File Formats

View or download a PDF file of this article: PDF (128k)

This outline should serve as a brief background on file formats and their uses at Primary Color. While the subject may seem dry, it is important to the successful production of a project to be aware of file formats and their influence on the final product.

At Primary Color, we have opted for application level trapping. We are currently researching a more automated approach to trapping, however we have not been satisfied with the trade-offs and the effect on the quality of our work.

Graphic files are either vector or bitmap (raster) format. Vector images use a mathematical formula to draw shapes and gradients. Bitmap images are composed entirely of raster data, commonly referred to as pixels.

Vector files include type, illustrations and AutoCAD files. Raster files include digital photos and scans made from photos, transparencies, or reflective artwork.

Definitions

EPS: Encapsulated Postscript is a standard format for importing and exporting postscript language files in all environments. It usually describes an illustration but it can contain any combination of text, graphics and images. The purpose of the eps file is to be included as an illustration in other PostScript language page descriptions. This is Primary Color's default file format for images.

TIFF: Tag Image File Format designed to promote the exchange of digital image data. It has been defined with primarily desktop publishing and related applications in mind. It is intended to be independent of operating systems, filing systems, compilers and processors. It is considered a rich format within which image data can be exchanged among various applications.

PDF: Portable Document Format designed to capture all image and text data in one file and make it device independent. These files have been "normalized" to eliminate PostScript page and device dependencies. The files can be viewed on any platform using the Acrobat Reader.
.
Tiff/IT-P1: Tag Image File Format for Image Technology. A locked, ripped, raster file format usually in three parts. (Based on old CEPS workflow of .lw and .ct with a .flyt "flight" file to put the two together). Tiff/IT files usually contain a .ct file for continuous-tone images, a high resolution .lw file for type and lineart, and a low resolution .fp placement file. Tiff/ITs may contain .hc files instead of .lw files in order to handle complex blends, define edges, and trapping. Tiff/IT maximizes the compatibility between CEPS and DTP systems.
.
PostScript: A page description programming language suited to graphic production applications and the de facto standard in our business.

CT: Continuous Tone picture data refers to all data rasterized for the image.

LW: Line Work refers to the raster data that is for fills and lines. Also includes type in a rasterized state.

HC: High resolution contone refers to raster data that defines edges and traps.

RIP: Raster Image Processor Creates on off signals needed to image plate or film.

CEPS: Color Electronic Prepress System: Early digital proprietary systems used to separate and output film, e.g. Scitex, Chromocom.

Delta List: Proprietary file format for Heidelberg prepress system used here at Primary Color. 100% raster file, highly compressed, full resolution. It contains instructions for the rip on screening. It is a locked format and is good for ROOM workflow.

DCS: Desktop Color Separations. These are pre-separated eps files. dcs-1 files are composed of five separate files, while dcs-2 files can also be saved as a single-file format. dcs-2 can optionally contain spot color channels.

JPEG: Joint Photographic Experts Group. A file format that uses a lossy form of compression. Data compression methods (jpeg) that selectively discard repetitive information to decrease file sizes. Depending on the amount of compression requested, the lost information may or may not be noticeable. At rates of 25:1 the results are easily seen.

PICT: Originated as a vector format specifically created for the Macintosh. Current implementations have support for separate raster and vector layers in color depths up to 24 bit.

OPI: Open Prepress Interface allows for the placement of low resolution files in the page layout program and it links to the high resolution image when the job is being ripped. Keeps down the size of the layout file, facilitates faster printing of output devices.

ROOM: RIP Once Output Many: A workflow designed to interpret the data once and render it as many times as need be for digital proofs, film or plate.

NORM: Normalize Once Render Many: A workflow suited for pdf production that normalizes the data once and lets the file be rendered as many times as need be for output.