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Article Number T111182001 DPI (dots per inch) - a simple explanation Many people that we in Technical Support speak to appear to be a little confused about the dpi setting. There is a difference between a monitor resolution (e.g. 96 dpi) and print resolution (e.g. 300 dpi). So let us go back to basics. The term dpi (Dots Per Inch) expresses a relation between the number of dots an image is made of and the distance over which it is displayed or printed. So: An image that is 300 x 300 pixels in size will be roughly 3 1/8 inches square on your screen at a screen resolution of 96 dpi (this is an average screen resolution) An image that is 300 x 300 pixels output to your printer at a resolution of 300 dpi will be 1 inch square (you are squeezing the available 300 dots into one inch in this case) . As you can see there is a physical size difference between the on-screen and printed image described; it's not a good idea to correlate on-screen size with printed size, instead focus on the relationship between the number of pixels in the image and the number of pixels (dots) per inch when printed. So now we know this, how do we apply it in a practical situation, say when you are scanning a photo and you want to print it bigger than its original size? Well, the trick to scanning and printing is to work backwards. Let me explain: You have a 6" x 4" photograph and you want to scale it up to say, 12" x 8". You also want it to look good when you print it out on your inkjet printer. The first thing you have to decide is the size and quality (resolution) you are going to print at - on the aforementioned inkjet a print resolution of about 300 dpi will look pretty good. So to find out what resolution to scan in the photo, we do the following calculation: Size you want to print the photo (in inches) multiplied by the resolution you want to print at (in dots per inch) = number of image pixels required 12 inches multiplied by 300 dots per inch (put simply, 12 multiplied by 300) equals 3600 dots. The scanned image needs to be 3600 pixels wide. Then No of pixels required divided by size of original photo = Scanning resolution! 3600 pixels wide divided by 6" width of photo (3600 divided by 6) equals 600 dots per inch! So 600 dpi is the required scanning resolution to satisfactorily increase the size of the image. I hope that has cleared up some of the misunderstandings that occur when confronted with this term. If you want to delve further into the mysteries of scanning and print resolutions try taking a look at some of the web sites listed below. There's plenty of other considerations to take in to account, and these sites cover them in depth (These sites are in no way linked to Serif or any of its subsidiaries or related companies and Serif cannot be held responsible for the content therein.) http://www.scantips.com http://sunsite.berkeley.edu/Imaging/Databases/Scanning http://graffiti.org/faq/scan.html http://www.jasc.com/tutorials/scantip.asp http://www.plu.edu/scanning/scantips.html http://www.ecse.rpi.edu/Research/Papers/Convert/scan.html http://www.zdnet.com/anchordesk/story/story_1946.html http://www.twain.org/ | \
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