Shiny objects fail in photogrammetry because their highlights and reflections slide across the surface as the camera moves, so the software has no stable features to match between photos. There are three practical fixes: make the surface matte with a removable coating, cross-polarise the light so specular glare is blocked, or at least soften and control the light. For glass, chrome and other mirror-like or transparent surfaces, a coating is the method the sources below treat as the dependable one.
This guide compares the methods, walks through a cross-polarisation setup and a coating routine, and lists the safety points from a scanning-spray maker’s safety data sheet, which you should read before spraying anything. Figures are quoted from Agisoft, the Meshroom manual, a scanning-spray maker and two vendor tutorials; where we give a rule of thumb it is labelled as such.
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- Glass, chrome, mirrors, clear plastic: coat it (spray or powder) or do not scan it with photogrammetry.
- Glossy plastic, painted or glazed objects: try cross-polarisation first, and coat the object if the result is still noisy.
- Bare polished metal: the hardest case. Test cross-polarisation, but a coating is the safer route (our assessment, not a published rule).
- Objects you cannot touch or spray: use diffuse light, polarisers and extra angles, and accept a lower-quality result.
Why shiny surfaces break the scan
Photogrammetry finds the same surface point in several photos and triangulates it. That only works if the point looks the same from different positions. Agisoft’s guidance is blunt: avoid untextured, highly reflective and transparent objects, because the dataset lacks reliable information for reconstruction. Meshroom’s manual says the same in its capture basics: avoid shadows, reflections and transparent objects. The spray maker AESUB adds the optics: on a reflective part, light is reflected in a focused way instead of a diffused way, and on a transparent part it passes through the surface instead of being reflected.
A reflection is not a feature of the object. It belongs to the room, so it moves when you move. The software matches it anyway and builds bumps, holes or warped geometry where the highlight was.
Methods compared
| Method | Works best on | Main trade-off | Source |
|---|---|---|---|
| Matte coating (spray or powder) | Glass, chrome, mirror finishes, deep pockets | Alters the object; needs cleaning or vanishing time; hides original colour | AESUB technical data sheet, Agisoft tips |
| Cross-polarisation | Glossy surfaces; Pix-Pro says it works on reflective objects “to a degree” | Needs polarising film, a circular polariser and strong, steady light; loses light | Pix-Pro tutorial |
| Diffuse light only (overcast, light tent, no flash) | Mildly glossy or satin finishes | Does not remove reflections from a mirror finish | Agisoft, Meshroom |
| Texture added to the surface (dots, markers) | Smooth, featureless coated objects | Extra prep; must be removable | Agisoft, 3D Scan Store tutorial |
Cross-polarisation setup
Cross-polarisation puts a polarising filter on the light and a second one on the lens, turned so it blocks the polarised glare that bounces straight off the surface while the diffuse colour still passes. A tutorial on the photogrammetry blog Pix-Pro describes a home setup:
- Equipment: polarising film for the light (it can be bought or salvaged from old LCD screens), a continuous light source such as an LED ring light, a circular polariser (CPL) filter for the lens, a tripod, and a matte black base and background.
- Light: put the film in front of the light. If the light has a diffuser, remove it, because some diffusers prevent polarisation.
- Dark room: switch off other lights so the polarised lamp is the main source of illumination.
- Find the angle: with the object in view, rotate the CPL while watching live view until the highlights disappear, and keep that position for the whole shoot.
- Black surroundings: a matte black base and background keep stray reflections out. If the background lights up, move it back or lower the light’s power.
- Expect long exposures: polarisers absorb light, so the tutorial used a tripod and exposures of several seconds.
Cross-polarisation is not a miracle for every material. Pix-Pro says it lets you scan reflective and glossy objects “to a degree”, and a 3D-scanning retailer notes a polariser alone will remove unwanted reflections but a surface with no detail will still scan badly. Test on your own object: if highlights remain at every filter angle, move on to a coating.
Matte coatings: sprays and powders
Scanning sprays come in two kinds, according to AESUB: semi-permanent sprays that leave a white surface and need cleaning (or disposing of the object), and vanishing sprays whose coating evaporates by itself. AESUB’s vanishing spray, for instance, forms a pigment-free layer of about 8 to 15 micrometres, applied from 15 to 20 cm away in even strokes, with 21 degrees C as the recommended ambient temperature. Its data sheet says objects stay scannable for about 1 to 2 hours, and sublimation can take over 4 hours when it is cold; colder rooms, thicker layers and recessed features slow the vanishing. If the coat fades mid-session, re-spray the contours.
Agisoft’s own tip is old-school: spread talc powder or something similar over a glittering object such as a car to turn it into a dull surface. A retailer tutorial applies a fine coating powder to a glass bowl, leaves it about 10 minutes to dry to a matte finish, and notes both the powder and the paint used below wash off.
A uniform white coat can leave nothing to match
Coating solves the reflection problem but can create a second one: photogrammetry needs visible features, and Agisoft recommends avoiding plain, monotonous surfaces. A perfectly even white layer is great for structured-light scanners and poor for matching photos. The same retailer tutorial fixes that by flicking a toothbrush loaded with black water-based face paint over the coated object to create thousands of small dots, then washing both off afterwards. Treat that as one workable approach from a vendor, not a standard. Whatever you use, test it on a hidden spot first: AESUB states that material compatibility cannot be guaranteed and that users must check it before use.
Stick scale markers or reference targets before spraying if you need measurements. AESUB notes reference points stick to its coating, and Agisoft recommends placing at least two markers a known distance apart for measurement. A coating also hides colour, so capture the colour texture separately (for example with a cross-polarised or uncoated set) if you need it.
Spray and powder safety
Read the safety data sheet (SDS) of the exact product you buy. For AESUB Blue the English SDS (revision 2023-06-01) lists the following, which is typical for solvent-based aerosols:
- Signal word Danger; hazard statements H222 (extremely flammable aerosol), H229 (pressurised container: may burst if heated), H336 (may cause drowsiness or dizziness) and H412 (harmful to aquatic life with long lasting effects).
- Use only in well-ventilated areas; avoid breathing the spray.
- Keep away from heat, sparks, open flames and other ignition sources, and do not spray on an open flame. Do not expose the can to temperatures above 50 degrees C (122 degrees F).
- Under “uses advised against”, the SDS lists use for private purposes (household) and use for products that come into contact with food.
That last point matters for hobbyists: this particular professional product is not intended for household use. We cannot recommend a consumer substitute (dry shampoo, baby powder, fixative sprays) from the sources we read; if you use one, check its SDS, ventilate, and keep dust and aerosol away from your lungs, eyes and camera. Never coat food-contact items or anything you cannot clean.
Light and capture without special gear
Even with a coating, the capture matters. Agisoft and Meshroom agree on the basics: diffuse light such as overcast or several indoor sources, no flash, no change of light between shots, and light sources kept out of the camera’s field of view. Agisoft’s turntable advice adds a white box or controlled environment with diffuse light rather than a point light. Use f/8 to f/11, the lowest practical ISO, and a tripod when light is poor (Agisoft’s figures).
On a turntable the background is static while the object turns, which confuses alignment. Meshroom recommends a plain background without distinguishable features; Agisoft suggests shooting blank frames of the empty background so Metashape can mask it automatically, then applying masks first. Plan the overlap as described in photo overlap, and see camera setups for gear.
Troubleshooting
| Symptom | Likely cause | Fix |
|---|---|---|
| Bumps, holes or noise where the object is glossy | Reflections matched as features | Matte coat, or cross-polarise and re-shoot |
| Smooth but featureless, alignment fails | Coating too uniform | Add dots or markers; raise overlap |
| Model seems to rotate with the background | Static background while turning the object | Plain backdrop or mask the background |
| Coating gone before the shoot ends | Vanishing spray sublimating (about 1 to 2 hours per AESUB) | Shoot faster, re-spray, or add layers |
| Colour looks flat or grey | Coating hid the surface colour | Capture colour separately before or after |
| Highlights remain with polarisers on | Cross-polarisation works only “to a degree” | Coat the part or accept a diffuse-light-only result |
After the scan
Scans of coated objects still need cleaning: see the mesh error checklist and the guide to closing holes. For where scanning sits among other ways to get a printable model, read the overview of types of 3D modeling.
Frequently asked questions
Can photogrammetry scan glass or mirrors?
Not reliably without preparation. Agisoft advises avoiding reflective and transparent objects, and a retailer tutorial says shiny or transparent objects cannot be scanned without surface preparation or a projection technique. Coating the surface with a removable matte layer is the usual solution, and some objects are better scanned some other way.
Does a polarising filter alone fix reflections?
It removes some unwanted reflections, but one polariser on the lens is not cross-polarisation. You also need polarised light, usually film over the light source, with the filters set 90 degrees apart. Even then, a surface with no visible detail scans poorly, so a coating may still be needed.
Does scanning spray damage the object?
AESUB states that material compatibility cannot be guaranteed and that users should test before use, and that its coating sublimates without residue according to independent analysis cited in its data sheet. Treat that as the maker’s claim and test on a hidden area first. The SDS also advises against household use.
Can I use dry shampoo or talc as a scanning spray?
Agisoft mentions talc powder as a way to dull a glittering car, and some makers use powders, but the sources we read do not endorse consumer sprays. Check the product’s SDS, ventilate, and test where it will not matter. Never coat anything that touches food.
Sources
- Agisoft Metashape: Image capture tips, equipment and shooting scenarios
- Agisoft Metashape: Close-range object scanning tips
- Meshroom manual: Capturing
- AESUB blue vanishing scanning spray: technical data sheet (rev. 02/2022)
- AESUB Blue: safety data sheet (English, rev. 2023-06-01)
- Pix-Pro: Cross polarization photogrammetry, how and when to use it
- 3D Scan Store: 3D scanning reflective objects with photogrammetry (retailer tutorial)
