Applies to: Mac or Apple TV connected to a television/projector; use a non-protected image with visible corner markers.
The useful distinctions
- Apple describes overscan as picture margins hidden beyond screen edges.
- Available size controls depend on the TV or projector.
- A Mac underscan control is available only for some connected TVs.
Make the edges observable
A normal scene rarely tells you where its original boundary lies. An owned reference with four distinct corner markers gives that boundary a visible form. Keep the markers slightly inside the image so you can distinguish image loss from the physical bezel. Record all four sides, since horizontal and vertical loss need not look identical.
Test one sizing stage
Keep source zoom fixed while comparing the display’s documented fit behaviour. If you instead adjust the computer and TV together, a restored corner could be compensation for continued cropping elsewhere. The immediate question is where the margin is removed. A successful comparison shows that the selected sizing stage affects visibility; it does not measure the original programme’s aspect ratio.
Apply the finding with care
Once the reference fits, return to the original video and check whether its visible edges improve. Remaining bars may belong to the material itself and require a different comparison. Avoid interpreting a full screen as the only correct result. Preserve the input and output mode in your note because a later mode change may use another picture-sizing path.
A focused way to proceed
- Display an owned reference with an inset border and four corner markers.
- Record which markers are missing at the current size setting.
- Compare one documented display-fit adjustment while holding player zoom fixed.
- Restore the original setting and check that the same edges disappear.
Worked example · synthetic
Hypothetical example: the reference’s left and right markers vanish in one display-fit state and reappear in a documented fit-to-image state. The user has evidence of display-side margin loss without needing to guess from a cropped news logo.
When to stop or ask for help
Use the exact model’s size controls. This comparison does not justify stretching or cropping content to remove intentional bars.