The Interoperability IFD is a tiny directory, reached through tag 0xA005 in the ExifIFD, that exists to say which rule set a file follows. Its main tag, InteropIndex (0x0001), is a four-byte string. It comes from DCF, the Design rule for Camera File system that also defines DCIM folders and eight-character filenames.
| Stored value | ExifTool prints | Meaning |
|---|---|---|
| R98 | R98 - DCF basic file (sRGB) | Main image in sRGB |
| R03 | R03 - DCF option file (Adobe RGB) | Main image in Adobe RGB |
| THM | THM - DCF thumbnail file | Separate preview file stored next to a video clip |
Next to it, InteropVersion (0x0002) is almost always 0100. On disk, R98 is the bytes 52 39 38 00: three letters and a null.
Why R03 exists
EXIF ColorSpace has no code for Adobe RGB. A camera shooting in Adobe RGB writes ColorSpace 65535 (Uncalibrated), which on its own just means "not sRGB". InteropIndex R03 is what tells a reader the actual space:
$ exiftool -G1 -s -n -ColorSpace -InteropIndex -InteropVersion adobe.jpg
[ExifIFD] ColorSpace : 65535
[InteropIFD] InteropIndex : R03
[InteropIFD] InteropVersion : 0100Software that ignores both tags and finds no ICC profile will show such a file as sRGB, with flat, undersaturated color. Applications that understand the convention assign Adobe RGB. Embedding the profile is the safer route, and some cameras do both.
Setting it
Our EXIF editor offers the three values in a dropdown for JPEG and TIFF files. With ExifTool, use the stored code:
exiftool -InteropIndex=R98 photo.jpgChanging it relabels the file and does not convert any pixels. Set R98 only if the image really is sRGB, and R03 only alongside ColorSpace Uncalibrated and an Adobe RGB image. The EXIF data guide shows how the ExifIFD links to sub-directories like this one.