Marker specifications

The study marker, the Color Multi-Marker, is a conformable, matte, non-reflective square target. It combines a high-contrast border for geometric calibration with an internal grid of colour patches for colour calibration.

The marker is designed to follow the local skin contour and stay in full contact with the skin on a curved site, rather than tenting or bridging. What it must not do is change size: creasing, folding and stretching alter the printed reference dimensions, and a marker that has creased, folded or been stretched is discarded and replaced rather than used.

1 cmMarker sizeConfirmed size, up to ~30 cm

2.5 mmWhite quiet zoneOn the 10 mm marker, and it scales with the marker

5 by 5Colour-patch gridCalibrates colour across visits

5Markers per lesionMinimum of three

What the marker looks like

Small10 × 10 mmcamera up to about 30 cmhandheld capture, in production

Medium (planned)20 × 20 mmfixed systems at about 70 cmawaiting confirmation by measurement

Large (planned)30 × 30 mmwider fields, full bodyneeds a different sheet format, not a stock size

10 mm scale

The 10 × 10 mm marker is the only size confirmed today, and it is the one we supply by default. The 20 × 20 mm marker now exists as finished, print-ready artwork, with its own sheet layout, but the size itself is still provisional: whether a 20 mm marker is read reliably by a particular fixed-distance camera is settled by measurement on that camera, and that measurement has not been made yet. The 30 × 30 mm size is a design study only and is not produced, and it is not simply the next size up the same ladder. A larger marker is never just a bigger print of the same sheet, because the white margin and therefore the peel label grow with it, and the arrangement of markers on a card and cards on a sheet has to be solved again. Above about 22 mm nothing fits an A4 sheet at the required margin at all, so a marker that size means a different sheet format with its own tooling and cost. Treat it as a development to discuss with us, not as a stock size a study can request.

The reason size follows distance is that the platform detects the marker from its border and reads colour from its patches, and both are resolved by fewer pixels the farther away the camera sits. A marker that works at 30 cm is not automatically usable at 70 cm, and the relationship is not a clean proportion. Scaling the confirmed 10 mm marker from 30 cm out to 70 cm gives about 23 mm, so a 20 mm marker at 70 cm actually fills slightly less of the image than a 10 mm marker does at 30 cm. It is the nearest size we produce, not a like-for-like substitute, which is exactly why a size is confirmed by measurement and never by scaling.

If your capture system has a fixed working distance, tell us what it is before ordering. It also helps to tell us the sensor resolution, the lens focal length, and whether the system writes one view or a stereo pair into each image file, because all three change how many pixels the marker occupies. We confirm the size for that system before any markers are supplied. Where a study uses a fixed-distance system at about 70 cm, the 20 × 20 mm marker is the candidate under confirmation for it; please do not order it as though the size were already settled.

What the colour grid does

• Greyscale steps: Anchor exposure and white balance from black to white.
• Skin tones: Calibrate colour across the Fitzpatrick range.
• Erythema reference: A known red so redness compares reliably between visits.
• Standard colour set: Macbeth sRGB colours for full-gamut correction.

Dimensions and borders

• Black border: a solid black square border whose side is the marker size, 10 mm on the confirmed marker and 20 mm on the provisional larger one. This is the physical reference the platform uses to recover the real-world scale of the image.
• White border: a white margin around the black border, sized as a proportion of the marker rather than as a fixed width. The marker is 7 cells across, so one cell is one seventh of its side, and the margin is one and three quarter cells on each side: 2.5 mm on the 10 mm marker, and 5 mm on the 20 mm marker. It has to scale because the platform detects that margin in pixels, and a marker used farther from the camera occupies fewer of them, so a margin that is generous at 30 cm becomes too thin to separate the black border from the skin around it at 70 cm. A width of about 2 mm is the floor at any size, so that trimming and handling cannot encroach on the marker, and whichever of the two requirements is wider is the one that applies. The margin must always be clearly visible and unobstructed.
• Colour-patch grid: an internal 5 by 5 grid of known colour patches, including greyscale, skin tones, and colours characteristic of erythema, scaling, and bruising. The platform reads these patches and calibrates colour so that it is comparable across visits despite differences in lighting and white balance.
• Marker size and distance: the 10 mm marker is used at a camera distance of no more than about 30 cm. Capture as close as the framing allows while keeping the whole lesion and all markers inside the image. The maximum distance is a property of the marker size, not of the platform, so a larger marker raises it, but the distance a given size supports is established by measurement on the camera in use rather than by scaling from a smaller size.

info

The colour-patch grid is what allows the same lesion to be compared reliably across visits even when ambient lighting changes. Geometric calibration recovers size and shape; colour calibration keeps colour consistent over time.

Requirements for reliable detection

When markers are used as a reference they must meet the following criteria:

• Keep markers as flat as the site allows, and choose the flattest nearby healthy skin. Moderate conformance to the skin contour is expected and accommodated; creasing, folding and stretching are not, because they change the printed reference dimensions.
• Keep markers in a planar orientation without strong perspective distortion.
• Use matte, non-reflective surfaces to prevent specular reflections and glare.
• Keep the white border around the marker clear and unobstructed. It is 2.5 mm on the 10 mm marker and 5 mm on the 20 mm marker, and it comes printed as part of the marker, so nothing has to be added at the site. Simply do not cover it, write on it, or cut into it.
• Keep the camera distance within the maximum for the marker (no more than about 30 cm for the 10 mm marker), and capture as close as the framing allows within that limit. On a fixed-distance imaging system, use the distance we confirmed for the marker size supplied for that system.
• Scatter markers across the image to capture depth variation, ideally at different distances from the camera.
• Ensure markers are fully visible and completely within the frame, with no partial occlusion.
• Capture markers free of shadows, reflections, and glare, and keep the white quiet zone clearly visible and unobstructed.
• Avoid areas with uneven lighting or background interference.

Non-adhesive alternative

The calibration markers are adhesive and are designed to be used that way in most cases. For patients with fragile or compromised skin, they can be used in a non-adhesive manner if needed, provided each marker is held still and in full, unfolded contact with the skin during capture. Adhesive application is generally preferred because it helps keep positioning consistent and improves image capture. Markers are single-use.