Understanding Pixels, Bytes and DPI
This is my site Written by rower on February 2, 2012 – 5:48 pm

An understanding of these basic measurements is vital when working with graphics

By Robin Rowe

HOLLYWOOD, CA ( 2012/2/2 -As with counting money or telling time, graphics uses measurements that often need to be analyzed or converted into another form. Let’s cover the essential basics of graphics measurements.

First, keep in mind that k means thousands, M means millions and G means billions. Think of it this way, 1,000,000,ooo byes = 1,000,000k = 1,000M = 1G. As when counting money, how many zeros is the most important part. And while it doesn’t typically matter, it’s worth noting that 1 k isn’t exactly 1,000, rather it’s 1,024.

Computer image sizes are measured three ways. In pixels (as width and height), or as a file size (in bytes), or as DPI. It’s quicker to look up file sizes, but when precision matters you need to know pixels. DPI is a relative measure similar to a car’s MPG. DPI tells you how “good” an image is, but as with a car, not how soon you’ll run out of gas.

Print images are often referred to as DPI (dots per inch), with 300 dpi being common. To convert DPI to pixels you multiply by the number of inches when printed. For example, a 300 DPI image printed 2 inches wide is 600 pixels, but if 4 inches wide that same image needs to be 1,200 pixels. Confusingly, the same image file can be said to have any DPI you like, depending upon how big you intend to print it. Speaking generally, if it’s 80 DPI it’s a web image. 300 DPI for newspaper. 1,200 DPI for a poster.

The number we care most about for computer images is pixels, how big the image will be on the screen. For the web we often want images that are 300 pixels wide. An image that size will typically be 50k to 500k in file size. Because images are compressed, image size and file size only track loosely. If you have a 300 DPI image or a 2.5M file or a 1k wide image, that’s too big for the web. You would open it in an image editor and resize it to be 300 pixels wide. A high definition image for film or HDTV is 2k, that is, about 2,000 pixels wide.

Read the above until all this makes sense. You can’t do graphics properly without understanding the basics above. It would be like trying to travel from Los Angeles to London without knowing how to count money or convert to pounds.

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