method and apparatus for generating image data capable of preventing the influence of the above.

(Prior Art and Problems Thereof) In an image recording apparatus such as a plate-making scanner, it is necessary to express a spatial gradation change of an image by a pixel array having discrete gradation. Therefore, Fig. 29 (a)
Even when it is desired to record a continuous tone image in which the gradation changes continuously according to the position change on the recording screen, as shown schematically in Figure 29, stepwise gradation change as shown in Fig. 29 (b). It is necessary to approximate such a continuous tone image by an image having Such a situation is common not only to the plate-making scanner but also to an apparatus that records an image using digitized image data.

On the other hand, in the image recording apparatus currently used, various improvements have been made so that such a discontinuous change in gradation, that is, the tone jump ΔG in FIG. Therefore, in general image recording, this tone jump ΔG is rarely visually recognized. However, in the following cases, the presence of this tone jump ΔG is visually recognized relatively clearly.

The first is the case where the gradation changes monotonously according to the specified gradation change rate, as in the case of recording on a slanted net in a platemaking scanner. In such a case, smoothness of gradation change is often hindered by the tone jump ΔG.

The second is an image, such as an image of human skin, in which the gradation gradually changes and which is easily noticed by a viewer of the recorded image. Also in this case, the presence of the tone jump ΔG is easily recognized as a disorder of the recorded image.

Thirdly, the original image is enlarged to create a large-screen recorded image. At this time, since the size of the pixel increases due to the enlargement processing, the presence of the tone jump ΔG will be recognized when performing detailed observation with the naked eye.

Various measures have been considered to deal with such a problem, and a typical one of them is described below along with its drawbacks.

(1) The data length of the image data, that is, the number of bits of the digital signal expressing the gradation is set sufficiently large to reduce the absolute value of the tone jump ΔG. This method is the most desirable method in principle. However, in reality, there is a drawback that the amount of data increases as the data length increases, and the processing time becomes considerably long. Also,
Since it is necessary to prepare a circuit for performing such a large amount of data processing, the size of the device and the cost are increased.

(2) The digitalized image data is once converted into an analog signal, and natural noise such as circuit noise added to the analog signal is used. In this method, the analog signal with noise added is converted back to a digital signal,
This is used for image recording. Then, the pixel causing the tone jump ΔG cannot be specified due to the natural noise or the like. However, since the level of natural noise is generally small, the number of bits of digital image data must be quite large to apply this method. Therefore, it has the same drawbacks as the first method.

(3) Digital random noise having a certain level is generated by the noise generating circuit and added to the digital image data. Unlike the first and second methods, this method can be expected to some extent by adding a relatively simple circuit. However, this method has a problem in that the image data cannot be modified according to the position where the tone jump ΔG occurs because noise unrelated to the nature of the image to be recorded is added to the image data.

In Japanese Patent Laid-Open No. 61-91661, a fluctuation signal (for example, a sawtooth wave or a triangular wave) is added to a gradation signal (continuous tone signal) to record an image with a discrete gradation number. However,
In this case, according to the increase rate or the decrease rate of the gradation signal,
The peak value and wavelength of the fluctuation signal must be selected appropriately. The reason is that it is necessary to match the time when the gradation signal on which the fluctuation signal is superimposed exceeds the threshold value with the pixel interval for recording as much as possible to achieve effective recording.

As described above, the conventional technique has a problem that it is difficult to effectively remove the influence of the tone jump ΔG when recording an image in which the gradation is continuously changed.

(Object of the Invention) The present invention is intended to overcome the above-mentioned problems in the prior art, and an image capable of effectively preventing the influence of tone jump in continuous tone image recording without complicating the data processing so much. An object of the present invention is to provide a data generation method and an apparatus thereof.

(Means for Achieving the Object) In order to achieve the above-mentioned object, in the image data generating method according to the first invention of the present application, an image in which gradation is continuously changed is used as a pixel having discrete gradation. Targeting at an image data generation method for scanning recording by an array, first, a first part including an integer part having a data length according to the number of discrete gradations used for image recording and a decimal part having an arbitrary data length The gradation data of 1 expresses the gradation of the image to be recorded for each pixel.

Then, while using a random number as an initial value for accumulation for each scanning line, the values of the fractional part are sequentially accumulated along the direction of the pixel array, and the accumulation result corresponds to a multiple of a predetermined reference value. Each pixel that reaches the value is a multiple reaching pixel.

Furthermore, by changing the value obtained from the integer part of the first gradation data for the multiple reaching pixel and / or the pixels in the vicinity thereof for each existence of the multiple reaching pixel by a predetermined integer amount, Then, the second gradation data is generated, and the second gradation data is used as image data for recording the image.

The image data obtained in this manner becomes image data having a spatial gradation change as shown in FIG. The reason why such image data is obtained by the above configuration will be described in detail in the description of the embodiment.

Further, in the second invention of this application, as an apparatus for realizing the first invention, an integer part having a data length corresponding to the number of gradations used for image recording and a decimal number having an arbitrary data length are provided. First gradation data generation, in which the gradation data of an image to be recorded is expressed for each pixel by the integer part and the decimal part And means for sequentially accumulating the values of the fractional part along the direction of the pixel array while using a random number as an initial value of accumulation for each scanning line, and the accumulation result is determined according to a multiple of a predetermined reference value. An accumulating means for generating a pulse of a predetermined size each time a predetermined value is reached; a value obtained from an integer part of the first grayscale data and the pulse are time-sequentially combined to generate a second pulse. Second gradation data generating means for generating the gradation data of Gradation data, an apparatus is provided for the image data for recording the image.

It should be noted that "the accumulated result reaches a value according to a multiple of the reference value." Means that the accumulated result coincides with these values as well as the case where the accumulated result jumps over these values. It is a concept that includes. Further, the identification of the multiple arrival pixel does not matter whether it is direct or indirect.

(Embodiment) A. First Embodiment FIG. 2 is an overall configuration diagram of a cylindrical scanning type plate-making scanner in which an image data generating apparatus according to a first embodiment of the present invention is incorporated. The overall configuration and schematic operation of the scanner will be described below with reference to FIG. 2, and then the characteristic parts of this embodiment will be described in detail.

(A-1) Overall configuration and schematic operation of the first embodiment In the plate making scanner 1 shown in FIG. 2, an original image drum 3 around which an original image 2 is wound, and a recording drum 5 around which a photosensitive material 4 is wound. Are fixed to the drum shaft 6. The drum shaft 6 is synchronously rotated by a driving force of a motor 9 given through a pulley 7 and a belt 8.

On the other hand, a pickup head 10 and an exposure head 11 are provided so as to be opposed to the original image drum 3 and the recording drum 5, respectively, so as to be movable in parallel to the drum shaft 6, and these are arranged to drive a pulse motor 12 for driving. , 13 to the feed screws 14 and 15, respectively.

The pickup head 10 has a photoelectric conversion element and the like built therein, and reads the image of the original image 2 to generate an image signal. This image signal is given to the A / D converter 16.
In this A / D converter 16, this image signal is a periodic pixel clock from a timing control circuit 24 described later.
Sampling is performed according to CKX and A / D conversion is performed sequentially.
Then, the image signal after A / D conversion is given to the image processing circuit 17.

The image processing circuit 17 has a gradation correction circuit (not shown) and the like, and performs predetermined processing such as gradation correction on the input image signal. The recording image signal thus obtained is applied to the halftone dot generator 18. The halftone dot generator 18 compares the recording image signal with the reference halftone dot signal to generate a halftone dot output, and the exposure head 11 records the halftone dot image on the photosensitive material 4 based on the halftone dot output. To do. Of course, continuous tone recording may be performed based on the recording image signal.

In the case of halftone printing, one halftone dot in FIG. 16 to be described later is represented by one small square representing the area of one pixel of printing, and is represented by, for example, 2.3 pixels × 2.3 pixels. Therefore, an image signal to be recorded is given to each pixel, and the image signal is recorded with a different halftone dot% for each pixel. For this reason, it is well known that halftone dots represented by 2.3 pixels × 2.3 pixels are recorded not only in a fixed shape such as a circle, an ellipse, a square, and a rhombus but also in a distorted shape.

On the other hand, the plate-making scanner 1 is provided with a gradation gradient image generation circuit 20 as an embodiment of the present invention. Then, when recording the slanted net on the photosensitive material 4, the image data generated by the gradation slanted image generating circuit 20 is applied to the halftone dot generator 18 via the image processing circuit 17. ing. At this time, the image signal read from the original image 3 is not used. However, these may be synthesized depending on the application.

Further, the platemaking scanner 1 is provided with a control circuit 21 connected to a keyboard 22 and an operation panel 23. The control circuit 21 is for controlling the above-mentioned circuits and performing various data processing. Further, the scanner 1 is provided with a timing control circuit 24. The timing control circuit 24 synchronizes with the pulse input from the pulse generator 25 which synchronizes with the rotation of the drum shaft 6 and indicates the pixel clock CKX and the exposure start position for each rotation of the main scan. Start clock CKY,
In addition, a control signal (indicated by a broken line in the drawing) to the driving pulse motors 12 and 13 is generated and given to each of the illustrated parts.

(A-2) Outline of Functions of Gradation Gradient Image Generation Circuit 20 FIG. 3 is a block diagram showing an internal configuration of the gradation gradient image generation circuit 20. As described above, the gradation gradient image generation circuit 20 is a circuit for generating image data for recording a gradient mesh on the photosensitive material 4 of FIG. 2, and an example of the gradation distribution of this gradient mesh is shown in FIG. It is shown schematically in FIG. That is, in the area 4a on the photosensitive material 4 in FIG. 4, a slanted net in which the gradation monotonously changes along the main scanning direction X (hereinafter referred to as “main scanning direction slanted net”) is shown. Further, in the region 4b, a slanted net in which the gradation monotonously changes along the sub-scanning direction Y (hereinafter referred to as "sub-scanning-direction slanted net") is shown. Further, in the region 4c, a slanting net whose gradation changes along an arbitrary direction P is shown.

As will be understood from the description below, the gradation gradient image generation circuit 20 of FIG. 3 can freely generate image data for recording a gradient mesh in such various directions. There is. Then, this image data is generated in such a manner that the effect of tone jump is effectively removed.

Therefore, hereinafter, an operation of generating image data for recording in the main scanning direction inclined mesh using the circuit in FIG. 3 will be described first, and thereafter, recording in the sub scanning direction inclined mesh and in any direction. The generation of image data for each of the inclined halftone recording will be described. However, in the description of the generation of the slanted net in the main scanning direction, general items required for the subsequent description will also be described.

In the following description, in order to distinguish “1” as a decimal integer value from “1” indicating the state of a specific bit of data, the decimal “1” is “1.”. Express. Also,
Similarly, “2” as a decimal integer value is expressed as “2.”.

(A-3) Generation of main scanning direction slanted mesh (A-3a) Data input In generating the main scanning direction slanted mesh, the operator first uses the keyboard 22 shown in FIG. The main scanning direction X is designated. Further, the following data are also input (see FIG. 5).

(1) Gradient mesh generation start position X _s Gradient mesh generation end position X _e (2) Gradation initial value G _{0 at the} gradient mesh generation start position X _s (3) Gradation change rate (gradation change straight line in FIG. 5 Parameter for instructing (inclination of L) When these data are input, the microcomputer (not shown) provided in the control circuit 21 in FIG. 2 changes the gradation per pixel in the main scanning direction X. Calculate the quantity g _X. Hereinafter, this gradation change amount g _{X is referred} to as “main scanning direction change amount”.
Call.

The main scanning direction change amount g _X thus obtained is supplied to the main scanning data generation circuit 100 provided in the gradation tilt image generation circuit 20 of FIG. This main scanning data generation circuit 1
Reference numeral 00 denotes a circuit that generates gradation data (first gradation data) for each pixel along the main scanning direction X and performs an accumulation operation described later. Further, the gradation initial value G ₀ input from the keyboard is given to the sub-scanning data generation circuit 200. The sub-scanning data generation circuit 200 has a configuration similar to that of the main scanning data generation circuit 100. To the sub-scanning data generation circuit 200, the gradation change amount per pixel in the sub-scanning direction Y (hereinafter referred to as “sub-scanning direction change amount”) g _Y is also input. However, in the case of the generation operation of the tilt net in the main scanning direction considered here, g _Y =
It is 0.

Of the various data thus provided, the gradation initial value G ₀ is taken in by the sub-scanning direction adder 210 provided in the sub-scanning data generation circuit 200. In addition, the change amount g
_Y (= 0) is also latched by the latch circuit 220 and then taken into the sub-scanning direction adder 210. On the other hand, the main scanning direction change amount g _X is latched by the latch circuit 120 and then taken into the main scanning direction adder 110 provided in the main scanning data generation circuit 100.

(A-3b) Configuration of Main Scan Direction Adder 110 FIG. 6 is a block diagram showing the internal configuration of the main scan direction adder 110. Of the circuits included in the main scanning direction adder 110, the adder 111 data selector 112 and the latch circuit 113 are configured to process data having a data length according to the data length of image data used for image recording. Has become. Therefore, for example, when expressing gradation with M bits in image recording, these circuits are also formed as circuits for processing M bits.

On the other hand, the other adder 114, the data selector 115, and the latch circuit 116 shown in FIG. 6 can process a predetermined arbitrary data length (for example, N bits). Then, as will be understood from the following description, since the carry signal CR ₁ output from the adder 114 is the carry input of the adder 111, the main scanning direction adder 110 as a whole has the upper M bits and the lower M bits. Bit and (M
+ N) -bit data can be processed.
As M and N, for example, 8 bits each are assigned.

Of these, the upper M bits are used for gradation expression at the time of image recording, and the least significant bit corresponds to the minimum unit of gradation expression. Therefore, the upper M bits have a meaning as an integer part of image data or gradation data. The lower N bits are not directly expressed in the finally obtained image data, and the gradation gradient image generation circuit 20
Only used within. Therefore, the lower N bits have a meaning as a decimal part of the gradation data.

(A-3c) Configuration of Sub-scanning Direction Adder 210 FIG. 7 is a block diagram showing the internal configuration of the sub-scanning direction adder 210 of FIG. As can be seen by comparing FIG. 6 and FIG. 7, this sub-scanning direction adder 210 has the same configuration as the main scanning direction adder 110 of FIG. 6, and the differences between the two are the data to be handled. Is only the content and operation timing. Also in the sub-scanning direction adder 210 of FIG. 7, an adder 211 for processing an M-bit integer part, a data selector 212 and a latch circuit 213, and an adder for processing an N-bit fractional part. 214, a data selector 215 and a latch circuit 216 are provided.

(A-3d) Relationship between integer part and fractional part Such a relationship between integer part and fractional part is shown in FIG. That is, in FIG. 8A, the integer part I _X and the decimal part D _X in the main scanning direction adder 110 are respectively
It is represented by M-bit data: a _M-1 , ..., A ₁ , a ₀ and N-bit data: b _N-1 , ..., B ₁ , b ₀ . In addition, in FIG. 8 (b),
Similarly, the integer part I _Y and the decimal part D _Y in the sub-scanning direction adder 210 are M-bit data: c _M-1 , ..., C ₁ , c ₀ and N-bit data: d _N-1 ,. They are represented by d ₁ and d ₀ , respectively.

(A-3e) Operation of Sub-scanning Data Generation Circuit 200 Under such a premise, first, the sub-scanning data generation circuit
The operation of 200 will be described. The gradation initial value G ₀ input to the sub-scanning direction adder 210 in FIG.
, As its B input. Corresponding to the use of an M-bit signal as image data for image recording, this gradation initial value G ₀ is also composed of M bits. As the select signal in the data selector 212, the recording start signal ST given from the control circuit 21 in FIG. 2 when the start switch (not shown) provided in the operation panel 23 in FIG. 2 is pressed is used. It Then, the recording start signal ST
Is given, the data selector 212 selects its B input, that is, the gradation initial value G ₀ , and outputs it to the latch circuit 213. The latch circuit 213 latches the input data and gives it to the A input of the adder 211. This adder 211
B input of "00 ... 00" (M bits) is given when the gradation is successively increased along the sub-scanning direction Y or when the gradation is not changed in the sub-scanning direction Y. When the gradation is sequentially lowered along the sub-scanning direction Y, "11 ... 11" (N bits) is given to the B input. Therefore, when the gradation change is given only in the main scanning direction X as considered here, the B input of the adder 211 is "00 ... 00".

This adder 211 is a carry signal from the other adder 214.
After considering CR ₂ , the A input and the B input are added, and the addition result is given to the A input of the data selector 212. After the operation starts, the recording start signal ST maintains the inactive level, whereby the data selector 22 selects and outputs its A input. This output is newly latched by the latch circuit 213.

In this way, the B input of the adder 211 and the carry signal CR ₂ from the other adder 214 are repeatedly added to the gradation initial value G ₀ . The repetition cycle is the latch circuit 213.
The main scanning start clock CKY is used as a latch signal for determining the latch timing. Therefore, the repetitive operation is performed only once for each main scan.

On the other hand, the B input of the adder 214 is supplied with the sub scanning direction change amount g _Y. The adder 214 adds the B input and the A input given from the latch circuit 216, and gives the addition result to the A input of the data selector 215. However, when carry occurs due to addition, carry signal CR _{2 is applied} to adder 211 as described above.

To the B input of the data selector 215, "00 ... 00" (N bits) is always given. Then, when the recording start signal ST as the selector signal is given, the B input is selected, and in other cases, the A input is selected. The data selected in this way is latched by the latch circuit 216 and then applied to the A input of the adder 214. The cycle of such repetition is determined by the main scanning start clock CKY as the latch signal of the latch circuit 216.

That is, at the start of the operation, the B input of the data selector 215 is taken in, the repetitive loop is initialized, and the N-bit sub-scanning direction change amount g _Y is sequentially added every time main scanning is completed. It will be done. Then, when a carry occurs in the adder 214, this carry is reflected in the integer part I _Y by the carry signal CR ₂ . The output of the latch circuit 216 is output as the decimal part D _Y.

The above can be summarized as follows.
That is, the sub-scanning direction adder 210, first, as shown in FIG. 9 (a), the gradation initial value G ₀ in the start of operation
Is taken as the value of the integer part I _Y. At this time, the decimal part D _Y
Is initialized to "0". In the next main scan cycle,
The sub-scanning change amount g _Y is added to the fractional part D _Y to obtain D _Y = g _Y (FIG. 9 (b)). In the next main scanning cycle, the sub-scanning variation amount g _Y is further added to the fractional part D _Y , resulting in D _Y = 2g _Y (FIG. 9 (c)). However, when 2g _Y ≧ 1, carry occurs, the integer part I _Y becomes (G ₀ +1.), And the decimal part D _Y
Becomes (2g _Y −1.). Hereinafter, such an operation is repeated. However, in the case of the slanted net in the main scanning direction considered here, g _Y = 0, so even if sub-scanning proceeds, the fractional part
D _Y remains “0” and the integer part I _Y remains G ₀ .

FIG. 10A is a diagram showing the above-described operation from another viewpoint when g _Y ≠ 0 (an actual example will be described later). As can be seen from this figure, when each pixel is displayed as P (x, y) by the main scanning coordinate x and the sub scanning coordinate y, the first pixel P (1,1) on each main scanning line, The value of the fractional part D _Y regarding P (1,2), ... Changes by the sub-scanning variation amount g _{Y for} each scanning line. Then, when the accumulated value reaches “1.”, carry signal CR ₂ is generated, and the value of the decimal part D _Y returns to (accumulated value−1.). However, FIG. 10A shows the case where the decimal part D _Y returns to “0”.

On the other hand, the integral part I _Y is each time receiving a carry signal CR ₂ (+
1.) increment by one. The gradation data formed by the integer part I _Y and the decimal part D _Y obtained in this way serves as a basis for generating the “first gradation data” described later.

Further, as already explained, in the case of the generation operation of the slanted net in the main scanning direction, since g _Y = "0", the fractional part D _Y is always "0" and the integer part as shown in FIG. 10B. I _Y is always G ₀ .
Therefore, in the case of the slanted net in the main scanning direction, I _Y = G ₀ , D _Y = “0” continues to be output from the sub-scanning direction adder 210 in FIG.

The loop 260 formed by the data selector 230, the latch circuit 240 and the adder 250 provided in the sub-scanning data generation circuit 200 of FIG. 3 is sub-scanned as described above each time the pixel clock CKX is applied. It has a function of accumulating the fractional part D _Y output from the direction adder 210. And
When the accumulation result reaches a value that is 1 bit (2- ^N ) larger than the maximum value that can be accommodated by the N-bit adder 250, that is, "1.", the carry signal CRY is output as a pulse from the adder 250. Will be output. When such a carry occurs, the output of the adder 250 becomes (cumulative value −1.), And then the accumulation starts again.

Therefore, this loop 260 has a function as a circuit that outputs a pulse each time the accumulation result of the fractional part D _Y reaches a multiple of “1.” (including “1.” itself). The "pulse" output from this loop 260 is the carry signal C
It is RY.

However, in the case of the generation operation of the inclined net in the main scanning direction,
Since D _Y = “0”, no matter how many fractional parts D _Y are accumulated, the accumulation result will not reach “1.”. For this reason,
In this case, carry signal CRY does not occur. The data selector 230 is provided with the random number RD from the random number generation circuit 30 as its B input. This random number RD is used as the initial value of the above accumulation, and the reason for giving such a random number RD will be described later.

(A-3f) Operation of Main Scan Data Generation Circuit 100 On the other hand, the integer part I supplied from the sub scan direction adder 210
_Y is a scanning direction adder in the main scanning direction data generation circuit 100
At 110, it is provided as an initial value for each scan line. The main scanning direction adder 110 has the configuration as shown in FIG. 6 as already described. The function thereof is substantially the same as the function of the sub-scanning direction adder 210 in FIG. 7, and the only difference is the data content and the operation timing. For this reason, the main scanning direction adder 110 of FIG. 6 performs the following operation.

First, the adder 114, the data selector 115, and the latch circuit 1
The loop formed by 16 is initialized to “0” (N bits) when the main scanning start clock CKY is given as the select signal of the data selector 115. After that, this loop sequentially adds the main scanning direction change amount g _X to the initial value pixel by pixel. Then, the N-bit adder 114
When a carry occurs in the carry signal CR ₁
And outputs the carry signal CR ₁ to the other adder 111.

Meanwhile, the adder 111, the data selector 112, and the latch circuit 1
The other loop formed from 13 is the sub-scanning data generation circuit.
The integer part I _Y given from 200 is taken in as the initial value for one main scan. Then, the integer part I _X is circulated in this loop in synchronization with the pixel clock CKX, and when the carry signal CR ₁ is given, the integer part I _X is incremented by (+1.). However, ALL "0" is given to the B input of the adder 111.

Therefore, the integer part I _X and the fractional part D _X output from the main scanning direction adder 110 are
It will change as shown in Fig. 11A. This integer part I
The gradation data for each pixel formed from _X and the fractional part D _X is the “first gradation data” in this embodiment.
Note that, as described above, in the case of the generation operation of the slanted net in the main scanning direction, the integer part I _{Y in the} sub scanning direction Y does not change even if the sub scanning proceeds. Therefore, the change shown in FIG. 11A is common to each main scanning line.

The fractional part D _X thus obtained is the adder 150 of FIG.
Given to. Then, the data selector 130, the latch circuit
By the loop 160 formed by 140 and the adder 150, this fractional part D _X is accumulated in synchronization with the pixel clock CKX. An N-bit random number RD given from the random number generator 30 is used as the initial value of this accumulation. The effect of using such a random number RD as the accumulation initial value will be described later, and for the time being, the explanation will be given assuming that the accumulation initial value is “0”.

As shown in FIG. 11A, the fractional part D along the main scanning direction X
_X changes like 0, g _X , 2g _X , 3g _X , .... For this reason, if this fractional part D _X is sequentially accumulated along the main scanning direction X, the accumulated value F _X will initially increase sequentially as shown in FIG. 12 (a). Then, when the accumulated value F _X reaches “1.”, carry occurs,
The carry signal CRX is output as a pulse from the adder 150 shown in FIG. 3, and the accumulated value F for the next pixel is calculated.
_Xi becomes F _Xi = F _{X (i-1)} + D _Xi −1 .... (1). However, F _{X (i-1)} and D _Xi are defined as follows.

F _{X (i-1)} : Cumulative value just before carry occurs D _Xi : Value of fractional part D _X of the pixel where carry occurs Therefore, by repeating such operation,
A pulse train PT composed of a chain of carry signals CRX is generated as shown in FIG. As can be seen from FIG. 12 (b), the pulse interval of the pulse train PT gradually decreases. This is because the value of the fractional part D _X to be accumulated is sequentially increased, so that the accumulated value F _X is “1.” along with the main scanning signal.
This is because the interval until reaching is gradually narrowed.

FIG. 13 illustrates this from another point of view. Of these, FIG. 13 (b) shows a cumulative value A _X obtained by sequentially accumulating the fractional part D _X for each pixel along the main scanning direction X. However, unlike the above-described accumulated value F _X , the accumulated value A _X is drawn in a continuous form without causing a carry problem. Further, in FIG. 13 (a), a numerical scale showing integers "1.", "2.", ..., "n." Which are multiples of "1." as a reference value is drawn. In addition, the accumulated value A _X
The fractional part corresponding to the pixels that reach these integers are shaded.

On the other hand, as described above, in the third diagram of the adder 150 sequentially accumulates the fractional part D _X, the accumulated value is generated a carry signal CRX each time it reaches the "1". Therefore, the adder 150
Has a function of indirectly identifying pixels having a fractional part with diagonal lines in FIG. 13 (b) (“multiple arrival pixel”) and outputting a carry signal CRX to the multiple specific pixels. Will be.

As described above, the pulse interval of the pulse train PT formed by the carry signal CRX is gradually narrowed as the fractional part D _X is increased, as shown in FIG. 13 (c). And
As shown in FIG. 11A, when a carry occurs in the decimal part D _X itself to be accumulated, the integer part I _X is incremented by (+1.), And the decimal part D _X is larger than “1.”. Go back to a smaller value (eg "0"). Therefore, the pulse train PT of FIG.
The sparse and dense change of will be repeated every time the integer part I _X is changed.

The above situation is shown in FIGS. 1 (a) to 1 (d). However, in FIG. 1, for convenience of illustration, fine stepwise changes in pixel units are omitted in broken lines.
In FIG. 1, the integer part I _X changes stepwise from the initial value I _Y (= G ₀ ) (FIG. 1 (a)). Also, the decimal part
D _X changes finely in a stepwise manner pixel by pixel, and returns to "0" or a value in the vicinity thereof at the position where the integer part I _X changes (FIG. 1 (b)). Further, the accumulated value F _X of the fraction D _X increases finely stepwise changed while parabolic, "1." Each time to reach, return to the value indicated by equation (1) (Figure 1 (C)). However, in FIG. 1 (c), only a part of the waveform is drawn. Further, in FIG. 1 (c), the period until the accumulated value F _X returns to the value of the expression (1) is gradually narrowed toward the position where the value of the integer part I _X changes.

Then, at the position where this accumulated value F _X returns to the value of expression (1),
The carry signal CRX shown in FIG. 1 (d) is generated. And
The intervals at which the carry signal CRX is generated gradually decrease toward the position where the integer part I _X changes. After the integer part I _X has changed, the carry signal C RX is generated again at wide time intervals, and thereafter, the generation intervals thereof are gradually narrowed. This sparse / dense period corresponds to the change period ΔX of the integer part I _X.

(A-3g) Combine operation of integer part and carry signal (pulse) In this way, the integer part _IX of FIG. 1 (a) is output from the main scanning direction adder 110 of FIG. The carry signal CRX shown in FIG. 1 (d) is output from the container 150. Of these, the integer part I _X is given to the B input of the adder 41 of FIG. Further, carry signal CRX passes through OR circuit 42 to become carry signal CR. In the case of the main scanning direction slanted net, the carry signal CRY which is the other input of the OR circuit 42 is always “0”, so the carry signal CR which is the output of the OR circuit 42 is the carry signal from the adder 150. It has the same data value as CRX. Then, the carry signal CR becomes the input signal of the least significant bit (LSB) of the A input in the adder 41 through the AND circuit 43.

As the other input of the AND circuit 43, a signal obtained by inverting the carry signal CR ₃ from the adder 41 by the inverter 44 is given. Therefore, unless carry occurs in the adder 41, the output of the inverter 44 is “1.” and the AND circuit 43
Will have the same value as the carry signal CR (= CRX).

Therefore, the adder 41 uses the integer part I _X and the carry signal CR (=
CRX) is combined with it to have the function of generating “second gradation data”. As a result, the image data S which is the addition output of the adder 41 has a waveform as shown in FIG.

As can be seen from FIG. 1 (e), the image data S thus obtained has a form in which the pulse train PT is placed on the stepped signal S ₀ corresponding to the integer part I _X. There is. Then, the pulse density in the pulse train PT sequentially increases toward the position where the level of the step signal S ₀ increases by (+1.). For this reason, when recording in the main scanning direction slanted mesh using such image data S, the gradation is visually recognized as a continuous gradation change macroscopically. Therefore, by using such a method, the effect of tone jump on the recorded image can be effectively prevented.

The adder 4 is added by adding the carry signal CRX in FIG.
When the carry to 1 occurs, the output of the AND circuit 43 becomes "0". Therefore, at this time, the A input of the adder 41 is "0".
And the value of the integer part I _X becomes the output S of the adder 41 as it is. Therefore, in this case, the image data S as shown in FIG. 14 (a) is obtained. If such a structure is not adopted, as shown in FIG. 14 (b), the upper limit value 2 ^M of gradation expression may cause an overflow effect,
It is desirable to provide the AND circuit 43 and the like as described above.

(A-3h) Significance of Random Numbers as Accumulated Initial Value and Operation of Random Number Generating Circuit 30 Next, the reason why the random number RD generated from the random number generating circuit 30 of FIG. 3 is used as the cumulative initial value will be described. As described above, by using the gradation gradient image generation circuit 20 of FIG. 3, the influence of tone jump is effectively prevented. However, the pulse train PT added to prevent the influence of this tone jump has a common arrangement for each main scanning line.

Therefore, if a schematic symbol as shown in FIG. 15 is used to indicate gradation, the image data obtained by the above method will be
The pixel arrangement is as shown in Figure A. As can be seen from FIG. 16A, in this image, the pulses generated from the carry signal CRX are arranged in a straight line along the sub-scanning direction Y. Then, there remains a possibility that these straight lines are visually recognized. In order to cope with this, in this embodiment, a random number RD is used as the cumulative initial value for accumulating the fractional part D _X for each main scanning line.

FIG. 17 is a block diagram showing the internal structure of the random number generation circuit 30 of FIG. In FIG. 17, when the main scanning start clock CKY is applied to the counter 31, this counter 31
Increments by (+1) and outputs the count value to the ROM 32 as address data. In this ROM32,
A series of random numbers is tabulated and stored in advance. And one random number RD from the specified address
Is output.

This random number RD is the B input of the data selector 130 shown in FIG. When the main scanning start clock CKY is given as the select signal of the data selector 130,
This B input is selected and given to the latch circuit 140.
After that, during the period until the start of the next main scan, the data selector 130 selects and outputs the A input given from the adder 150. Therefore, the random number RD
Is used as a common value on one main scanning line, and a new random number is generated and used every time the scanning is moved to the next main scanning line.

In this way, by using the random number RD as the initial value of the accumulation operation of the decimal part D _X , the generation timing of the carry signal C RX changes for each scanning line. Therefore, the 16th
As shown in FIG. B, the pulses obtained from the carry signal CRX are dispersed in units of scanning lines, which can prevent the pulses from being arranged in a straight line along the sub-scanning direction Y.

(A-3i) In the case of a slanted net whose gradation decreases along the main scanning direction X In the above, a slanted net whose gradation increases along the main scanning direction X was considered, but along the main scanning direction X In the case of a slanted net whose gradation decreases, the following may be done. That is, first, the B input of the adder 111 included in the main scanning direction adder 110 of FIG. 6 is set to "11 ... 11" (M bits). Then, each time the carry signal CR ₁ is given to the adder 111, the data “11 ... 11” is added to the integer part _IX .

As is well known, addition of "11 ... 11" (M bits) and "00 ... 01" which is the complement of 2 of this data.
It is equivalent to subtracting (M bits). Therefore, when carry signal CR ₁ is not generated, integer part _IX is decremented by (−1.). Conversely, when the carry signal CR ₁ occurs, "11 ... 11" + CR 1 = "11 ... 11" + "00 ... 01" = "00 ... 00" for is satisfied, the integral part I _X is the verge The value will be maintained.

On the other hand, in this case, as the main scanning direction change amount g _X , the complement of 2 of the absolute value to be reduced along the main scanning direction X is given. For example, when it is desired to reduce the gradation by "00 ... 01" (N bits) as a decimal value per pixel, g _X = "11 ... 11" (M bits). Then, the adder 114 shown in FIG. 6 substantially subtracts "00 ... 01" (N bits) for each pixel. As a result, the adder 114 repeats the following operation.

"00 ... 00" + g _X = "11 ... 11""11 ... 11" + g _X = "11 ... 10" + CR ₁ "11 ... 10" + g _X = "11 ... 00" + CR ₁ ... "00 ... 01" + g _{X = "00 ... 00" +} CR 1 "00 ... 00" + g X = "11 ... 11" ... Thus, in this example, a carry signal CR ₁ every 2 ^N pixels
A pixel that does not generate appears and the integer part I _X
Decrements.

By changing the integer part I _X and the fractional part D _X in this way, the waveform diagram corresponding to FIG. 1 becomes as shown in FIG.
Therefore, even in the case of such a gradation reduction network, the effect of tone jump can be effectively prevented.

(A-4) Generation of Tilt Net in Sub-scanning Direction Next, the operation of generating the tilt net in the sub-scanning direction will be described. When generating a slanted net in the sub-scanning direction, change amount in the main scanning direction
“0” is given as g _X , and a value (≠ “0”) according to the gradation change rate is given as the sub scanning direction change amount g _Y.
Then, the loop formed by the adder 214, the data selector 215, and the latch circuit 216 provided in the sub-scanning direction adder 210 of FIG. 7 synchronizes with the main scanning start clock CKY,
The amount of change g _{Y in} the sub-scanning direction is accumulated.

As a result, the fractional part D _Y changes as 0, g _Y , 2g _Y , 3g _Y , ... As the sub-scanning progresses. When a carry occurs in the adder 214, the output of the other adder 211 is (+1.) Or (-
1.) changes, and the integer part I _Y is also incremented or decremented accordingly. Therefore, the sub-scanning direction Y
In the case of a slanted net whose gradation increases along with, the integer part I _Y and the fractional part D _Y for the first pixel of each main scanning line change as shown in FIG. 10A. Then, the fractional part D _Y is sequentially given to the adder 250 of FIG.

The adder 250 includes a data selector 230 and a latch circuit.
Accumulate the fractional part D _Y via 240. However, the timing of this accumulation processing is determined by the pixel clock CKX given to the latch circuit 240. Therefore, the fractional part D _Y itself input to the adder 250 keeps a constant value until the scanning moves to the next main scanning line, while the fractional part D _Y
The accumulated value F _Y of will vary from pixel to pixel. Therefore, the fractional part D _Y for each scanning line changes as shown in FIG. 19 (a), and the cumulative value F _Y for each pixel changes as shown in FIG. 19 (b). However, in FIG. 19 (b), RD ₀ , RD
₁ , ... Are random numbers given from the random number generation circuit 30 of FIG. 3 for each scanning line.

On the other hand, in the main scanning direction adder 110 of FIG. 6 which receives the integer part I _Y as an initial value, the value of this integer part I _Y is latched by the latch circuit 113 via the data selector 112 of FIG.
However, since the main scanning direction change amount g _X given to the adder 114 in FIG. 6 is “0”, the fractional part D _X is always “0”. Therefore, the carry signal CR ₁ is not generated from the adder 114, and as a result, the integer part I _X also maintains the value of the initial value I _Y. Therefore, the decimal part D _X input to the adder 150 of FIG. 3 is always “0”, and the integer part I _X input to the adder 41 matches I _Y. Further, since D _X = “0”, the accumulated value F _X of the accumulation loop 160 in FIG. 3 also maintains the value of the random number RD given as the initial value. As a result, carry signal
The CRX is not generated, and the carry signal CR that is the output of the OR circuit 42 has the same waveform as the carry signal CRY from the sub-scanning data generation circuit 200.

The generation principle of the carry signal CRY given from the adder 250 of FIG. 3 to the OR circuit 42 has been already described in the section (A-3e). However, although the accumulation loop 260 including the adder 250 is included in the sub-scanning direction data generation circuit 200, the accumulation operation is repeated according to the pixel clock CKX. Therefore, the carry signal CRY forms a pulse train that is arranged according to a different rule from the pulse train obtained by simply replacing the "main scanning direction X" with the "sub scanning direction Y" when the main scanning direction tilted mesh is generated. Become. Hereinafter, this will be described in detail.

First, on the first main scanning line,
As shown in FIG. 6B, the accumulated value F _Y is RD ₀ (<1.) Regardless of the position X on the main scanning line. Therefore, carry signal CRY does not occur. Next, on the second main scanning line, as shown in FIG. 19 (b), the accumulated value F _Y is D _Y (= g _Y ) for each pixel with RD ₁ as the initial value.
It increases in steps. Then, carry signal CRY is generated each time this accumulated value F _Y reaches “1.”. This is 20A
As shown in the figure. However, in FIG. 20A,
Pixels in which the carry signal CRY is generated are indicated by "x" marks. Also, for convenience of explanation, g _Y = 2 ⁻⁴ and random number RD
Is ignored.

Third main scan line (straight line at position Y = 2 in Fig. 20A)
Since D _Y = 2g _{Y in the} above, the accumulated value F _Y increases by 2 × 2 ^-4 = 2 ^{-3 for} each pixel along the main scanning direction X. Therefore, on this main scan line, 1/2 ^-3
= F _X = “1.” For every 8 pixels, and the carry signal CRY is generated at each pixel as shown by the “x” mark in FIG. 20A. The same applies to the other main scanning lines.

As can be seen from FIG. 20A, the array of carry signals CRY along the sub-scanning direction Y does not necessarily have a narrower interval in sequence, but an array including partial density. However, this is a case where microscopic observation is performed, and when viewed macroscopically, the pulse intervals are sequentially narrowed. Therefore, when such a carry signal CRY is combined with the integer part I _Y in the adder 41 of FIG. 3,
The image data S shown in FIG. 21, for example, is obtained along the sub-scanning direction Y. Therefore, also in this case, the effect of the tone jump is effectively removed.

As can be seen from Figure 20A, in this case the carry signal C
The pulse due to RY is not aligned in the direction parallel to the main scanning direction X. However, because the accumulated value F _Y is obtained according to the predetermined rule, as shown in FIG. 20A, a straight line l ₁ along the sub-scanning direction Y or a diagonal straight line
There is a possibility that pulses due to carry signal CRY will line up on l ₂ . Therefore, in this embodiment, the random number RD from the random number generation circuit 30 of FIG. 3 is taken into the accumulation loop 260 via the data selector 230 as an initial value for each main scan, and thereby the carry signal CRY. Randomness is added to the distribution of. As a result, image data as shown in FIG. 20B can be obtained.

The main scanning start clock CKY is input to the latch circuit 240 in FIG.
By applying such a modification as described above, the same waveform as that shown in FIG. 1 can be obtained in the sub-scanning direction Y.
Even if such deformation is applied, no particular problem occurs.

(A-4) Generation of Slanted Net in Arbitrary Direction Next, generation of a slanted net having a gradation change direction in an arbitrary direction P (FIG. 4) instead of a direction parallel to the scanning direction will be described. In this case, finite values (g _X ≠ 0, g _Y ≠ 0) according to the gradation changing direction are given to both the main scanning direction changing amount g _X and the sub scanning direction changing amount g _Y. Then, the integer part I _Y changes along the sub-scanning direction Y, and the integer part I _{X in the} main scanning direction changes with the integer part I _Y as an initial value in each main scanning line. In addition, two types of carry signals CRX, CR
Y occurs independently. And these carry signals CR
The carry signal CR including both X and CRY is the OR circuit 42 of FIG.
The carry signal CR is combined with the integer part I _X to form the image data S.

For this reason, as shown in FIG. 22 as a schematic three-dimensional diagram, a pulse group having a high density in the flat mesh portion FD below the step of the gradation jump point J and a low density in the flat mesh portion FU above the step. The image data S for PG is obtained. As a result, the tone jump is macroscopically removed, and a slanted net having a smooth spatial gradation change is provided.

B. Second Embodiment (B-1) Schematic Configuration of Second Embodiment FIG. 23 is a partial schematic view of a plate-making scanner incorporating an image data generating device according to a second embodiment of the present invention. Is.
The structure of the part not shown in FIG. 23 is the same as that of the scanner shown in FIG. 2, and the description thereof will be omitted.

In FIG. 23, this scanner has a configuration different from that of the first embodiment in the following points. First, the image data generating device according to the present invention is configured not as a gradation gradient image generating circuit but as a tone jump removing circuit 50 whose input data is image data obtained by reading from the original image 2. is there. That is, in the first embodiment, the circuit for generating the image (gradient net) to be recorded inside itself is targeted, but in the second embodiment, when the image given from the outside is recorded, the tone I'm trying to eliminate the jump.

Therefore, the tone jump elimination circuit 50 of FIG.
The A / D converted image input is provided by the D converter 60. The output of the tone jump removing circuit 50 is subjected to processing such as gradation conversion in the image processing circuit 17, and then output to the halftone dot generator 18. It should be noted that although FIG. 23 does not show the gradation gradient image generation circuit 20 of FIG.
This is because it is unnecessary for the description of the embodiment. Therefore, the gradation gradient image generation circuit 20 is set in the same manner as in FIG.
It can be installed in the device shown in Fig. 23 at all.

The second characteristic of the device shown in FIG. 23 is that the A / D converter 60 is
This is to use a high resolution A / D converter that can obtain (M + N) bits of digital data. However, M
Is the data length of the image data to be output, as in the first embodiment, and N is the data length of the decimal part described later.
This is because in the second embodiment, as will be described later, the integer part and the decimal part are extracted from the input image data.

(B-2) Configuration and Operation of Tone Jump Removal Circuit 50 FIG. 24 is an internal configuration diagram of the tone jump removal circuit 50. First, the configuration of this circuit will be described. In the figure, of the input image data converted to (M + N) -bit digital data by the A / D converter 60, the upper M bits are given to the A input of the M-bit adder 51 as an integer part I. On the other hand, the lower N bits are given to the B input of the N-bit adder 54 as the fractional part D.

The adder 54 includes a data selector 52 and a latch circuit 53.
At the same time, an accumulation loop 57 for sequentially accumulating the fractional part D for each pixel is formed. And the data selector 52
When the main scan start clock CKY is input, the B input “0” (N bit) is selected as an initial value,
In other periods, the output of the adder 54 is selected and output to the latch circuit 53. Therefore, this accumulation loop
57 will perform the same function as the accumulation loop 160 in FIG. However, the circuit of FIG. 24 does not use random numbers. When using a random number, the output of the random number generation circuit may be input to the B input of the data selector 52.

Then, when a carry occurs in the adder 54 of FIG. 24, a carry signal CR ₃ is generated, and this carry signal CR ₃ is ANDed.
It is given to the least significant bit of the B inputs of the other adder 51 via the circuit 56. The AND circuit 56 and the adder 5
The inverter 55 that inverts the carry signal CR _{4 of} 1 and supplies it to the AND circuit 56 is provided to prevent the overflow of the adder 51, as in the first embodiment.

Next, the operation of the tone jump removing circuit 50 will be described by taking the case where the input image data R shown in FIG. 25 (a) is given to the A / D converter 60 as an example. However, the horizontal axis t in FIG. 25 indicates the time or the scanning distance corresponding thereto.

First, the input image data R converted into (M + N) -bit digital data by the A / D converter 60 has an M-bit integer part I and an N-bit decimal part D as shown in FIG. 25 (b). Is separated into However, in FIG. 25 (b), the shaded portion corresponds to the decimal portion D.

This fractional part D is accumulated pixel by pixel in the accumulation loop 57 shown in FIG. Then, each time the accumulated value F reaches “1.”, the carry signal CR ₃ is output, and the accumulated value F becomes (F−
Return to the value of 1.). Therefore, also in the accumulation loop 57, the accumulated value of the decimal part D is substantially an integer value (“1.”).
Of the carry signal CR ₃ as a pulse signal each time it reaches the number of times).

The carry signal CR ₃ is combined with the integer part I in the adder 51 shown in FIG. As a result, the image data S changes as shown in FIG. 25 (c). As can be seen from FIG. 25, in the area 71 where the level of the input image data R increases with respect to the time t, the fractional part D also sequentially increases.
As a result, carry signal CR ₃ has its generation intervals gradually narrowed. On the other hand, in the area 72 where the level of the input image data R decreases, the opposite phenomenon occurs. For this reason,
A high-density pulse is applied to portions 75 and 76 on the low gradation side in the vicinity of the point where the tone jump occurs (for example, points 73 and 74). Further, a high-density pulse is given near the local maximum point 77 of the gradation, and the pulse density becomes low near the local minimum point 78.

Therefore, the image represented by the gradation change in FIG. 25 (c) is macroscopically viewed as an image having a smooth gradation change close to the input image data R in FIG. 25 (a). become.

Further, when the level of the input image data R, as shown in FIG. 26 (a) is an integral value, since the fractional portion D is "0", the carry signal CR ₃ is not generated, Figure 26 (B)
As described above, the same image data S as the input image data R is output.

Further, as shown in FIG. 26 (c), when the input image data R keeping a non-integer constant level is given, the decimal part D
Since it also holds a constant value, a periodic carry signal CR ₃ is superimposed on the integer part I as shown in FIG. For this reason, this device not only has the effect of removing the effect of tone jump, but also has the effect of faithfully expressing halftones in the portion where the input image data R is constant. become.

(B-3) Insertion Position of Device In FIG. 23, the A / D converter 60 and the tone jump removing circuit 50 are inserted between the pickup head 10 and the image processing circuit 17. 17 and halftone dot generator 18
It may be inserted between. In this case, the A / D converter 16 shown in FIG. 2 is unnecessary. Of course, the image processing circuit 17 uses an analog processing circuit.

C. Modifications The embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and the following modifications are possible.

When obtaining the pulse train by accumulating the fractional part, the carry signal does not have to be used as it is. For example, a circuit for generating a pulse having a desired size by inputting a carry signal may be provided, and the pulse thus obtained may be combined into an integer part. Therefore, the pulse may be generated not in the multiple arrival pixel itself but in the pixels in the vicinity thereof. Further, the pulse may be generated in a small area including both of them (for example, an area for several pixels). An example of this case is shown in FIG.

Furthermore, the height of the pulse is not limited to "1.", for example, "2." is not prohibited.

Therefore, according to the present invention, it is sufficient to change the value of the integer part in a pulse-like manner by a predetermined amount for the pixels reaching the multiple and / or the pixels in the vicinity thereof.

When changing the value of the integer part in a pulse,
It may be changed in the negative direction as shown in FIG. In this case, find the two's complement of the fractional part and accumulate it,
As a result, the negative pulse density change direction is reversed.

When specifying the multiple reaching pixel by the accumulation of the decimal part, a desired reference value and the accumulated value may be compared using a comparator. It is not essential to set "1." as the reference value, and any other value may be set. For example, if you use a circuit that can handle numbers up to “2.” as the accumulation loop and use the carry signal that is generated when the accumulated value reaches “2.” 2. "is set. The pulse density in this case is half that in the above-mentioned embodiment.

In the above example, the integer digit of the accumulated value is not counted,
The adders 150, 250, and 54 that can accommodate only decimal digits are used. By using “1.” as the standard value,
This is because the multiple arrival pixel can be specified only by the carry signals CRX, CRY, CR ₃ without counting the integer digits of the accumulated value. However, it is not prohibited to count the accumulated value up to an integer digit. It is also possible to use a subtracter to perform accumulation and generate a pulse by a borrow signal.

Further, it is not essential to generate the image data S online as in the above embodiment, and the image data S may be obtained offline and stored in a large capacity memory such as a magnetic disk. It is also possible to transfer the image data S obtained in this way to another place via a communication line and then record it.

Although the embodiment of FIG. 2 uses the halftone dot generator 18, it is not essential to use the halftone dot generator 18 and continuous tone recording based on image data may be used.

The present invention is not limited to the cylindrical scanning type plate making scanner, but can be applied to a plane scanning type plate making scanner as well as a facsimile or a copying machine having gradation reproducibility.

D. Addendum By the way, in Japanese Patent Laid-Open No. 57-160264, a periodic decimal is combined with the decimal part of the gradation data for each pixel, and the integer part is corrected for the pixel whose composite result is equal to or higher than the slice level. That technology is disclosed.

However, in the case of synthesizing periodic decimals in this conventional technique, as disclosed in FIG.
Pixels whose integer part is corrected are spatially continuous, and the change in the continuous width represents a pseudo gradation change.

For example, if the periodic decimal is a repetition of a numerical sequence such as 0.1 0.2 0.3 0.4 0.5 0.6 0.7, and the pixel array has a decimal part of approximately "0.5" as the grayscale data before conversion, the composition result is Since 0.6 0.7 0.8 0.9 1.0 1.1 1.2 , when the slice level is “1.0”, the combined result of each of the three consecutive pixels becomes equal to or higher than the slice level, and the “corrected pixel” continues.

Therefore, in the technique of the above publication, the correction pixels are likely to be continuous,
In a region where the continuous width is large, it may be visually noticeable, resulting in insufficient removal of tone jump.

On the other hand, in the present invention, since the fractional part is accumulated, the correction pixel (multiple arrival pixel) is unlikely to be continuous unless the pixel having a relatively large decimal part is continuous.

For example, if the fractional part is an image sequence such as 0.30 0.31 0.32 0.33 0.34 0.35 0.36, when accumulating these, only the underlined pixels such as 0.30 0.61 0.93 1.26 1.80 2.15 2.51 are the pixels that reached the multiple pixels. Next to
These are discrete distributions and are not continuous.

When the decimal part is close to “1”, for example, the decimal part is almost “0.
When pixels such as "6" are consecutive, the cumulative value is 0.6 1.2 1.8 2.4 3.0 3.6 4.2 4.8 5.4 ..., so the corrected pixels are not continuous at all, but the continuous width is above. It is smaller than the technology and has a great effect of visually preventing tone jump.

(Effects of the Invention) As described above, according to the present invention, the gradation changes in a pulse manner in each of the multiple arrival pixel and / or the pixels in the vicinity thereof, and the interval of the pulse array changes in the gradation. Therefore, it is possible to obtain an image data generating method and its apparatus that can effectively prevent the influence of tone jump in continuous tone image recording.

In addition, in the process of generating this image data, two types of data, an integer part and a decimal part, are used, but the generated image data itself does not require a particularly large data length, so the data processing becomes complicated. Nothing.

Further, the image data (second tone data) after the correction by the decimal part accumulation is composed of the integer part, and does not include the decimal part. Therefore, there is an effect that the circuit configuration for processing the second gradation data is simplified.

In addition, compared with the technique of combining periodic decimals in the decimal part,
In the present invention, pixels whose integer part is modified are less likely to be continuous, and the effect of visually preventing tone jump is high.

Furthermore, since a random number is used as the cumulative initial value for each scan line, the gradation change position due to the modification of the integer part will be aligned with the adjacent scan line (so-called "straight line").
Can be prevented.

Further, since the random number is given for each scanning line, the effect of preventing "uniform streaks" can be obtained even when compared with a case where a common random number is used for a screen pattern signal for each block of a halftone dot image recording, for example. It is expensive.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing a process for obtaining image data according to the first embodiment of the present invention, FIG. 2 is an overall configuration diagram of a cylindrical scanning type plate-making scanner incorporating the first embodiment, and FIG. The figure shows a gradation gradient image generation circuit 20 as the first embodiment.
FIG. 4 is an explanatory view of a slanting net, FIG. 5 is an explanatory view of data inputted from the outside in the generation of a main scanning slanting net, and FIGS. 6 and 7 are main scanning respectively. FIG. 8 is a block diagram showing an internal configuration of a direction adder and a sub-scanning direction adder, FIG. 8 is an explanatory diagram of an integer part and a decimal part of the first gradation data, FIG. 9, FIG. 10A, FIG. 10B, and FIG. 11A and 11B are explanatory views of addition processing of a decimal part and carry, FIGS. 12 and 13 are explanatory views of accumulation of a decimal part and generation of a carry signal, and FIG. 14 is overflow inhibition processing. Explanatory diagrams, FIGS. 15, 16A and 16B are explanatory diagrams of the effect of random number assignment, FIG. 17 is an internal configuration diagram of the random number generation circuit, and FIG. First
FIG. 19 to FIG. 21 are explanatory views of the image data generating operation for the sub-scanning direction slanting net, and FIG. 22 is an image for the slanting net having an arbitrary gradation slanting direction. FIG. 23 is an explanatory diagram of data, FIG. 23 is a partial configuration diagram of a plate-making scanner incorporating the second embodiment, and FIG. 24 is a block showing an internal configuration of the tone jump removing circuit 50 formed as the second embodiment. FIG. 25, FIG. 25 and FIG. 26 are waveform diagrams showing the operation of the second embodiment, FIG. 27 and FIG. 28 are explanatory views of a modified example of the present invention, and FIG. 29 is an explanatory view of tone jump. . 1 ... Cylinder scanning type plate making scanner, 2 ... original image, 20 ... gradation gradient image generation circuit, 30 ... random number generator, 50 ... tone jump removal circuit, 100 ... main scanning data generation circuit, 200 …… Sub-scan data generation circuit, 160,260 …… Accumulation loop, I _X , I _Y , I …… Integer part, D _X , D _Y …… Decimal part, F _X , F _Y , F …… Accumulated value ( Lower N bits)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-57-160264 (JP, A) JP-A-58-96459 (JP, A) JP-A 61-5677 (JP, A) JP-A 54- 59820 (JP, A) US Patent 4196454 (US, A) US Patent 4196452 (US, A)

Claims (6)

[Claims] 1. A method for generating image data for scanning and recording an image, the gradation of which continuously changes, by a pixel array having discrete gradations, wherein the discrete gradations used for the recording. The first gradation data, which includes an integer part having a data length corresponding to the number and a decimal part having an arbitrary data length, expresses the gradation of the image for each pixel and sets it as a cumulative initial value for each scanning line. A random number is given, the values of the fractional part are sequentially accumulated along the direction of the pixel array, and each pixel whose accumulated result reaches a value according to a multiple of a predetermined reference value is defined as a multiple arrival pixel. , For each existence of the multiple reaching pixel, by changing the value obtained from the integer part of the first gradation data of the multiple reaching pixel and / or the pixels in the vicinity thereof by a predetermined integer amount, Second gradation data Generated, the second tone data, characterized in that the image data for recording the image, the image data generating method for the continuous tone image recording. 2. An image in which gradation changes continuously is an image in which gradation changes in accordance with a specified gradation change rate along a specified gradation change direction. The first gradation data has a gradation value designated for a predetermined pixel as an initial value, and a change amount determined according to the gradation change direction and the gradation change rate is sequentially set to the initial value. The image data generating method for continuous tone image recording according to claim 1, which is obtained by addition or subtraction. 3. An image in which gradation changes continuously is an image obtained by reading an original image, and the integer part and the fractional part of the first gradation data represent the gradation of the image of the original image. The image data for continuous tone image recording according to claim 1, which is given by upper side data and lower side data when digitized with a number of gradations larger than the number of gradations in the scan recording. Generation method. 4. An apparatus for generating image data for scanning and recording an image of which gradation is continuously changed by a pixel array having discrete gradation, the discrete gradation used for the recording. A first gradation including an integer part having a data length corresponding to the number and a decimal part having an arbitrary data length, and expressing the gradation of an image to be recorded for each pixel by the integer part and the decimal part. First gradation data generating means for generating data in time series in a scanning order, random numbers are given as cumulative initial values for each scanning line, and the values of the fractional part are sequentially arranged along the direction of the pixel array. Accumulation means for accumulating and generating a pulse of a predetermined size each time the accumulation result reaches a value according to a multiple of a predetermined reference value; and an integer part of the first gradation data. By synthesizing the pulse value and the pulse in time series. A second gradation data generating means for generating second gradation data consisting of an integer part, wherein the second gradation data is image data for recording the image. , An image data generation device for continuous tone image recording. 5. An image in which gradation changes continuously is an image in which gradation changes at a specified gradation change rate along a specified gradation change direction. The generation unit sequentially adds or subtracts a change amount, which is determined according to the gradation change direction and the gradation change rate, to the initial value by using the specified gradation value for a predetermined pixel as an initial value. The image data generating apparatus for continuous tone image recording according to claim 4, which is a means for generating the first gradation data. 6. An image in which gradation changes continuously is an image obtained by reading an original image, and the integer part and the decimal part of the first gradation data are gradations of the image of the original image, The image data for continuous tone image recording according to claim 4, which is given by upper side data and lower side data when digitized with a gradation number larger than the gradation number in the scan recording. Generator.