Pixels and Megapixels

When purchasing a digital camera one of the main features of the camera is its “megapixels”. Just what is a megapixel. The simple answer is 1 million pixels. But then you have to understand the concept of a pixel.

Pixel: A pixel is a dot of a certain color and brightness. All electronic images are made up of pixels. On a TV screen, on a computer monitor, and in a digital camera, and on a printed image the images are made up of these dots or pixels. The more pixels the clearer the image will be to the human eye. For example, a low resolution computer screen might be 800 pixels wide by 600 pixels high. But a high resolution monitor might be 2048 by 1536 pixels or even higher. Objects on the high resolution screen would appear sharper (but maybe smaller) than those on the low resolution screen.

Megapixel: If a camera takes an image that is 1500 pixels high and 2000 pixels wide then the total number of pixels would be 1500 times 2000 which is 3,000,000 (or 3 million). This is three megapixels. Digital cameras take images that have a width to height ratio of 4 to 3. (Some can also take images with other ratios) The following table gives the pixel dimensions of images of various megapixel sizes. Note that cameras almost never take photos that are exact megapixel sizes. A three megapixel camera might, for example, take photos that are 3.1 or 3.2 megapixels in size.

Print Size: The more megapixels that an original image has the larger print can be made with that image. Again this is due to the fact that the more pixels (or dots) that are on the completed print the sharper the print will appear. While most photo printers print at 1440 dots per inch (dpi) or more, the optimum resolution for the original image is 300 dpi. This is due to the way the computer and the printer interact. However, an image can be enlarged within Photoshop Elements to allow for photo-quality prints larger than might otherwise be expected. In the table below are the print sizes for the various megapixel and dpi combinations. Anything less than the 120 dpi will exceed the recommendations of the camera makers. However good results can be made at lower resolutions if the original is of excellent quality.

On a side note, very small images such as those used for e-mail can be printed up to 5 x 7 provided one accepts a lower standard of quality.

Megapixels	pixel dimensions	inches @ 300dpi	inches @ 150 dpi	inches @ 120 dpi
0.2*	387 x 516	1.3 x 1.7	2.6 x 3.4	5.4 x 7.2**
2.0	1225 x 1633	4.1 x 5.4	8.2 x 10.8	10.2 x 13.6
3.0	1500 x 2000	5.0 x 6.7	10.0 x 13.3	12.5 x 16.7
4.0	1732 x 2309	5.8 x 7.7	11.6 x 15.4	14.4 x 19.4
5.0	1936 x 2582	6.5 x 8.6	12.9 x 17.2	16.1 x 21.5
6.0	2121 x 2828	7.1 x 9.4	14.2 x 18.9	17.7 x 23.6
8.0	2449 x 3266	8.2 x 10.9	16.3 x 21.8	20.4 x 27.2
12.0	3000 x 4000	10.0 x 13.3	20.0 x 26.7	25.0 x 33.3

* This size, two tenths of a megapixel, is a good size for sending as an e-mail.

** The size in inches for the lowest resolution for the e-mail size is calculated using 72 dpi instead of 120 dpi. As a print this will not be of photo quality but will be acceptable for many purposes.