PostScript: Flying DTPs
2018-07-08 05:01:00
Postscript is a programming language that describes text and images on a page. Postscript commands control a laser printer (or any Postscript device) to put a line of text, a circle, a Bezier curve, or a bitmap image in its designated place. Macromedia FreeHand, QuarkXPress, and Apple's LaserWriter software and drivers write Postscript commands to disk files and send the files to the printer. The printer's interpreter reads the Postscript commands and converts them into tags on the page.
Adobe originally launched the Postscript code, and many other companies later developed an interpreter that can read Postscript code. In the past few years, Adobe has released three versions of the Postscript language. These are Postscript, Postscript Leve1 2, and Postscript Leve1 3. However, many of today's imaging devices can only handle Postscript Leve1 2 commands, and only a few new imaging devices can handle Postscript Leve1 3 commands (including the ability to handle Adobe's own Acrobat PDF files and automatic printer trapping). Fundamentally, applications and drivers using Postscript Leve1 3 are few in order to be compatible with previous imaging devices.
First, the basic concept of page generation
Understanding how Postscript generates pages helps understand how desktop publishing applications work and knows why the output results are different from the expected results. Each time Postscript describes an object on a page, it may be a picture or some text. Each object is pressed on the previous one. For example, to create a text box in QuarkXPress, the text box has a white background in the field and the words "print technique". When outputting, the QuarkXPress and LaserWriter drivers convert the above content into Postscript code, which fills the rectangle with white and places the text on it. If the text includes operations such as kerning, Postscript may only place one character at a time. People often mistakenly believe that when the background of a text box is empty, the output of the QuarkXPress page takes more time. In fact, if the text box is transparent rather than white, the only difference is that the Postscript command does not need to fill the text box with white before placing the text. Therefore, the actual output of the transparent text box is faster.
Postscript is a non-transparent fill imaging mode, meaning that no matter what kind of page you place, the page placed behind will completely cover the page below it. For example, if you use Postscript to describe a 50% grayscale text box on a page and then put a 20% grayscale text box on top of it, then you wouldn't be able to get a 70% grayscale text box. Only see 20% gray text boxes.
When you place a soft shadow on an object in QuarkXPress, you cannot see the shadow effect. Because the top image completely obscured the image below. Therefore, any desktop application that provides a transparent effect must use a virtual method to achieve transparency when outputting.
Second, examples: remove the white box in the figure
Postscript is actually a very simple programming language. You can use a text editor to write or edit Postscript code, but do not use a word processor like Microsoft Word because it has a formatting process. The BBEdit editor at Bare Bones Software (http://) works well. It also allows you to quickly download Postscript to the printer in order to see the results.
Here we talk about a problem that is often encountered in practice. The QuarkXPress4.X version generates an EPS file slightly different from the previous version of QuarkXPress. It always leaves a white box at the last level on the page. It cannot place the EPS file on top of other images or make the background transparent. Only solve this problem by editing Postscript code.
figure 1
Figure 1 shows the effect before editing. When you open or place a QuarkXPress4.X EPS file in Photoshop (or other application software), the effect is that there is a white background frame on the image.
figure 2
Figure 2 shows the effect after editing. By editing the Postscript code of the EPS file, you can remove the white box and create a transparent image effect.
The editing steps are as follows:
1. Open the EPS file in a text editor, such as the BBEdit editor. Do not use word processing software such as Microsoft Word, because such software will make the text mess up by increasing the formatting process.
2. After opening, find the line "%% E-ndsetup" and you will immediately see the line "gnp clippath 1 HVG calcbnd".
3. "g, np, H," and other commands are all procedures that have been defined in the file. Delete the character "1 HV" and save the file. The role of these three characters is to generate a white box, "1" represents white, if you want to "1" into 0, the box becomes black.
If you put the EPS file in other applications, the preview effect will not be transparent, but when you output it to a Postscript printer or other imaging device, the desired transparency effect comes out.
Third, the mistakes in the explanation
Postscript is a very sensitive language. Even a small mistake can have serious consequences on the page. For example, the "Lineto" command draws a line from one page to another. If the computer has encountered an error while writing Postscript code, the computer may write this command as "Lneto". Since the interpreter cannot know what the "Lneto" command means, it will respond to the "Undefined Command" error accordingly. On older printers, the usual wrong command is "Limitcheck" because of an internal limit. For example, older imaging devices cannot handle long, complex Bezier curves. If you do not simplify the shape, the computer will return a "Limitcheck" error message.
To use the QuarkXPress or Adobe Pagemaker application software, in order to understand the exact meaning of the error, open the error-handling feature field of the Print dialog box. In other application software, you can open the pop-up menu General of the Print dialog box and select Error Handling. With these two open methods, you can get a page about the wrong command and the type of error message. If the command of "Undefined Command" is wrong, then there is a problem with the print stream. At this time, you may wish to reprint the output job; if you see the "Limitcheck" error message, then you'd better do your page content. Simplify processing.
Fourth, the future of Postscript
Although Postscript has long been a core technology for desktop publishing, prepress is now moving toward Acrobat PDF as the standard imaging language. However, the long-established Postscript language still has tenacious vitality, because Adobe originally designed the PDF features based on the Postscript language. Postscript language knowledge is still helpful to understand how Acrobat PDF works. Even to the extent that most imaging devices can read PDF files, PDF still requires the interpretation of the file (usually through a printer or imaging device driver) to become a Postscript file. Obviously, Postscript will not be out of date.
Adobe originally launched the Postscript code, and many other companies later developed an interpreter that can read Postscript code. In the past few years, Adobe has released three versions of the Postscript language. These are Postscript, Postscript Leve1 2, and Postscript Leve1 3. However, many of today's imaging devices can only handle Postscript Leve1 2 commands, and only a few new imaging devices can handle Postscript Leve1 3 commands (including the ability to handle Adobe's own Acrobat PDF files and automatic printer trapping). Fundamentally, applications and drivers using Postscript Leve1 3 are few in order to be compatible with previous imaging devices.
First, the basic concept of page generation
Understanding how Postscript generates pages helps understand how desktop publishing applications work and knows why the output results are different from the expected results. Each time Postscript describes an object on a page, it may be a picture or some text. Each object is pressed on the previous one. For example, to create a text box in QuarkXPress, the text box has a white background in the field and the words "print technique". When outputting, the QuarkXPress and LaserWriter drivers convert the above content into Postscript code, which fills the rectangle with white and places the text on it. If the text includes operations such as kerning, Postscript may only place one character at a time. People often mistakenly believe that when the background of a text box is empty, the output of the QuarkXPress page takes more time. In fact, if the text box is transparent rather than white, the only difference is that the Postscript command does not need to fill the text box with white before placing the text. Therefore, the actual output of the transparent text box is faster.
Postscript is a non-transparent fill imaging mode, meaning that no matter what kind of page you place, the page placed behind will completely cover the page below it. For example, if you use Postscript to describe a 50% grayscale text box on a page and then put a 20% grayscale text box on top of it, then you wouldn't be able to get a 70% grayscale text box. Only see 20% gray text boxes.
When you place a soft shadow on an object in QuarkXPress, you cannot see the shadow effect. Because the top image completely obscured the image below. Therefore, any desktop application that provides a transparent effect must use a virtual method to achieve transparency when outputting.
Second, examples: remove the white box in the figure
Postscript is actually a very simple programming language. You can use a text editor to write or edit Postscript code, but do not use a word processor like Microsoft Word because it has a formatting process. The BBEdit editor at Bare Bones Software (http://) works well. It also allows you to quickly download Postscript to the printer in order to see the results.
Here we talk about a problem that is often encountered in practice. The QuarkXPress4.X version generates an EPS file slightly different from the previous version of QuarkXPress. It always leaves a white box at the last level on the page. It cannot place the EPS file on top of other images or make the background transparent. Only solve this problem by editing Postscript code.
figure 1
Figure 1 shows the effect before editing. When you open or place a QuarkXPress4.X EPS file in Photoshop (or other application software), the effect is that there is a white background frame on the image.
figure 2
Figure 2 shows the effect after editing. By editing the Postscript code of the EPS file, you can remove the white box and create a transparent image effect.
The editing steps are as follows:
1. Open the EPS file in a text editor, such as the BBEdit editor. Do not use word processing software such as Microsoft Word, because such software will make the text mess up by increasing the formatting process.
2. After opening, find the line "%% E-ndsetup" and you will immediately see the line "gnp clippath 1 HVG calcbnd".
3. "g, np, H," and other commands are all procedures that have been defined in the file. Delete the character "1 HV" and save the file. The role of these three characters is to generate a white box, "1" represents white, if you want to "1" into 0, the box becomes black.
If you put the EPS file in other applications, the preview effect will not be transparent, but when you output it to a Postscript printer or other imaging device, the desired transparency effect comes out.
Third, the mistakes in the explanation
Postscript is a very sensitive language. Even a small mistake can have serious consequences on the page. For example, the "Lineto" command draws a line from one page to another. If the computer has encountered an error while writing Postscript code, the computer may write this command as "Lneto". Since the interpreter cannot know what the "Lneto" command means, it will respond to the "Undefined Command" error accordingly. On older printers, the usual wrong command is "Limitcheck" because of an internal limit. For example, older imaging devices cannot handle long, complex Bezier curves. If you do not simplify the shape, the computer will return a "Limitcheck" error message.
To use the QuarkXPress or Adobe Pagemaker application software, in order to understand the exact meaning of the error, open the error-handling feature field of the Print dialog box. In other application software, you can open the pop-up menu General of the Print dialog box and select Error Handling. With these two open methods, you can get a page about the wrong command and the type of error message. If the command of "Undefined Command" is wrong, then there is a problem with the print stream. At this time, you may wish to reprint the output job; if you see the "Limitcheck" error message, then you'd better do your page content. Simplify processing.
Fourth, the future of Postscript
Although Postscript has long been a core technology for desktop publishing, prepress is now moving toward Acrobat PDF as the standard imaging language. However, the long-established Postscript language still has tenacious vitality, because Adobe originally designed the PDF features based on the Postscript language. Postscript language knowledge is still helpful to understand how Acrobat PDF works. Even to the extent that most imaging devices can read PDF files, PDF still requires the interpretation of the file (usually through a printer or imaging device driver) to become a Postscript file. Obviously, Postscript will not be out of date.
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