As a technical support engineer for Plugable Technologies I see a lot common threads in the questions asked by our customers.
A typical example would be:
“I bought your dual monitor docking station to use with my Lenovo Yoga 2 Pro. It seems to work OK, but the size of the information on my two external displays doesn’t look right. Is this a problem with the dock?”
The short answer to this question is, no it is not a problem with the dock. The long answer is that the problem lies with how Windows scales information on multiple displays. What does that mean exactly? Let’s break down the example above…
We have a Yoga 2 Pro in our test lab like the one the customer is using and it has an internal 13.3 inch diagonal display that supports a maximum resolution of 3200 x 1800 pixels. Simply put that means if the entire display was a sheet of graph paper, there would be 3200 columns across the page horizontally and 1800 rows down the page vertically. Each single block on the page would represent one picture element, or pixel. These pixels are illuminated with different colors to form the images you see on the screen. This is very simplified version of what is happening but for our example it works just fine.
A typical monitor that we could add to this system using our docking station would have a resolution of 1920 x 1080 pixels in a 24 inch diagonal display. In our test case (and to replicate what the customer has) we add two of these monitors using the dock to the Yoga which is running Windows 8.1. After adding the additional monitors I notice that the icons on the newly added monitors look much bigger than I expect. What is going on?
The answer lies in how Windows is trying to scale the information on each monitor connected to the system. Windows will try to automatically scale the content on each of these displays using an equation to make everything appear in the best way possible. Sometimes this system works very well and in other instances not so much, but why? The answer has to do with pixel density.
Remember that graph paper analogy I used earlier? Let’s take a look at a real word example:
The image above shows the same background image on both displays, but at a different resolution. This is a simplified example of our graph paper analogy but shows the how the difference in pixel density of each display can cause the same objects to appear differently.
So how does that explain our mysteriously large icons from earlier? Windows by default will try to scale the content on each monitor to make everything look as good as possible. When it is faced with such a large disparity in terms of pixel density, resolution and physical size it can wind up scaling things too much and cause things to look out of proportion.
So how do we deal with this? Windows allows us to manually control the scaling settings via the ‘Display’ application within the Control Panel.
There is a sliding control that allows us to change the scaling of items on all of the screens connected to the Yoga from smaller to larger by dragging the slider from left to right. However, this method is still applying Windows scaling equation to each monitor differently. If we want to set the scaling to the same value for each display, we can select the checkbox for ‘Let me choose one scaling level for all of my displays’
Now we have options to pick the same level of scaling for each display by clicking a radio button to pick between 100% (the default) up to 200%. However, Windows 8 does not allow for setting the scaling manually for each display connected to the system. You have to make the choice to use the slider to allow Windows to scale each display independently or manually pick the same scaling factor for all. The next release of Windows, Windows 10 will be the first to allow you to manually pick the scaling on each display.
So what does all of this mean? When you have a Windows system with multiple monitors with widely different pixel densities, resolution and physical size the automatic mechanisms to scale the image on each monitor may not be ideal. You can manually change these settings to something that suits your personal preference using the options in the ‘Display’ application. This behavior is not just limited to our docking station but can occur on any Windows system.
I know that is a lot to take in, and that is even with us presenting a simplified version of what goes on behind the scenes. To sum everything up neatly:
1. Monitors can have not only different resolutions but also different PPI/DPI measurements depending on physical size
2. Windows attempts to take these factors into account when scaling content on multiple displays
3. The effectiveness of this automatic scaling can vary depending on the disparity between all the displays connected to a system
4. While there has been some level of end user customization of scaling, the first version of Windows that will allow for manual scaling adjustment of individual displays in a multi-monitor setup is Windows 10
I hope this information proves useful and allows you to make use of multiple displays well in the future. I relied heavily on many sources while writing this post, and I list them below should anyone wish to dive deeper into what is going on behind the scenes.