Build flat-field correction

Before you start

Have flat-field RAW references captured with the same camera, lens, aperture, focus, magnification, and illumination as the film.

Steps

1. Photograph the flat-field reference

   Keep the capture setup unchanged, remove the film, and retain the diffuser and optical path used for digitization. Capture one or more RAW references; multiple references can reduce noise. Smooth brightness or color gradients from illumination or lens falloff are precisely what the flat field should record, so do not change the light just for the reference. Avoid film remnants, dust, visible texture, local obstructions, reflections, and clipping in any channel. Do not substitute a gray-card photograph with scene content or an already-corrected JPEG or TIFF.

2. Open Flat Field and choose the reference files

   Open a frame from the Contact Sheet, then choose Flat Field in the Viewer’s top toolbar to open Flat-field Calibration. Select matching references with Choose RAW Files and inspect the file list and count. These are uniform no-film references, not the film photographs to convert.

   

   Select references before building

   The selected flat-field files should appear under Reference RAW files. Confirm they are matching no-film references. No flat-field calibration still means no correction has been built; click Build Calibration after checking.

   

3. Build and wait for reanalysis

   Click Build Calibration. Flat-field calibration is active means correction is enabled. Photos may still show Calibrating while they are reanalyzed. Wait for analysis to finish before comparing the result.

   

4. Inspect the gain map and compare the result

   Inspect the gain map and Warning messages. Smooth changes may reflect uneven illumination or lens falloff; local marks, texture, or warnings mean the references need checking. The map shows correction strength, not the final photograph. It need not be perfectly flat, and there is no universal pass value. Keep the photograph, View, and edits unchanged and compare edges and uniform areas with Turn Off / Turn On. Click Done when finished. Disable or rebuild the flat field if the capture conditions no longer match.

   

   Pause switchingBeforeAfter

   Switches every 2.8 seconds. Inspect relatively uniform areas such as the sky, then compare brightness and color toward the edges. Natural gradients in a sky need not become uniform. Pause or choose a state manually; select the image to enlarge.

5. Check compatibility with the existing CCM

   If Use CCM with different flat-field settings? appears, check the existing profile. Cancel abandons the change. Disable CCM turns off the old profile so you can make a matching one. Use CCM keeps the existing profile but does not recalibrate it. To keep flat-field and CCM settings consistent, enable the correct flat field, remake the CCM, and check several photographs.