High or Low resolution?

on Feb 10 in useful stuff

It’s all about resolution. Not the new year’s sort but pixels per inch. There are two types of resolution. Low resolution and high resolution. Low resolution refers to a number of pixels per inch on a screen. 72 pixels per inch or another term that gets thrown around is 72dpi. One inch square is evenly broken up into 72 pixels in both directions. On screen that is a one to one ratio. Our eye is able to pretty much piece together anything with that amount of pixels. There is enough detail for our eye to view things like pictures and this blog post. Low resolution is mostly for things that one is producing to be viewed on a display or a television.

High resolution has a different aim. When something is printed it needs a lot more dots per inch to create a crisp clear image. Otherwise you get the newspaper affect, or pixelation, where you have printed dots that are too far apart and the image looks less crisp. So in the same inch as before we have 300 pixels in both directions to make for even more detail more subtle gradiation and a much larger file size. You would think that with more quality the high resolution would be used everywhere. This is just not practical because of the extra information that this file carries with it. For the web you would be wasting space and slowing down how fast your web pages load.

How is this useful for me? This is very important concept for people who work with digital imagery. If you have a digital camera, that means you! If you were to go to a photo printer with a low resolution image it would not be crisp and the figures of photograph may not be distinguishable from the background. You could end up with pixelation. Pixelation occurs when a document is stretched or printed at a non optimal resolution. Printing a low resolution photograph through a photo printer is an example.

How can I check? If you have photoshop you can check by selecting the image item from the menu bar and then image size. It will give you a read out of the pixel dimensions of your document. If you do not have photoshop you can use the get info function in finder on a mac or the properties function on a PC to view the file size. This is not ideal but it will give you somewhat of an indication. If your file falls between 30 and 150k you probably are looking a low resolution. If you file is pushing over the 1MB range for a smaller image it is most likely high resolution.

What type of files should I look for? Designers and creators of digital files and imagery sometimes offer clues to resolution of files by their names. Some creatives will name them with the type of resolution of the file or use a different extension. Here are some pretty standard types:

Output File extension	File size	Low or High resolution?
JPEG/JPG	under 200KB	LOW
JPG/JPEG	800KB +	HIGH
GIF	under 200KB	LOW
PNG	under 200KB	LOW
TIF/TIFF	800KB +	HIGH
EPS	anysize	HIGH

In some cases JPEG files can be high resolution if they come from a digital camera for instance. With JPEG files use the file size as a guide or if you do have photoshop verify using that method.