pixel & megapixel vs. DPI

Pixels or resolution- why is this so confusing?

Actually, it's the same thing, but you need a little math to convert one to another. DPI, as I've discussed before, has to do with with how many dots, or pixels, there are in one inch of your image. 72 dpi is screen resolution— what your monitor can display. Printed pieces can accommodate many more pixels per inch than electronic displays.

One mega pixel refers to a size of one million pixels. A one mega pixel image that is 1000 x 1000 pixels @ 300 dpi is 3.33” x 3.33”- which is an 3.8mb document (in CMYK for printing, 2.86mb in RGB for screen). That same image resized to 250 dpi is 4” x 4” and at 72 dpi (screen resolution) it is 13.88” x 13.88”- all 3.8mb documents.

So if your camera is advertised at 4 megapixels, that means that if it is set for it's highest resolution, it will give you 4 million pixels— and 8” x 8” print at 250 dpi- which is an 15.3 mb document (in CMYK for printing, 11.4mb in RGB for screen). This is good to keep in mind when buying storage cards; I prefer to shoot at the highest resolution and then reduce the document size on Photoshop, so I buy huge cards so as not to run out of space. If you get a great shot, you don’t want to find out it’s the size of a postage stamp and can’t be blown up enough to make it into your client’s poster or trade show banner.

But you should also know that if you’re shooting your child’s weekend game, that even the $10,000 printer at the local photo shop can’t utilize all the pixels in a 12 megapixel image.

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