<div dir="ltr">Hi David,<div><br></div><div>first of all, thank you for your reply.</div><div>No, the difference is not related to disk caching issues. Here are two test methods that I've written:</div><div><br></div><div>
<br></div><div><div>public static void testVTKImageReader()</div><div> { </div><div> long startTime = System.currentTimeMillis();</div><div> </div><div> vtkImageReader testReaderVTK = new vtkImageReader();</div>
<div> testReaderVTK.FileLowerLeftOn();</div><div> testReaderVTK.SetFileDimensionality(3);</div><div> testReaderVTK.SetFileName("C:\\Test\\SeriesVolume.raw");</div><div><br></div><div> testReaderVTK.SetDataExtent(0, 511,</div>
<div> 0, 511,</div><div> 0, 520);</div><div> testReaderVTK.SetDataSpacing(1.0, 1.0, 1.0);</div><div> testReaderVTK.SetDataOrigin(0.0, 0.0, 0.0);</div><div> testReaderVTK.SetDataScalarTypeToUnsignedShort();</div>
<div> testReaderVTK.SetDataByteOrderToBigEndian();</div><div> testReaderVTK.UpdateWholeExtent();</div><div> </div><div> long endTime = System.currentTimeMillis();</div><div> </div><div> System.out.println("Volume read by vtkImageReader. Total time millis = " + (endTime - startTime));</div>
<div> }</div><div> </div><div> public static void testVTKImageReader2()</div><div> {</div><div> long startTime = System.currentTimeMillis();<br></div><div> </div><div> vtkImageReader2 testReaderVTK = new vtkImageReader2();</div>
<div> testReaderVTK.FileLowerLeftOn();</div><div> testReaderVTK.SetFileDimensionality(3);</div><div> testReaderVTK.SetFileName("C:\\Test\\SeriesVolume.raw");</div><div><br></div><div> testReaderVTK.SetDataExtent(0, 511,</div>
<div> 0, 511,</div><div> 0, 520);</div><div> testReaderVTK.SetDataSpacing(1.0, 1.0, 1.0);</div><div> testReaderVTK.SetDataOrigin(0.0, 0.0, 0.0);</div><div> testReaderVTK.SetDataScalarTypeToUnsignedShort();</div>
<div> testReaderVTK.SetDataByteOrderToBigEndian();</div><div> testReaderVTK.UpdateWholeExtent();</div><div> </div><div> long endTime = System.currentTimeMillis();</div><div> </div><div> System.out.println("Volume read by vtkImageReader2. Total time millis = " + (endTime - startTime));</div>
<div> }</div></div><div><br></div><div>After doing a couple of "cold starts" in order to "warm up" disk caches, on my test PC method "testVTKImageReader()" executes in around 2 seconds, while method "testVTKImageReader2()" executes in around 10 seconds.</div>
<div>I've tried executing testVTKImageReader() before and testVTKImageReader2() after or viceversa during the same execution session, but the result doesn't change: testVTKImageReader() is always around 5 times faster than testVTKImageReader2().</div>
<div><br></div><div>Can you guess why?</div><div>Thanks and best regards,</div><div><br></div><div>Marco Sambin</div><div><br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Thu, Jun 12, 2014 at 7:12 PM, David Gobbi <span dir="ltr"><<a href="mailto:david.gobbi@gmail.com" target="_blank">david.gobbi@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi Marco,<br>
<br>
When used the way they are in your example code, vtkImageReader and<br>
vtkImageReader2 should be exactly the same speed.<br>
<br>
Can you explain your testing methodology in more detail? I suspect that<br>
when you tested vtkImageReader2, it was reading from disk, and when<br>
testing vtkImageReader, it was reading from disk cache. The only part<br>
of the "read" operation that actually requires any CPU time is the byte<br>
swapping, but that should be identical for the two readers.<br>
<br>
- David<br>
<br>
<br>
On Thu, Jun 12, 2014 at 11:00 AM, Marco Sambin <<a href="mailto:m.sambin@gmail.com">m.sambin@gmail.com</a>> wrote:<br>
> Hi all.<br>
> I am reading a volume made up of a set of "slices" stored in a single large<br>
> raw file, containing just the raw pixels of each slice (unsigned short<br>
> values), one slice after the other. I know in advance image size, position,<br>
> orientation and spacing information related to each slice.<br>
> I used to read my input raw volume through the vtkImageReader2 class, as<br>
> documentation of vtkImageReader states:<br>
><br>
> "vtkImageReader provides methods needed to read a region from a file. It<br>
> supports both transforms and masks on the input data, but as a result is<br>
> more complicated and slower than its parent class vtkImageReader2."<br>
><br>
> so I always assumed vtkImageReader2 to be faster than vtkImageReader to read<br>
> a simple volume made up of a set of raw slices.<br>
> This until today, when I tried replacing my instance of vtkImageReader2 with<br>
> an instance of vtkImageReader. Guess what? My volume reading code now<br>
> executes around 10 times faster!<br>
><br>
> Is this expected? Can you guess what may be the reason for such a<br>
> significant difference in performance between vtkImageReader2 and<br>
> vtkImageReader, the latter being much faster in my scenario (despite what<br>
> the documentation states)?<br>
><br>
> For completeness, I am using VTK 6.1 64-bit from Java 7 64-bit, under<br>
> Windows 7 Professional 64-bit. Here is a code fragment showing how I<br>
> configure my reader:<br>
><br>
> [...]<br>
> imageReaderVTK = new vtkImageReader(); // much slower if I use<br>
> "vtkImageReader2" here<br>
> imageReaderVTK.FileLowerLeftOn();<br>
> imageReaderVTK.SetFileDimensionality(3);<br>
> imageReaderVTK.SetFileName(curRawVolFile.getAbsolutePath());<br>
> imageReaderVTK.SetDataExtent(0, sliceCols - 1,<br>
> 0, sliceRows - 1,<br>
> 0, numOfUsedImages - 1);<br>
> imageReaderVTK.SetDataSpacing(xSpacing, ySpacing, zSpacing);<br>
> imageReaderVTK.SetDataOrigin(0.0, 0.0, 0.0);<br>
> imageReaderVTK.SetDataScalarTypeToUnsignedShort();<br>
> imageReaderVTK.SetDataByteOrderToBigEndian();<br>
> imageReaderVTK.UpdateWholeExtent();<br>
> [...]<br>
><br>
> My typical input raw volume is made up of around 500 slices, each one<br>
> 512x512 pixels large.<br>
><br>
> Thanks in advance for your feedback.<br>
> Best regards,<br>
><br>
> Marco Sambin<br>
</blockquote></div><br></div>