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RSS OnLine: File Formats

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Folks Sure Find Themselves Confounded By Them!

A Look @ File Formats

Graphic File Formats. I could go on forever and list the most esoteric, remote formats known to mankind but, it only makes sense to me to discuss those I am likely to use in my lifetime, as that may also be your situation as well.

Graphic file formats, at the top of the categoric hierarchy, come in to flavors:

Vector. These are the most powerful and flexible, but also tend to be the least used at the mainstream level. Vector graphic formats create, execute and store their images as mathematical calculations of descriptions and coordinates. The PostScript® page description language does this, as do drawing programs such as Adobe Illustrator® and Macromedia Freehand®.

The most well-known of the vector formats is EPS or EPSF (for Encapsulated PostScript format). An image created as an EPS vector can be created any size and yet scale up or down and retain full resolution. In other words, you can create an EPS image that measures 2 pixels by 2 pixels and blow it up 800% and it will not get jagged, either on-screen or upon printed output. Speaking of the latter, an EPS file will conform to the resolution of the output device; that is, it will output at 600 dpi on a 600 dpi laser printer, or even rise to 2,540 dpi on an imagesetter. The only exception would be an output device that does not contain a PostScript interpreter, as EPS is based on the PostScript language. Therefore, a gorgeous EPS image sent to a $100 inkjet printer will output at only 72 dpi, even if the inkjet is a 1440 dpi device. Without a PostScript engine in the printer (or a software interpreter loaded on the computer), the PostScript information cannot be interpreted, leaving the printer to recognize only the 72 dpi representation of the image that is created for presentation to the computer monitor's screen.

Not all EPS files are vector files, however. Some applications and graphic utility programs allow a pixel-based (see "Raster," below) to be saved as an EPS file that is "EPS for Placement" or "Placed EPS" representation of the file. No application I know of is capable of taking a drawing that was not created from inception as a vector file and save it as an editable EPS. Just as Adobe Photoshop® can save its pixel-by-pixel images as EPS, when this is done the EPS is a "faux EPS" for placement and sizing only. (This "faux eps" is also of value in Photoshop for saving a clipping path within an otherwise continuous-tone image file.)

Other vector formats include:

  • DXF. Most often found in CAD applications such as AutoCAD or ArchiCAD. One of the better EPS-to-DXF converters, and vice versa, was found in a program called SmartSketch™ that was released in 1995, and has laid mostly dormant since; to my knowledge, it may be unavailable. The company, Future Wave, was started by the same Charley Jackson that established Silicon Beach Software in 1985, one of the Mac pioneers.

  • WPG. A basic vector format created by WordPerfect Corporation in the early 1990s. Not a bad format, as it kept file sizes small, but its adoption has been limited by its proprietary source (as well as the bumpy road that WordPerfect has taken since the corporation was abandoned and the product became an orphan).

  • MacDRAW PICT. Remember this defunct Apple program? The grand-daddy of vector programs that was packaged alongside its pixel-based, raster sibling, MacPaint. Of similar capability as WPG, it is neither as precise or powerful as DXF or EPS.

  • CVS.Created by Deneba Systems for their application, Canvas. Gives Canvas distinct powers, but is a largely proprietary format.

  • DCS. DCS stands for Desktop Color Separation. It is a file format that is based on the EPS file format. DCS files act, in large part, as a collection of EPS files. DCS, as a version of the standard EPS format, lets you save color separations of CMYK (Cyan-Magenta-Yellow-Black) or multichannel files.

    The main advantage of DCS over its parent EPS file format is that it adds a kind of OPI (Open Prepress Interface)-functionality to the file format. Since DCS files contain separate EPS-files for each plate, an application can generate and print color separations faster when the DCS format is used. This was of particular value when desktop computers and their software were not as powerful as they are today and when all output was done from the lay-out application. In today's world of in-rip separations as well as improved support of EPS-files within applications like QuarkXPress, DCS can actually be a very inefficient file format.

  • PDF
  • PDF. In the strictest sense, Portable Document Format is not considered a graphic file format to purists. But I mention it here, as it will be the default "image distribution" format for Apple since Mac OS X (OS Ten) was released in 2001. It is a format that permits anyone with a free PDF Viewer/Reader to review someone else's work with full design integrity, regardless of what application the file was created in. PDF is derivative of Adobe's PostScript PDL (page description language), complete with vector information, but is more readily viewable and editable. A mainstream file-distribution format on the Web and fast-becoming a powerful, consistent workflow format for the pre-press industry.

  • WMF. A Windows MetaFile format (hence,'WMF'), this is what EPS files are often converted to in the Windows world, as Windows still is largely PostScript-ignorant and only higher-end Windows apps, (such as Illustrator, obviously) fully recognize and support EPS in the world according to Bill Gates.

Graphic images on the Web should soon evolve to take advantage of the power of vectors (Macromedia's Flash and Adobe's SVG, to mention two of t hem), where small files can yet render large, high-resolution images. But, in the mean time, if pixel-based images are most common in print, they almost exclusively dominate image presentation on the Web. So read on.

Raster. If vector programs are usually "drawing" programs, then raster applications tend to be considered "painting" programs. Just as Van Gogh used to paint a brush point or dot at a time, raster applications create their images a pixel (based on "picture element") at a time. While most raster formatted images can be reduced from their original proportions and hold resolution fairly well, don't try blowing them up. They are defined by their number of pixels and blowing up the image makes the pixels get bigger, degrading the image. Some programs will permit you to resample the image, and thereby redefine them with more pixels per inch, but this is still no substitute for the power of the vector. The most common raster formats are as follows:
  • BMP. A Windows-based BitMaP format, not unlike TIFF, but far less universal. Photoshop-friendly, however, so it does have some cross-platform virtue, albeit limited.

  • GIF. A Compuserve®-trademarked format for online transmission and display of pixel-based images. These files are generally small, and images best saved as GIFs are line art, those containing solid blocks of color, and lacking in continuous tone, gradient-type images. Limited to 256 colors, GIF files work well in the 216-lookup table listing of Web-friendly colors.

  • JPEG. Also seen as "JPG" (for Windows extensions that prefer to abide by the "8.3" convention, thereby limiting JPEG to three letters: "JPG). A format developed by the Joint Photographic Expression Group, it is popular for Web use with continuous-tone (read: photographic) images, but is less appropriate for use in print, as it achieves its economic file sizing by being a "lossy" format — it eliminates image data from the file that it believes is redundant or unnecessary.

  • PCX. A pixel-based Windows "paint" format that was quite prominent in the early 1990s, a bit less so today.

  • PICT and PICT2. An early Apple default file format, PICT is limited to 72 dpi, black-and-white images only. PICT 2 is a limited enhancement that supports color. This is the graphical layer — QuickDraw® — of the traditional Mac OS, through OS 9.2.2 ... it has been replaced by the PDF 1.4-based Quartz graphical layer in the new, UNIX-based OSX.

  • PNG. Designed to eliminate the need for GIF (and any royalties due CompuServe), this Portable Network Graphics format is far more potent and flexible than GIF, retaining all of GIF's latest improvements (such as GIF89a transparency) while adding features, such as full 8-bit and 24-bit color palette options. Not yet mainstream, nor is it supported well in many browsers, if at all. Some day, however, this may be the de facto graphics standard on the Web — that is, unless vector formats take over, which they well might (Macromedia's Flash and Adobe's SVG).

  • TIFF. The Tagged Image File Format is, perhaps, the most cross-platform-friendly of file formats, at least for the printed world (obviously, JPEG and GIF speak fluently on the Web for all platforms). Created by Aldus Corporation about the time of PageMaker's inception, TIFF supports one-bit (i.e., black-and-white) to eight-bit color, high-resolution images for output to PostScript and non-PostScript output devices alike. Windows-based TIFF files often have a different byte-order than Mac ones, however, and occasionally cause viewing problems on-screen; also some Windows apps don't like TIFF images that have been LZW-compressed, while all Mac programs aren't the least-bit bothered by a TIFF file that has had some its "air" vented out of it. (Some folks refer to file compression as taking the "air" out of a file.)

As you may be able to tell, this page has been posted in unfinished form. But, hey, that's the Web: always evolving, never done. I'll get back to this soon, however (as if you're actually waiting for it). But, for now, the most common graphic file formats are here for digestion and discussion. But there's yet more where this came from; and then there's non-graphic file formats — a new arena of potential confusion.

Perhaps that can be explored at an even more distant point in the future.