Portrait video wall black bars: the resolution check

Where the bars come from

A 43-inch class panel carries a 1920x1080 raster however it hangs. Turn the glass 90 degrees and that same raster covers 1080 columns and 1920 rows of wall. Four panels across in portrait give 4 x 1080 = 4320 columns by 1920 rows, an aspect of 4320 / 1920 = 2.25:1. The controller manual that says to export at 4320x1920 has the figure right.

The mismatch lives in the controller's two resolution tables. On the input side the documented range runs from 640x480 upward, and a canvas 4320 px wide sits outside it. The source falls back to the largest standard mode under the 3840x2160 cap and the 4K canvas fix and letterboxes the canvas inside it, with blank rows above and below.

On the output side, each documented output is a landscape size: 1280x720, 1280x800, 1366x768, 1280x1024, up to 1920x1080. Every entry is wider than it is tall. Portrait glass needs a per-output entry of 1080x1920, or a named rotation mode that turns the picture 90 degrees on the way out. Where neither exists, the quarter that reaches each panel was never cut for the glass it lands on.

The third table is on the display: the picture-size or aspect setting. A panel set to a bordered picture mode adds its own frame on top of the short frame coming from the controller. Set every panel to full or native picture size, so the only geometry in play is the one the controller applies.

Symptoms and what each points to

• Bars across the top and bottom of every panel, picture correct in width but short. The source letterboxed the 2.25:1 canvas into a 16:9 mode to get under the input cap; the blank rows are the bars.
• No picture at all, or the source calls the display unsupported. The exported canvas mode sits outside the documented input range, so the two ends never agree on a mode. Export a standard mode and let the source do the scaling.
• Stutter on movement through one input and not another. The HDMI 1.4 input tops out at 30 Hz for 4K; the HDMI 2.0 and DisplayPort 1.2 inputs run 4K at 60 Hz. Move the cable to a 60 Hz socket.
• Bars on all four edges of every panel. The display's picture-size setting is letterboxing on top of the controller's output. Switch it to full.

The checks, in order

1. Write the canvas down first: panels across, times 1080 px of portrait width, 1920 px tall. Four panels make 4320x1920.
2. Read the input line of the controller spec and take the largest mode. If the canvas is wider, the bars are arithmetic and no setting removes them.
3. Read the per-output resolution list. If every entry is wider than tall and no portrait or rotation entry is named, the box cannot drive portrait glass full-bleed.
4. On each display, set picture size to full, then check the manual for a tile matrix function and whether it documents portrait layouts.
5. Bench test before the screens go up: feed a numbered grid at the size you plan to export and note where each number lands on each panel.
6. Total the panels' weights from their spec sheets and rate the mounting rail for the sum; four panels of glass are a two-person hang.

Example: a 4x1 portrait wall against a 3840x2160 input cap

Inputs, and where each comes from:

• Four 43-inch class panels, 16:9, 1920x1080 native each, hung portrait. This is the common panel for a shop wall of this shape, and the canvas below confirms the per-panel figure.
• Canvas: 4320x1920 px, the figure a 4x1 portrait layout table prints.
• Input cap: 640x480 to 3840x2160 px, from the controller spec sheet.

The rule in words: the wall's picture width is the panel count times the portrait width of one panel, and a source can only send a mode the controller documents. A canvas wider than the largest documented mode gets scaled down and letterboxed.

The arithmetic:

• Wall width: 4 x 1080 px = 4320 px. Aspect: 4320 / 1920 = 2.25:1.
• Distance over the cap: 4320 - 3840 = 480 px.
• Scale to fit: 3840 / 4320 = 0.889. Scaled canvas height: 1920 x 0.889 = 1707 px, so the canvas rides as 3840 x 1707 px.
• Blank rows in the frame: 2160 - 1707 = 453 px, and 453 / 2160 = 21% of the frame height.

Result: every panel receives a picture short by about a fifth of its height, and that fifth is the bars.

Decision: at a canvas width of 3840 px or more, an input capped at 3840x2160 produces bars, and 4320 px is 480 px over. Remove the bars at the path level, not in a menu: tile the displays and draw the file at the input size against the grid, or give each panel its own file.

Three ways to fill a portrait wall

Three paths fill portrait glass. A splitter is not on the list: the difference between an HDMI splitter and a video wall processor is that a splitter repeats one whole picture to every screen, and this wall needs cutting, not repeating.

Tile matrix in the displays

Commercial displays built for walls document a tile matrix function, and their manuals state whether it runs in portrait. Feed one signal to all four, set the layout and the bezel correction in the displays, and leave the splicer out. Draw the file at the size the chain passes, set picture size to full on every panel, and confirm the mapping with the numbered grid before anything hangs on the wall: the grid shows in ten minutes whether circles arrive as circles.

A processor with portrait in its resolution table

Buy a processor only when its resolution table names a portrait entry per output, 1080 wide by 1920 tall, or names a rotation mode and the resolution that mode keeps. Headlines say portrait; resolution tables say what it does. One current listing, for instance, offers 90-degree rotation and states 1920x1080 at 60 Hz as the only resolution for that mode, which is a figure worth reading before the purchase.

One portrait file per panel

For pages, price boards, menus and slides, drop the controller entirely: each panel plays its own portrait file at exactly the panel's resolution, 1080x1920, full-bleed by construction. Our panel-mount signage screens play picture and video files straight from a memory card or USB stick, with no subscription. Slicing one canvas across four screens is the same job as laying out one menu board canvas across four screens. One trap on the player side: a 4K portrait player can show a quarter of the layout when its canvas is set larger than the panel, so keep each file sized to the glass. A single picture split across four standalone players will not stay in step, so split moving pictures need the tile path.

Recommendation

Recommendation: Check two spec lines before any portrait wall purchase: the largest input mode and the per-output resolution list. If the input tops out at 3840x2160 and every output entry is a landscape size, that controller letterboxes the full portrait canvas; walk past it. Run slides and pages as one portrait file per panel with no controller at all. Run a single split picture on displays whose manual documents tile matrix in portrait, with picture size set to full on every panel, and draw the file against a numbered grid before the panels go up.

Questions