When modifying and saving your images do you consider the DPI of the image or the pixels or both? What the heck are pixels anyway you ask? Let me try to guide you into a world of understanding as we take an important side trip that doesn’t quite relate to the archival process specifically, but more importantly, how to save them before you archive them so you don't make the "Big Mistake". I consider this a very important step in the overall process because you need to know the difference between manipulating and presenting images on screen and printing them in the physical world. Most importantly, you need to understand how DPI and pixels affect the printed photo quality. To completely understand how your images are displayed on your screen and how to print them in the physical world we need to understand three main concepts. The first one is DPI, the second is monitor size and resolution, and the third is the always confusing pixel. Lets look closer...
Dots Per Inch (DPI)
To start off this discussion, lets examine resolution or DPI. (Dots per inch) DPI is a physical measurement used in the print world to describe the amount of printed dots contained within one inch of a printed image. The term is also used by some people to measure the space your dots take up on your computer monitor but that is more acuarately referred to as PPI or pixels per inch. We’ll discuss this further in a bit.
The concept of dots per inch is easy to understand if you look closely at an actual printed image. There you may see very fine dots that actually come together and form that image as you move farther away. In almost all printed material these dots are made up of only four colors Cyan, Magenta, Yellow, and Bladk (CMYK). When you pull back from the image the four colors all visually gel together and form the image that you see on the paper. The mysterious "DPI" concept determines how close those dots are printed per inch of actual paper and how sharp the image appears to your naked eye. For example a newspaper might print their images at something like 170 dpi because it is a lower quality paper and may tend to bleed so it really doesn’t do much good to print at a higher DPI in this case. For your full color glossy magazine photographs though you need a minimum of 300 DPI if possible to attain a decent sharpness and quality level. If you double that to 600 or more you will start to get a really vibrant, sharp image. So when editing and saving your images keep in mind that DPI only controls photo size in the physical world.