Have you ever tried to print a photo from your digital camera that looked great on your screen but didn't on paper? It all has to do with the resolution and quality settings on your camera. When you get a grasp on how these two relate to printing pictures, then you will be on your way to printing great photos.
Digital pictures are made up of pixels, which are tiny little squares of solid color. This is where the term megapixel (MP) comes from, which is a measurement of how many millions of pixels a camera captures in each shot.
Nearly all digital cameras offer you three or more different resolutions (or sizes) for shooting your photos. They're usually designated something like small, medium, and large. For instance, if you have a Canon 20D, which is an 8.2 MP camera, your large resolution setting records an image at 3,504 pixels by 2,336 pixels (which is 8.2 MP). The medium will record at 2,544 x 1,696 (4.3 MP), and the small at 1,728 x 1,152 (2.0 MP).
Other digital cameras will be similar. If your camera has three settings, the medium setting will contain roughly half of the pixels as the large, and the small will contain roughly half of the medium.
But no matter what resolution setting you pick, you are still capturing the same image. Therefore, the higher resolution you pick, the more pixels you will have in an image. More pixels give you more detail. And the more detail you have, the better your prints will look.
Therefore, when you go to print your photos, you want to have a lot of pixels packed into the image. The way we refer to how many pixels there are is by pixels per inch (ppi).
A basic rule of thumb is if you don't have at least 200 ppi in your photo, you will likely see jagged little edges along the lines in your print. If you want something that will be "picture perfect," then you need 300 ppi.
"But wait a minute," you might be thinking, "my camera only said how many megapixels it shoots, not how many pixels per inch the photos will have!" You're right - the amount of ppi is up to you when you go to print a photo.
Let's refer back to the resolution settings in the Canon 20D. If you divide the large resolution setting by 200 ppi, you will see you can make a 17.5" x 11.7" print from it. That can easily be developed into a nice looking 11 x 14 that will be full or detail!
If you divide a small resolution photo by 200 ppi, the resulting print can be 5.8" x 8.6". That's barely big enough for a 5 x 7 photo! However, if you print a 5 x 7 from a large resolution photo, you will be packing 467 ppi into your photo. That's way more than you need for a perfect looking print!
Now that you have resolution straight, lets talk about how the quality setting fits in. Unless you are shooting in what's called a "loss-less" mode like RAW or TIFF, your photo will be recorded as a JPEG. The data for all JPEGs are compressed (or shrunken). Your quality setting tells the camera how much compression to use.
If you select a setting for a low compression, your photo's file size will be larger, which means you won't fit as many photos on your memory card as compared to using a high compression setting.
So why wouldn't you use a higher compression setting all of the time? Because the main thing sacrificed by compression is color quality. And the larger your prints are, the more noticeable the color quality will be.
So, putting it all together, shooting at the camera's highest resolution and lowest compression setting will give you plenty of detail and the best color quality for your prints. Considering how cheap memory cards have become, why would you ever want to shoot on any other setting?