Cameras Radiography

Defining Resolution

Line Pairs per Millimeter (lp/mm). This is a measure of resolution, which refers to pairs of lines pressed tighter and tighter together until they eventually merge into a single line. The more lines that can be pressed into a millimeter and still be seen as individual lines, the higher the resolution. Digital radiography sensors can acquire images ranging from 8 to <20 lp/mm. The unaided human eye can distinguish about 10 to14 lp/mm. Is that extra resolution lost? Not really that’s where the software takes over.

Pixel and Megapixel. Pixel is short for picture element. Basically it is a dot on the computer screen. The dots are arranged in rows and columns and are so close together they appear to be connected. The dot can be a shade of gray or a color. A typical 800 x 600 image has 480,000 pixels. The more dots that make up an image the better the resolution. A megapixel is simply one million pixels.

8 bit or 12 bit. A bit is short for binary digit. In graphics the term refers to the number of different shades or colors a single pixel can display. An 8 bit image is 2 x 2 x 2 x 2 x 2 x2 x 2 x 2 or 2 to the 8th power. If you do the math that comes to 256. Most monitors display an 8 bit image meaning each pixel could be one of 256 different shades of gray. A twelve bit image is 2 to the 12th power or 4,096. True color is 24 bits which allows for 16 million different shades. At most the unaided human eye can distinguish 100 shades of gray. Is the extra detail useless? It depends on the software.

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