Pixels, Megapixels – What do they mean?
Courtesy of Nikon and www.nikonusa.com

 

A digital image (from either a film scanner or a digital camera) is basically a grid of numerous tiny dots called pixels. Pixel is an abbreviation for Picture Element.

A digital image is usually stated in terms of the number of pixels in the image which can be expressed several ways. One is the actual dimensions, such as 2272x1704 pixels. This means that for this particular image there are 2272 vertical columns of pixels and 1704 horizontal rows.

A second way to express the number of pixels is the "megapixel" rating. A megapixel is simply the number of pixels in millions of a particular image. For the example above; if we multiply 2272 by 1704 we get 3,7951,488 total pixels in the photo. With a little rounding off this is referred to as 4 megapixel (4 million pixels) image.

Comparing digital images to film is difficult. Film images are made up of many tiny pieces of silver grain or dye pieces. Since these pieces are not all regular shaped they appear as many little dots, or grain, in the print. Different film types have larger or smaller pieces of grain which makes it hard to compare with digital images which have nice, uniform size and shape picture elements.

In general, the industry uses about 20 megabytes of information for a high-quality 35mm transparency. If you scan a 35mm slide at more than about 20MB you only get larger pieces of film grain and not necessarily more data from the scan. Twenty MB (if you do the math described above in reverse) comes out to about a 6 megapixel image. Scanning at higher resolutions (or using a higher megapixel camera) gives you the ability to both print a larger image and crop in on a small portion of an image. However, you do not get more image detail in a given area from the larger file.

Since color negative film has much less detail than slide film, we can assume that anything less than 6MP is equal to 35mm color film.