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Too many suffixes so little time...
Here's a list of basic file formats used in vector and raster graphics and where they work and when they don't.
Every one of these file formats does some kind of squishing of data. Your life will center on how to make that the least problem. "Lossless" compression techniques lose the least amount of data and color. "Lossy" compression techniques take out some "irrelevant" or "hardly used" data and throws it away. If you have a critical color or detail, be assured the great demigods of encapsulated postscript will deem that the byte they toss is exactly what you wanted to keep...
RLE
Run Length Encoding; lossless, used in creating TIFFs and several PhotoShop file formats. Also seen in a few Windows documents.
LZW
Lemple-Zif-Welch; lossless, used in creating PostScript formats like TIFFs, PDFs, and GIFs. This compression can play havoc with some Mac programs but is easily "undone" in Photoshop. Makes for smaller files, but uncompresses a bit slower. In fact Photoshop is the best program to swap to and from LZW.
Named for Abraham Lempel, Jakob Ziv, and Terry Welch, scientists who developed the algorithm for compressing raster files.
It's actually a dictionary based algorithm that scans the file for "like" sequences of pixels and assigns them an entry in the "dictionary", then each recurrence of that pixel (which is really just a colored block, not a specific virtual item) isn't stored as much as it is referenced. So let's take a sample from above and run an LZW compression of the text. Everytime the "pixel" for the word BUT is used it would become a dictionary reference, say #. The word FOR becomes %. The word IS becomes *. The word PROGRAM would be $. The word IN would become ~. The word PhotoShop becomes @, etc. Unique or one-time use word pixels aren't compressed per se.Uncompressed:
Mac programs but is easily "undone" in Photoshop. Makes for smaller files, but uncompresses a bit slower. In fact Photoshop is the best program to swap to and from LZW.Compressed:
Mac $s # * easily "undone" ~ @. Makes % smaller files, # uncompresses a bit slower. ~ fact @ * the best $ to swap to and from LZW.
JPEG
Joint Photographic Experts Group; lossy technique used in creating JPEGs, PDFs and several PostScript formats. Good for continuous tone images (Photographs).
CCITT
French acronym for "International Telegraph and Telekeyed Consultive Committee; lossless used in creating black and white images. PostScript compatible.
ZIP
Lossless technique used in creating Windows documents. Most effective for images with large areas of single color.
Windows standard "Bitmap" that works in several color modes (RGB, Indexed, and grayscale). Does not work if you hope to use alpha channels. Limited to 1-, 4-, 8-, or 24-bit color. Not a great choice for offset printing and/or non-PostScript printers.
Desktop Color Separations created by the geniuses at Quark. It acts like an EPS file until you really need it to. Supports CMYK color separations. DSC 1.0 doesn't work with alpha channels. DSC 2.0 does.
Encapsulated PostScript. Works great for both vector and raster work and is supported by nearly every layout and graphics application out there. It is a PostScript based file (obviously) so you can use several color modes (CMYK, RGB, Indexed, duotones, Lab, bitmap color modes, and grayscale). Does support clipping paths. Does not print well on low-end inkjet color printers that are not PostScript compatible.
Used for RGB animation and for Adobe Premiere movie files. If you do any resizing resampling, or removing channels, you won't be able to save it back as a Filmstrip file. Save to EPS or PhotoShop document, then export to filmstrip again.
A Kodak creation for making large and in charge high resolution files. PhotoShop can deal with them, but it is not optimized for them. Flashpix supports both grayscale and RGB, but no alpha channels.
Graphics Interchange Format. A great little web-based compression format--but it chooses its own colors and doesn't care what you want. The GIF library of color is all of 256 shades. That's it. And you thought PMS colors were limiting to your artistic expression. It is set up to create optimized, low weight files perfect for the high download speed needs of the World Wide Web. Don't try to print from it. No alpha channels. The people that created this format still hold a kind a patent on it, so that they actually license its use.
Interchange File Format. An Amiga creation used with the Video Toaster transfer world of Commodore Amiga Systems. Basically an IBM paint program. Supports several color modes (RGB, Indexed, bitmap, and grayscale). No alpha channels.
Joint Photographic Experts Group. Good for the web, can be easily converted to CMYK for printing. Watch that resolution though, just because a video monitor only needs 72 dots per inch to fool your eye, doesn't mean that coarse of a screen will be considered better than the worst newspaper printing you've ever paid for. Acts like a GIF but doesn't toss out colors--it tosses selective bits of "redundant" data. Works so well you don't even realized it is a "stuffed" or "zipped" file.
An old Windows document that may or may not allow all the colors you hope to use. Does support RGB and indexed colors. Grayscale too, but no alpha channels, no custom colors. Not a good format for offset printing.
Portable File Format. Adobe Acrobat's answer to all things portable! In reality it matches all one billion fonts available to its own library, so don't be surprised if GildedAge looks a lot like Garamond. It takes JPEG/GIF-like of photos and graphics. Does a great job making pages of info from applications like PageMaker. PhotoShop can open each page for page at a printable resolution, but only by rasterizing every element. Does a horrible job with color separations unless you are going full color. No alpha channels. If you really want it to work you have to read the directions and learn to embed (I know I hate that word too) the fonts, use the correct resolution photos, and actually create the right spot colors way back in the drawing-vector-based-graphics stage. But I know you can do it!
Supports Alpha channels, RGB, grayscale, and bitmap color. Supposed to be good for transferring files and graphics between layout applications. PICT Resources is new and only available for the Mac OS.
Specifically designed to make exchange files for animation done on PIXAR computers. So if you're not working on a sequel to Toy Story or Bug's Life don't bother.
Portable Network Graphics. Acts like a GIF without those nasty patent and licensing fees. Better than GIF in that you can have transparencies. Supposedly better than GIF's in color support. Works with grayscale, RGB, and indexed colors. Alpha channels define transparent areas and then need to be deleted before saving the final PNG. When saving chose "Adam7" to let you see what is happening. Compression demands a "filter"; Sub optimizes horizontal bands, Up is best for vertical bands and patterns. Average takes a guess. Paeth helps adjacent color compressions. Adaptive looks and chooses for you.
Flexible, uncooked format supports CMYK, RGB, and grayscale. Alpha channels too. Doesn't always pop open a file when you attempt to open an unknown file using this format in Photoshop, but it is worth a try.
Continuous Tone by Scitex. Great for high end computing power when making big critical color jobs. Make sure you have the power to use it. BIG files are created with this format. Handles CMYK, RGB and grayscale. No alpha channels.
TGA from Targa is for MS-DOS Truevision systems video board. Works with RGB, indexed, and grayscale. It has an option to choose pixel depth when saving it as RGB. Wow...
Tagged Information File Format works great between graphic programs, photo retouching programs and betwixt Mac and PC. Very flexible CMYK, RGB, grayscale with alpha channels, Lab color, indexed color, and even bitmap color. You can save to LZW compression as well (which can be messy in Mac, but not always) this makes the file smaller, but somewhat slower in uncompressing.
Windows Metafile Format is a cool Windows catalog of superior clipart that far surpasses anything ever created before. No, really it's a clunky pile of pictures that: One may contain raster images, but aren't recognized by programs like InDesign. Two; WMFs don't support color separations--that is what we up North call "a problem." Three; WMFs are limited to 16-bit RGB color mode, so they're really cute on screen but useless as far as offset printing. Don't use them. If you have to use them, convert them to a real file format and get the colors turned into either CMYK or Pantone Spot Colors. While you're at it, can you fix the trapping as well? Or don't complain about it later.
When setting a file to be a raster graphic, think about where you want it to finally go. If you have a postage stamp sized graphic and you have to run it as a poster document, you need to recreate it to the size you will output it. The file may be huge, but the data you need will be there. Choose the right format (BMP, GIF, JPG, EPS) for your specific needs.
Depending on the photo you can manipulate it in PhotoShop (or similar raster imaging software that ships with your scanner). You can run a few filters to make a crummy photo a halfway decent piece of illustration. For way too much information on that, click here.
New set of problems. The web is for viewing, not printing. The average screen displays images at 72 dots per inch (dpi). So your FINAL graphics (JPEGs, GIFs) don't need to be more memory intensive than that. Once you get the graphic to the SIZE (width and height) you want, then you can distill the image to 72 dpi to keep your graphics small enough to download sometime this week. Again the trick is to aim for your final output target. The web (right now with the current technology) wants small, easy to download graphics. GIFs and JPEGs can be used perfectly for this use. You can reduce the number of pixels, delete unused colors, optimize and streamline each graphic. But I would keep high resolution copies of stuff you intend to use in printing in the real world.