Keep signatures and white borders in the plan.

Identify what must remain visible.

Look beyond the main image. A signature, title, edition number or embossed mark may sit in the paper margin. A white strip is not automatically expendable, and the advertised image size may exclude it. Start with the actual sheet rather than a product listing’s nominal art size.

Imagine the smallest rectangle that encloses every detail you want to keep, including both the image and any marks. Measure the distances from the paper’s left, right, top and bottom edges to that rectangle. These are protected-area insets, not extra mat borders.

Compare the protected area with the window.

In the visibility tool, coverage defines how far the opening lies inside each paper edge. A protected-area inset at least as large as the corresponding coverage lies within that edge of the mathematical window. All four edges must pass for the whole protected rectangle to be within it.

For example, a signature’s lowest point 0.05 inch above the bottom paper edge meets a mat that covers 0.125 inch there. The difference is 0.075 inch, so that much of the protected rectangle’s bottom edge is outside the opening. The tool also reports the visible area of the entire protected rectangle; it does not recognize a handwritten signature or an uploaded picture.

A boundary match leaves no allowance.

If the protected rectangle touches the opening exactly, the model calls it within the mathematical opening. There is no spare space at that edge. Measuring error, the cut, the bevel and the way the sheet is positioned can affect the real result. A zero calculated clip is not a promise that a detail will look clear in the assembled frame.

White-border example.

Take a centered 8 × 10 image on 10 × 12 paper. Its image-only insets are 1 inch on all four sides. With 1 1/8-inch coverage per edge, the opening becomes 7 3/4 × 9 3/4 inches and cuts into the image by 1/8 inch at each edge. With a signature below the image, the protected rectangle may extend further down than the image-only rectangle.

Record the whole region you need, not just the main picture. If the mark and image cannot both be exposed with the intended mounting, discuss a different window or presentation with the framer. Do not trim the paper or apply adhesive merely to make a calculation fit.

Turn the check into an order conversation.

Send exact window dimensions and a clear note identifying what must remain visible. Confirm the supplier’s interpretation and practical allowance before ordering. Our check is a rectangular geometry aid for flat paper; irregular marks, float mounting and conservation decisions need separate judgment.