One of the common problems people have with QuarkXPress is with images. No matter what the source image looks like, once it gets placed into your document, it seems to turn into a grainy, low-resolution mess. Sometimes the picture doesn't even appear at all.
PostScript To understand what is happening, you need to understand a little bit about PostScript. Basically, this is a technology developed by Adobe to describe a page layout. Instead of sending millions of bytes of information to the printer describing each individual dot, PostScript sends instructions, much like a programming language. If you have a PostScript printer, it can be told to draw a red square starting 3 inches from the top of the page, and it will interpret it to the best of it's abilities.
Like most programming languages, PostScript can be difficult to learn, and many designers find it difficult to visualize the end result. Because of this, companies such as Quark created page layout software to hide these complexities. When you create a document, behind the scenes, QuarkXPress is really preparing something that can be easily converted to PostScript.
Display Problems Because the emphasis is on producing a printed page, QuarkXPress uses a few optimizations for screen display. Sometimes, instead of placing the full image, it will create a low-resolution 'preview' image, to speed up drawing the document. With EPS pictures, Quark won't create a preview It uses the built in preview within the image itself, which is faster again and keeps the QuarkXPress file size down to a minimum.
There are a few ways to improve the display of an image, although they will usually slow down screen display, increase the size of the document and/or make it difficult to get an accurate idea of image size.
Enhance Preview XT This is an XTension that comes with QuarkXPress. It should be under the Utilities menu (if not, go to Utilities > XTensions Manager... and reactivate it). Using it is easy: select the picture, go to Utilities > Enhance Preview XT > Enhance Selected Preview. It doesn't add to the size of the Quark document (it stores the high quality preview in a separate file), but it has been linked to a number of ambiguous error messages and conflicts with other XTensions.
Improve the color depth Quark-generated previews may be set to 8-bit. This means that only a limited number of colors (256 to be precise) can be used in the preview image. For many images, this can result in very poor quality. Go to Edit > Preferences > Application... and change Color TIFFs to 16-bit (32-bit is possible too, but generally unneccessary for most image previews). Using twice as many bits to describe each pixel will obviously add to the size of your document and won't affect all image formats.
Improve the built in preview Some image applications have a few options for saving. Often, there are a variety of ways to save a preview image, if the format supports it. As mentioned previously, Quark will use the preview image built into EPS files, so you will need to improve the quality in the source application. Some vector applications allow you to create 'enhanced' previews, for example, that retain vector quality when imported into Quark. This has been known to cause other problems, though, such as fonts not installed not showing up in the preview without any warning.
Change the image dimensions This is a complicated one to understand. When QuarkXPress creates a preview, it takes the image at 100%, resamples it to 72 dpi (dots per inch) and stores this image in the document. If you open the original image in, say, Photoshop, and increase the physical dimensions while proportionally decreasing the resolution of the image, Quark will import more detail. For example, if your Photoshop image is 1"x1" at 288 dpi, reducing it to 144 dpi while increasing it to 2"x2" will actually give the same quality final image (144 dots per inch over 2 inches is the same as 288 dots per inch over 1 inch). However, Quark will now be importing a 2" image rather than a 1" image, and if you reduce it to 50%, you now have twice the resolution. Conversely, importing a small image into Quark and enlarging it will diminish the quality even further. Besides being a little complicated, the other disadvantages to this method include adding unnecessarily to the document size.
When an image doesn't display at all, there can be a few causes. Sometimes an EPS file doesn't have a preview, and in that case Quark just displays a gray box that matches the size of the image. To get around this, you'll need to open the image in the original application and resave it with a preview. Another cause is when QuarkXPress doesn't have enough available to it. Closing other applications, increasing QuarkXPress's memory allocation and restarting Quark can all help. The other common solution is to check Edit > Preferences > Document... and see if Greek Pictures is checked. If it is, uncheck it and that should solve your problem.
Printing Problems In theory, when you print a QuarkXPress document, a PostScript file is sent to a PostScript printer, and no matter how bad things look on screen, it prints just as intended.
Now the bad news: most printers are not PostScript printers. Therefore, Quark will fall back on the regular print drivers that, in turn, print the document exactly as it appears on screen. In a PostScript workflow, Quark will look for the original images, disregard the preview image and use the data from the original file. Not so in a non-PostScript workflow, which is why the printed images often look as bad as they do on screen. Improving the display quality as described above will improve the printed result, but it's not ideal.
Most professional print companies use PostScript devices, so you shouldn't have to worry about the end result unless you're printing it yourself. If you really need high quality proofs, you've three main options. You could get a PostScript printer (expensive), create a PDF file, or get a software RIP for your printer.
Creating a PDF is an art in itself! Usually, you create a PostScript file (you just need a PostScript print driver for this, not the actual printer), then use Adobe Distiller or a similar piece of software to convert this to a PDF file. This can be opened in Acrobat Reader and printed from there.
A software RIP is a sort of 'virtual' PostScript printer. It interprets the PostScript commands and creates a file that your non-PostScript printer can understand. Check with your printer manufacturer to see if they have one available. Otherwise, you may have to look for a generic solution.
Conclusions Normally, QuarkXPress should be treated as a means to lay out page elements rather than as an accurate representation of what the printed page will look like. Images should be created at actual size in the original applications so they don't need any resizing in Quark. This gives a good balance between document size and quality. The quality can be improved for screen display, but it won't make any difference to how a PostScript device will print it, and will increase the document size, sometimes drastically.
As an aside, a PostScript printer may also print an image incorrectly if QuarkXPress cannot find the original image. This is one reason why you should always supply all files to a printer, not just the Quark document on it's own.