PostScript (PS) – Precursor of PDF and still popular in the control of small to industrial printing systems
PostScript (PS) is a programming language to describe document pages using geometrical objects, i.e., raster images, vector graphics, fonts, and shading. PS documents are almost completely device-independent and can be sent to printers, copiers, screens, etc. The document therefore needs to be converted into picture elements page by page during output. This requires a PostScript interpreter, also known as a Raster Image Processor (RIP). It processes the PostScript instructions and does not create the required picture elements until output to ensure that the best possible printed image is always created on the selected output device. The advantage: a page described in this way is largely deviceindependent and can be enlarged as required without creating "saw-tooth distortion". PS files can also be output on all common platforms – using a Mac or PC – without the program used to create the document.
Since its creation in the 1980s, PostScript has developed into a standard for the management of small to industrial printing systems and remains popular today. In the printing industry, PS was the common format for document files for a long time, but has recently been overshadowed by its successor, the portable document format or PDF. PostScript was particularly successful because this language was one of the first of its kind for device-independent saving of electronic documents. The Postscript language supports mathematical calculations and logical operations in formulas used to generate output objects.
Programs commonly used in the prepress stage and in advertising agencies, such as QuarkXPress, Photoshop, Illustrator, and InDesign, still support PostScript.
The PostScript specification includes the following color spaces:
1. Device-dependent color spaces
- These can be used to add color values to the page descriptions that are specially adapted to control a specific output device. The disadvantage: The appearance of colors on another device can deviate significantly.
- DeviceGray: Definition of a grey-level value on a scale of 0.0 (black) to 1.0 (white)
- DeviceRGB: Definition of the three values in the RGB color model on a scale from 0.0 (none) to 1.0 (maximum intensity). The RGB model is based on the colors red, green and blue in an additive mixture.
- DeviceCMYK: Definition of the four values in the CMYK color model on a scale from 0.0 (none) to 1.0 (maximum intensity). CMYK is based on the colors cyan, magenta, yellow and black in a subtractive color mixture.
2. CIE-based color spaces
- PostScript supports the CIE XYZ and CIELab color spaces, among others, which were developed by the international organization CIE (Commission internationale de l’eclairage) and are commonly used for general purposes in the graphics industry. These two color spaces code colors on the basis of human perception rather than a special input or output device. CIE values are therefore device-independent.
3. Special color spaces
- Separation and DeviceN color spaces enable spot colors to be described.
Compart’s MFFPOS filter is a formatting tool to support PostScript during both input and output processes.
Compart’s MFF filters (mixed format filter) are the basis of the MFF architecture for DocBridge products. Some MFF filters read files in different formats (input filters) while others are used to write files in the respective output format (output filters). In many cases, a format is supported for both input and output.
The strength of the Compart MFF architecture is its ability to quickly and effectively convert documents in various formats into others, or integrate them into a document using a specific format. For example, documents in AFP, SAPGOF or PCL can be converted to PDF and can also be merged into a single PDF document.
When converting one format into another, Compart uses the shared object format, the so-called presentation area (PA), which is able to represent the visual data and metadata of all supported formats. An MFF input filter converts an input file into the PA format in main memory and an MFF output filter then converts the PA format saved in main memory into an output file.
PostScript Conversion Directions
A complete overview of all supported input and output formats is provided in the Compart Matrix. Compart software solutions enables highly complex, single pass operations with flexibility and reliability for high availability, high volume environments.