[gdal-dev] Question on scaling between tif and vrt

[Stephen Woodbridge]

Hi all,

I have a .tif file with -ot Int16 and an associated .vrt file that is 
applying a color palette and is type Byte.

How does if decide on how to scale the pixel values?

Does it compute the range and then just scale and offset that values to 
the new range?

Below are the gdalinfo for each.

Thanks,
   -Steve

gdalinfo -stats MODIS_SST_EAST-201405190900.tif
Driver: GTiff/GeoTIFF
Files: MODIS_SST_EAST-201405190900.tif
        MODIS_SST_EAST-201405190900.tif.aux.xml
Size is 8800, 6600
Coordinate System is:
GEOGCS["WGS 84",
     DATUM["WGS_1984",
         SPHEROID["WGS 84",6378137,298.257223563,
             AUTHORITY["EPSG","7030"]],
         AUTHORITY["EPSG","6326"]],
     PRIMEM["Greenwich",0],
     UNIT["degree",0.0174532925199433],
     AUTHORITY["EPSG","4326"]]
Origin = (-125.000000000000000,54.931818190930159)
Pixel Size = (0.009090548548341,-0.009058565004476)
Metadata:
   AREA_OR_POINT=Area
Image Structure Metadata:
   INTERLEAVE=BAND
Corner Coordinates:
Upper Left  (-125.0000000,  54.9318182) (125d 0' 0.00"W, 54d55'54.55"N)
Lower Left  (-125.0000000,  -4.8547108) (125d 0' 0.00"W,  4d51'16.96"S)
Upper Right ( -45.0031728,  54.9318182) ( 45d 0'11.42"W, 54d55'54.55"N)
Lower Right ( -45.0031728,  -4.8547108) ( 45d 0'11.42"W,  4d51'16.96"S)
Center      ( -85.0015864,  25.0385537) ( 85d 0' 5.71"W, 25d 2'18.79"N)
Band 1 Block=8800x1 Type=Int16, ColorInterp=Gray
   Min=-10004.000 Max=6035.000
   Minimum=-10004.000, Maximum=6035.000, Mean=-673.234, StdDev=268.660
   Overviews: 4400x3300, 2200x1650, 1100x825, 550x413, 275x207
   Metadata:
     STATISTICS_MAXIMUM=6035
     STATISTICS_MEAN=-673.23378700069
     STATISTICS_MINIMUM=-10004
     STATISTICS_STDDEV=268.66013989253

gdalinfo -stats -noct MODIS_SST_EAST-201405190900.vrt
Driver: VRT/Virtual Raster
Files: /maps/wms/data/MODIS_SST_EAST/MODIS_SST_EAST-201405190900.vrt
        /maps/wms/data/MODIS_SST_EAST/MODIS_SST_EAST-201405190900.tif
Size is 8800, 6600
Coordinate System is `'
Origin = (-125.000000000000000,54.936579299999998)
Pixel Size = (0.009090548056818,-0.009058564515152)
Corner Coordinates:
Upper Left  (-125.0000000,  54.9365793)
Lower Left  (-125.0000000,  -4.8499465)
Upper Right ( -45.0031771,  54.9365793)
Lower Right ( -45.0031771,  -4.8499465)
Center      ( -85.0015886,  25.0433164)
Band 1 Block=128x128 Type=Byte, ColorInterp=Palette
   Minimum=0.000, Maximum=255.000, Mean=1.885, StdDev=21.797
   Metadata:
     STATISTICS_MAXIMUM=255
     STATISTICS_MEAN=1.8849891356749
     STATISTICS_MINIMUM=0
     STATISTICS_STDDEV=21.796961177215
   Color Table (RGB with 256 entries)