When you look at scanners and printers, you have to be very careful. The dpi of a scanner and the dpi of a printer have very little to do with each other. It's too bad they don't have different names. The scanner dpi refers to how this device captures information about the photo. The printer dpi refers to how the printer puts ink down on the paper. If an image had 4 pixels in an inch (4 dpi) and was printed on a 1440 dpi printer, all 1440 dpi of the printer would be used to make these 4 pixels. Think of it this way--scanner or image dpi refers to how much information is in the image in a given area; printer dpi gives you an idea of how the ink goes onto the paper. The latter also gets complicated with photos because how photo-realistic a print is can depend as much on the pattern and size of ink drops as on how many fit in an inch.

When a printer specifies a resolution of 600 dpi, it's not spitting out one droplet of ink for each "dot." One 1440 dpi inkjet might be placing six drops of ink for any particular dot. Various printer manufacturers use different methods of applying ink. Epson, for example, uses four inks (Cyan, Magenta, Yellow and Black) on its general-purpose printers and six inks (Cyan, Magenta, Yellow, Black and lighter versions of Cyan and Magenta) for the Stylus Photo units. Epson also varies the size of the ink droplet in one model and keeps the droplet size consistent in another. Not only may the droplet size vary, but the number of droplets per dot may vary as well!

All of those droplets in the printer must work together to convince your eye that you see a spot on the page that's a particular color. Comparisons to color film and paper are a different matter and can't be compared by the numbers. If you're trying to get to the age-old question of how to scan/capture your image to print on your printer, remember that scanning resolution depends on the image size that you'll end up using. If you're scanning something that's 2x3-inches at 300 dpi and will be printing it twice as large into a 4x6-inch print, you're halving the resolution of your image. Too low a resolution is a common problem with poor inkjet prints.

The editors at PCPhoto Magazine recommend a conservative number of 300 dpi for the working image at the size you want to print. Every inkjet printer on the market today will do a great photographic-quality print at 300 dpi for the image. That's very important for the image because the printer is doing something else. Some printers will do fine at lower resolutions (dpi for the image); you'll have to test it. And no inkjet needs more than 300 dpi (even though they print, or lay down ink, much higher). Don't get caught in the trap of trying to match your image resolution with your printer's specified dpi.

Before you start compressing images for storage, you have to consider what type of images you're trying to compress. There are many methods or algorithms for compressing files. Some of these algorithms use inherent mathematical patterns to reduce the amount of information in a file, others use known limitations in human perception. Some compress files to very small sizes (image be damned!), while others compress moderately, and still others can be scaled by the user. Unfortunately, there isn't one miracle compression scheme that works for all files and images.

In your case, you've probably been saving some of your photo images (that you needed to reduce in size) using JPEG compression, and you were probably very satisfied (as long as you didn't try to compress them too far). While there might not be one miracle compression scheme, JPEG is still magical in what it can do. JPEG is one of those methods that uses the limitations in our visual system to reduce unnecessary data in a file. It works best when it's working on continuous-tone images such as photographs. Our eyes, while amazing biological machines, are more adept at noticing high-contrast detail as opposed to the subtle change you might find in smooth gradients.

Your screen captures aren't generally made up of continuous tones; the captures contain more things like text and high-contrast lines or drawings. It's difficult for JPEG compression to handle this kind of file. Look at the screen grab image accompanying this column. I started with a screen capture with a file size of 650 K. Using JPEG compression, I reduced it to 163 K. The left side of the image is a magnification of a section of the JPEG image. The right side isn't the original, but actually a GIF file. Graphics Interchange Format (GIF) was invented by CompuServe as a means of enabling its online users to transport image files among themselves. Now it's frequently used on Web pages. GIF files are limited to only 256 colors (8-bit) and the format is really happy compressing graphics files like screen shots.

So consider both of these file formats. Stick with JPEG for your photos, as GIF does poorly with them. Try GIF for screen captures and other graphics files.

While it might seem logical to convert your image file from RGB to CMYK, the inkjet manufacturers have designed their printers expecting to receive an RGB file. Because of this, you'll get better results if you let the printer do the proper color space conversion.

The way your slave works is by waiting for the internal flash of your camera to fire. When its sensor picks up that flash, it triggers the external or slave flash to fire at the same time. It doesn't happen exactly this way with most consumer digital cameras. When you asked if you're missing something, in actuality you're missing the slave's flash.

Here's why: Your Olympus D600L image sensor needs to calibrate to the color temperature or white balance of the flash. Of course, regular film cameras don't do anything regarding white balance because that's accounted for in the type of film you use. With digital cameras, the compensation for different color temperatures can be adjusted electronically. The camera does this by quickly doing a pre-flash (similar to the red-eye reduction flash, only faster). Your flash slave picks up this pre-flash and triggers your external flash too early.

When the camera captures the image on its main flash, your second unit has already fired. If only your slave unit could "miss" that first flash. Well, there's a company that makes slave units that take care of this problem. The name of the company is SR Inc. You can find them at (800) 324-7745 or on the Web at www.srelectronics.com.