Graphics for Genealogists Introduction How computer images are formed Computer Screens screen size total pixels 640 x 480 307,200 800 x 600 480,000 1024 x 768 786,432 1152 x 864 995,328 pixel is an abbreviation for picture elements Screen grid Images are formed (which includes all surrounding windows with their icons) by colouring the individual pixels - and widows divide the screen area into separate variable zones within the whole screen. Moving and changing screen images requires a lot of processing power - most of which is provided by the graphics card. The processing power of a graphics card can equal that of the main microprocessor - but is optimised for the dedicated task of updating the display. Example for 800x600 pixel screen - this is the size now recommended for web page design,   but there is now a definite trend towards 1024 X 768   Individual pixels are identified by [column,row] from a top left origin (NOT bottom left like a conventional graph)    origin pixel 0,0 at top left    end pixel 799,599 bottom right NOTE: - the first pixel has a zero address - and consequently the end address is one less than the screen size. An analogy would be to number 10 houses from 0 to 9. It would appear strange because it's not something that is normally done - but you would expect to find house zero at the beginning of a road. That's if you didn't assume it was house 10 or 20 or.... with a digit missing. It should be noted that the use of address zero is fundamental to the internal operations of a computer. Bits and Bytes  bits colours description  levels bytes/pixel 1 2 black and white 2 eigth 4 16 - [palette] 2x2x2x2 half 8 256 - [palette] 2x2x2x2x2x2x2x2 1 16 65,536 "high color" 2x2x2x2x2x2x2x2 x2x2x2x2x2x2x2x2 2 24 16,777,216 "true color" 2x2x2x2x2x2x2x2 x2x2x2x2x2x2x2x2 x2x2x2x2x2x2x2x2 3   Bytes required at various screen settings screen size total pixels number of colours 16 256 65k 16M 640 x 480 307,200 pixels 153,600 307,200 614,400 921,600 800 x 600 480,000 pixels 240,000 480,000 960,000 1,440,000 1024 x 768 786,432 pixels 393,216 786,432 1,572,864 2,359,296 1152 x 864 995,328 pixels 497,664 995,328 1,990,656 2,985,984 - actual availability of individual screen settings depends on the graphics card you are using together with its drivers You can see from the above table that the screen memory requirements are not very great by modern day standards - but when you look at the situation when the PC was first designed - its a different matter. The first PC's had a total memory of 512 kbytes (thats only half a meg) to do everything - and a hard drive of 10 MB was a thing to die for!!! But that's not the full story with Windows as each window requires its own 'screen' memory block - some times greater than the display memory. e.g. Windows can be greater than the screen size and you only see part of it at any one time - hence scroll bars. Graphics programs are one of the more memory hungry application and more so with the advent of digital cameras with their large file sizes.

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