Wallpaper spanning with advanced options: what the pixel density and perspective corrections are about
This page describes what the advanced spanning options of Superpaper do and how to configure them.
Below you can see in three pairs of images how the spanned wallpaper looks like on the display setup with different advanced options enabled. Left display is a 27" 4K monitor and the right one is a 25" 1440p display in portrait. First we will look at how wallpapers are conventionally spanned.
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| 1.1 Simple wallpaper span |
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| 1.2 Wallpaper image |
In the first pair of images above is shown for reference what the simple span looks like: it is just the original image cut up by display resolution and then shown on each display. This means that display pixel size is going to affect the shown image: larger pixels means the image is scaled up in size. Think of a 1080p laptop screen versus a 1080p TV: the image is split evenly between them and then scaled up immensely on the TV. Bezels are not taken into account and the image continues on the second display where it ended on the first one. This is what most multi monitor wallpaper tools do. If your displays are of the same size and resolution, aside from bezels, this issue does not affect you.
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| 2.1 Advanced span with pixel density and bezel corrections |
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| 2.2 Wallpaper image |
In the second pair of images is shown what the wallpaper looks like when the pixel sizes and bezels are taken into account. The image is essentially divided between the screens to have "the same amount of image per unit length" and to do this the physical sizes and positions of the displays are needed. Superpaper attempts to detect the display sizes automatically and guesses what arrangement your monitors are in based on the topology of your desktop but you will need to adjust the display positions shown in the preview in the application as necessary. In the upper image 2.1 it can be seen that the image is not scaled up anymore on the right display and the wallpaper is aligned on the whole length of the display border. However, it looks like as if the image is bent; horizontal lines in the image are bent sharply at the display border. This happens because the displays are rotated to face the viewer/camera.
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| 3.1 Advanced span with pixel density, bezel and perspective corrections |
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| 3.2 Wallpaper image |
In the third set of images the bent lines are fixed by adjusting the perspective of the image on the display on the right. This is done by telling Superpaper where the viewer's head / camera is located respective to the displays and how the displays are tilted and swiveled relative to each other. In the above example image both of the displays are told to have been tilted 5 degrees up and the right display is swiveled 35 degrees counterclockwise around the left edge of that display. This creates an illusion that the wallpaper continues in the plane of the left display; as if the image is not rotated at all while the display of course is. In other words the image is made to look like it was on a single large display that is in the same plane as the left display and that continues behind the right display.
All of these are only available in the "advanced span" mode.
To configure your bezel sizes, look for the "Adjust bezel sizes" section in "Advanced wallpaper adjustment, which is in the rightmost column in the new UI. Once you enter the configuration a number of buttons show up in the preview at the display edges. Selecting any of these you can enter a bezel thickness in millimeters. Only bezels in between of displays are meaningful.
Pixel density correction needs two things to work: correct display sizes and the positions of your displays relative to each other on your desk (to tell how you pixels are located in physical space and what size they are). Display sizes are detected automatically and shown in the preview; a warning is given if the detection fails and then you can enter correct sizes with the "Override detected sizes" button.
To tell how your displays are positioned you use the "Positions" tool, the button for which is in the bottom right corner of the wallpaper preview panel. When you press it the display previews become drag-able and you adjust the guessed arrangement as needed. If you only have displays that are side-by-side and vertically aligned the guess should match your setup.
Perspective settings are configured in the "Perspectives" dialog that opens from the button near the lower left corner. You'll need to measure your distance to one of the displays you consider central, though this can be done in relation to any of your displays, just choose the display that you use. Other details are explained in the configuration help pop-ups.
Second vital thing is the rotation information about your displays. Angle signs are determined by the right hand rule around the axis, where the axis points up for swivels and left for tilts. This rule is explained in the configuration help. This probably isn't superbly exact and on the other hand is somewhat a matter of taste so this will likely need some trial and error to get the settings tuned in the way you like. The rotation angles are thought to be in relation to a flat display arrangement, like your displays were all wall mounted next to each other, all in a common plane.
For swivels you can choose whether a display is rotated around its left or right edge, or not at all, and the angle it rotated by, in relation to the flat display arrangement. As for tilts, the axis is around the horizontal midline of the display, though for more accurate results you may tell how much the tilt axis of your display mount is offset in depth behind the screen. Then the tilt angle is (probably) a small one around this axis.
In the above example I've chosen the left display as the central display. Viewer offset is 500mm in distance and 100mm (up) from the display's center. Rotation settings are:
- Left display:
- No swivel
- Tilt angle 5 degrees
- Tilt axis depth offset 50mm
- Right display:
- Swivel axis = Left (edge)
- Swivel angle = -35 degrees
- Tilt angle 5 degrees
- Tilt axis depth offset 50mm