# Compute Between Display Resolutions, Graphics Dimensions, and File Sizes

May 30, 2012 —

I was a child of the late 70s and early 80s, so I was witness to the early evolution of home computers and the trends that came along with them. It’s amazing when you see the large-screen displays of today and compare them to the giant bulky monitors from those early days. It’s also amazing to see how the capabilities of these displays have improved with time, something we often take for granted. We are spoiled with giant widescreen monitors that sometimes exceed 2500x1400 pixels in size. I remember taking my first steps in computer science in school using graphics on an Apple IIe that supported 280x192 pixels! (We also walked to school uphill both ways in the snow with no shoes, because those were a luxury.) I’m sure there are those of you in the audience who remember even earlier days with even more primitive capabilities (TRS 80?).

Today there are a high number of devices that support all manner of display resolutions. Many applications that deal with graphics will often present you with dialog boxes when you save your images that give you things like a pixels per inch (PPI) setting as well as the memory used by the image. Often these little things are taken for granted, but they can be useful for planning how to use your results. Wolfram|Alpha has now added some extensions to its functionality that provide some basic tools to help in this area.

Let’s start simple. A fairly common display size (maybe on the low end by today’s standards) is 1024x768 pixels.

This information tells us a number of useful facts and, with a few assumptions, can be used to predict the size of an image if it were printed at various common printing resolutions. Also, if saved to a JPEG file with various compressions, how large would that file typically be? Exact sizes vary depending on the content of the image.

If you also know the diagonal of your screen or you know what the pixel resolution is, you can do a direct computation to a physical size, such as “1280x1024 pixels at 300 ppi” or “1280x1024 pixels, 17″ diagonal”.

Notice that you can now compare this to a standard paper size. These comparisons and computations might benefit graphic designers who need to know what size paper to print a given image on.

We can also handle print sizes directly. This is the inverse of the previous problem. We have a known physical size and want to know how that translates to pixels (making certain assumptions about the pixel resolution):

Besides these number-based display sizes, there are a number of devices out now with various screen sizes. The variety of these sizes is staggering, but we support some of the more popular ones.

This information might be useful to you if you are planning to buy one of these devices and you need to know if the resolution is high enough to meet your requirements. I’m amazed that such small devices can handle these resolutions when I remember being awestruck by the 320x200 pixel size of MCGA back in the day. Why do I have this vision of myself standing on my front porch shaking a cane at kids running across my lawn?