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Old 01-26-2006, 02:40 PM   #1
johnfowles
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Further to my display of picture of Gord on the general forum at:-
http://www.corfid.com/cgi-bin/ubb/ul...replyto=000030
Here are more things to ponder aboot digital picture file sizes
I was describing a large sample raw (bitmap) file of 3601 KB (actually 3,686,455 bytes)
It was a picture whose dimensions in pixels was only 1280 by 960=122800 pixels
Note that this is obviously from a camera taking pictures of a bit more than 1.2 megapixels considering that the price of digital cameras has fallen so much you can see how gigantic files from say an 8 megapixel camera will be in their raw uncompresed state
I converted the bmp to the jpg compressed "lossy" format using MGI Photosuite which also told me that it was only 1280 by 960 pixels.The bmp filesize can be calculated simply by multiplying the pixel dimensions and then multiply the resulting mumber which is the total number of pixels by three (since each pixel's colo(u)r has to be individually defined by one "byte" for each of the three colors magenta cyan and blue that combine to produce the RGB
"red", "green" and "blue") color code. in this case 1280x960x3=3,686,400 the actual file is a bit larger as it also has a file detail header).

Fair enough but why "cyan" and "magenta" instead of "red" and "blue"?I never knew but a google revealed
"Cyan and magenta are actually old printing terms for blue and red"
and are used for reasons fully discussed at:-
http://www.atlascopy.com/newsletters...oofy_Names.htm
see also:-
http://en.wikipedia.org/wiki/Highcolour
where you can read:-
"The amount of memory, in bytes, that a 24-bit image occupies in its raw state, can be found by multiplying the number of pixels in the image by 3. A 640 480 24-bit RGB color image will have 640 480 = 307,200 pixels. Thus, the memory space required is 307,200 3 = 921,600 bytes = 900 kilobytes"
These "wiki" pages are something else!!
John Fowles

[ January 26, 2006, 14:48: Message edited by: johnfowles ]
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