JPS5827493B2 - Method for recording a halftone image with contours faithful to the original image - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention, when recording a mesh plate image from a continuous tone original image, detects the contour of the original image from the image signal and detects the shape of the halftone dots to be recorded on the contour portion or its shape. The present invention relates to a method for recording a halftone image having an outline faithful to that of an original image by controlling the recording position.

Image scanning recording devices such as scanners, especially devices that electrically create halftone dots, control the area ratio according to the image signal level from the original image, and record a halftone image corresponding to the original image are available in various types. Some have been developed and some are already in practical use.

However, in either case, the overall level of each pixel, which is determined by the scanning line width and sampling pitch when photoelectrically scanning the original image and picking up the image signal, is used as the image signal level to control the halftone area ratio. Because of this, the outline of the original image tends to become somewhat unclear when it is copied.

That is, as shown in FIG. 1, when the outline AI of the original image A to be reproduced and recorded as a halftone image is only partially included in the scanning line, in the conventional method, the scanning line width is equal to the sampling pitch. Since the average value level of the original image A included in each pixel B determined by If there is
In the pixel B, halftone dots with an area ratio corresponding to the average value level, in other words, halftone dots with a smaller area ratio than the halftone dots that should originally be recorded, are recorded as a halftone image. The outline of the original image becomes unclear.

This tendency is more noticeable in the outline of the text when an original drawing containing a picture and text is recorded as a halftone plate. A mesh plate was created by shading the area separately using a contact screen or the like and pasting the shading character area onto the shading pattern area.

An object of the present invention is to provide a method for recording halftone images that solves the above-described conventional drawbacks and inconveniences, and will be described in detail below with reference to the drawings.

In FIG. 2, the original image is divided into a large number of pixels determined by the scanning line width in the sub-scanning direction and the sampling pitch in the main scanning direction, and the image signal value in each pixel is calculated as Mll for the first line (one scanning line), M1□・・・・・・Mln, 2nd line M212M22・・・・・・M2 n,
The nth line is Mn1. Mn2...This is schematically shown as Mn n.

In the method according to the present invention, first, such an original image is photoelectrically scanned sequentially in scanning lines, and, for example, the image signal values of pixels included in each scanning line corresponding to the ① line to the third line, Ml 15 Ml2-・－・・・・・・Ml n:M
212M22. ...M2n: and M317 MB21...M3n are written in the memory device in advance.

After that, the original image is photoelectrically scanned to obtain the image signal value M4 of the fourth line. tM42...M4n is picked up sequentially, while the recorded image signal value M212M22...M2n of the second line is picked up from the first and third lines on both sides. Corresponding image signal values M, 1, Ml□...--M
ln and M31゜M3□-...M3Tl, that is, 3 pixels are read out from the memory device at the same time, and their sizes are sequentially compared, and based on the magnitude relationship of the image signal values, it is determined which corresponds to the second line of the original image. The shape of the halftone dots reproduced is controlled to record a mesh board that is faithful to the original image.

The picked up image signal value of the fourth line is read out from the memory device and sequentially written to the address corresponding to the erased first line.

When controlling the halftone dot shape after the 3rd line, it is the same as above, and the picked up image signal value of the 5th line is
The read and erased image signal values of the second line are sequentially written to the addresses of the memory device where they were written.

FIG. 3 shows an example of a block diagram for comparing such image signal values and creating a signal for controlling the halftone dot shape to be recorded. Memory device 2 is a memory device in which the image signal values of the pixels included in each are written sequentially for each scanning line; A selection circuit such as a data multiplexer or the like selects and outputs an input signal so as to be input to the input signal, and 3 is a comparison circuit that compares the magnitude of the input image signal values of three pixels and outputs a control signal.

According to this embodiment, in order to obtain a halftone dot shape control signal when copying and recording an original image as a halftone image as shown in FIG. 2, first, pixels included in each scanning line from the first line to the third line are The image signal value of Mll 7Ml 2 ,...
......M, n: M242M22.・・・・・・
M2 n; M3. , MB2. −=−・−−−−M
Write 3o to memory device 1 (.

Thereafter, in parallel with the photoelectric scanning of the fourth line, M2) is first read out from the memory device 1 as the main signal MM, and Mll and M3□ are read out as the left sub-signal ML and right sub-signal MR, respectively, and selected. The signal is input to a comparator circuit 3 via a circuit 2, and the magnitude relationship between MM and ML and between MM and MR is determined to obtain a signal for controlling the halftone dot shape to be recorded at the location corresponding to MM, that is, M2H.

An example of this comparison circuit 3 is shown in FIG. 4, including comparators 4, 5, AND circuit group 6°7...
...14, and OR circuits 15, 16, and 17.

Therefore, each comparator 4 and 5 has MM and MR.
When l, MM and ML are input, each comparator 4
And 5, a comparison signal is inputted to one of the AND circuit groups 6, 7, .

For example, ML, M, , = MM, M28MM7M2 t
> In the case of M B + M31, the image outline exists in the scanning line portion of the MM, that is, the second line, and the image area is on the ML side, so the halftone dot to be recorded is at the location corresponding to MM, that is, M21. This causes the OR circuit 15 to output a control signal so as to record only on the image area side using this image contour line as a boundary.

Specifically, the halftone dot exposure device is controlled based on the output of the OR circuit 15, and M2. Either delete the right half of the halftone dot (the side facing outside the image area) recorded at the position corresponding to Bye.

In addition, in the case of ML-MM, MM<MR, the image contour still exists in the second scanning line, or the image area is on the right MR side, so the OR circuit 16 outputs a control signal, and the left Either record the halftone dot with half removed, or shift the entire halftone dot to the right.

If ML>MMlMM>MR, ML<MM, MM<MR, or ML-MM-MR, it is not an image contour, so a normal halftone dot can be recorded based on the control signal from the OR circuit 17. .

In this way, all the image signal values of the second line and all the corresponding image signal values of the first and third lines are sequentially compared and recorded at the location on the photosensitive material corresponding to the second line of the original image. While obtaining a signal that controls the halftone shape to be
The picked up image signal values of the fourth line are sequentially written to the addresses of the memory device where the image signal values of the first line were written.

Similarly, for the second and subsequent scanning lines,
A control signal is obtained for each pixel.

By controlling the recording side of the image scanning recording device using this control signal, it is possible to record a halftone image having an outline faithful to the original image.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of the relationship between the original image and pixels when the original image is optically scanned and image signals are picked up. A schematic diagram showing the image signal value of each pixel divided into a number of pixels determined by the scanning line width in the direction, and the image signal value of each pixel written in each pixel. FIG. 4, which shows an example of a block diagram for creating a signal for controlling the shape, is a diagram showing in detail an example of the comparison circuit in FIG. 1 and FIG. 3. 1... Memory device, 2-... Selection circuit.

Claims (1)

[Claims] 1. When creating a halftone image by sequentially recording halftone dots corresponding to image signal values obtained for each unit pixel of each scanning line by photoelectrically scanning the original image sequentially in scanning lines, Among the image signal values corresponding to the plurality of scanning lines written in the memory device, the signal value of each unit pixel of the scanning line to be recorded is recorded in advance in the plurality of scanning lines written in the memory device. By reading the signal values of each unit pixel corresponding to the surrounding area and comparing these signal values, the image contour part in the original image is detected, and it is determined that the image contour part is included in each unit pixel of the scanning line to be recorded. In the case where the halftone dot is recorded based on the signal value of the unit pixel, the outer part of the image outline of the halftone dot is deleted or the position of the entire halftone dot is moved inward of the image outline. A method for recording a halftone image having limbus faithful to the original image, characterized by: