When we are projection mapping with QLab, there's one important thing we need to take into consideration, which is the desired resolution of the surface we want to projection map. Today I'm going to show you how to calculate this resolution for both simple and complex surfaces so your projection design will look the way it is supposed to.

Say we want to projection map onto this square shape. In QLab we can go ahead and create a surface with a display assigned to it. Next we proceed with the usual Corner pinning. Now if we were to assign an image of a circle and show it on that surface we would expect it to be a circle. But as we can see that's not the case. What is happening here is we are taking a rectangular aspect ratio and trying to cram it into a square, and when you do this it takes our circle and it squeezes it inwards. 

The way we are going to solve this issue is by calculating the proper resolution for our surface size. This is done independently of your content at the QLab level. Let's start off with a simple example. The first thing we need to know is the dimensions of the surface we are projecting on. My square projection surface is 11 inches by 11 inches. Since the height and the width of the surface are the same, the number of pixels for the height and the width will also need to be the same. We could arbitrarily choose a resolution of say a 100 by 100 pixels or a million by a million pixels. If the number is too low the image will be very pixelated, and if the number is too high we will be wasting much of our computers compute power. So we need to find a sweet spot that is just right. 

Buy and large most projectors output a resolution of 1920 x 1080. So it would not make much sense to create a surface with a higher resolution than the projector can output in the first place. If we were to draw out our projectors output we can see that we can fit our square inside of it. If we were to overlay the dimensions we would find that our surface resolution at maximum could be 1080 by 1080 pixels. However, in this case I would most likely round down to 1000 by 1000 pixels since we hardly ever line up the projectors output to the surface exactly in practice.

Let's now look at a surface where the width and the height are different. This rectangle measures 11 in wide by 14 in tall. Once again we can draw out our projectors output and put our surface inside of it. We can pretty easily see that the height of the surface will be 1080 pixels once again. However, it's not immediately apparent what the width should be. To get this number we need to find the ratio between the height and width of the surface.

To do this we need to take the width of the surface and divide it by the height, which will equal 0.78. Now, we can take the number of pixels we found for the height and multiply it by 0.78 which equals 842 pixels, which will be our desired width for the surface. Together, we know that the resolution of this surface will be 842 by 1080.

We can now enter this resolution when creating a surface inside QLab.

But you may be asking what if I have a surface that is not a rectangular shape? The calculations are the exact same as before, however, we need one extra step. First, we take the shape and draw a rectangle around it making sure that the whole shape fits inside. We then need to measure the dimensions of the rectangle. For example, in my last video I had a weird shape and when I fit it into a rectangle it measured 14 inches wide by 11 inches tall. I then used the math from above to find the proper surface resolution.