<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman, new york, times, serif;font-size:12pt"><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;">Hello Dan,<br><br> Thank you for your reply. I did read the manual, but it talks of conversions in general and I wanted some info on whether the 'extra' 8 bits were dropped off from LSB or MSB. I guess this is more of a C++ thing than an ITK thing. <br><br> Thank you for your suggestions, though. I guess its the only way I can ensure less information loss.<br><br>Emma<br><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;">----- Original Message ----<br>From: Dan Mueller <d.mueller@qut.edu.au><br>To: Emma Ryan <eryanvtk@yahoo.com><br>Cc: insight-users@itk.org<br>Sent: Friday, July 6, 2007 5:55:08 PM<br>Subject: Re: [Insight-users] 16-bit IO in ITK<br><br><title></title>
<font face="Helvetica, Arial, sans-serif"><small>Hi Emma,<br>
<br>
Please read the ITK Software Guide, in particular Chapter 7: Reading
and Writing Image, and Section 6.3: Casting and Intensity Mapping:<br>
<a rel="nofollow" class="moz-txt-link-freetext" target="_blank" href="http://www.itk.org/ItkSoftwareGuide.pdf">http://www.itk.org/ItkSoftwareGuide.pdf</a><br>
<br>
If the pixel type your specify is not the same as the underlying pixel
type on disk, then the ImageIO object uses a <font face="Courier New, Courier, monospace">static_cast</font> to convert
the data, which can result in information loss if the given pixel type
is too short. For example, if the data is <font face="Courier New, Courier, monospace">signed short</font> on disk and
ranges from -1000 to +1000 (which is typical for CT images), then
reading as <font face="Courier New, Courier, monospace">unsigned char</font>
will result in information loss. However, if your data is <font face="Courier New, Courier, monospace">signed short</font> on disk and
ranges from 50 to 200, then reading as <font face="Courier New, Courier, monospace">unsigned char</font> will be
fine.<br>
<br>
Assuming you have read a 16-bit image without information loss, there
are a number of ways to 'convert' it to 8-bits -- depending on your
requirements. Please note these methods also result in 'information
loss', albeit in a somewhat more controlled manner. </small><small>One
possibility is to linearly rescale the values so that the minimum (eg.
-1000) maps to 0 and the maximum (eg. 1000) maps to 255. The <font face="Courier New, Courier, monospace">itkRescaleIntensityImageFilter</font>
achieves this:<br>
<a rel="nofollow" class="moz-txt-link-freetext" target="_blank" href="http://www.itk.org/Doxygen/html/classitk_1_1RescaleIntensityImageFilter.html">http://www.itk.org/Doxygen/html/classitk_1_1RescaleIntensityImageFilter.html</a><br>
<br>
You may also be interested in the <font face="Courier New, Courier, monospace">itkIntensityWindowingImageFilter</font>
which allows you to specify a focus window before rescaling:<br>
<a rel="nofollow" class="moz-txt-link-freetext" target="_blank" href="http://www.itk.org/Doxygen/html/classitk_1_1IntensityWindowingImageFilter.html">http://www.itk.org/Doxygen/html/classitk_1_1IntensityWindowingImageFilter.html</a><br>
<br>
HTH<br>
<br>
Cheers, Dan<br>
<br>
<br>
Emma Ryan wrote:</small></font>
<blockquote type="cite">
<style type="text/css"></style>
<div style="font-family: times new roman,new york,times,serif; font-size: 12pt;">
<div><font face="Helvetica, Arial, sans-serif"><small>Hi,<br>
<br>
Just wanted to add....<br>
<br>
If the dicom file were read as <unsigned char, 2>, how does it
convert the 16-bit to 8-bit ?<br>
<br>
How does ITK handle 16-bit data conversion to 8-bit ?
For example : if I were to read a dicom series (16-bit) as 'signed
short 'and store it as a volume in .vtk format using OutputPixelType
<unsigned char, 3>, how does the conversion take place ?<br>
<br>
Or this conversion not possible in ITK ?<br>
<br>
Thanks in advance,<br>
Emma</small></font></div>
</div>
</blockquote>
</div><br></div></div><br>
<hr size=1><a href="http://us.rd.yahoo.com/evt=48226/*http://new.toolbar.yahoo.com/toolbar/features/norton/index.php">Get the free Yahoo! toolbar</a> and rest assured with the added security of spyware protection.
</body></html>