The one thing budding digital photographers must know by heart is the pixel and how many of it they would need in a picture if it is to come out really nice.

A digital image like the image you see on your computer, your camera LCD or even your television is made up of tiny dots called pixels. A pixel is an abbreviation of the term “picture element” presented in a manner that acknowledges the word “pix” to denote “picture.” A pixel is one of the many tiny dots that make up an image in a way a computer would “understand.” Pixels are the dots you see when you blow up, resize or distort an image way beyond its resolution “capacity”. The intensity of each pixel will vary from system to system. Each pixel typically has 3 or 4 dimensions of variability as red, green and blue (RGB) or cyan, magenta, yellow and black (CMYK)

A megapixel is 1 million pixels and is often used not just to state the number of pixels in an image but also the number of sensor elements of a given digital camera or even the number of display elements in digital displays like LCD monitors. For example, a camera with an array of 2048x1536 sensor elements is commonly said to have 3.1 megapixels (2048x1536=3,145,728).

The advantage of having a camera with a higher resolution is you have more pixels to work with. That's important when having your prints made. The difference? Check out the quality of the pictures taken with your camera phone (often only as high as 2megapixels) compared to your digital camera (most often from 4 to 8megapixels) and you're bound to see a remarkable difference.

In general, more resolution means better print quality. It also gives you an advantage if you need to crop the image. Cropping is when you only use part of the image for the final print. It also gives you an advantage when creating 5x7, 8x10 or bigger prints. The more you have to blowup an image, the more defects will become apparent. Starting with a higher resolution image means there's less magnification necessary to achieve the desired print size. The less magnification, the better the quality.

Just how big a digital image really is, is a matter of math. One must understand though that pixels are more tightly packed for printing than for display on a computer screen. The image might look just fine for you when viewed in your computer but would look far from “acceptable” when printed.

Computer monitors display images at 72 ppi (pixels per inch). This means that there are 72 pixels for every 1 inch of linear space you see on your screen. Therefore, if you have an image on the screen that's 720 pixels wide, it will take up 10 inches of linear space (72dpi x 10 inches = 720 pixels). This may look beautiful on screen but if you print this image on a printer at 72dpi, the result will look “jagged.”

To get a good looking print from your printer, you'll need to print at 300ppi (pixels per inch), which means that the 10 inches across the screen will be reduced to 2.4 inches on paper (720/300=2.4 or 24% of the original 10 inches). The result is smaller, but much cleaner image on paper,

A good rule of thumb about how physically big an image will be on paper is that it should be 25% of the size that's on your screen.

Common image sizes and print sizes at 300ppi