http://www.rideau-info.com/photos/index.html
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Read especially - The Myth of DPI -
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There are or is no DPI in digital photos. If changing the so called DPI of a image changes it's quality, why doesn't the image change when you change DPI settings in your camera (for them cameras allowing such)..? In my D-SLR when I have the camera set in the 6Mp mode, it remains 3000x2000 pixels regardless of the DPI setting be it set at 72 or 600. On the screen and when printed, the images look exactly the same...
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If I have a 800x600 pixel image why is it you can have 10 DPI or 1,000 DPI set to it but yet the picture remains 800x600 PIXELS..?? Most better image editing programs allow you to adjust the "DPI" of a image but yet, the image it's self remains the same.
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Digital images are made of pixels. Period. It takes so many pixels (pixel density) to make a good looking photo quality image. The number of pixels needed is usually around 180 to 200 PIXELS per inch of photo you want to make. A 8x10 inch image needs at least 1600x2000 pixels to look good. The DPI 'settings' tho can be anywhere from 0 to 1000 for they mean squat. However....
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Another factor in getting good images is the size of the chip that sees in the camera. A small fingernail size chip of 12Mp will not give as good of a image as a larger chip of the same 12Mp. A fingernail size chip (like in many quality pocket point n shoot digital cameras) is like comparing early 16mm miniature film to full frame 35mm film. Both can take a image, both of the same thing, but the small one can be blown up only so much before the image falls apart.
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Why is it "pro" photographers always want or use larger format film cameras for a lot of their work..? A 35mm camera with Tri-X film will see the same image as a 120 camera with the same film or even a 4x5 camera with the same film. Why is it then the larger format camera(s) can take better images..? Think about it...
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This same logic goes into digital cameras with their chip that sees, be it a CCD or CMOS chip. A larger chip of the same Mp will deliver a better image and NO DPI are needed for there are none there. Film never had a DPI.. You never bought film based on a DPI number. DPI was and is a term used and need in the old mechanical way of printing from a roller onto paper via tin plates or masks. 300 DPI was about the smallest of hole they could make IN the mask, allowing ink to go through to the paper and because the holes were so close (as in good quality magazines then) the human eye almost couldn't see the actual dots making up the image. With todays ink jet photo quality printers some are able to produce dots of ink smaller than 1/1200 or 1/2000 of a inch. Far better than 1/300 of a inch for mechanical printing. Thus 300 DPI was a PRINTING photographic standard using tin plates and roller transport machines.Today it is a term that just gets in the way and mucks up and confuses everyone other than them who have learned to step around this quagmire when talking of images or printing.
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Read the article and try to understand it because it is ALL in the chip size and pixel count and nothing else. If anyone tries to word it differently so they can get some insane logic in there for using DPI, they are confusing them selves and others on a rather simple and straight forward concept for print or image quality.