VTK：频率处理——高通滤波（巴特沃斯高通滤波）

1.巴特沃斯高通滤波

理想的高通滤波不能通过电子元器件来实现，而存在振铃现象。在实际中最常见使用的高通滤波是巴特沃斯高通滤波器。

D(u,v)表示频域中点到频域平面的距离，是截止频率。当D(u,v)大于时，对应的H(u,v)逐渐接近1，从而使得高频部分得以通过；而 D(u,v)小于时，H(u,v)逐渐接近于0，实现低频部分过滤。巴特沃斯高通滤波器在VTK中赌赢vtkImageButterworthHighPass类。

2.代码

下面代码说明VTKImageButterworthHighPass对图像进行高通滤波：

#include 
VTK_MODULE_INIT(vtkRenderingOpenGL2);
VTK_MODULE_INIT(vtkInteractionStyle);

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

int main(int argc, char* argv[])
{
	vtkSmartPointer<vtkJPEGReader> reader =
		vtkSmartPointer<vtkJPEGReader>::New();
	reader->SetFileName("data/Lena.jpg");
	reader->Update();

	vtkSmartPointer<vtkImageFFT> fftFilter =
		vtkSmartPointer<vtkImageFFT>::New();
	fftFilter->SetInputConnection(reader->GetOutputPort());
	fftFilter->Update();

	vtkSmartPointer<vtkImageButterworthHighPass> highPassFilter =
		vtkSmartPointer<vtkImageButterworthHighPass>::New();
	highPassFilter->SetInputConnection(fftFilter->GetOutputPort());
	highPassFilter->SetXCutOff(0.1);
	highPassFilter->SetYCutOff(0.1);
	highPassFilter->Update();

	vtkSmartPointer<vtkImageRFFT> rfftFilter =
		vtkSmartPointer<vtkImageRFFT>::New();
	rfftFilter->SetInputConnection(highPassFilter->GetOutputPort());
	rfftFilter->Update();

	vtkSmartPointer<vtkImageExtractComponents> ifftExtractReal =
		vtkSmartPointer<vtkImageExtractComponents>::New();
	ifftExtractReal->SetInputConnection(rfftFilter->GetOutputPort());
	ifftExtractReal->SetComponents(0);

	vtkSmartPointer<vtkImageCast> castFilter =
		vtkSmartPointer<vtkImageCast>::New();
	castFilter->SetInputConnection(ifftExtractReal->GetOutputPort());
	castFilter->SetOutputScalarTypeToUnsignedChar();
	castFilter->Update();

	vtkSmartPointer<vtkImageActor> originalActor =
		vtkSmartPointer<vtkImageActor>::New();
	originalActor->SetInputData(reader->GetOutput());

	vtkSmartPointer<vtkImageActor> erodedActor =
		vtkSmartPointer<vtkImageActor>::New();
	erodedActor->SetInputData(castFilter->GetOutput());
	//
	double leftViewport[4] = { 0.0, 0.0, 0.5, 1.0 };
	double rightViewport[4] = { 0.5, 0.0, 1.0, 1.0 };
	vtkSmartPointer<vtkRenderer> leftRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	leftRenderer->AddActor(originalActor);
	leftRenderer->ResetCamera();
	leftRenderer->SetViewport(leftViewport);
	leftRenderer->SetBackground(1.0, 1.0, 1.0);

	vtkSmartPointer<vtkRenderer> rightRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	rightRenderer->AddActor(erodedActor);
	rightRenderer->SetViewport(rightViewport);
	rightRenderer->SetBackground(1.0, 1.0, 1.0);
	rightRenderer->ResetCamera();

	vtkSmartPointer<vtkRenderWindow> rw =
		vtkSmartPointer<vtkRenderWindow>::New();
	rw->AddRenderer(leftRenderer);
	rw->AddRenderer(rightRenderer);
	rw->SetSize(640, 320);
	rw->Render();
	rw->SetWindowName("Frequency_ButterworthHighPass");
	//
		vtkSmartPointer<vtkRenderWindowInteractor> rwi =
		vtkSmartPointer<vtkRenderWindowInteractor>::New();
	vtkSmartPointer<vtkInteractorStyleImage> style =
		vtkSmartPointer<vtkInteractorStyleImage>::New();
	rwi->SetInteractorStyle(style);
	rwi->SetRenderWindow(rw);
	rwi->Start();

	return 0;
}

3.运行截图

vtkImageButterworthHighPass与理想高通滤波使用方法一致。需要设置和Y轴的截止频率，为了便于比较，其截止频域与高通滤波设置一致。