Number 239 - April 2003

Digital Camera Flash Cards How Many Pixels Will They Hold?
By John Hoffmann, CAUG Coastal Computer News, January 2003
One must go back and ask, "What are you going to take pictures of? Portraits, scenery, grandkids growing up? All of the above I assume.    The following is MEMORY 101, I guess. A digital sensor (CCD for Charged Coupled Device) is a small card (2 X 3 inches) made up of many photocells which respond to light intensity to generate a given voltage. The voltage represents shades of gray but can be converted into colors. Each cell is then digitized into a 24-bit pixel, which represents a point on your computer screen or a point on your printed picture. A few other things are also done when converting the cell data to picture data.    Now let's do the Math. Suppose you have a 5 MegaPixel digital camera. This means you can set about 5,000,0000 pixels of picture data from side-to-side across the sensor.    Now recall that each pixel is 24-bits (8 each for Red, Green, Blue) that can produce 16 Million colors--a very common setup for your computer viewers. Then there are 8 bits per byte--OK! 5,000,000 pixels per pictures time 24 bits (on or off data, i.e. 0 or 1s) per	pixel divided by 8 bits per byte equals 15,000,000 bytes per picture. We usually say 15 Megabytes or just 15 MB. So, you want a Flash card? How about buying a 128-MB card for about $70 although I heard Fry's has them for $40. 128 MB divided by 15 MB per highest resolution picture yields 8 pictures. WOW! Flash cards do come in the Gigabyte memory amounts but they cost more than the camera.    If that is not enough pictures, be prepared to lower your quality standards. Compressing the data so less memory is used reduces the storage requirements. Now one loses quality as the picture is uncompressed i.e., not all the original pixels were stored and the missing ones are calculated out via math techniques.    My Nikon 5700 5 Megapixel camera has compression levels of 4, 8, and 16. OK, now, so I am on a long vacation and will take lots and lots of pictures of Granny, etc. For my 128-MB card and maximum compression, I can take about 16 times 8 equal 128 pictures. That ought to be enough.    John Hoffmann is CAUG's Digital Camera SIG Leader. Email him: mhoffman@Stx.rr.com
Number 239 - April 2003