JPH0449472B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is designed to set the ink supply amount for each ink key of an offset printing machine in advance by adjusting the picture area ratio of each ink zone corresponding to each ink key of an offset printing plate. The present invention relates to a picture area ratio measurement method for measuring picture area ratios, and particularly relates to correction of measured area ratios for printing plates with extremely few pictures, such as encyclopedias, books, and maps.

[Conventional technology]

Recently, in offset printing, an ``ink preset system'' has been widely introduced, which adjusts the amount of ink according to the pattern before printing to reduce paper waste at the beginning of printing. This is done by measuring the image area ratio on the printing plate in advance for each ink zone corresponding to the ink keys of the printing press, and then, based on the measured image area ratio, opening the keys of the ink keys of the ink fountain of the printing press. The amount of ink is determined before printing, and the amount of ink is adjusted according to the pattern before printing. This system has already been put into practical use for some time and is becoming established as a general printing technology.

However, the state of advance adjustment of the ink amount is not perfect, and in reality, it is essential to make fine adjustments manually at the start of printing. This can be caused by various factors such as the emulsification balance of ink and water, the transfer of ink to paper, and the measurement accuracy of the pattern area ratio. It can be said that it is impossible to completely perform an ink preset just by determining the amount.

For this reason, as seen in Japanese Patent Application Laid-Open No. 59-5910, ``A device for measuring the picture area ratio of offset printing plates,'' it Some attempts have been made to correct the image area ratio of printing plates by taking into account trends in ink consumption.

[Problem that the invention seeks to solve]

However, even with this correction method, ink presets will inevitably become unstable in printed matter with extremely few pictures, such as encyclopedias, where black characters are present throughout and color images are rare. In actual operation, there are problems in which this method does not go well. This is because the measurement accuracy of the pattern area ratio measuring device is insufficient in the highlight areas of the pattern (image area ratio is 5% or less) due to the grains of the plate material and the rubber material coated on the surface of the plate material to prevent oxidation. Possible causes are that it becomes extremely poor due to the influence of non-uniformity, and that it is difficult to balance the emulsification of ink and water on printing plates with few patterns. In addition, in printed materials with extremely few patterns, there is a large difference in the pattern area ratio between the black plate and other color plates even in the same ink zone, and it is difficult to determine the exact amount of ink depending on the area ratio measured using the same method. cannot be preset.

This invention was made in order to cope with the above-mentioned circumstances, and is a method for measuring the pattern area ratio to correct the measured value of the pattern area ratio in order to improve the effect of ink presetting on printed matter such as encyclopedias that have extremely few images. Its purpose is to provide a method.

[Means for solving problems]

According to the pattern area ratio measuring method according to this invention,
Different correction processes are performed on the pattern area ratios measured for the black version and other color versions. For black plates, if the area ratio calculated for each ink zone is below a certain value, correction will be performed by rounding up, and for plates other than black plates, if the area ratio for each measurement point is below a certain value, correction will be performed. The area ratio is set to zero, and if it is not below a certain value, it is assumed that there is a pattern, and when the area ratio of each measurement point is aggregated for each ink zone, the area ratio of the ink zone that includes the measurement point with a pattern is set to a constant value. [Operation] According to the picture area ratio measuring method according to the present invention, correction is made so as to avoid the following:
For black plates, the minimum value of the area ratio for each ink zone is guaranteed, so even if the image area ratio is small, characters can be printed with a high density, and for other color plates, background smear will occur. Since sufficient ink can be supplied to the difficult-to-print areas, high-quality printing is possible and the effect of ink preset is achieved.

〔Example〕

An embodiment of the pattern area ratio measuring method according to the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of a picture area ratio measuring device to which the method according to this embodiment is applied. Here, a laser scan method will be explained as an example of a method for measuring the picture area ratio, but the present invention can be applied to a television camera method, a sensor scan method, etc. without any problem.

In FIG. 1, in order to measure the pattern area ratio on the printing plate 1 for each ink zone 2 corresponding to the ink key, a laser beam from a laser light source 3 is scanned over the printing plate 1 in the X direction and the Y direction by a scanner 4. be done. Beam spot 5 irradiated onto printing plate 1
The reflected light is converted into an electrical signal proportional to the amount of reflected light by the photoelectric conversion element 6, converted into a digital signal by the A/D converter 7, and input to the CPU 8.

Control of the scanner 4 and sampling control of the A/D converter 7 are controlled by the CPU 8.

A calibration mark 9 indicating 0% white (no halftone dots) and 100% black (solid) is printed outside the picture area of the printing plate 1. CPU8 is 0% white (no halftone dot) in advance when measuring the pattern area ratio.
The 100% black (solid) area is measured in advance, and the partial picture area ratio data of the beam spot 5 is obtained from the ratio of the levels of the white level signal, black level signal, and output electric signal of the photoelectric conversion element 6. Calculate.
The CPU 8 totals this for each ink zone 2, and
Calculate the required pattern area ratio for each ink zone. The obtained pattern area ratio is set in the printing machine, the opening degree of the ink key of the ink fountain of the printing machine is determined, and the amount of ink is adjusted in advance.

Here, since the color of the printing plate 1 is green or blue, the laser light source 3 is a He-
A Ne laser is often used, a galvanometer mirror or a polygon mirror is often used as the scanner 4, and a photomultiplier is often used as the photoelectric conversion element 6 because the amount of reflected light is small.

By the way, as mentioned above, even if you calculate the image area ratio for each ink zone by simply adding the image area ratios for each beam spot 5, the ink preset will not work properly for printed materials such as encyclopedias that have extremely few images. is often ineffective.

Therefore, in this embodiment, as shown in FIGS. 2a and 2b, correction is performed when the pattern area ratio measured for each beam spot is totaled as the pattern area ratio for each ink zone.

An embodiment of the area ratio measuring method according to the present invention will be described according to the flowcharts shown in FIGS. 2a and 2b.

First, the presence or absence of correction is determined (S1). This can be done by an operator using an operation panel or the like. If there is no need for correction, normal measurement (the area ratio data of beam spots is totaled for each ink zone to determine the pattern area ratio of each ink zone) is performed.

If correction is necessary, it is determined whether the printing plate to be measured is a black plate (S2). In general, encyclopedias have very few pictures and other pictures, and most of the text is made up of fine black ink. Therefore, the black version and other colored versions (indigo, red,
It is necessary to distinguish between the two (yellow) and correct them.

Correction for the black version will be explained. At the start of the measurement, the printing plate 1 is scanned with a laser beam from the laser light source 3, and the pattern area ratio of each beam spot is measured (S3a). The pattern area ratio for each beam spot is totaled to calculate the pattern area ratio for each ink zone (S4).

The pattern area ratio calculated for each ink zone is 10%
Determine whether the following is true (S5). If it is not 10% or less, the pattern area ratio is set as the corrected pattern area ratio of the ink zone (S6), and if it is 10% or less, the corrected pattern area ratio of the ink zone is forcibly set to 10% (S7). Here, the threshold is not only 10%, but also
A value of 5-10% is suitable. This is because the actual pattern area ratio of ink characters is often 5 to 10%, and the pattern area ratio in this range is easily affected by the grain of the printing plate when measuring. This is because, considering the emulsification balance, it is known that ink presetting is more effective if the ink key is forcibly opened to a certain level.

As a result, black characters are printed clearly and stably.

Next, correction for color plates other than black plates will be explained. Here, too, at the start of the measurement, the pattern area ratio is measured for each beam spot (S3b). but,
Next, before totaling the pattern area ratio for each ink zone, the pattern area ratio for each beam spot is corrected.

In other words, the pattern area ratio for each beam spot is 10
% or less (S8). If it is less than 10%, the corrected pattern area ratio for each beam spot is forcibly set to 0% (S9). If it is not 10% or less, the value obtained by multiplying the measured value by 120% is set as the corrected pattern area ratio (S10). Here, the threshold is not only 10%;
A value of 5-10% is desirable. As mentioned above, this value takes into consideration the influence of the grain of the printing plate. Also, the multiplication value is not limited to 120%, but may be a value of 100 to 150%. This is a correction that takes into account the image area ratio and ink emulsification balance of color plates other than black plates in the encyclopedia. As a result, ink supply is reduced to zero for white backgrounds to prevent background smearing, and sufficient ink supply is ensured for picture areas, allowing high-quality printing.

After multiplying the measured value by 120% and setting it as the corrected pattern area ratio (S10), a bit (flag) indicating that a pattern is present is set at the corresponding address in the pattern presence/absence table (S11). This is to eliminate the influence of grain on printing and to use the presence or absence of a pattern for correction, and it is sufficient to provide flags only for addresses corresponding to each ink zone in the pattern presence/absence table. As a result, it becomes possible to determine whether a pattern exists or not in each ink zone based on the pattern presence/absence table.

Next, the pattern area ratio for each beam spot is totaled, and the pattern area ratio for each ink zone is calculated (S12). Referring to the pattern presence/absence table, it is determined whether a pattern exists or not for each ink zone (S13). If there is no pattern, the pattern area ratio of the ink zone is set to 0% (S14).

For an ink zone with a pattern, it is determined whether the pattern area ratio of that ink zone is 3% or less (S15). If it is 3% or less, the pattern area ratio of the ink zone is forcibly set to 3% (S16), and if it is not 3% or less, the pattern area ratio of the ink zone is left as is (S17).

As a result, the pattern area ratio of the ink zone with the pattern is at least 3%. Even if the emulsification balance of ink and water is taken into consideration, the amount of ink supplied to areas with few images is compensated, so the effect of ink presetting is further improved. Here, the threshold value is not limited to 3%, but is preferably about 2 to 5%.

By performing such processing, the effect of ink presetting can be considerably improved for printing printed materials such as encyclopedias.

In this embodiment, the vibration of the ink roller is further corrected. The inking mechanism of a general printing press consists of a combination of many metal rollers and rubber rollers, and the ink source roller with an ink key passes through multiple rolling rollers and is applied to the plate surface of the plate cylinder by an ink forming roller. This is due to the supply of ink. Even if ink is applied to the ink source roller in a stepwise manner, the thickness of the ink film becomes sinusoidal as it passes through the rolling rollers. Therefore, the opening degree of each ink key does not correspond one-to-one to the pattern area ratio of each ink zone. This embodiment performs correction taking this into consideration.

First, it is determined whether the pattern area ratio of the ink zone is 0% (S18). If it is not 0%,
The value as it is is set as the corrected pattern area ratio (S19).

If it is 0%, it is determined whether the left and right ink zones are 0% (S20). If it is 0%, it is assumed that there is no pattern at all, and the pattern area ratio of the ink zone is set to 0% (S19). If there is a pattern on either the left or right side, in order to compensate for the influence of vibration of the ink roller, the corrected pattern area ratio is the value obtained by multiplying the larger pattern area ratio of the left and right ink zones by 25%. (S21). This is because the ink supplied to each ink zone through each ink key tends to escape to the adjacent zone where it is consumed.
This is to utilize this to ensure that ink is stably supplied to the plate cylinder. Here, the value to be multiplied is 25
%, but 20-50% has been found to be suitable.

As explained above, according to this embodiment, if the area ratio calculated for each ink zone is below a certain value for black plates, correction is made by rounding up, and for plates other than black plates, each For each measurement point, correction processing is performed to emphasize the image area ratio at each measurement point, and then each correction data is aggregated for each ink zone to determine the area ratio. By performing different corrections on the picture area ratio measured in , an effective ink preset can be made even for printing plates with extremely low picture area ratios, such as encyclopedias.

Although the present invention has been described above based on specific embodiments, the present invention is not limited to the above embodiments, and as long as the purpose is similar, the effects of ink presetting can be obtained in the same way, so various modifications can be made. It is possible.
Further, in the above embodiment, the correction was performed by program processing using a microcomputer, etc., but there is no problem if similar processing is realized by a circuit configuration.

〔Effect of the invention〕

As explained above, according to the present invention, in printed matter such as an encyclopedia with extremely few pictures,
The effect of ink preset is that it is possible to measure the pattern area ratio by taking into consideration the influence of grain of the printing plate, the emulsification balance of ink and water, the vibration of the ink roller, the degree of ink characters, etc. is significantly improved compared to the conventional method.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a picture area ratio measuring device to which an embodiment of the picture area ratio measuring method according to the present invention is applied, and FIGS. 2a and 2b are flowcharts showing the picture area ratio measuring method according to this embodiment. be. 1... Printing plate, 2... Ink zone, 3... Laser light source, 4... Scanner, 5... Beam spot, 6... Photoelectric conversion element, 7... A/D converter,
8...CPU.

Claims (1)

[Claims] 1. In order to preset the ink supply amount for each ink key of the printing press according to the area ratio of the printing plate, the area ratio for each measurement point measured at each point on the printing plate is aggregated for each ink zone. In the pattern area ratio measuring method that calculates the area ratio for each ink zone, it is determined whether the printing plate to be measured is a black plate, and for the black plate, the area ratio calculated for each ink zone is below a threshold value. In this case, the first constant value is used as the aggregate value of the area ratio of the corresponding ink zone, and for plates other than black plates, if the area ratio of each measurement point is less than the first threshold determined for each color, the corresponding ink zone is used. The area ratio of a measurement point is set to zero, and if it is not below the first threshold, the measurement point is considered a pattern point, and when the area ratio of each measurement point is totaled for each ink zone, the ink zone including the pattern point is totaled. A pattern area ratio measuring method characterized in that when the value is less than or equal to a second threshold value, the second constant value is used as the total value of the ink zone.