Recently I attended a seminar in Atlanta on Postscript Level 2. Adobe and Agfa were both represented, and in the course of the day I not only learned a great deal about Postscript in general, but about many other new products as well.
In the Mac world most designers are aware of Postscript — the page description language that creates illustrations and type which print at the highest resolution possible, independent of the output device. It is Postscript that has caused the desktop publishing profession to exist, and it is the improvements to Postscript which have allowed the industry to grow, as designers forced their desktop publishing equipment to do more and more difficult jobs.
Postscript was developed in 1985 by Adobe Systems as a general programming language and a page description language. As a page description language it could describe the appearance of text, graphics, and even images. But what really made Postscript great was the Postscript Interpreter which was first built into the Apple LaserWriter™. In the years to follow, Adobe developed interpreters for many devices, allowing Postscript to work independently of the output device. A designer’s artwork would print at 300 dpi on his/her laser printer and at much higher resolutions on the service bureau’s imagesetter.
Postscript Level 2 is simply an enhanced version of Postscript which includes several new features such as Display Postscript, composite fonts, and color extensions. Level 2 has also standardized the programming environment for software developers. Now programmers can simplify drivers that create Postscript code, causing there to be fewer instructions. Jobs that previously failed will probably run to completion using Postscript Level 2.
There were also improvements made to the Postscript Level 2 Interpreter which make it more efficient and much faster. Level 2 has also improved the virtual memory manger and garbage collection routines which increases the amount of memory available. Level 1 had a preset restriction of 1500 points per path regardless of the available memory. Level 2 does not have that restriction, reducing the number of limit checks.
Another efficiency improvement occurs when color separation files are created. In Postscript Level 1, separations had to be created before they could be sent to the printing device. This caused 4 files (CMYK) to be processed. With Level 2 the separation occurs within the RIP (Raster Image Processor). Because only one file must be processed, performance is improved.
Beyond memory and speed improvements, there have also been additions of features which improve quality and production abilities. One such added feature is composite fonts. These are huge character sets such as non-Roman alphabets or sets that need to include more than 256 Roman characters. This feature is obviously Postscript’s step into the international market, now allowing oriental languages to be produced as Postscript fonts.
Another feature, called forms, is a great time saver for the user. A form is any combination of graphics, text, or images no matter how complex or simple. The forms feature is the ability to cache forms in memory in a format defined for speed and reuse. This allows a user to quickly reproduce logos or other commonly used images throughout his/her system.
A couple of quality improvements are Adobe Accurate Screens and Device Independent Color. Accurate Screens allows for the generation of halftone screens with more accurate screen angles and frequencies. This reduces the chances of moiré patterns, which is especially important to designers working in 4-color process.
Another problem which makes working in CMYK on the desktop difficult is the inconsistency of color from one output device to another. The designer’s screen may show one color, the color proofing printer may print something different, and the final printed piece created from imageset separations may still be another color. This makes it incredibly difficult for a designer to maintain any type of color consistency.
Postscript Level 2 has incorporated a mechanism which describes color in a color coordinating system. The color the designer sees on his/her RGB screen can now accurately be linked to the coordinating color on a CMYK output device. Each output device can describe color through the color coordinating system instead of its own colorants. This system allows for the closest possible match from machine to machine.
Postscript Level 2 also includes filters for compression such as JPEG (for color images), LZW, and CCITT Group 3 and 4. A nice feature of JPEG compression is that it can be adjusted. The higher the compression the less resolution after decompression. At certain compression rates no information is lost, but higher ones result in information loss.
Many Mac users are already taking advantage of Postscript Level 2. Many laser printers are already equipped with Level 2 Interpreters. There is no problem running Level 1 files on a Level 2 printer. Adobe was very careful about keeping Postscript Level 2 compatible with Level 1. Both Level 1 and Level 2 files run on both types of interpreters. Level 2 is a true superset of Level 1; therefore there is no problem converting information between the two.
Adobe is pushing forward the creation of new software and hardware devices which are making our lives easier. But it is the designers’ push forward which has caused this to happen. As users try to force their equipment to produce more difficult jobs with increased quality, the industry has pressed forward to meet those demands. Postcript Level 2 is just one example of how the industry has pushed to keep up with users’ increasing demands.
Misty Spinelli
Assistant Professor of Art
Jacksonville State University
Jacksonville, Alabama
(Misty is also an ex vice president of the Savannah Macintosh Users Group)
