On Sat, 05 Jan 2002 14:21:25 -0800, Shel Belinkoff wrote: >Could someone please explain this to me like I >was a child, and perhaps avoid jargon, acronyms, and the like. I'm >really ignorant about this and I'd like to buy a scanner this year. But >I'm afraid that, if I don't understand even the most rudimentary >information, I'll end up with the wrong scanner. Describing bit depth >as color depth, for example, doesn't help me. I'm having the same >problem with this as I have with understanding electricity, and all the >analogies people give me about garden hoses and water pressure don't >seem to make sense. > >What is "bit depth" and, perhaps even more important, what's important >about it? >
Hi Shel, here is another attempt to explain this (the more you can choose from, the better :-) The "bit depth" as used in scanner specifications, is a measure of how well it can detect and represent small color and luminance differences. (shades) It is represented as "bits" because that relates to the electronic digital implementation, but that is not really important. What IS important is to recognize the two common ways to express this: 1) The bit-depth for each of the three basic colors (Red Green and Blue), usually a value between 8 and 16 2) A combined value for all three colors, usually a value between 24 and 48 (just multiply value (1) by 3) As you can expect, the second one is just another way of expressing the first. The numbers used (8 .. 16) are the number of binary-digits that are used to hold a color / luminance value, and the more bits available the better the value can represent the "real world". As an indication, with only 8 bits (24 for all 3 colors) you can only have 256 different shades for each color, this is OK for a computer screen but it will cause artifacts called "banding" when used for photgraphic images with subtle color shades, like the sky. For a perfect sky you might want to use a 1000 different shades of blue, but the 8 bits only allow 256 different ones ... For the most other often used bit depths these numbers are: 8 bits per color (total of 24 bits): 256 shades per color 10 bits per color (total of 30 bits): 1024 shades per color 12 bits per color (total of 36 bits): 4096 shades per color 14 bits per color (total of 42 bits): 16384 shades per color 16 bits per color (total of 48 bits): 65536 shades per color As you can see, each extra bit used, DOUBLES the number of shades that can be represented. So, the more bits the better. But, more bits also means larger files! There can also be a difference between the number of bits used internally by the scanner-element and the electronics (example, using 12 bits per color, total of 36) and the number of bits used for the resulting image file which can be a little less (example 10 bits per color, total of 30). Hope this doesn't confuse you even more :-) Regards, Jan van Wijk --------------------------------------------------------- Jan van Wijk; www.fsys.demon.nl - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
