You are here: Appendix A - Technical Notes > Metadata Tags

Metadata Tags

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.

General Tags

The tags in the table below apply to MrSID encoding.

General Metadata Tags
Tag Description Notes
IMAGE::BITS_PER_SAMPLE Number of bits per sample (uint16)  
IMAGE::COLOR_SCHEME Colorspace of image (uint32) Values: 0 for RGB, 3 for grayscale, 2 for CMYK, 10 for multispectral
IMAGE::DATA_TYPE Datatype of samples in image (uint32) Values: 0 for unsigned 8-bit int, 1 for 32-bit float, 2 for unsigned 16-bit int
IMAGE::DEFAULT_DATA_VALUE Sample values for background pixel

Stored as an array of values, one for each band, in order. The values are stored in the datatype of the samples

NOTE: With older images containing uint8 data, the tag IMAGE::NO_DATA_VALUE may be used

IMAGE::DYNAMIC_RANGE_WINDOW Custom contrast setting (double) Represents the size of the range of the data. This tag can have per-band values for MG4 images
IMAGE::DYNAMIC_RANGE_LEVEL Custom brightness setting (double) Represents the midpoint of the range of the data. This tag can have per-band values for MG4 images
IMAGE::ENCODING_APPLICATION Name and version of encoding application Required tag
IMAGE::ENCODING_COMMENT Context of encoding operation  
IMAGE::EOM End of metadata  
IMAGE::FORMAT Text representation of the format Examples: "MrSID/MG4", "JPEG 2000"
IMAGE::HEIGHT Height of the image, in pixels (uint32)  
IMAGE::INPUT_FILE_SIZE Size of the input image or mosaic in bytes (double)  
IMAGE::INPUT_FORMAT Name of input image type (string)  
IMAGE::INPUT_LUT Color lookup table Stored as an array of 256*3 values, one value for each band (R,G,B) for each of the 256 entries in the table
IMAGE::INPUT_NAME Filename of the input image (string)  
IMAGE::LTI_ESDK_VERSION The LizardTech SDK version number  
IMAGE::MODIFICATIONS Changes to input pixel data

See list following this table for values.

 

IMAGE::NO_DATA_VALUE Sample values for background pixel Used only by older MrSID images; see IMAGE::DEFAULT_DATA_VALUE
IMAGE::SOM Start of metadata  
IMAGE::TRANSPARENT_DATA_VALUE Sample values for the "no data" pixel Stored as an array of values, one for each band, in order. Values are stored in the datatype of the samples
IMAGE::WIDTH Width of the image, in pixels (uint32)  
IMAGE::X_RESOLUTION Georeferencing pixel resolution in x-direction (double)  
IMAGE::XY_ORIGIN Georeferencing (x,y) location for the center of the upper left corner pixel Stored as an array of two doubles
IMAGE::Y_RESOLUTION Georeferencing pixel resolution in x-direction (double)  
Values for IMAGE::MODIFICATIONS Tag

The following are acceptable as values for the IMAGE::MODIFICATIONS tag:

Area of Interest (AOI) Tags

The tags in the table below apply only to images encoded with areas of interest:

Area of Interest (AOI)Tags
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:

  • "shift inner"
  • "shift outer"
  • "weight"
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)  

MG2-Only Tags

The classical tags in the table below apply to MG2 images only:

MG2-Only Tags
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

Other Metadata Tags

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.