Common Imagery File Formats

TIFF (TIF)
- TIFF is sometimes accompanied by a TFW (TIFF World File) which gives:
  - the coordinates of the top-left corner of the image
  - the spacing of the pixels in the image (units per pixel)
  - it is a simple 6-line text file with the following:
    - Line 1 - Cell size in the "X" direction
    - Line 2 - "Rotation" term for the row
    - Line 3 - "Rotation" term for the column
    - Line 4 - Cell size in the "Y" direction
    - Line 5 - Easting value of insertion point "X"
    - Line 6 - Northing value of insertion point "Y"
  - importantly, it doesn't indicate what coordinate system
- the most common standard is GeoTIFF, a format in which the full geographical information is embedded in the TIFF file
  - there's a free library Libgeotiff for reading GeoTIFF
MrSID
- a proprietary format (of LizardTech, Inc.) with a very high degree of compression
- many imagery agencies now distribute data in this format
- there is no publicly available way to read MrSID files, other than the plugins and free viewer (Download MrSID GeoViewer) which LizardTech provides
- fortunately, their GeoViewer is quite powerful - it can crop, resample and export areas of interest to TIF/GeoTIFF files
ECW
- another proprietary format (started from the historical software ER Mapper, now ERDAS which is owned by Intergraph) with similar compression to MrSID
- it also provided a free viewer (Windows only), although this seems lost in the sands of time
- advantages over MrSID includes Compression and SDK software which are free (as in beer) and less restricted, although still closed-source and single-platform
BIL (Band Interleaved by Line) and BSQ (Band Sequential)
- these are binary formats which are commonly used in remote-sensing and high-end GIS
- in a BIL, the data is arranged in headerless columns sorted by row ("row-major")
- BIL and BSQ are just raw data, so a separate text header file (.hdr) is required to indicate the rows, columns, bit depth, etc.
- the following diagram shows the difference between BIL, "band interleaved by pixel" (BIP), and BSQ, for an RGB image which is 5 pixels wide and 3 pixels high

BIL	BIP	BSQ
R R R R R G G G G G B B B B B R R R R R G G G G G B B B B B R R R R R G G G G G B B B B B	R G B R G B R G B R G B R G B R G B R G B R G B R G B R G B R G B R G B R G B R G B R G B	R R R R R R R R R R R R R R R G G G G G G G G G G G G G G G B B B B B B B B B B B B B B B

BIL

BIP

BSQ

 R R R R R
 G G G G G
 B B B B B
 R R R R R
 G G G G G
 B B B B B
 R R R R R
 G G G G G
 B B B B B

R G B R G B R G B R G B R G B
R G B R G B R G B R G B R G B
R G B R G B R G B R G B R G B

 R R R R R
 R R R R R
 R R R R R
 G G G G G
 G G G G G
 G G G G G
 B B B B B
 B B B B B
 B B B B B

JPEG2000 - standards page
- claims to provide better compression than standard JPEG, and adds support for storing a CRS, which would make it a promising format for geospatial imagery
- drawbacks: not widely supported yet, e.g. PhotoShop requires a commercial plugin such as Lead Tech's JPEG2000 PhotoShop Plug-in ($30)
- did some testing (Oct. 2002) using the above plugin, and found that JPEG2000 had a lot more blurring and artifacts than normal JPEG at the same file size. Did more testing in Nov. 2006, which confirmed the blurring behavior.