DPI stands for ‘dots per inch’ and you need to know a little about it when you are into digital photography, or design for that matter. As we know, digital images are made up of thousands of dots, and the more the number of these dots, the more is the resolution of the camera, of course. Also, the closer you are to the image, the better can are you able to make out these dots. There is a lot more that can be said about the relation of the human eye to the number of dots it can see at a given viewing distance; but it is sufficient to state here, that this relation is what makes it possible for a six mega pixel camera to make an acceptable giant size print.

The larger the image, the more is the viewing distance of course. Take for example a cinema screen on which you see a huge image made from a 35mm size transparency. Everything look sharp when you are in a back row, but things start looking low quality if you were in the first row! That’s the effect of viewing distance for you.

Now, any image that you run through Photoshop needs to be well optimized for its final usage. Apart from colour correction, sharpness and such, image size plays an important role here, and one of the factors that affect image size is DPI. Any image is usually optimized keeping in mind either a computer monitor as final presentation, or a print format.

The computer monitor displays images at 72 DPI, and that is the resolution of the monitor. Anything higher than this is a lost cause. Also, when you are optimizing an image for web usage, you want to keep the file sizes as low as possible without sacrificing on appearance; thanks to the importance of page load times. Anyway, always remember that you need to save an image at 72DPI for online usage. By the way, Photoshop also has a very useful ‘save for web’ option that really helps you reduce file sizes. Use this option if you are thinking of file size as an important factor – this helps web pages load quickly, and is great to send out your images as email attachments.

On the other hand, if you were optimizing an image for print usage, 300DPI is what is usually considered as a standard resolution, and this is required from your camera in the first place. Do keep in mind, that 300 DPI at a 12 by 8 image size would be equal to 600 DPI at 6 by 4, and 150 DPI at 24 by 16. Usually, upsizing your images by increasing the DPI from say 72 to 300 does little to really give you better quality.

To put it in a nutshell, you need to save your images at 72 DPI for web usage, and 300 for print. Whenever you are considering an image for print, do look at the DPI in comparison to the image dimensions as described above.