Live positioning arrows: how they work and their limits
MedCam offers optional arrows that help aim a phone at an X-ray film, CT or MRI sheet, ECG printout or medical report. These arrows guide composition; they do not certify medical image quality.
What the arrows can suggest
When the preview has a likely outer boundary, MedCam estimates whether the film is to the left, right, above or below the image center. It may suggest moving closer if the subject appears small or farther away if edges appear too close to the preview border. These are relative visual suggestions, not measurements.
What they cannot measure
A normal 2D web camera cannot reliably report the physical distance in centimetres between its lens and an arbitrary film from one image. Gyroscopes report phone rotation relative to gravity, not necessarily the plane of the film. Most browsers do not offer consistent depth, camera intrinsics or WebXR support. The arrows do not provide true 3D pose, accurate depth, a calibrated tilt angle or clinical interpretation.
How to take a more useful photograph
Use an evenly illuminated medical lightbox for transparent films. Keep the entire film and its labels within the frame. Aim as perpendicular to the film surface as practical; move to reduce glare. Hold the phone steady and inspect small text at full size after capture. An unreadable original is better recaptured than aggressively processed.
What happens on older devices?
Arrows are drawn only on the live preview and are never stamped into the captured photo. If boundary detection is uncertain, MedCam shows an unknown state and allows Manual Capture. If the live browser camera cannot start, use the device camera or upload an existing image. No sensor data or image is sent to MedCam's server by the local workflow.
Safety
Do not rely on this tool for diagnosis or medical measurements. A smartphone photograph does not replace original DICOM studies, radiology reports or a doctor's review. Check patient names and IDs before sharing with a clinician.
Return to MedCam camera · Medical safety disclaimer · Privacy policy
How to interpret uncertain guidance
Imagine holding a phone above a glossy film: a border detector may see the reflected ceiling as an edge, causing arrows to jump. Treat an unstable arrow as a reason to adjust lighting and inspect the preview, not as an instruction to keep moving blindly. The device does not measure calibrated depth or certify a perpendicular camera angle.
- Start with the film fully visible and a steady camera.
- Move slowly enough for successive frames to settle; avoid sudden rotation.
- Prefer physical alignment using visible corners when arrows disagree with the scene.
- If arrows disappear, continue with Manual Capture; that is an expected fallback, not a missing medical function.
- Review the captured original for cropped edges, reflections and unreadable labels before export.
Two devices can display different hints because autofocus, frame rate, browser APIs and lighting vary. The relevant goal is a reviewable photograph, not a particular arrow color or a perfect synthetic score.