Printer Command Language

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The Printer Command Language ( PCL ; German printer command language ) is a command language for controlling printers . It was developed by Hewlett-Packard with the aim of being able to control all printer types using a common standard language.

PCL is based on escape sequences and in its complexity lies between ASCII plain text (which only allows the simplest teletype commands , such as line feed ) and PostScript (a separate, complex programming language for describing pages ).

During the dot matrix printer era, the Epson command set ESC / P (Epson Standard Code for Printers) still dominated. PCL has largely replaced this standard.

history

PCL development began in the early 1980s. The basis was u. a. the control commands of the graphics-capable intelligent terminals of the type HP 2648 (1979) and subsequent models. Their instruction set represents a subset of the PCL, which is still understood today by PCL-compatible printers.

Versions

During the further development, care was taken to ensure that the new PCL version contains the previous version as a subset and only extends it - the versions build on each other. They are therefore referred to as a level. The underlying philosophy was that simple printers should understand PCL Level 1, for example, which kept production costs low. More complex devices, on the other hand, should be equipped with higher levels according to their capabilities, but at the same time not only understand the old commands, but also be able to implement them identically. In addition, the PCL specifies that unknown commands (such as color selection on a black and white device) should simply be ignored.

PCL 1 to PCL 5

The versions PCL 1 to PCL 5e / c are command-based languages ​​whose command sequences are processed and interpreted in the order in which they arrive in the printer. The data stream is normally generated by a printer driver, but it is also possible to have PCL instructions created by your own applications.

  • PCL 1 was introduced in 1984 with the HP ThinkJet 2225 and supports printing of text and graphics with a resolution of up to 150 dpi .
  • PCL 1+ was released together with the HP QuietJet 2227.
  • PCL 2 added processing of electronic data.
  • PCL 3 was introduced along with the first HP LaserJet in 1984. This version supports raster graphics fonts and increases the maximum resolution to 300 dpi. PCL 3 is still used in most HP inkjet printers today.
  • PCL 3+ (monochrome, "mono") and PCL 3c + (colored, "colo (u) r") were later used for the HP DeskJet and HP PhotoSmart printers.
  • PCL 3GUI is used in HP DesignJet printers. It uses a compressed raster format and is not compatible with other PCL-3 standards.
  • PCL 4 appeared with the HP LaserJet II in 1985, adding macro programming, larger bitmap fonts, and graphics to the standard.
  • PCL 5 appeared in 1990 with the HP LaserJet III. The standard was expanded to include the "Intellifont" font scaling (developed by Agfa ) and support for HP-GL / 2 (vector) graphics.
  • PCL 5e (PCL 5 extended, "enhanced") was released in October 1992 together with the HP LaserJet 4. It extends the standard to include bi-directional communication between printer and PC and support for Windows fonts. PCL5e also supports double- sided printing .
  • PCL 5c appeared in 1992 with the HP Color LaserJet family. It contains the functionality of PCL 5e, but has been expanded to include color and palette commands.

PCL 6

PCL 6 was introduced in 1995 and consists of:

  • PCL 6 Enhanced : A completely new, compressed page description language that is syntactically in no way related to the previous PCL versions. Formerly known as PCL XL .
  • PCL 6 Standard : Equivalent to PCL 5c or 5e to ensure compatibility with old PCL versions.

The structure of PCL XL can best be thought of as a binary XML document. Like PCL 5c, PCL XL maps those GDI objects that are required for print output. In PCL XL, however, the constant context changes between PCL and HPGL are no longer necessary, as one language is used for text, graphics and raster objects. In PCL XL, an explicit grayscale color space for raster data and foreground colors was introduced, with which achromatic gray can be combined with colored objects. With the exception of RGB, XL separates itself from all other color spaces of PCL5c, some of which are only implemented in individual printers. The maximum resolution of transferred raster objects has been increased to 1200 dpi. With JFIF, a strong raster compression method was also introduced in protocol class 2.2.

The PCL-5c component of PCL 6 is backwards compatible with earlier versions. It is thus possible to address a printer that works under PCL 6 with a PCL 3 printer driver.

Jet ready

Jet Ready is a simplified version of PCL XL, which is used in HP laser printers in the lowest price range. PCL XL has been stripped of all objects except JFIF. This created a new low-level printer language based on an existing syntax. The transmitted JFIF images must have exactly the format that is normally transferred from the RIP to the print engine. This makes it possible to transfer the image information preprocessed in the computer to the output hardware without a raster process in the printer. With the introduction of Jet Ready, slimmed-down versions of the well-known office laser jets on existing hardware and software could be made affordable for home users. The bypass process for JFIF in laser printers is currently still subject to patents from HP.

Available color models

  • CIELab : Is no longer supported by HP as an addressable color space in PCL5c printers today. This color space is usually used as a reference color space in color management and is still available in the Océ Production PCL according to the original PCL5c specification.
  • CMY : According to the HP specification, this is exclusively a DeviceCMY color space. At best, this is suitable for color printing, since without color management you cannot tell which color is assigned to a CMY triplet. Some manufacturers rely on the sRGB for color management here.
  • Gray : Can only be addressed directly in PCL5c in dithered form or as a shaded pattern for foreground color objects. Using the Monochrome Printing Mode Command, however, real gray levels can be displayed in raster graphics. For this purpose, the real grayscale image (with only one 8-bit pixel component, i.e. 256 shades of gray) is sent to the printer in indexed by pixel mode. A suitable RGB palette has been sent to the printer beforehand, which it in turn converts into a grayscale palette due to the monochrome printing mode command. The driver of the purely monochrome HP9000 PCL5c printer, which can process all PCL5c data in grayscale, works according to this procedure.
  • RGB : represents the main color concept of PCL 5c. In the early days of PCL 5c there was a colorimetric (parameterized) and a device RGB color space. Today this concept has been changed in favor of real color management with ICC profiles to the use of the sRGB profile. (Some Production PCL dialects, such as from Océ or Xerox , support the free choice of ICC-RGB profiles, which is particularly useful with regard to production-independent document creation.)
  • YCbCr : Was included in the original PCL5c specification, but according to the HP Laserjet Comparison Guide it was only installed in a single printer type and is therefore no longer relevant for PCL5c today. (In PCL6 and systems that allow JPEG passthrough, this color space is implicitly contained in the JPEG format)

PCL in high-performance printing

Océ ColorStream 10000

Manufacturers such as Konica Minolta , Unisys , Xerox , Canon - Océ , Ricoh or Lexmark offer PCL in their high-performance and mid-range production printers. PCL is extremely efficient and is therefore particularly suitable for controlling machines that can print more than 1000 pages per minute. Such systems are used, for example, in transaction printing by banks, insurance companies and authorities.

PCL from Sato

Sato , manufacturer of label printers , also called its command language PCL in the past. However, this has nothing in common with the PCL from Hewlett-Packard. It was later renamed SBPL (first as an abbreviation for Sato Basic Programming Language , later Sato Barcode Programming Language ).

Individual evidence

  1. ↑ http://computermuseum.informatik.uni-stuttgart.de/dev/hp2648/
  2. ↑ https://web.archive.org/web/20151122184353/http://download.brother.com/welcome/doc002907/Tech_Manual_Y.pdf CHAPTER 1 INTRODUCTION - 3

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