Wednesday, June 29, 2011

Making Sense out of Pixels

In choosing a camera, you are impressed by the size of the numbers.  Sony's Alpha 35 mm camera has an effective resolution of 24,640,000 pixels.  If the sensor is 36:24mm (3:2 ratio), its size is 36X24 mm--giving it an effective size of 864 mm^2.  How many pixels per square mm is this?  This is simple division, and the answer is 28483.8.  To arrive at the pixels per mm (a linear figure), you take the square root of this figure, and you come up with 168.77 pixels per mm or 4286 pixels per inch.  Most computer monitors display only 76 to 96 pixels per inch--with high-end monitors reaching the 250 pixels per inch limit.  If the screen is HD1080X1920, the total pixels in this display is approximately 2.1 Mp.  You can take a 4 Mp shot in JPG mode, and when you reduce it down to HD1080X1920 format, you end up with a file under 1 Mp.  If you use the file again, the compression will take it down to .4 Mp.  If the file gets passed out on the Internet highway, the file has pixel stretch marks.  Models look like their their skin is peeling off.   The JPG file is obsolete when pixel density reaches the 200-300 range on monitors.   


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