[Insight-users] Import a boolean image from an array

[frankmiller at jhmi.edu]

Dan,

A variable of type bool probably has a size of 8-bits on your system.
You can do a

  std::cout << sizeof( bool )          << std::endl;
  std::cout << sizeof( unsigned char ) << std::endl;

to see. The sizeof operator returns the size in bytes.

The reason that a bool is not 1-bit is because you can only get the
address of a variable at byte resolution.

Thus an array of 16 bools is larger than an array of 2 chars. You are
experiencing a buffer overrun when USE_BOOL_ARRAY is defined as 0. You
have to be very careful when you do low-level stuff like this. sizeof()
is you friend.

Hope this helps.

Frank

On Thu, Nov 13, 2008 at 06:15:00PM +0100, Dan Mueller wrote:
> Hi Insight Users,
> 
> I am struggling to understand how to import a data array into an
> itk:Image< bool, 2 >.
> 
> I get unexpected results when I use an array of something other than
> bool[], for example unsigned char[]. As far as I understand unsigned
> char is 8-bits (although doing some googling says that is a /minimum/
> of 8-bits, whatever that means). If unsigned char = 8-bits, I would
> expect that creating an unsigned char[], setting some values, casting
> to bool* and importing should operate the same as using a bool[]. But
> the code below does not produce the same result (see attached).
> 
> Why not? Is this because of my compiler (Visual Studio 2005)? My
> machine (Windows XP 64-bit)? Or some logical error I can't spot?
> 
> Thanks for any advice.
> 
> Regards, Dan
> 
> === CMakeLists.txt ===
> PROJECT(BoolImageTest)
> CMAKE_MINIMUM_REQUIRED(VERSION 2.6)
> 
> FIND_PACKAGE(ITK REQUIRED)
> INCLUDE(${ITK_USE_FILE})
> 
> ADD_EXECUTABLE(BoolImageTest main.cxx)
> TARGET_LINK_LIBRARIES(BoolImageTest ITKCommon ITKIO)
> 
> === main.cxx ===
> 
> #define USE_BOOL_ARRAY 0
> 
> #include "itkImage.h"
> #include "itkImportImageFilter.h"
> #include "itkCastImageFilter.h"
> #include "itkImageFileWriter.h"
> 
> int main( int argc, char* argv[] )
> {
>   typedef bool BoolPixelType;
>   typedef unsigned char UnsignedCharPixelType;
>   const unsigned int Dimension = 2;
> 
>   typedef itk::Image< BoolPixelType, Dimension > BoolImageType;
>   typedef itk::Image< UnsignedCharPixelType, Dimension > OutputImageType;
>   typedef itk::ImportImageFilter< BoolPixelType, Dimension > ImportType;
> 
>   BoolImageType::SizeType size;
>   size[0] = 16;
>   size[1] = 1;
>   BoolImageType::RegionType region( size );
>   BoolImageType::SpacingType spacing;
>   spacing.Fill( 1.0 );
>   BoolImageType::PointType origin;
>   origin.Fill( 1.0 );
> 
> #if USE_BOOL_ARRAY
>   bool data[16];
>   for (unsigned int i=0; i<8; i++)
>     data[i] = true;
>   for (unsigned int i=8; i<16; i++)
>     data[i] = false;
>   void* ptr = (void*)&data;
> #else
>   unsigned char data[2];
>   data[0] = 0xF;
>   data[1] = 0x0;
>   void* ptr = (void*)&data;
> #endif
> 
>   ImportType::Pointer import = ImportType::New();
>   import->SetRegion( region );
>   import->SetSpacing( spacing );
>   import->SetOrigin( origin );
>   import->SetImportPointer( (bool*)ptr, size[0]*size[1], false );
>   import->Update();
> 
>   typedef itk::CastImageFilter< BoolImageType, OutputImageType > CastType;
>   CastType::Pointer cast = CastType::New();
>   cast->SetInput( import->GetOutput() );
>   cast->Update();
> 
>   typedef itk::ImageFileWriter< OutputImageType > WriterType;
>   WriterType::Pointer writer = WriterType::New( );
>   writer->SetInput( cast->GetOutput() );
>   writer->SetFileName( "D:/Temp/BoolTestOutput.mhd" );
>   writer->Update();
> 
>   return EXIT_SUCCESS;
> }
> 
> === Machine ===
> ITK 3.10
> CMake 2.6.0
> Visual Studio 8.0.50727.762
> Windows XP SP2 X64



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