How it works

Start with the physical card outline

Centering Lab finds four card edges in the photo and maps the quadrilateral onto a rectangle. This perspective correction straightens a tilted photo. The original image supplies the rectified pixels; a smaller copy is used to search for the outline.

A plastic sleeve, toploader or binder pocket can create a second rectangle. Check the cyan lines against the actual cut of the card. Remove rigid plastic before measuring.

Two independent border signals

The color method looks for a sustained change from the outer printed border. A second method looks for a continuous gradient ridge across many scanlines. Agreement supports the measurement; disagreement increases the uncertainty.

Text, foil reflections and artwork crossing the frame can confuse both methods. The lime lines are the best detected starting points. They need manual review when the border is not read precisely.

Measure the most off-center point

Each axis is measured at three stations: 20%, 50% and 80% along the straight edge. For each pair of borders, the wider border divided by their total gives the major percentage. The app keeps the most off-center station.

Left/right and top/bottom stay separate. BGS can require different limits for the two axes. Rotating the image exchanges the axes and preserves their ratios.

What the ± means

The uncertainty includes fitting residuals and disagreement between border signals. Systematic errors are not made smaller merely by sampling more stations. A displayed ± is an error estimate, not a calibration certificate.

If either axis exceeds ±3 points, the result needs review and automatic grade ceilings are hidden. Open Adjust lines, check the cyan cut and lime print lines with the magnifier, then confirm. Reflections and narrow silver borders remain difficult; a clearer photo helps.

A ceiling, not a predicted grade

Centering Lab measures centering and shows the best grade that centering allows. A photo of the borders cannot assess corners, edges, surface defects or authenticity. A good centering ceiling does not promise that grade.

Full-art designs may have no usable printed border. Measure the reverse or set a clearly identifiable frame manually. Artwork is not automatically treated as the physical card edge.

Take a useful photo

Place the card flat on a dark, matte surface. Photograph it from straight above, with all four corners visible. Use diffuse light and remove the sleeve or toploader when possible.

A short card side under 300 original-image pixels is too small. Between 300 and 600 pixels the app recommends getting closer. Keep the image sharp and avoid digital zoom, glare and strong perspective.

The photo never leaves your browser. No account is required. The analysis runs locally in a worker; exported results are created on your device.