Image Metadata Guidelines

It is helpful if the GAIA images contain metadata giving details about what they represent (but entirely optional). We may add options for the user to query the image for information such as spatial extent and data limits, in which case it is necessary for some degree of standardisation.

Metadata values

All PNG files can include extra parameter name/values pairs, and this provides a means by which additional metadata can be included. The value is always a string. The following table describes the different metadata, and whether or not they should be included in keogram and thumbnail images.

You can add as many or as few of these as you choose, but please follow the conventions below.

Name ValueSorted ascending Keogram Thumbnail
DataQuality Flag indicating quality issues which may affect the result in a negative way (eg Preliminary Y Y
DataLimitMin Lower limit for data value (ie corresponging to 0 in the 8-bit image Y Y
DataValueMax Maximum data value within the image (float) Y Y
PositionXMax Maximum X value N Y
PositionYMax Maximum Y value Y Y
DataValueMin Minimum data value within the image (float) Y Y
PositionXMin Minimum X value N Y
PositionYMin Minimum Y value Y Y
DateTimeEnd The exclusive end time of the period that the image represents. Must be in YYYY-MM-DD hh:mm:ssZ format. Z indicates UTC. Y Y
DateTimeStart The inclusive start time of the period that the image represents. Must be in YYYY-MM-DD hh:mm:ssZ format. Z indicates UTC. Y Y
GaiaChannel The textual name (not refname) of the GAIA channel Y Y
GaiaProject The textual name (not abbreviation) of the GAIA project Y Y
GaiaStation The textual name (not abbreviation) of the GAIA station Y Y
DataUnits The units for the data. Use raw for cases like ADC count. Y Y
PositionUnits The units for the position Y Y
DataLimitMax Upper limit for data value (ie corresponging to 253 in the 8-bit image Y Y
PositionX X value for the keogram Y N

bubble Comments sought on GaiaProject, GaiaStation and GaiaChannel. Should we use GaiaProjectAbbrev, GaiaStationAbbrev, GaiaChannelRefName instead? -- SteveMarple - 23 Jan 2008

Adding metadata to PNG images

Matlab

Matlab allows the user to specify extra metadata when a PNG image is saved with imwrite. You can use a combination of imread and imwrite to add metadata to existing images.

Python

The Python Imaging Library (PIL) supports reading and writing PNG metadata. See also http://blog.client9.com/2007/08/python-pil-and-png-metadata-take-2.html. Image.load() loads the metadata into the Image.info dict. Extra effort appears to be required to write this dict back out (see previous link), although this may have changed by now.

Topic revision: r3 - 2010-01-20 - 23:26:25 - MartinGrill
 
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