AFP and Color – a Duet?
The AFP document format undoubtedly has a number of advantages processing high document volumes. AFP is very much in favor with user communities due to its comprehensive and flexible resource management capabilities and compact datastream. Product and application developers appreciate the thorough, well documented AFP architecture. But how useful is this datastream in dealing with color? What capabilities does the AFP architecture offer color applications in a production environment?
As the main force behind the development of the AFP architecture, IBM founded the “AFP Color Consortium” in October 2004. Closely coordinated with IBM, a body of printer hardware manufacturers, software and applications developers (including by the way Compart) are attempting to create a unified system platform for production color printing. In the meantime, the basic work has been completed and with agreement from a number of key users, the initial draft of the extensions to the AFP architecture should be passed sometime in 2006. The goal is a complete open standard for precision, repeatable high-quality color printing.
Whereby, the current AFP specification already supports the use of color. Firstly, within the OCA[1] architecture every object may have a color attribute, the “OCA Color” selected from a list of predefined colors. The specification includes 19 colors, from the various RGB[2] values through to special colors such as the “Color of Medium”. This allows for the selection of color beyond the standardized color index. The “Extended Colors“ were added later, comprising in addition to “OCA Color“ also ”Highlight Color“ and various color spaces such as RGB (additive color mix), CMYK[3] (subtractive color mix), and CIE-Lab[4] (device independent color space). ”Highlight Color“ can be selected by simply activating the appropriate attribute. The actual color used is decided upon in the output device, for example by the use of special toner in a printer.
Additional possibilities for using color in AFP can be selected within the framework of the IOCA[5] Specification for color images. The use of images in AFP documents has a long history. Over time, many new specifications and extensions have been added in the form of “Function Sets” (abbreviated “FS”). In this context, a quick review of the more interesting Function Sets produces the following list:
· FS10: Integration of black and white images
· FS11: Image compression (FAX G4 and MMR)
· FS20: Integration of color images, including among other forms JPEG
· FS42: Introducing extended colors and image tiles
· FS45: Introducing a layer concept with various resolutions.
Special emphasis here is placed on the layer concept and the possibility of storing different layers at different resolutions (MRC – “Mixed Raster Content“). This means color images can be stored so they produce a good optical impression, without requiring a lot of storage space. Thereby it is for example possible to save the less important background in low resolution and the foreground in high resolution.
In a more recent development, AFP additionally offers the possibility of working with “Object Containers”. The following list provides an overview of the object classes which can be used within an object container.
· Images (TIFF or JPEG)
· PDF documents
· PCL documents or macros
· PostScript documents or code
Object containers can be embedded as blocks in AFP documents. The content of an object container is not interpreted by applications processing AFP. Meaning embedded objects can of course contain color information!
As with other object types, references to object containers can be created by various methods: The object can be included in a datastream (“inline” or “self contained”) or presented as an externally referenced file. The externally referenced object can be “Raw Data” or already be in an AFP package”. In this case the encompassing AFP records must already exist, and if required, properly segmented (the maximum valid record length of an AFP document is dependent on the local installation).
Entirely new operations are possible using this mechanism. Embedded objects can be integrated into existing AFP workflows. The content must not necessarily be evaluated for this to happen. Which means the conversion of the referenced object from its original format to AFP is not required, the embedded object can be held in its original format. The complete datastream is converted (once only) to the required final format (AFP, PostScript, PCL …) just before final printing.
Likewise imprecise conversions during the workflow are minimized, normally resulting in small data volumes, since the object is left in its “optimal” format. An example of this approach is the integration of pre-prepared PDF documents in AFP datastreams. This is the way in which complex, full color marketing brochures find their way through existing AFP workflows.
But, just being able to pass along color information is not enough. When handling input and output devices, evaluating color information (“Color devices”) always raises questions about color spaces supported by a particular device. A color space is a collection of colors, recognized or produced by a device (scanner, screen, printer, etc., the eyes are also such a “device”) under a given set of conditions. As a consequence, color spaces associated with input and output devices need to be aligned. The color space of an input device is firstly transformed in the “objective” device independent LAB set. The LAB color space (also written as L*a*b color space) has its beginnings in the color models developed by the Commission Internationale d`Eclairage (CIE) in the 1930s. On the output side, the device independent color space is transformed into the color space used by the specific output device.
Color space transformation is described in the standard profiles. These profiles stem from the efforts of the International Color Consortium (ICC). The ICC began life in 1993 with the goal of unifying color management systems. Named after the organization, the ICC profiles have become an accepted, standardized method of describing device color characteristics. To make the point, every good quality printer comes with its associated ICC profile. Using an ICC workflow is illustrated in the following diagram:
The integration of ICC workflows in the AFP specification is one of the missions of the AFP Color Consortium.
In many cases, applications cover the need to handle color processing of external resources. Examples of this are color page segments and overlays, or colored text and vector graphics. Nowadays, bringing color to these type of applications can be achieved with relatively simple means. This provides for the integration of color images e.g. in the form of logos in AFP datastreams. For external image objects, this occurs by way of a simple item substitution with the full color image. For example, in a DCF[6] environment the text color can be set from various color spaces with the “.dc” command. We have seen by using some of the current capabilities of the AFP specification it is literally possible “to bring color to applications”.
Conclusion
There are a myriad of workflow applications, built on the core structures of AFP. Many of these applications are concerned with the preparation and restructuring of datastreams directed towards output. Some of the most important examples are:
· Post optimization
· Application of control information
· Document separation and collection
· Document sorting
· Meta data processing
· Archiving
· … and many more …
Considering the investment made by companies in the large number of applications in use year in - year out, it is reasonable to assume they want to continue using these applications. The concept of the object container aspires to meet this goal, since full color document segments can be processed within existing workflows. Conversion of the AFP datastream, together with its embedded objects, to the required target format is only done right at the end of the process chain, immediately before the final step. This protects existing investments while at the same time being able to take advantage of a modern color architecture.