June '22

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G R A PH I C S - PR O.C O M 2 0 2 2 J U N E G R A P H I C S P R O 8 3 processing time is reduced. Furthermore, TIFF and PDF les are universal and can be opened or placed in any graphic soft- ware application. Images destined for web are usually saved as JPEGs (for photographic images) or GIFs for graphics with limited color and small animations and PNG 24, which has similar features of both JPEG and GIFF. COMMON FORMATS Here are breakdowns of the most com- mon image formats that you are likely to consider when saving a le. TIFF (Tagged Image File Format) is universal format can be lossless or lossy (see Fig. 1) A choice of image stor- age algorithms can be specied when sav- ing an image. Usually, TIFFs are saved ei- ther without compression or in a lossless scheme that applies limited compression called LZW (Lempel, Ziv, Welsch after the scientists who invented the format). TIFF is among the best quality output from digital cameras and for large-format prints. TIFF can also be used as a work-in- progress storage format because it supports most of image editing features including layers, alpha channels annotations, and color proles. TIFF images are not com- patible with web browsers. EPS (Encapsulated Postscript) and DCS (Desktop Color Separations) ese les are more or less self-contained PostScript documents that describe an im- age or drawing and can be placed within another document generated by a post- script compatible program like Adobe Illustrator, Adobe InDesign, or Corel- DRAW. At minimum, an EPS file contains a bounding box that contains the image de- scribed by the EPS encoding. A common use for EPS les is as clipping paths that knocks out a portion of an image dened by Bezier curves as in Fig. 5. Another type of EPS document is the DCS format that contains a ve channel EPS, including a channel for each CMYK color and a composite channel. DCS was invented by Quark Inc. and is used for creating color separations for oset lithog- raphy. PDF (Portable Document Format) PDF is a universal format for document exchange. Created by Adobe Systems in 1993, PDF is used to represent the ap- pearance of documents independent of the software in which they were created regardless of platform. A PDF le renders a complete description of a xed-layout, attened document, including the text, fonts, graphics, pictures, and other infor- mation needed to display it. It also con- tains CMYK information that can be used to create color separations. JPEG ( Joint Photographic Experts Group) Photographs and similar continuous tone- looking images that contain a large gamut of colors can be saved in JPEG format. JPEGs eciently compress images while allowing a choice of quality. JPEG can be expressed as either a four-letter extension or the three-letter JPG, depending on the platform. JPEG stores information as 24-bit color. At its highest quality it produces no com- pression, however the degree of compres- sion is adjustable. At higher compression levels it's dicult for the eye to discern any dierence from the original. Lower settings produce pixel clusters and artifacts that erode detail. JPEGs are useful for archiving attened images to read-only media. When they are opened, altered, and saved, however they can deteriorate with each saved version. ey are also useful for saving images to Fig. 5: oriina a n ir r a a an an pa in a top piin pro- ra a a ippin pat

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