Advanced Exposure Calibration
The Advanced Exposure Solve allows Marso Measure to calculate an accurate exposure compensation directly from a photogrammetry reconstruction. This allows precise exposure calibration.
Why complete an advanced exposure calibration?
This process helps with maintaining colour accuracy and an even exposure.
Prerequisites
Before starting, ensure you have:
A colour checker, check compatible colour checkers here
Your chosen lighting preset configured
Final camera settings locked in (shutter speed, ISO, aperture)
A capture space with textured surfaces and markers for a clean photogrammetry solve
Notes & Best Practices
Always use consistent lighting between calibration and real captures
Recreate the exposure solve whenever lighting presets or camera settings change
Ensure the grey tile mesh is smooth and evenly reconstructed - clean the tile before capturing if there are any scuffs or marks on the grey tile you want to capture
Use plenty of markers to guarantee scale accuracy
1. Capture your grey card
The goal is to create a high-quality reconstruction of the grey tile under your chosen lighting conditions.
Use a flat, detailed surface on the ground and surround the chart with markers and measurements for alignment accuracy.
1. Capture
Set the lighting and camera exposure Use the exact lighting strength, flash mode, and exposure settings you intend to use in production captures.
Top-down orthographic pass Capture the colour checker in a grid pattern from above.
Purpose: the grey value should be lit evenly from all frontal angles.
Ring formation pass Capture the colour checker in a circular sweep at multiple heights.
Purpose: to provide data from different incidence angles for a more robust 3D solve.
Example capture
2. Process the Images Through Marso Measure Develop
Once all photos are captured:
Run the images through Marso Measure Develop step → this converts the raw files into a format suitable for your photogrammetry software.
3. Create a Mesh of the Colour Checker
Import your processed images into your photogrammetry software (Metashape or Reality Capture).
Steps
Solve alignment
Build the dense cloud and mesh
Use markers and scale bars for maximum accuracy
Ensure the colour checker surface is reconstructed cleanly
4. Isolate the Grey Tile
The Advanced Exposure System requires a mesh containing only the grey tile.
How to Isolate
Metashape:
Select the grey region using the bounding box
Right-click the mesh → Duplicate
Clip by Region to isolate the patch
Reality Capture:
Use:
Scene 3D > Tools > Mesh Model > Cut by Box
5. Export Required Files
Export the following from your isolated grey tile:
Alembic (.abc)
3D mesh of the grey square
ST Map (EXR)
Lens distortion map from solve
PNG UV Mask
Isolates the grey patch during processing
6. Create the Advanced Exposure System in Marso Measure
If you haven’t already, create a Light System for your light
Then, in Marso Measure, navigate to:
Exposure Systems → New Exposure System → Toggle from “Basic” to “Advanced”
7. Configure the Advanced Exposure System
Fill in the following fields:
Exposure System Name
Use a clear naming scheme including camera model + exposure + light preset.
e.g.,
A7R4_ISO100_F11_1/125_PtLight70%
Light System
Select the light system previously created for your rig.
Raw Calibration Image(s)
Raw images used for the colour checker photoscan.
Raw Image Extension
Colour Card Mesh File
The Alembic mesh of the isolated grey tile.
Reconstruction Tool
Photogrammetry tool used:
Metashape
Reality Capture
ST Map File
EXR export from your grey square mesh.
Colour Card UV Mask
PNG mask defining the grey region.
Grey Value
Decimal place of the percentage of the grey value of your selected grey tile. Reference values can be found here.
8. Finalise the Exposure System
Click Create Exposure System → Marso will now use the 3D geometry and lighting information to accurately calculate grey values across your capture workflow.
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