To copy a picture, the key is to have a good manuscript. This is almost axiom. Unfortunately, the manuscript is often very good, and the printed copy is not very good. The manuscript, which does not look like much, has been reproduced with good results after proper processing. Why is that? Although there are many reasons, I think the points mentioned in this paper are the main reasons. The so-called satisfactory copying effect is the ability to copy as much of the original content as possible. This mainly depends on a wide gradation space! The shape of the dot and the number of screen lines are the main factors that must satisfy the minimum gradation space required for the entire copying process.
What is the relationship between the number of circular dots, elliptical dots, and the number of lines in the screen and copying tone space? Regardless of the network point, once the screen number of the screen is set, the center position of the screen point is determined. For a circular or elliptical dot, the maximum diameter or long axis is the center distance of the adjacent lines. Moreover, the maximum area of ​​each of the two mesh points is also determined and proportional to the center distance of the mesh lines. As for the proportion of the size, for elliptical mesh points depends on the ratio of the major and minor axes. This conclusion is precisely the central issue of this article. The area surrounded by the center lines of the four largest area dots has a large space occupied by circular dots and a small space, while the duty cycle of the oval dots is just the opposite. With regard to the duty ratios of the two types of outlets, it is intuitively easy to see that the copying capacity of the elliptic outlets at the fine end of the black field is stronger than that of the circular outlets. Then reduce this maximum area to 1%. It should not be hard to imagine that the ability of elliptical dots to replicate at the finer end of the white field is stronger than that of the circular dot. Because it is also under the condition of 1% outlets. The elliptical dots can duplicate the white field more precisely than the circular dots. Since the circular dot network, whether white or black, is less delicate than the elliptical dot, the advantage of the elliptical dot is clear. However, this kind of analysis is at best theoretical and ideal. At best, it can be done in computers. There is also a practical application problem.
For the current prepress printing process, the processing results in the computer must be converted into film by a laser photocopying machine and then printed into a printing plate. The entire prepress processing process is completed. In the computer processing process, it is necessary to go through two processes of laser photocopying and printing. Both of these processes are photosensitive processes and each have their own development and fixing requirements. These requirements relate to the concentration of each liquid, the temperature, and the duration of developer fixation. The power supply and a series of uncertainties derived from the power supply have different degrees of influence on the entire physical processing process. All of these, as long as one or more of them are uncertain, the problem will arise. The most common problem (taking Yang pictures as an example) is that the film density (blackness) is not enough. If you use a film with a density that does not meet the requirements of the normal printing plate (positive PS plate) and print it according to the normal printing parameters, it is not hard to imagine what consequences will be caused by the dots on the plate. What's more, there are many variable factors derived from such things as plate, power supply, light source, vacuum, developer, etc. during the printing process. The result becomes difficult to estimate. However, one thing is certain: due to the above-mentioned many variable factors, the outlets that come out after processing are more or less lost. Especially in the film where the density does not meet the requirements, the loss of the outlets is not more or less a problem. Although the loss of outlets exists throughout the pre-press processing process, relative control of these uncertain factors is directly related to the extent of network loss, especially in the printing process.
Also take the positive film, PS version as an example. Assume that all the steps before the printing, the formation of the network, forming there are not any problems, including the film density is not enough, the loss of the site all occurred in the printing process. The print loss is assumed to be 3% dot (line). For the assumed 3% here, we must make some necessary explanations: First, it represents a 3% outlet (line); in addition, it also indicates that the outer edge of the outlet (line) with more than 3% is equivalent to 3% of the outlet ( Point) a circle of width. This fixed circle is determined by the performance of the platen and the plate used and the corresponding developer. But the width of the "fixed circle" is linked to the added network cable and it becomes undecided. It is not known because it is equal to a few percent of dot diameter or cable width. Therefore, for the convenience of narrative, it is easy to assume that a relatively specific figure is more intuitive. This is 3%.
The explanation given above for 3%, specific to the loss of the printing plate, means that the outlets (lines) below 3% of the printing plate are dried out and lost. Only up to 4% of the outlets can be sun dried. In other words, an area that should have 3% or below of the outlets was lost to the prints. The outlets that were supposed to be 4% were left with only 1% of outlets. Now, we can see only this 1% point. And what is the point of this 1% point: For the circular point, there is no difference between the long axis and the short axis, so it is evenly scaled down in proportion, and there will be 1% of the dots; The elliptical point is not the case. If the ratio of the length of the elliptical point to the length of the minor axis is set to 4:3, then the 4% of the original elliptical spot sunrayed on the plate will not be 1%, but it will be completely sunless! Because the short axis length of this point is exactly the diameter of a circular 3% dot. According to the 3% "Note", it was all lost. So, although the long axis has 1% numerically, the short axis is already zero. This is the situation at the end of the white field.
At the black end, because the entire copying process is a systematic project that includes all the contents of a series of processing processes from prepress to postpress, the maximum dot resolution of the relevant printing press must be given as the processing basis of the previous process. . The maximum resolution of the print outlets given here is assumed to be 75%. 75% is the critical value of the print at the outlet/field. Reference is also made to FIG. 1 for the sake of illustration, and it is assumed that the print loss of the dots is still 3% as shown in FIG. 2 . In this way, if you want to get a good copying effect at the fine end of the black field, if you use a circular dot, the dot size of the black end can not be greater than 78%. Under the same conditions, if the ratio of the long axis to the short axis is still 4:3 elliptical dots, what is the critical value of the black field at the dot/field? First, compare the blanks between the two dots on the minor axis line between the circular and elliptical dots. Calculate the proportions of the major and minor axes. The calculation results show that the elliptical dot gain is 78% multiplied by (1/4) twice the gap of about 40% compared to the circular dot. This result shows that the two minor edges of the elliptical dot on the short axis line can increase the short axis by nearly 20% at the same time as the space occupied by 78% circular dots. This means that when using an elliptical dot, the size of the dots can reach almost 100% under such conditions as the duty ratio is basically the same. Of course, this result is only for elliptical dots with a ratio of 4:3 for the long axis and the short axis. At the same time, as the minor axis increases, the long axis also increases in the same proportion. With the increase of the number of outlets in the direction of the long axis, the outlets have become "solid" in the direction of the long axis. And the area of ​​the "solid line" also increases with the increase of the long axis. In fact, given the maximum resolving power of the outlets, the outlets are already at the critical point of the outlets/fields in the direction of the long axis. However, even if the size of the elliptical dot has reached close to 100%, there will be a blank “line†that can be distinguished in the direction of the short axis as the 78% circular dot. Moreover, the total area of ​​this "line" is even greater than the "line" of a circular dot. Regardless of whether or not it actually achieves such an ideal result in practical applications, it is certain that the ability of the elliptical dot to replicate at the black end is much stronger than that of the circular dot. There is no doubt that the gradation space in the black field is larger than the gradation space in the circular dot. As for the magnitude of the post-hoc expansion of the tone space, it depends on the ratio of the length and the short axis of the elliptical dots used.
To sum up, the advantages and disadvantages of the “round talks†on circular and elliptical outlets and the number of screens they add are as follows:
Circular outlets: The disadvantages are the poor copying ability at the black end of the site, and the small space for copy reproduction. However, the white field end is better at copying than elliptical ones, and it is also less likely to have a net out.
Oval outlets: The biggest advantage is that it has a large space for reproduction. The disadvantage is that the white field end of the copying ability is worse than the round point in practical application. In addition, the whole gradation space of the circular dot is shifted backwards, and the white dot end is more likely to produce a net stop than a circular dot. Especially when the number of screen lines is high, the white field end is more likely to be out of network. In addition, the higher the number of screen lines, the more unavoidable is the white-field end of the network and the gradation space corresponding to the absolute network segment. This must be given full attention
What is the relationship between the number of circular dots, elliptical dots, and the number of lines in the screen and copying tone space? Regardless of the network point, once the screen number of the screen is set, the center position of the screen point is determined. For a circular or elliptical dot, the maximum diameter or long axis is the center distance of the adjacent lines. Moreover, the maximum area of ​​each of the two mesh points is also determined and proportional to the center distance of the mesh lines. As for the proportion of the size, for elliptical mesh points depends on the ratio of the major and minor axes. This conclusion is precisely the central issue of this article. The area surrounded by the center lines of the four largest area dots has a large space occupied by circular dots and a small space, while the duty cycle of the oval dots is just the opposite. With regard to the duty ratios of the two types of outlets, it is intuitively easy to see that the copying capacity of the elliptic outlets at the fine end of the black field is stronger than that of the circular outlets. Then reduce this maximum area to 1%. It should not be hard to imagine that the ability of elliptical dots to replicate at the finer end of the white field is stronger than that of the circular dot. Because it is also under the condition of 1% outlets. The elliptical dots can duplicate the white field more precisely than the circular dots. Since the circular dot network, whether white or black, is less delicate than the elliptical dot, the advantage of the elliptical dot is clear. However, this kind of analysis is at best theoretical and ideal. At best, it can be done in computers. There is also a practical application problem.
For the current prepress printing process, the processing results in the computer must be converted into film by a laser photocopying machine and then printed into a printing plate. The entire prepress processing process is completed. In the computer processing process, it is necessary to go through two processes of laser photocopying and printing. Both of these processes are photosensitive processes and each have their own development and fixing requirements. These requirements relate to the concentration of each liquid, the temperature, and the duration of developer fixation. The power supply and a series of uncertainties derived from the power supply have different degrees of influence on the entire physical processing process. All of these, as long as one or more of them are uncertain, the problem will arise. The most common problem (taking Yang pictures as an example) is that the film density (blackness) is not enough. If you use a film with a density that does not meet the requirements of the normal printing plate (positive PS plate) and print it according to the normal printing parameters, it is not hard to imagine what consequences will be caused by the dots on the plate. What's more, there are many variable factors derived from such things as plate, power supply, light source, vacuum, developer, etc. during the printing process. The result becomes difficult to estimate. However, one thing is certain: due to the above-mentioned many variable factors, the outlets that come out after processing are more or less lost. Especially in the film where the density does not meet the requirements, the loss of the outlets is not more or less a problem. Although the loss of outlets exists throughout the pre-press processing process, relative control of these uncertain factors is directly related to the extent of network loss, especially in the printing process.
Also take the positive film, PS version as an example. Assume that all the steps before the printing, the formation of the network, forming there are not any problems, including the film density is not enough, the loss of the site all occurred in the printing process. The print loss is assumed to be 3% dot (line). For the assumed 3% here, we must make some necessary explanations: First, it represents a 3% outlet (line); in addition, it also indicates that the outer edge of the outlet (line) with more than 3% is equivalent to 3% of the outlet ( Point) a circle of width. This fixed circle is determined by the performance of the platen and the plate used and the corresponding developer. But the width of the "fixed circle" is linked to the added network cable and it becomes undecided. It is not known because it is equal to a few percent of dot diameter or cable width. Therefore, for the convenience of narrative, it is easy to assume that a relatively specific figure is more intuitive. This is 3%.
The explanation given above for 3%, specific to the loss of the printing plate, means that the outlets (lines) below 3% of the printing plate are dried out and lost. Only up to 4% of the outlets can be sun dried. In other words, an area that should have 3% or below of the outlets was lost to the prints. The outlets that were supposed to be 4% were left with only 1% of outlets. Now, we can see only this 1% point. And what is the point of this 1% point: For the circular point, there is no difference between the long axis and the short axis, so it is evenly scaled down in proportion, and there will be 1% of the dots; The elliptical point is not the case. If the ratio of the length of the elliptical point to the length of the minor axis is set to 4:3, then the 4% of the original elliptical spot sunrayed on the plate will not be 1%, but it will be completely sunless! Because the short axis length of this point is exactly the diameter of a circular 3% dot. According to the 3% "Note", it was all lost. So, although the long axis has 1% numerically, the short axis is already zero. This is the situation at the end of the white field.
At the black end, because the entire copying process is a systematic project that includes all the contents of a series of processing processes from prepress to postpress, the maximum dot resolution of the relevant printing press must be given as the processing basis of the previous process. . The maximum resolution of the print outlets given here is assumed to be 75%. 75% is the critical value of the print at the outlet/field. Reference is also made to FIG. 1 for the sake of illustration, and it is assumed that the print loss of the dots is still 3% as shown in FIG. 2 . In this way, if you want to get a good copying effect at the fine end of the black field, if you use a circular dot, the dot size of the black end can not be greater than 78%. Under the same conditions, if the ratio of the long axis to the short axis is still 4:3 elliptical dots, what is the critical value of the black field at the dot/field? First, compare the blanks between the two dots on the minor axis line between the circular and elliptical dots. Calculate the proportions of the major and minor axes. The calculation results show that the elliptical dot gain is 78% multiplied by (1/4) twice the gap of about 40% compared to the circular dot. This result shows that the two minor edges of the elliptical dot on the short axis line can increase the short axis by nearly 20% at the same time as the space occupied by 78% circular dots. This means that when using an elliptical dot, the size of the dots can reach almost 100% under such conditions as the duty ratio is basically the same. Of course, this result is only for elliptical dots with a ratio of 4:3 for the long axis and the short axis. At the same time, as the minor axis increases, the long axis also increases in the same proportion. With the increase of the number of outlets in the direction of the long axis, the outlets have become "solid" in the direction of the long axis. And the area of ​​the "solid line" also increases with the increase of the long axis. In fact, given the maximum resolving power of the outlets, the outlets are already at the critical point of the outlets/fields in the direction of the long axis. However, even if the size of the elliptical dot has reached close to 100%, there will be a blank “line†that can be distinguished in the direction of the short axis as the 78% circular dot. Moreover, the total area of ​​this "line" is even greater than the "line" of a circular dot. Regardless of whether or not it actually achieves such an ideal result in practical applications, it is certain that the ability of the elliptical dot to replicate at the black end is much stronger than that of the circular dot. There is no doubt that the gradation space in the black field is larger than the gradation space in the circular dot. As for the magnitude of the post-hoc expansion of the tone space, it depends on the ratio of the length and the short axis of the elliptical dots used.
To sum up, the advantages and disadvantages of the “round talks†on circular and elliptical outlets and the number of screens they add are as follows:
Circular outlets: The disadvantages are the poor copying ability at the black end of the site, and the small space for copy reproduction. However, the white field end is better at copying than elliptical ones, and it is also less likely to have a net out.
Oval outlets: The biggest advantage is that it has a large space for reproduction. The disadvantage is that the white field end of the copying ability is worse than the round point in practical application. In addition, the whole gradation space of the circular dot is shifted backwards, and the white dot end is more likely to produce a net stop than a circular dot. Especially when the number of screen lines is high, the white field end is more likely to be out of network. In addition, the higher the number of screen lines, the more unavoidable is the white-field end of the network and the gradation space corresponding to the absolute network segment. This must be given full attention
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