Why a high resolution digital camera needs more memory

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

07 October 2007

With everything going digital these days, Oscar Omondi has some questions about modern Cameras. He writes: “Could you please shed some light on digital cameras? What do they mean by Pixels and what is the difference between the different pixels indicated on different cameras? What is the difference in the memory size (one may have 25MB and another 56MB)? And finally, which is more economical - using two size AA batteries or rechargeable Lithium Batteries?”

Inside a digital camera, the picture is formed on a screen that has very many “dots” of light-sensitive material. (But don’t confuse this with the image you see on the viewing window behind the camera – this is INSIDE the camera).

Each of these “dots” (they are actually square in shape) capture a very tiny portion of the image and transfers it to the camera’s memory. The dots are called “picture elements” or, “picture cells”. In short hand, this is abbreviated to “pixels”.

Following the standard notation, 1,000 pixels are a kilo-pixel and one million are a megapixel (MPx). Thus a 2.7MPx camera splits the picture into 2.7 million dots while a 3.6MPx one produces 3.6 million dots per image.

Clearly, the greater the number of dots per image, the sharper the picture that the camera take will take (and save). Comparing a digital camera to the traditional film, the megapixels would be analogous to the film speed (not to be confused with shutter speed). An ISO100 film has finer grains than an ISO200; hence the former produces sharper pictures.

In addition to producing a sharper image, a higher megapixel camera will require more memory space to save each image. Most cameras use 3 bytes per pixel – in other words, 3 megabytes (MB) per MPx. Thus in a 3.6 MPx camera, each photograph will require 10.8MB of memory.

In a 3.6 megapixel camera, a 25MB memory card would only save two pictures while the 56MB will store five. But of course, the great advantage is that the memory you can download the images into a computer and re-use the memory card.

Obviously, then, the high the number of megapixels, the higher the resolution of the camera: But also, the larger the size of memory (MBs) required for storing the pictures.

Nevertheless, when the pictures are printed on the normal postcard size (4-inch) paper, it is difficult to distinguish images taken with a resolution higher than 3 megapixels. That is a 3.6 megapixel photo looks as sharp as a 7.2 megapixel one.

Finally, the comparison of alkaline to rechargeable batteries is a longer story that can’t fit here today. So, digest this article and wait till next week when I shall work out the costs of powering these cameras.