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Image Sensors and How It Relates to Pixels and Image Size

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Digital cameras use image sensors, also called CCD (charged coupled device) or CMOS (Complementary Metal-Oxide Semiconductor). An image sensor made of CCD is a chip that is made of many small electrical receptors that are contained in a continuous matrix. This matrix converts the light and colors from the image being projected through a lens, into a matrix of pixels of the image. This is also referred to as a bitmapped image, because the digital image file that contains a computer word ‘map’ containing the color information for each pixel. To further break this down: after the pixels are exposed with light from the image going through the lens, the charges are then transferred from the first row to a place on the sensor called the read out register. After this happens, all the signals are sent to an amplifier and then converted. At this point the charges on the readout register are removed and the next row of exposed pixels enters. The first row now moves down to the second row. This whole sequence continues until the last row is used up.

With CMOS image sensors, they are more popular because many more of them can be manufactured at one time. Because of the low cost of making these chips, cameras that have this type of image sensor are lower in cost.

Because there are two types of resolutions for digital camera images (actual image resolution and print resolution), you need to know the two common ways pixels are known for when viewing the actual image on a computer screen. These two standards include:

• DPI: This stands for Dots Per Inch. It represents the number of dots per linear inch. Usually this is the setting for when images are scanned into a computer.
• PPI: This stands for Pixels Per Inch and represents the number of pixels per linear inch of an actual photo. In many cases or situations you may find DPI and PPI used to mean the same thing. DPI is used more often when dealing with film or photos while PPI is used when dealing with digital images.

Next Page: Choosing the Correct Resolution For Your Digital Image

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