What does EXIF "ResolutionUnit = 2" mean?
Asked 2/27/2018
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In image metadata I found an EXIF field called "ResolutionUnit" with the value "2". I’m not asking what image resolution is in general — I want to know what this specific metadata value means. Does it indicate the unit used for XResolution/YResolution, such as inches or centimeters?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
19
This is in the Exif standard for metadata, on page 26:
ResolutionUnit The unit for measuring XResolution and YResolution. The same unit is used for both XResolution and YResolution. If the image resolution in unknown, 2 (inches) is designated.
Tag = 296 (128.H) Type = SHORT Count = 1 Default = 2 2 = inches 3 = centimeters Other = reserved
So, indeed, "2" is inches and "3" is cm — but "1" and other values are "reserved", which is to say not supposed to be used.
The Windows Explorer dialog is interpreting other values (e.g., "ColorSpace = 1" has become "Colour representation sRGB"), it's a bit odd that this value is shown as a number rather than just "inches" — or, indeed, left out, because the Horizontal Resolution and Vertical Resolution (from XResolution and YResolution) are labeled "dpi" — where the "i" is inches.
Originally by user1943. Source · Licensed CC BY-SA 4.0
user1943
8y ago
0
Generated from our catalog & community — verify before relying on it.
Yes. In EXIF metadata, ResolutionUnit specifies the unit used for the XResolution and YResolution values.
The standard meanings are:
2= inches3= centimeters
In the EXIF spec, 2 is also the default value, so ResolutionUnit = 2 means the resolution is being expressed in pixels (or dots) per inch.
Some documentation also mentions:
1= no absolute unit
However, in EXIF, values other than 2 or 3 are generally treated as reserved/not normally used.
Practically, this field mostly matters for printing or software that interprets print size. It does not change the actual pixel dimensions of the image; it only affects how the image’s resolution metadata is interpreted for physical size output.
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