Exposure mode (EXIF ExposureMode)

ExposureMode is a three-value EXIF tag (0xA402, SHORT, Exif IFD) that says whether the camera set the exposure itself, the photographer set it by hand, or the shot was part of an automatic bracket. That's all it records. If you want the actual shooting mode, read ExposureProgram instead.

Auto in aperture priority

"Auto" here is not limited to the green full-auto mode. Program, aperture priority and shutter priority all come out as 0, because the camera computed part of the exposure. A Canon EOS RP JPEG shot in Av mode:

$ exiftool -G1 -s -ExposureProgram -ExposureMode -AutoExposureBracketing photo.jpg
[ExifIFD]       ExposureProgram                 : Aperture-priority AE
[ExifIFD]       ExposureMode                    : Auto
[Canon]         AutoExposureBracketing          : Off
$ exiftool -G1 -s -n -ExposureProgram -ExposureMode photo.jpg
[ExifIFD]       ExposureProgram                 : 3
[ExifIFD]       ExposureMode                    : 0

In practice ExposureMode = Manual comes with ExposureProgram = Manual, and the tag adds little beyond that. Its one useful job is value 2.

Finding bracketed frames

Exposure brackets for HDR merges are easy to lose in a folder of thousands of files. If the camera wrote value 2, ExifTool can list them:

exiftool -q -if '$ExposureMode eq "Auto bracket"' -p '$FileName' DIR

Canon also records BracketMode, BracketValue and BracketShotNumber in its maker notes, which tell you which frame of the sequence you are looking at and by how much it was shifted. The standard tag only says "bracketed". Exposure offsets the photographer dialed in by hand are a different tag: exposure compensation.

Editing the exposure mode

The EXIF editor has a drop-down with the three values for JPEG and TIFF (more options in how to edit photo metadata). ExifTool takes either form:

exiftool -ExposureMode="Auto bracket" photo.jpg
exiftool -ExposureMode#=1 photo.jpg

The same tag sits in the Exif IFD of any JPEG, TIFF or RAW file that has EXIF.