Dots per inch (DPI) and Megapixels

[CP/M User]

I was wonderning - I wanted to take some of my old photos from my Analogue camera days and digitise them. I was wonderning though how many dots per inch would I need to set the Scanner too to be able produce something which is equivalent to a 1 Megapixel Digital photo? (Just so I could work out from that what the rates are).

[carlsson]

As far as I understand, 1 MP equals approx 1200 x 900 pixels (1.08 MP) for a typical 4:3 ratio? Many old photos are 6x4", which gives a 3:2 ratio. Let's aim for a picture that once scanned, it is 1200 x 800 pixels = 0.96 MP. 1200 dots / 6 inches = 200 dpi. If you scan in 300 dpi, you'd get the corresponding to 2.16 MP.

[CP/M User]

carlsson wrote:

As far as I understand, 1 MP equals approx 1200 x 900 pixels (1.08 MP) for a typical 4:3 ratio? Many old photos are 6x4", which gives a 3:2 ratio. Let's aim for a picture that once scanned, it is 1200 x 800 pixels = 0.96 MP. 1200 dots / 6 inches = 200 dpi. If you scan in 300 dpi, you'd get the corresponding to 2.16 MP.

Okay so what you're saying is a 6x4 photo is equivalent to 2.16 MP?

CP/M User.

[carlsson]

.. if you scan in 300 dpi. I could be wrong, but this is how I understand it. A bit of search on the Internet probably can give you more accurate answers.