You can use Flat-Field Correction to remove shading or lens cast, a typical optical artifact, from your digital photos. Shading is a generic form of Lens Vignetting, where light falloff can be asymmetrical and can have a color cast. For example, green on the left side of the image and magenta on the right side. Shading is most often seen with mirrorless camera systems, medium format digital backs on technical cameras with third-party, non-retrofocus lenses..
The standard way to fix shading is with a calibration photo. While taking a regular photo, you can also shoot a reference or calibration frame with the same optical set-up, at the same time. You can then use Flat-Field Correction in Lightroom Classic to automatically detect and analyze the calibration frame and remove the light falloff and color cast from the corresponding regular photo.
For best results, shoot the calibration frame with a plastic diffuser card under the same optical configuration i.e. same lens, f-stop number, focal length, focal distance etc. to create the calibration frame.
Flat-Field Correction is available in the Library module. To apply the correction, follow the steps below:
In the Flat-Field Correct and Convert Photo To DNG dialog box, select any of the following conversion options:
Only Correct Color Cast
Only corrects the color cast but not the light falloff. Deselecting this option corrects both, color cast and light falloff.
Only Convert RAW Files
Ignores photos that are not camera raw files. Deselecting this option converts all selected photos, including JPEGs, TIFFs, and PSDs.
Delete Originals After Successful Conversion
Deletes the original photo file after the conversion process ends. Deselecting this option preserves the original file on disk.
Specifies the versions of Camera Raw and Lightroom Classic that can read the file. Use the tool tips to help you choose.
Embed Fast Load Data
Lightroom Classic automatically detects the interleaving calibration frames, applies the flat-field correction to the corresponding regular photos, and converts the results to DNG file format.
Lightroom Classic requires that the first or last photo in the selection is a flat-field calibration frame. If the first photo is determined to be a calibration frame, then Lightroom Classic assumes that calibration frames would precede regular photos in the interleaving selection. Otherwise, it assumes that regular photos would precede the interleaving calibration frames.