I'm reading a book by Rob Sheppard " Computer Photographers Handbook"He says that to print a good 8X12 print you need 3600x2400 size in pixels. Most printers print at 300 DPI. A 8x12 is 96 Sq inches. at 300DPI you would need 24,000 dots to fill the page. A 3600x2400 resolation would be 8,640,000 pixels. I thought pixels was the same as DPI Thanks in advance Glenn Patch

-- Glenn Patch (GEPatch@aol.com), December 29, 1999

Answers

I would agree that 3600 pixels on 12 inches would give you a very nice print. I use my camera of 1280x960 pixels as a reference in printing very nice 4x6 inch. prints. 640x480 would be just "Pleasantly OK" prints.

I remember someone asking Kodak what "archive" quality resolution would be for a 35mm size frame. The answer was 6000x4000 pixels at 24 bit color (3 bytes per pixel).

I use the above as my references - hope this helps you as well.

-- Kurt A. Pochert (kurtpochert@usol.com), December 29, 1999.

The problem with your calculations is that 300 DPI means 300 dots per linear inch... Not per square inch. :-) 300 DPI is equivalent to 90,000 Dots per square inch, or 300x300 dots per square inch.

So 8 x 12 = 96 sq. inches, 96 sq." x 90,000 PPI = 8,640,000 Pixels

Another thing you might want to remember is that DPI is not PPI. With images we're talking Pixels Per Inch(PPI), with printers usually Dots Per Inch(DPI). The catch is that 300 Dots, which can only be one of 6 or 8 basic colors each, can't properly represent 300 Pixels each of which could be any of 16.8 Million colors. If you have a 1440 DPI printer(vertically & Horizontally) and use 4 dots in each direction, or a matrix of 16 dots, to represent each pixel you get 360 Pixels Per Inch. Not too shabby at all!

For comparison's sake, I get by printing about 128 PPI at 720 DPI on my old epson inkjet. This yields a decent enough 8x10" print from a 1024x1280 Pixel file.

1280 pixels / 10" = 128 PPI 1024 pixels / 8" = 128 PPI 720 DPI/ 128PPI = 5.625 printed dots per pixel in each direction. 5.625 x 5.625 = about 31.64 dots per pixel

So the printer gets lots of dots to represent the color of the pixel. A 1280x1024 pixel image is a perhaps a slight touch grainy at 8x10", but at a distance of 18", OR SO, IT LOOKS GREAT!

-- Gerald Payne (gmp@francorp.francomm.com), December 29, 1999.