ITK: CannyEdgeDetectionFilter issues - c++

Question

I'm trying to use the CannyEdgeDetectionImageFilter but the GetPixel() method doesn't seem to be properly referencing the filtered image. I've tried a lot of different tactics to attempt to resolve the issue, but the only thing that seems to work is writing and reading the image to/from the disk (which is not ideal). My code is below:
typedef itk::Image<unsigned char, 2> ImageType;
typedef itk::Image<float, 2> floatImageType;
...
floatImageType::Pointer to_float(ImageType::Pointer image){
typedef itk::CastImageFilter <ImageType, floatImageType> CastFilterType;
CastFilterType::Pointer castToFloat = CastFilterType::New();
castToFloat->SetInput( image );
castToFloat->Update();
return castToFloat->GetOutput();
}
...
ImageType::Pointer check(ImageType::Pointer image){
typedef itk::ImageDuplicator <ImageType> ImageDuplicatorType;
typedef itk::RescaleIntensityImageFilter
<floatImageType, ImageType> RescaleFilter;
typedef itk::CannyEdgeDetectionImageFilter
<floatImageType, floatImageType> CannyFilter;
RescaleFilter::Pointer Rescale = RescaleFilter::New();
CannyFilter::Pointer Canny = CannyFilter::New();
ImageDuplicatorType::Pointer Duplicator = ImageDuplicatorType::New();
ImageType::Pointer cannyImage;
Canny->SetVariance( 20 );
Canny->SetUpperThreshold( 2 );
Canny->SetLowerThreshold( 20 );
Rescale->SetOutputMinimum( 0 );
Rescale->SetOutputMaximum( 255 );
Duplicator->SetInputImage(image);
Duplicator->Update();
ImageType::Pointer img_copy = Duplicator->GetOutput();
floatImageType::Pointer floatImage = to_float(img_copy);
Canny->SetInput(floatImage);
Rescale->SetInput( Canny->GetOutput() );
Rescale->Update();
cannyImage = Rescale->GetOutput();
/* Insert odd work-around here */
const ImageType::SizeType img_size = cannyImage->GetLargestPossibleRegion().GetSize();
itk::Index<2> loc = {{img_size[0]/2, 0}};
int top_edge = 0;
bool contin = true;
for (int i = 0; ((i < img_size[1]) && contin); i++){
loc[1] = i;
if (cannyImage->GetPixel(loc) != 0){
top_edge = i;
contin = false;
}
}
...
}
When a pixel value of cannyImage later on, the value should be either 0, or (if an edge) 255. However, it produces values that appear to belong to a gray-scale image.
However, if I include the following code in he section above, it works as one should expect:
std::string fname = "/tmp/canny_" + to_string(getpid()) + ".tmp";
writeImage(cannyImage, fname);
cannyImage = readImage(fname);
(Methods writeImage(ImageType::Pointer image, std::string filename) and ImageType::Pointer readImage(std::string filename) were defined earlier the program.)
Anyone know what's going wrong with my program? Why does pushing it through the disk IO cause it to work?