Encoded within each MrSID (and JPEG 2000) file is a set of metadata tags, used to convey additional information about the image. These tags are similar to TIFF tags, although the actual encoding mechanism is different. The mrsidinfo tool can be used to dump the metadata for an image.
The standard metadata tags used by all MrSID images, referred to as the "classical" tags, are listed below. Other than the "start" and "end" tags, the tags may appear in any order.
For mosaicked images, the metadata encoded with the image generally corresponds to the first image in the mosaic. The filename metadata tag contains a comma-separated list of the input files. The metadata refers to the image as presented to the encoder; this means that any filter or transforms operations will be correctly accounted for.
The metadata is supplemental information only. Some of this metadata is also contained in the LTIImage class; in general, querying the LTIImage class is preferred to evaluating the metadata, for example for information such as geographic position, background color, etc.
The tags in the table below apply to MrSID encoding.
The following are acceptable as values for the IMAGE::MODIFICATIONS tag:
The tags in the table below apply only to images encoded with areas of interest:
Tag | Description | Notes |
---|---|---|
IMAGE::AOI::n::REGION::VECTOROVERLAY | Name of vector overlay file, if any – (string) | |
IMAGE::AOI::n::REGION::VECTOROVERLAY_LAYER | Layer number from vector overlay file (if one is used) – (integer) | |
IMAGE::AOI::n::REGION::X | Upper left X pos of region – (integer) | |
IMAGE::AOI::n::REGION::Y | Upper left Y pos of region – (integer) | |
IMAGE::AOI::n::METHOD | The AOI method used – (string) |
Values:
|
IMAGE::AOI::n::WEIGHT | Weight value used – (double) | |
IMAGE::AOI::n::MAGNIFICATION | Magnification at which AOI was applied – (double) | |
IMAGE::AOI::n::NAME | Optional name of AOI region – (string) | |
IMAGE::AOI::n::COMMENT | Optional comment for AOI region – (string) | |
IMAGE::AOI::n::URL | Optional URL referring to AOI region – (string) |
The classical tags in the table below apply to MG2 images only:
Tag | Description | Notes |
---|---|---|
IMAGE::COMPRESSION_BLOCK_SIZE | Block size used in MrSID encoding (uint32) | |
IMAGE::COMPRESSION_GAMMA | G-weight value used in MrSID encoding (float) | |
IMAGE::COMPRESSION_VERSION | Version of encoder used (array of 3 sint32 values) | |
IMAGE::COMPRESSION_WEIGHT | Weight value used in MRSID encoding (float) | |
IMAGE::CREATION_DATE | Date and time of image encoding (string) | |
IMAGE::COMPRESSION_NLEV | Number of zoom (resolution) levels in the image (uint32) | |
IMAGE::STATISTICS:MAXIMUM | Maximum sample values for each band in the input image (array of values) | The number and datatype of the values correspond to the number of bands and sample type of the image |
IMAGE::STATISTICS:MINIMUM | Maximum sample values for each band in the input image (array of values) | The number and datatype of the values correspond to the number of bands and sample type of the image |
IMAGE::STATISTICS:MEAN | Average value of all samples for each band (array of doubles) | |
IMAGE::STATISTICS:STANDARD_DEVIATION | Standard deviation of all samples for each band | |
IMAGE::TARGET_COMPRESSION_RATIO | Compression ratio used for encoding (float) | For MG2, this only approximates the actual compression ratio achieved |
When using GeoTIFF input images, the GeoTIFF metadata tags are copied directly into the MrSID or JPEG 2000 file. When using ERDAS IMAGINE and USGS DOQ metadata, certain other custom metadata tags are inserted as well.