Le vendredi 06 août 2010 23:41:37, Greg Coats a écrit : > I agree that unsigned byte does not support -128. Signed byte does support > -127.
Yes > Signed byte does not could support -128. No, the validty range of a signed byte is [-128,127]. > I note that > http://www.gdal.org/gdal_translate.html shows that gdal_translate supports > 11 data types > Byte/Int16/UInt16/UInt32/Int32/Float32/Float64/CInt16/CInt32/CFloat32/CFlo > at64, and "Byte" is included, but I think this "Byte" refers to unsigned > byte. I do not see any indication that gdal_translate supports signed > byte. It's a bit more complex than that... GDAL can actually deal with signed byte datatype in a limited way. A few drivers like GTiff, HFA, EHDR or ERS can return a band of type Byte with PIXELTYPE=SIGNEDBYTE in the IMAGE_STRUCTURE metadata domain. This means that the data returned by ReadBlock()/RasterIO() must be interpretated as a signed byte instead of the default unsigned byte. See http://gdal.org/gdal_datamodel.html. GTiff and HFA drivers also support a SIGNEDBYTE creation option to mark a dataset as being of type signed byte instead of unsigned byte. I'd note that there have been fixes a few month ago in GDAL statistic computations to take into account the SIGNEDBYTE case (http://trac.osgeo.org/gdal/ticket/3151 -> fixed after 1.6.2), but there are perhaps other areas where it isn't properly taken into account. > > On Aug 6, 2010, at 12:23 PM, Even Rouault wrote: > > Filippo, > > > > What is the format of that raster file ? Can you share a link to the > > dataset ? or the output of gdalinfo at the very least > > > > I'd note that -128 can only be considered a valid value for a 8bit raster > > if the metadata item PIXELTYPE at band level is set to SIGNEDBYTE > > (IMAGE_STRUCTURE metadata domain). > > > > Best regards, > > > > Even > > > > Le vendredi 06 août 2010 18:08:56, Filippo Corò a écrit : > >> Hi List, > >> > >> I have a problem with the function GetNoDataValue () of GDAL 1.6.2 ver. > >> I use some raster where the nodatavalue is equal to -128 and the pixel > >> depth is 8bit. Opening the raster with the following code (with pydev > >> end python 2.6): > >> > >> # Get the bands and block sizes > >> primoBand primoDs.GetRasterBand = (1) > >> noval primoBand.GetNoDataValue = () > >> > >> Get noval = 0.0 and not -128 as I expected. > >> Is there any option I can use to solve the problem? > >> > >> Thanks in Advance > >> > >> Greetings > >> Filippo Corò > > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/gdal-dev _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
