Pixels

Vincent Bockaert, 123di.com

Sensor Pixels

Similar to an array of buckets collecting rain water, digital sensors consist of an array of "pixels" collecting photons, the minute energy packets of which light consists. The number of photons collected in each pixel is converted into an electrical charge by the light sensitive photodiode. This charge is then converted into a voltage, amplified, and converted to a digital value via the analog to digital converter, so that the camera can process the values into the final digital image.

As explained in the sensor sizes topic, sensors of digital compact cameras are substantially smaller than those of digital SLRs with a similar pixel count. As a consequence, the pixel size is substantially smaller. This explains the lower image quality of digital compact cameras, especially in terms of noise and dynamic range.

Typical sensor size of 3, 4, and 5 megapixel digital compact cameras Typical sensor size of 6 megapixel digital SLRs
Typical pixel size of 4 megapixel compacts and 6 megapixel SLRs

Digital Image Pixels

A digital image is similar to a spreadsheet with rows and columns which stores the pixel values generated by the sensor. Pixels in a digital image have no size until they are displayed on a monitor or printed. For instance, on a 4" x 6" print, each pixel in a 5 megapixel image would only measure 0.01mm, while on an 8" x 10" print, it will measure 0.05mm.

This article is written by Vincent Bockaert,
author of The 123 of digital imaging Interactive Learning Suite
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