Open Printable/Searchable Copy - Global Mapper

Global Mapper User's Manual
images generated with this option will maintain good color fidelity and often be highly compressed,
although they will lose some information as compared to the uncompressed 24-bit RGB option.
Something else to keep in mind if selecting this option is that many software packages do not yet
support GeoTIFF files that use the JPEG-in-TIFF compression option. By default the JPG
compression used in the GeoTIFF file uses a quality setting of 75, but you can modify this on the
displayed options dialog.
• Multi-band - This option generates a raster GeoTIFF file with 1 or more bands of data at either 8-,
16-, or 32-bits per band of data. This option is very useful when working with multi-spectral imagery
with more than 3 bands of data, like RGBI or Landsat imagery, or data sets with more than 8 bits per
color channel. If you select this option, after hitting OK to start the dialog additional dialogs will be
presented allowing you to further setup the multi-band export by choosing the input sources for each
band in the output image.
• Black and White- This option generates a two color GeoTIFF file with 1 bit per pixel. This will
generate by far the smallest image, but if you source image had more than two colors the resulting
image will be very poor. By default, white will be a value of 0 and black will be a value of 1, but you
can reverse this by selecint the Grayscale - Min Is Black palette option.
• Elevation (16-bit integer samples) - This option generates an elevation GeoTIFF using the currently
loaded elevation grid data sets. Elevation samples will be stored as signed 16-bit integers. There are
only a handful of software packages that can recognize a vertical GeoTIFF properly, so only use this
if you know it works.
• Elevation (32-bit floating pointr samples) - This option generates an elevation GeoTIFF using the
currently loaded elevation grid data sets. Elevation samples will be stored as 32-bit floating point
values. There are only a handful of software packages that can recognize a vertical GeoTIFF properly,
so only use this if you know it works.
When generating a 256 color (8-bits per pixel) GeoTIFF, it is necessary to select a palette indicates what 256
colors will be used to describe the image being exported. The following choices of palette are available:
• Image Optimized Palette - The palette generated will be an optimal mix of up to 256 colors that will
closely represent the full blend of colors in the source images. This option will generate the best
results, but can more than double the export time required if any high color images are present in the
export set. If all of the input data is palette-based and the combined palette of those files has 256
colors or less, then the combined files of the input file will just be used with no additional export time
being required.
• Grayscale Palette - This palette consists of 256 scales of gray ranging from black to white.
• DRG Optimized Palette - This palette is optimized for the exporting USGS DRG data. The palette
consists of only the standard DRG colors.
• DRG/DOQ Optimized Palette - As the name suggests, this palette is optimized for exporting a mixture
of USGS DRG data and grayscale satellite photos (i.e. USGS DOQs). The palette consists of the 14
standard DRG colors with the remaining 242 colors being a range of gray values ranging from black
to white.
• Halftone Palette - The palette consists of a blend of 256 colors evenly covering the color spectrum.
This palette is the best choice when exporting anything but DRGs and grayscale satellite photos.
• Custom Palette from File - This option allows the user to choose a .pal file describing the palette to
use for the export. A .pal file should be a text file with one line per color, with the red, green, and blue
color components for each color in the palette separated by a comma. You can save a .pal file for an
existing palette-based file by opening the Overlay Control Center, selecting the palette-based layer,
press Options, then the Transparent Color button, then selecting the option to save a color palette file.
• Grayscale - Min is Black Palette - This palette creates an 8-bit per pixel grayscale image with no
color map stored in the image. Black will be stored as zero with varying shades of gray up to white
with a value of 255.
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