Camera

A digital image, just like the image you see on your computer monitor or television, is made up of multitudes of tiny dots called pixels.  The term "Resolution", when used to describe a digital camera, typically refers to the size of the digital image the camera produces, and is usually expressed in terms of "megapixels", which is equivalent to 1 million pixels.   In most cases the camera's CCD  is rated at a certain resolution, meaning that it can capture images of that given resolution.  For example, a camera with a CCD rated at 2.1 megapixels produces an image with a resolution of 1600x1200 pixels (which is really 1.92 million "effective" pixels).  When you multiply the vertical and horizontal dimensions of an image you get a product in the "megapixel" rating.   One technicality is what's called "effective" resolution; many CCDs are rated at a certain size but produce an image that is a little smaller (they don't use the entire CDD).  In these cases, the true image size is the "effective" resolution that might be smaller than the CCDs "stated" resolution...this is not a problem, and the industry has now adopted "effective" pixels as standard.

These are the relative "resolution" sizes of today's common digital cameras; in actual size even the smallest one of them would more than cover up your entire computer screen...notice the tremendous difference between 2.1 megapixel and 3.3 megapixel.   This is why you can get much better printed results from a 3 megapixel camera compared to a 2 megapixel camera.

Advantage of high-res: The advantage of having a camera with a higher resolution is that you have many more pixels to work with, which is very important when getting digital prints made, and high resolution is critical when you need to tightly crop an image.  A very good example of this is represented by the images above.  The picture in back represents a 5 megapixel image which would have dimensions of 2560x1920 pixels.  The picture in front of it represents a 4 megapixel image, which would have dimensions of 2272x1704 pixels, and the one in front of it represents a 3 megapixel image with resolution of 2048x1536, and the one in front of it represents a 2 megapixel image with resolution of 1600x1200, while the top picture represents a 1 megapixel image, which would have dimensions of 1280x960 pixels.  As you can see, the 4 and 5 megapixel photos are much larger than the 1 and 2 megapixel ones, which allows for much greater detail and the ability to crop (or "cut off") parts of the photo down and still retain enough pixels for a good print.

More is better: As mentioned earlier, the more pixels your image has, the larger you can produce a clean printout.  You can produce a printout from just about any image, but when you have to "scale up" an image (making it appear larger), it always degrades in quality.  You're much better off to have too many pixels and then "scale down" with no loss in image quality.  You may have seen printers that are rated at a certain "dpi" or dots per inch resolution; it is generally understood that if you can cram more dots into the same amount of space your image quality will improve.  The same is true with digital image resolution; the more pixels you have, the more you can "cram" them down into a photograph and the cleaner and sharper your final image will be.

Doing the math: One point of confusion that I've often noted is that people get confused about how "big" (in inches) a digital image is.  The answer to this simply depends upon how tightly packed the pixels are, and whether the image is for screen viewing or for printing.  For example, most computer monitors display images at 72 dpi, meaning that there are 72 pixels for every 1 inch of linear screen space you see.  Therefore, if you have an image on the screen that is 720 pixels wide, it will take up 10 inches of linear screen space (72 dpi x 10 inches = 720 pixels).  This may look beautiful on the screen, but if you try to print this on a printer at its native 72 dpi, it will look extremely choppy at its full 10 inches of width.  To get rid of this choppiness, you need to print it at at 300 dpi, which means that the 10 inches across the screen will be reduced to only 2.4 inches wide on paper (720 / 300 = 2.4, or 24% of the original 10 inches) because you are "cramming" 4 times more pixels into the same inch as before.  The result is a smaller, but much cleaner, image on paper.  So a good rule of thumb about how physically big on paper an image will be at 300 dpi is simply to cut its screen measurement by 75%.  This again makes a good argument for having as many pixels as you can get.

To state it another way, I recently received a letter from a reader asking, "I'm trying to find out what a 1.3 megapixel camera would be the equivalent of in dpi...and also how does one know what the dpi of a camera is if it's listed in megapixels?".  Here is my reply:

Beware of Imposters: There is true resolution and "implied" resolution, usually called interpolation.   Interpolation is the process of "sizing up" a digital image by adding pixels that were not there originally.  Since every pixel must have a color, this process usually involves assigning an intermediate color to the "invented" pixels based upon the colors of the pre-existing pixels surrounding the new ones.  The result is a larger image in terms of resolution, but one that now has much less clarity because you simply cannot produce something from nothing; the data was not on the original image and thus has been artificially created.  Interpolation has its place in limited circumstances, but I would strongly advise against buying any digital camera that performs interpolation in-camera.  One manufacturer comes to mind who sometimes use interpolation: Fuji, in models with the SuperCCD.  Fuji models with the SuperCCD can produce images that are twice the size of the CCD's rating, but are not as sharp as uninterpolated images.  I'm not saying to avoid the SuperCCD; I'm saying to simply know what you're getting and don't be oversold on the the SuperCCD.

Summary: I'm often asked, "How many megapixels do I really need?"  My general answer is "As many as you can afford."   I recommend a bare minimum of 3.2 megapixels.  However, as mentioned above, if you have more pixels to shoot, you have more pixels to crop or you can make larger prints in the 5x7 to 8x10 range.