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<p class="MsoNormal">I recently learned that <b>jpegtran</b> from the JPEG library has the ability to crop and save a new jpeg losslessly:
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><i>These transformations are each completely lossless and reversible. The transformations on the image data comprise:
<o:p></o:p></i></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1">
<![if !supportLists]><span style="font-size:10.0pt;font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><i>eliminate non-standard application-specific data inserted by some image programs,<o:p></o:p></i></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo1">
<![if !supportLists]><span style="font-size:10.0pt;font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><i>perform certain transformations on a file, such as:
<o:p></o:p></i></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:108.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-size:10.0pt;font-family:"Courier New""><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><i>discarding of colour channels (conversion to greyscale),<o:p></o:p></i></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:108.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-size:10.0pt;font-family:"Courier New""><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><i>rotating and flipping in steps of 90 degrees,<o:p></o:p></i></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:108.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-size:10.0pt;font-family:"Courier New""><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><i><span style="background:yellow;mso-highlight:yellow">cropping at image block borders</span> (every 8×8 or 16×16 pixels),<o:p></o:p></i></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;margin-left:108.0pt;text-indent:-18.0pt;mso-list:l0 level2 lfo1">
<![if !supportLists]><span style="font-size:10.0pt;font-family:"Courier New""><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><i>rescaling.<sup id="cite_ref-jpegtran_7-0"><a href="https://en.wikipedia.org/wiki/Libjpeg#cite_note-jpegtran-7">[7]</a></sup><o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:36.0pt"><i><span style="background:yellow;mso-highlight:yellow">These are lossless</span> and reversible only regarding the image data that is kept. Reencoding with repeated lossy quantisation of the image data (generation
loss) does not take place.<o:p></o:p></i></p>
<p class="MsoNormal" style="margin-left:36.0pt"><i><o:p> </o:p></i></p>
<p class="MsoNormal" style="margin-left:36.0pt"><i>-- <a href="https://en.wikipedia.org/wiki/Libjpeg#jpegtran">
https://en.wikipedia.org/wiki/Libjpeg#jpegtran</a> <o:p></o:p></i></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">Can GDAL take advantage of this for jpeg-in-geotiff images?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-top:4.0pt;line-height:115%;text-autospace:none;vertical-align:middle">
<b><span lang="EN-US" style="font-size:9.0pt;line-height:115%;font-family:"Arial",sans-serif;mso-fareast-language:EN-CA">Matt Wilkie</span></b><span lang="EN-US" style="font-size:9.0pt;line-height:115%;font-family:"Arial",sans-serif;mso-fareast-language:EN-CA"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:9.0pt;font-family:"Arial",sans-serif;mso-fareast-language:EN-CA">Geomatics Analyst<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:9.0pt;font-family:"Arial",sans-serif;mso-fareast-language:EN-CA">Environment
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