Marker specifications

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

1 cmMarker sizeSmallest size, at ~30 cm

2 mmWhite quiet zoneEnables automatic detection

5 by 5Colour-patch gridCalibrates colour across visits

5Markers per lesionMinimum of three

What the marker looks like

Small10 × 10 mmcamera under <=30 cmsmall, well-defined lesions

Medium (planned)20 × 20 mmcamera <=30 to 70 cmlarger body areas

Large (planned)30 × 30 mmwider fields, full bodyfull-body capture

10 mm scale

Only the 10 × 10 mm size is finalised today; the larger sizes are planned and scale roughly with the capture distance.

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 with a side length of exactly 1 cm. This is the physical reference the platform uses to recover the real-world scale of the image.
• White border: a white margin of at least 2 to 3 mm around the black border. The contrast between the white margin and the black border is what lets the platform detect the marker automatically, so it 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 1 cm 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.

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:

• Use planar, non-deformable markers. The marker is a rigid, flat plane that must not bend, curl, or wrap to follow the skin's curvature.
• Keep markers in a planar orientation without strong perspective distortion.
• Use matte, non-reflective surfaces to prevent specular reflections and glare.
• Keep a white border of at least 2 to 3 mm around the marker so contrast is sufficient for automated detection.
• Keep the camera distance within the maximum for the marker (no more than about 30 cm for the 1 cm marker), and capture as close as the framing allows within that limit.
• 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 they stay flat and still during capture. Adhesive application is generally preferred because it helps keep positioning consistent and improves image capture. Markers are single-use.