ITK Importing Image Data from a Buffer

Question

I have coded a method to create an Itk image from a buffer (in my case it's a Cimg image type). This is the algorithme :

void Cimg_To_ITK (CImg<uchar> img)
{

    const unsigned int Dimension = 2;
    typedef itk::RGBPixel< unsigned char > RGBPixelType;
    typedef itk::Image< RGBPixelType, Dimension > RGBImageType;
    typedef itk::ImportImageFilter< RGBPixelType, Dimension > ImportFilterType;
    ImportFilterType::Pointer importFilter = ImportFilterType::New();
    typedef itk::ImageFileWriter<  RGBImageType  > WriterType;
    WriterType::Pointer writer = WriterType::New();


    RGBImageType::SizeType imsize;
    imsize[0] = img.width();
    imsize[1] = img.height();

    ImportFilterType::IndexType start;
    start.Fill( 0 );
    ImportFilterType::RegionType region;
    region.SetIndex( start );
    region.SetSize( imsize );
    importFilter->SetRegion( region );

    const itk::SpacePrecisionType origin[ Dimension ] = { 0.0, 0.0 };
    importFilter->SetOrigin( origin );

    const itk::SpacePrecisionType spacing[ Dimension ] = { 1.0, 1.0 };
    importFilter->SetSpacing( spacing );

    const unsigned int numberOfPixels = imsize[0] * imsize[1];
    const bool importImageFilterWillOwnTheBuffer = true;

    RGBPixelType * localBuffer = new RGBPixelType[ numberOfPixels ];
    memcpy(localBuffer->GetDataPointer(), img.data(), numberOfPixels);
    importFilter->SetImportPointer( localBuffer, numberOfPixels,importImageFilterWillOwnTheBuffer );
    writer->SetInput( importFilter->GetOutput() );
    writer->SetFileName( "output.png" );
    writer->Update();
}

I dont have what i want as a output :

input :

output :

Answer 1

CImg stores different RGB Pixels as separate componentes

You must prepare an RGBPixel buffer and iterate over the image and save to the buffer:

 RGBPixelType *buffer=new RGBPixelType[img.width()*img.height()];
 cimg_for(img,x,y)
 {
          // Now allign three colors
          buffer[x+y*img.width()]= RGBPixelType({img(x,y,0,0),img(x,y,0,1),img(x,y,0,2)});
 }
 importImageFilterWillOwnTheBuffer=true; // To avoid leaks

Answer 2

This is probably because you just copy one byte per pixel. Each RGBPixelType is likely several bytes in size:

memcpy(localBuffer->GetDataPointer(), img.data(), numberOfPixels * sizeof(RGBPixelType));

Answer 3

Might be also good idea to check how the Cimg stores the pixels for image and if it differs from the RGBPixelType. I suspect that the RGBPixelType array has pixels stored in rgbrgbrgbrgb while the other may have them in some rrrrggggbbbb style format. Or, as already hinted, if the input is a gray-scale image with single channel you have to replicate the value for each rgb value (or if both are rgb you have to copy data from all the three channels)...