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

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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

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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

1. Set the lighting and camera exposure Use the exact lighting strength, flash mode, and exposure settings you intend to use in production captures.

2. 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.

3. 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

You will see on the image below, we have placed the colour card on a pair of jeans with detail that helps align the mesh. You can use any object that has enough detail, avoid glossy or featureless floors.

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2. Process the Images Through Marso Measure Develop

Once all photos are captured:

1. Run the images through Marso Measure Develop step → this converts the raw files into a format suitable for your photogrammetry software.

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3. Create a Mesh of the Colour Checker

Import your processed images into your photogrammetry software (Metashape or Reality Capture).

Steps

1. Solve alignment

2. Build the dense cloud and mesh

3. Use markers and scale bars for maximum accuracy

4. Ensure the colour checker surface is reconstructed cleanly

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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

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5. Export Required Files

Export the following from your isolated grey tile:

File Type	Purpose
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

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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”

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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.

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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.