Graphic File Formats
CT and LW (Continuous Tone and Line Work files): Scitex two-part file format. Photoshop will open and save files in Scitex CT format. CT and LW are also used generically when referring to continuous tone or black and white (line work) files.
DCS (Desktop Color Separations): Developed by Quark, this extension of the EPS format creates a 5-part file: a low-resolution image for placement and one file each for Cyan, Magenta, Yellow and Black.
EPS (Encapsulated PostScript):
Photoshop EPS files: Scanned images must be saved in EPS format if a clipping path is used to drop out a background, if the image is in Duotone mode (a Monotone, Duotone, Tritone, or Quadtone), or to preserve "transparent whites" in a bitmap image. The TIFF format creates smaller files and is preferable to EPS for CMYK scanned images that don't require EPS format. Graphics may be saved in the five-part EPS-DCS format for separations.
EPS files from other applications: Applications vary on how they write an EPS file and its preview image. Avoid "nested" EPS files (one EPS imported into a file to create another EPS file). If an application doesn't create an "editable" EPS file, always include the original source file(s) used to create the EPS.
PDF (Portable Document Format): File format developed by Adobe Systems, Inc. that allows file sharing across platforms. A PDF can be generated by any application and viewed with Acrobat Reader, a free application. There are a variety of ways to save a PDF, such as low-resolution RGB for screen viewing, medium resolution RGB or CMYK for laser printing, or high-resolution CMYK for print. Currently, the preferred format for print is PDF/X-1a. Although PDFs are typically used as stand-alone files for printing, viewing, and annotating, they can also be placed into page layout applications as a graphic, just like a TIFF or EPS. Because of its reliability and the fact that the creating software is not required to view or rip a PDF, this format has become the dominant standard for printers and publications.
PICT (Picture format): Mac only. This format is not suitable for print, and we strongly recommend against using it in files intended for color separated plates or film.
TIFF (Tagged Image File Format):
Mac or PC; can be saved in a variety of sub-formats:
Bitmap TIFF: Tonal values are captured as either black or white based upon the threshold setting when scanned or converted. This format is primarily used for line art. Minimum resolution for quality line art scans is 1200 ppi.
CMYK (Cyan, Magenta, Yellow, Black) color TIFF: Format for four-color reproduction or for imaging to digital color proofing devices. Although some imaging devices can convert RGB files "on-the-fly," it is preferable to convert them to CMYK before placing in a page layout application.
Grayscale TIFF: Up to 256 levels of gray can be captured to reproduce high-quality black and white halftones.
RGB (Red, Green, blue) color TIFF: Used primarily for video or transparency output.
Tiff/It (Tagged Image File Format for Image Technology): File format designed for transferring ripped, trapped files from pre-press shops to printers. The basic format is Tiff/It; the commonly used variation of this format is Tiff/It P1 (Profile 1). Special software is required to create Tiff/It files.
Other Image Formats: CGM (Computer Graphic Metafile), PCS (Z-Soft PC Paintbrush format), TGA (Targa Image File), WPG (Word Perfect Graphics Metafile) and WMF (Microsoft Windows Metafile) are image formats, but not suited for print reproduction.
RASTER VS. VECTOR GRAPHICS
Raster graphics are images formed by pixels, such as a scanned image or a Photoshop graphic. Raster graphics are resolution dependent because the final image resolution is limited to how many pixels per inch are contained in the image.
Vector graphics are constructed of outlines that include fill and stroke instructions, created in applications such as Adobe Illustrator. Since vector graphics are not converted to pixels until the final imaging stage they are referred to as "resolution independent" because they are limited only by the format and resolution of the imaging device. Vector graphics are also referred to as object-oriented graphics.