Page Description Languages - PDL
Earlier on in history, printers viewed text as text, and graphics as graphics. A page was created from a combination of separate entities. The page images can be created by having raw text like, the word "Hello World", combined with Escape codes and possibly embedded graphic pictures. Different programs have different file formats.
To overcome this problem, Page Description Language (PDL) is developed. PDL is a language to describe the layout or graphical representation of ink and toner on sheets of paper (or other output devices, like monitors, photo typesetters, etc) in a higher level than an actual output bitmap.
Instead of sending raw text to the printer, a PDL output file is created and sent to the printer. Basically PDL describe the page in vector form -- that is, as mathematical values of geometric shapes, rather than as a series of dots (a bitmap image). It instructs the printing device exactly how to handle text, graphics, and pictures in reproducing the page layout created by a computer user. The 'page' could be of any size, color, or resolution the printing device can handle. The printer itself takes the vector images and converts them into a bitmap page.
By having PDL, an application programmer could concentrate on making his program to output result in a standard PDL - with description of his printable page. The printing device developers could focus on making their devices with related PDL literate.
Various PDL exist. The primary printer languages these days are Hewlett Packard's Printer Command Language (PCL) and Adobe's Postscript. Other example of PDL are "UFR" (from Canon), “ESC/P” (from Epson) and GDI (“Graphical Device Interface” from Microsoft).
the host computer creates the dot array itself, so
Low cost printers often use "host based" print techniques. In this system, the computer driver makes a bitmap image and transmits this to the printer. The printer controller does not have to process anything -- it just sends the dot instructions on to the laser. However, the host computer CPU are busier and memory are much loaded than they would be with a conventional printer language.
PDL files can be textual or binary data streams. If a printer supported the related PDL, it means that there is a specialized processor within the printer is functions as an interpreter for that particular PDL. This PDL interpreter will processes the supplied file and creates the requested page image. The printer's drawing engine then takes the image and draws it on the page.
The appearance of these PDL eased life, and facilitated further development for everybody.
To overcome this problem, Page Description Language (PDL) is developed. PDL is a language to describe the layout or graphical representation of ink and toner on sheets of paper (or other output devices, like monitors, photo typesetters, etc) in a higher level than an actual output bitmap.
Instead of sending raw text to the printer, a PDL output file is created and sent to the printer. Basically PDL describe the page in vector form -- that is, as mathematical values of geometric shapes, rather than as a series of dots (a bitmap image). It instructs the printing device exactly how to handle text, graphics, and pictures in reproducing the page layout created by a computer user. The 'page' could be of any size, color, or resolution the printing device can handle. The printer itself takes the vector images and converts them into a bitmap page.
By having PDL, an application programmer could concentrate on making his program to output result in a standard PDL - with description of his printable page. The printing device developers could focus on making their devices with related PDL literate.
Various PDL exist. The primary printer languages these days are Hewlett Packard's Printer Command Language (PCL) and Adobe's Postscript. Other example of PDL are "UFR" (from Canon), “ESC/P” (from Epson) and GDI (“Graphical Device Interface” from Microsoft).
the host computer creates the dot array itself, so
Low cost printers often use "host based" print techniques. In this system, the computer driver makes a bitmap image and transmits this to the printer. The printer controller does not have to process anything -- it just sends the dot instructions on to the laser. However, the host computer CPU are busier and memory are much loaded than they would be with a conventional printer language.
PDL files can be textual or binary data streams. If a printer supported the related PDL, it means that there is a specialized processor within the printer is functions as an interpreter for that particular PDL. This PDL interpreter will processes the supplied file and creates the requested page image. The printer's drawing engine then takes the image and draws it on the page.
The appearance of these PDL eased life, and facilitated further development for everybody.
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