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I COPIED AND PASTED THIS FROM ANOTHER PLACE, THIS SHOULD HELP OTHERS AS WELL AS ME

DPI is a very confusing term, and I'm sure after reading this, you'll be more confused. Yes, it refers to the resolution for both a scanner and a printer, but it means different things.

For a scanner, dpi means the number of pixels which the scanner will generate per inch of original material being scanned. For example, if you scan a photo which is 4"x6", and you choose a resolution of 300 dpi, the number of pixels generated will be (4x300) x (6x300) = 1200 x 1800 = 2.16 Mega pixel.

For an inkjet printer, dpi (printer rating) means dots per inch, i.e. the number of dots of ink sprayed on to per inch of paper. When you print a photo, several dots of ink are needed to create the colour represented by a single pixel in the digital file. The finer the dots, the more dots are theoretically available to represent the colour of a particular pixel. There are certain fixed levels you can use. For example, an HP printer might call them, draft, normal, best. You can't actually specify something in between.

Deciding at what resolution to scan depends on the purpose, and the original size of the material being scanned. If the digital file is ultimately to be viewed on a computer monitor, there's no need to scan at a high resolution. Say, if the monitor has a maximum resolution of 1024 x 768 pixels, and you have an original photo of 6"x4", a scanning resolution of 200 dpi will produce a file 1200 x 800 pixels, which is already too big for the monitor. If you want to send it by email, you want an even smaller size, and a scanning resolution of 100 dpi will give you 600x400 pixels, which is quite decent and not too big a file to send as an attachment.

To decide on the scanning resolution, in order to create a digital file ultimately for printing, you need to know a 3rd parameter, which is also dpi. This means the number of pixels (from the digital file) being printed per inch of paper, to give the quality you need for the photo being printed.

Here the printer rating dpi (your 1200x2400) does not really help, except that the higher printer rating you use to print, the more number of pixels there should be, otherwise the lack of pixels will become even more apparent.

For example, for Epson printers, they recommend that if you use their printer rating of 1440 dpi, you should choose a printing resolution of 300 dpi (in the 3rd sense, no. of pixels per inch of printed paper). This is in fact quite high, and many people find that they don't need to have so many pixels per inch of printed paper in order to generate a good printed photo. Many are happy with a printing resolution of 240 dpi (pixels per inch of printed paper). If you use a lower printer rating, say 720 dpi for an Epson printer, you can have an even smaller printing resolution. This is something you need to test for yourself, to decide whether you need 300 dpi or 240 dpi or lower, for a particular printer rating.

So if you want to print a really high quality photo, output size is, say 6"x9", to be printed at 300 dpi as recommended by Epson, you can work backwards and do the calculation. The picture file should be (6x300)x(9x300) pixels = 1800x2700 pixels. Note, there's no point in going too high. 300 dpi is very good already. If you have too many pixels, the printer will not be able to reproduce all the pixels and will discard some.

If your original material is say a photo which is 4"x6", you need the scanner to generate a picture file of 1800x2700 pixels from a 4"x6" original material. You will need to scan at a scanning resolution of 450dpi (1800 pixels divided by 4").

Of course, although your scanner is capable of scanning at high resolutions, the quality of the product will also depend on the quality of the original material being scanned.

I'm pretty sure I've confused you even more, but that's the problem created by the industry by using the term dpi for completely different, but related things.

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This is not going to help at all but....

Another thing to bear in mind is if you really want good output you need to see if you can configure your monitor, scanner, printer and art package to each other. Otherwise it can be fairly hit and miss to try for what the picture looks like on your monitor, chances are it won't look like it in the print out. (But I think this can be regarded as really applying to the fairly serious side of image output and manipulation.)

Just to mess you up a bit more.

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