使用 ITK 计算图像梯度的错误结果
在头文件中，我声明了所有这些类型，“Gradient ImageFilter”用于计算 2D 图像的梯度，“VectorIndexSelectionCastImageFilter”用于选择梯度计算的“x”和“y”分量，因为事实上，计算梯度的结果是矢量图像。
typedef double operatorValueType;
typedef double outputValueType;
typedef double InputPixelType;
typedef itk::Image<InputPixelType, 2> InputImageType;
typedef itk::GradientImageFilter< InputImageType, operatorValueType, outputValueType> GradientFilterType;
//for extracting a scalar from the vector image
typedef double OutputPixelTypeImage;
typedef double ComponentType;
typedef itk::CovariantVector<ComponentType,2> OutputPixelType;
typedef itk::Image <OutputPixelType, 2> OutputImageType;
typedef itk::VectorIndexSelectionCastImageFilter<OutputImageType,InputImageType> SelectionFilterType; // < intputType , outputType>
声明之后，代码的主要部分如下：
GradientFilterType::Pointer gradientFilter = GradientFilterType::New();
gradientFilter->SetInput(T_g->GetOutput()); // From T_g (is a reader) comes the image
gradientFilter->Update();
SelectionFilterType::Pointer componentExtractor_x = SelectionFilterType::New();
SelectionFilterType::Pointer componentExtractor_y = SelectionFilterType::New();
componentExtractor_x->SetIndex(0);// x component of the gradient
componentExtractor_y->SetIndex(1);// y component of the gradient
componentExtractor_x->SetInput(gradientFilter->GetOutput());
componentExtractor_y->SetInput(gradientFilter->GetOutput());
componentExtractor_x->Update();
componentExtractor_y->Update();
似乎一切正常，但问题是，当我读取图像并将其与 Matlab 中梯度的计算进行比较时（我假设是正确）结果完全不同......有人在“VectorIndexSelectionCastImageFilter”之前使用过并看到一些奇怪的东西吗？或者在计算梯度的过程中？
非常感谢！
安东尼奥
In the header file, I declare all of this types, The “Gradient ImageFilter” is for calculate the gradient of a 2D image, and the “VectorIndexSelectionCastImageFilter” is for selecting the ’x’ and ‘y’ component of the gradient calculating, due to the fact that the result of computing th gradient is a vector image.
typedef double operatorValueType;
typedef double outputValueType;
typedef double InputPixelType;
typedef itk::Image<InputPixelType, 2> InputImageType;
typedef itk::GradientImageFilter< InputImageType, operatorValueType, outputValueType> GradientFilterType;
//for extracting a scalar from the vector image
typedef double OutputPixelTypeImage;
typedef double ComponentType;
typedef itk::CovariantVector<ComponentType,2> OutputPixelType;
typedef itk::Image <OutputPixelType, 2> OutputImageType;
typedef itk::VectorIndexSelectionCastImageFilter<OutputImageType,InputImageType> SelectionFilterType; // < intputType , outputType>
After the declarations, the main part of interest of the code is below:
GradientFilterType::Pointer gradientFilter = GradientFilterType::New();
gradientFilter->SetInput(T_g->GetOutput()); // From T_g (is a reader) comes the image
gradientFilter->Update();
SelectionFilterType::Pointer componentExtractor_x = SelectionFilterType::New();
SelectionFilterType::Pointer componentExtractor_y = SelectionFilterType::New();
componentExtractor_x->SetIndex(0);// x component of the gradient
componentExtractor_y->SetIndex(1);// y component of the gradient
componentExtractor_x->SetInput(gradientFilter->GetOutput());
componentExtractor_y->SetInput(gradientFilter->GetOutput());
componentExtractor_x->Update();
componentExtractor_y->Update();
It seems that everything works fine, but the problem is that when I read the image and I compare it with the calculation of the gradient in Matlab (which I assume to be correct) the results are completely different…Anyone has used before the “VectorIndexSelectionCastImageFilter” and see something strange? Or in the process of calculating the gradient?
Thanks so much!
Antonio
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ITK 在计算中应考虑体素间距。您的图像具有各向同性单位间距吗？
这可以解释与 matlab 的差异。
ITK should respect voxel spacing in the computations. Do you images have isotropic unit spacing?
This could account for the differences with matlab.
问题出在图像的间距上，只需添加这一行：
问题就解决了，并且在各向同性空间中进行了推导
The problem was in the spacing of the image, just by adding this line:
the problem was solved, and the derivation was done in an isotropic space