SpreadPaper is written in Swift and SwiftUI, sandboxed, and released under the MIT licence. It needs macOS 15 Sequoia or later, on Intel or Apple silicon. The code is at github.com/spreadpaper/SpreadPaper, so none of the above has to be taken on trust.
Got an arrangement this handles badly, a mix of densities that comes out wrong, or a correction to the write-up? Open an issue and it gets fixed in the app or on this page.
Next: if you came for the theory and now want the steps, spreading one wallpaper across two monitors on a Mac covers the practical side, from choosing an image to applying it across both screens. The rest of the writing is on the guides page.
+Next: if you came for the theory and now want the steps, spreading one wallpaper across multiple monitors on a Mac covers the practical side, from choosing an image to applying it across every screen. The rest of the writing is on the guides page.
+ Each display takes its own image. System Settings sets one image per display, and macOS runs + no single image across all of them. +
++ Spanning one image therefore means cutting the photograph into one piece per display, sized to + that display's own resolution, positioned to match where the monitors sit on your desk, then + setting each piece as that display's wallpaper. An app can do it in a few clicks, or you can + do it by hand. Both routes are below. +
+ ++ The image has to cover the bounding box of your display arrangement: the arrangement in + System Settings, in points, times the scale of the sharpest display. Summed widths give the + same number only for matched displays side by side. Anything smaller is enlarged to fit, which + is where soft wallpapers come from. +
++ Aim a little above the number. Bezel compensation hides a strip of the image behind each + monitor's housing, and you want those pixels to exist rather than be invented by the scaler. +
+ ++ SpreadPaper needs macOS 15 Sequoia or later. It reads your display arrangement and does the + slicing for you. +
+Arrange
++ Open System Settings, then Displays, and drag the rectangles until they match + how the monitors sit on your desk. SpreadPaper reads that arrangement, so + getting it right here is what makes everything afterwards line up. +
+Install
++ Download SpreadPaper and drag it to your Applications folder. macOS + warns you the first time you open it, and the help page walks you + past that. +
+Choose
++ Open the app and choose your image. The preview draws your displays in + their real arrangement with the photograph laid across them. +
+Position
++ Drag the image into place, zoom to fill the width and flip it if the + composition works better reversed. Aim for a subject that no bezel cuts in half. +
+Bezel gap
++ Raise the bezel value until a horizon or a roofline runs through the seam + unbroken. This is the step that makes the picture read as one picture instead + of two neighbouring ones. +
+Apply
++ Click Save & Apply. Each display is rendered at its own native + resolution, so a 4K monitor gets 4K pixels and the 1080p monitor beside it gets its own. +
+Save
++ Keep it as a preset to bring it back later. From there you can also set + a separate Light and Dark wallpaper, or put a set of images on a time of day schedule. +
++ The same steps spread one image over any number of displays. What changes is the size of the + image you need and how you arrange the displays. +
++ Arrange all of them in System Settings and choose an image as wide as the whole row. Three 4K + monitors side by side want 11520 pixels across. Set the bezel on each display: the gap between + two neighbours is the sum of their two facing frames. +
++ Size the image for the sharpest display. Every display gets its own slice, rendered at its own + resolution, so a 4K display and a 1080p display beside it share one photograph and each + keeps its own pixels. +
++ Rotate the display in System Settings and arrange it beside the others. It takes a taller + slice of the same photograph, so choose an image tall enough to stretch over the portrait + screen as well as wide enough to spread across the row. +
++ Arrange them one above the other. The image now needs height: two 4K monitors stacked want 4320 pixels + tall. The vertical bezel is the one to set, because the frames that matter are the top and + bottom edges. +
++ Place the laptop in the arrangement where it sits on the desk, including how much lower its + screen is. SpreadPaper reads that offset and slices to match. Bezels are set per display, so + give the laptop its own value. +
+ ++ The housings of two monitors sit between their panels, and the picture has to carry on behind + them the way a view carries on behind a window frame. Without compensation a horizon steps as + it crosses the join and a road kinks. +
++ Bezel compensation leaves out the strip of image that would fall behind the frames. The value + is in points, the same units as the display arrangement. Set it by eye: raise it until a long + straight line crosses the seam intact. On a pair of 27 inch 1440p monitors that usually lands + near 70. +
++ The bezel compensation guide goes through what to + measure, how to check the result, and why the gap is not the same as the frame you can see. +
++ You can do it in an image editor. Scale the photograph to the arrangement, cut one file per + display, and set each file as that display's wallpaper in System Settings. +
++ For each display, the slice is the part of the image over that display's rectangle in the + arrangement, with the bezel strips left out, exported at the display's own native resolution. + Nudging the photograph, moving a monitor or plugging in a laptop means cutting every slice + again. +
+ ++ Where to go next: bezel compensation is the detail + behind the step that does most of the work. Help walks the first launch + warning through in three steps. The guides have the rest. +
+- macOS treats each display as its own canvas. Pick a wide panorama in System Settings and every - monitor shows a scaled copy of the whole photograph, so a desk with two screens on it ends up - with two identical pictures. There is no hidden preference for this and no keyboard trick that - reveals one. The behaviour is the design. -
-- Spanning one image therefore means doing something macOS will not do for you: cutting the - photograph into one piece per display, sized to that display's own resolution, positioned to - match where the monitors sit on your desk, then setting each piece as that display's - wallpaper. That is the work. An app can do it in a few clicks, or you can do it by hand, and - both routes are below. -
- -- Width is the part people get wrong, so do the arithmetic first. Add up the horizontal - resolution of the displays you want to cover. Two 1080p monitors side by side want about 3840 - pixels across. Two 1440p monitors want about 5120. Two 4K monitors want roughly 7680. Anything - narrower than that is being enlarged to fit, which is where soft, mushy wallpapers come from. -
-- Aim a little above the number rather than exactly at it. Bezel compensation hides a strip of - the image behind each monitor's housing, and you want those pixels to exist rather than be - invented by the scaler. -
- -- The gap between two monitors is physical. Their housings sit next to each other and the - picture has to carry on behind that housing, the way a view carries on behind a window frame. - Without bezel compensation the wallpaper is continuous in pixels but not to your eye: a - horizon steps up as it crosses the join, a road kinks, a face gains a slice of extra cheek. -
-- Bezel compensation deals with it by leaving out the strip of the image that would fall behind - the frames. The number you enter is how much housing sits between the two panels, in points, - the same units as the display arrangement. How many points a millimetre of plastic comes to - depends on the display, so set it by eye: raise the value until a long straight line crosses - the seam intact. On a pair of 27 inch 1440p monitors that usually lands near 70. -
-- The bezel compensation guide goes through what to - measure, how to check the result, and why the gap is not the same as the frame you can see. -
-- You do not have to install anything. The manual route works, and it is worth knowing so you - can decide whether an app is worth it. -
-- That is a reasonable afternoon's work for one image you intend to keep for a year. It becomes - tedious the moment anything changes. Nudging the photograph a little to the left means - recalculating every slice. A new picture means the whole sequence again. So does plugging in a - laptop, moving a monitor to the other side of the desk, changing a resolution, or deciding the - bezel strip was a bit too narrow. The arithmetic is not hard, there is only a lot of it, and - it comes back every time. -
- -- Nothing here is specific to two monitors. The same steps cover three, a portrait screen - standing beside a landscape one, or a laptop open next to an external display. Mixed - resolutions are fine, because each display is rendered at its own, and a portrait screen is a - taller slice of the same photograph. -
-- What does change is the width you need. Three 4K monitors side by side want something close to - 11520 pixels across, and a laptop parked at the end of the row adds its own. If a wallpaper - looks soft on a wide setup, the source image is almost always the reason. -
- -- Bezel compensation is the detail behind the step that - does most of the work. Help walks the first launch warning through in three steps. The guides have the rest. -
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