<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:x="urn:schemas-microsoft-com:office:excel" xmlns:p="urn:schemas-microsoft-com:office:powerpoint" xmlns:a="urn:schemas-microsoft-com:office:access" xmlns:dt="uuid:C2F41010-65B3-11d1-A29F-00AA00C14882" xmlns:s="uuid:BDC6E3F0-6DA3-11d1-A2A3-00AA00C14882" xmlns:rs="urn:schemas-microsoft-com:rowset" xmlns:z="#RowsetSchema" xmlns:b="urn:schemas-microsoft-com:office:publisher" xmlns:ss="urn:schemas-microsoft-com:office:spreadsheet" xmlns:c="urn:schemas-microsoft-com:office:component:spreadsheet" xmlns:odc="urn:schemas-microsoft-com:office:odc" xmlns:oa="urn:schemas-microsoft-com:office:activation" xmlns:html="http://www.w3.org/TR/REC-html40" xmlns:q="http://schemas.xmlsoap.org/soap/envelope/" xmlns:rtc="http://microsoft.com/officenet/conferencing" xmlns:D="DAV:" xmlns:Repl="http://schemas.microsoft.com/repl/" xmlns:mt="http://schemas.microsoft.com/sharepoint/soap/meetings/" xmlns:x2="http://schemas.microsoft.com/office/excel/2003/xml" xmlns:ppda="http://www.passport.com/NameSpace.xsd" xmlns:ois="http://schemas.microsoft.com/sharepoint/soap/ois/" xmlns:dir="http://schemas.microsoft.com/sharepoint/soap/directory/" xmlns:ds="http://www.w3.org/2000/09/xmldsig#" xmlns:dsp="http://schemas.microsoft.com/sharepoint/dsp" xmlns:udc="http://schemas.microsoft.com/data/udc" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:sub="http://schemas.microsoft.com/sharepoint/soap/2002/1/alerts/" xmlns:ec="http://www.w3.org/2001/04/xmlenc#" xmlns:sp="http://schemas.microsoft.com/sharepoint/" xmlns:sps="http://schemas.microsoft.com/sharepoint/soap/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:udcs="http://schemas.microsoft.com/data/udc/soap" xmlns:udcxf="http://schemas.microsoft.com/data/udc/xmlfile" xmlns:udcp2p="http://schemas.microsoft.com/data/udc/parttopart" xmlns:wf="http://schemas.microsoft.com/sharepoint/soap/workflow/" xmlns:dsss="http://schemas.microsoft.com/office/2006/digsig-setup" xmlns:dssi="http://schemas.microsoft.com/office/2006/digsig" xmlns:mdssi="http://schemas.openxmlformats.org/package/2006/digital-signature" xmlns:mver="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns:mrels="http://schemas.openxmlformats.org/package/2006/relationships" xmlns:spwp="http://microsoft.com/sharepoint/webpartpages" xmlns:ex12t="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:ex12m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:pptsl="http://schemas.microsoft.com/sharepoint/soap/SlideLibrary/" xmlns:spsl="http://microsoft.com/webservices/SharePointPortalServer/PublishedLinksService" xmlns:Z="urn:schemas-microsoft-com:" xmlns:st="&#1;" xmlns="http://www.w3.org/TR/REC-html40">

<head>
<meta http-equiv=Content-Type content="text/html; charset=us-ascii">
<meta name=Generator content="Microsoft Word 12 (filtered medium)">
<style>
<!--
 /* Font Definitions */
 @font-face
        {font-family:Calibri;
        panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
        {font-family:Tahoma;
        panose-1:2 11 6 4 3 5 4 4 2 4;}
@font-face
        {font-family:Verdana;
        panose-1:2 11 6 4 3 5 4 4 2 4;}
 /* Style Definitions */
 p.MsoNormal, li.MsoNormal, div.MsoNormal
        {margin:0in;
        margin-bottom:.0001pt;
        font-size:11.0pt;
        font-family:"Calibri","sans-serif";}
a:link, span.MsoHyperlink
        {mso-style-priority:99;
        color:blue;
        text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
        {mso-style-priority:99;
        color:purple;
        text-decoration:underline;}
span.EmailStyle17
        {mso-style-type:personal;
        font-family:"Verdana","sans-serif";
        color:#003399;}
span.EmailStyle18
        {mso-style-type:personal;
        font-family:"Verdana","sans-serif";
        color:#003399;}
span.EmailStyle19
        {mso-style-type:personal-reply;
        font-family:"Verdana","sans-serif";
        color:#003399;}
.MsoChpDefault
        {mso-style-type:export-only;
        font-size:10.0pt;}
@page Section1
        {size:8.5in 11.0in;
        margin:1.0in 1.0in 1.0in 1.0in;}
div.Section1
        {page:Section1;}
-->
</style>
<!--[if gte mso 9]><xml>
 <o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
 <o:shapelayout v:ext="edit">
  <o:idmap v:ext="edit" data="1" />
 </o:shapelayout></xml><![endif]-->
</head>

<body lang=EN-US link=blue vlink=purple>

<div class=Section1>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Ok, here is how a GDAL caller can detect that a file is signed
8-bit:<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; band.GetMetadata('IMAGE_STRUCTURE')<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>{'PIXELTYPE': 'SIGNEDBYTE'}<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Thanks to Frank W for giving me a clue about this a week ago
that I promptly forgot about. Sorry about that.<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>So&#8230; does anyone know whether band.GetStatistics is
supposed to work for these signed 8-bit files? If not, I guess I will write a
workaround so my app will calculate statistics itself for signed 8-bit files.<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Thanks,<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Jason<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<div>

<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>

<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Jason Roberts
[mailto:jason.roberts@duke.edu] <br>
<b>Sent:</b> Wednesday, September 23, 2009 4:18 PM<br>
<b>To:</b> 'gdal-dev'<br>
<b>Subject:</b> RE: [gdal-dev] GetStatistics and signed 8-bit IMGs and GeoTIFFs<o:p></o:p></span></p>

</div>

</div>

<p class=MsoNormal><o:p>&nbsp;</o:p></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Someone suggested that I try this with 1.6.2 without saying
whether it might be a bug or by design. The behavior is the same with 1.6.2,
using binaries produced by Tamas Szekeres (thanks Tamas, for providing those on
your website).<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Back to the original question: is it a bug or by design? How
does the GDAL caller determine through GDAL that a given file is signed 8-bit
or unsigned 8-bit? <o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Thanks again,<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Jason<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<div>

<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>

<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
gdal-dev-bounces@lists.osgeo.org [mailto:gdal-dev-bounces@lists.osgeo.org] <b>On
Behalf Of </b>Jason Roberts<br>
<b>Sent:</b> Wednesday, September 23, 2009 3:11 PM<br>
<b>To:</b> 'gdal-dev'<br>
<b>Subject:</b> [gdal-dev] GetStatistics and signed 8-bit IMGs and GeoTIFFs<o:p></o:p></span></p>

</div>

</div>

<p class=MsoNormal><o:p>&nbsp;</o:p></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Is band.GetStatistics() supposed to work with signed 8-bit
integer rasters with the HFA or GTiff driver?<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>With GDAL 1.6.0, I can successfully create a signed 8-bit raster
with the HFA or GTiff driver using the PIXELTYPE=SIGNEDBYTE option:<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; a = numpy.array([[-128, -1, 0, 1, 127]],
dtype='int8')<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; a<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>array([[-128,&nbsp;&nbsp; -1,&nbsp;&nbsp;&nbsp;
0,&nbsp;&nbsp;&nbsp; 1,&nbsp; 127]], dtype=int8)<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; b = numpy.cast['uint8'](a)<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; print b<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>[[128 255&nbsp;&nbsp; 0&nbsp;&nbsp; 1 127]]<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt;<o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; gdal.UseExceptions()<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; driver = gdal.GetDriverByName('HFA')<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; dataset = driver.Create(r'C:\Temp\test_int8.img',
5, 1, 1, gdal.GDT_Byte, ['PIXELTYPE=SIGNEDBYTE'])<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; band = dataset.GetRasterBand(1)<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; band.WriteArray(b)<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>0<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; del band, dataset, driver<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>When I look at that raster with ArcGIS, it shows it is signed
8-bit integer and the five values show up properly. But when I open it with
GDAL and call band.GetStatistics(), it looks like the calculation is performed
using unsigned 8-bit integers:<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; dataset = gdal.Open(r'C:\Temp\test_int8.img',
gdalconst.GA_ReadOnly)<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; band = dataset.GetRasterBand(1)<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>&gt;&gt;&gt; band.GetStatistics(False, True)<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Courier New";
color:#003399'>[0.0, 255.0, 102.2, 95.199579831005551]<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>I am wondering if this is a bug or by design. If by design, is
there any way my application can tell through GDAL that it is a signed 8-bit
file rather than an unsigned 8-bit file?<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Thanks very much for your help,<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'>Jason<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:10.0pt;font-family:"Verdana","sans-serif";
color:#003399'><o:p>&nbsp;</o:p></span></p>

</div>

</body>

</html>