VTK编程指南＜十四＞：VTK图像颜色映射

1、转化灰度图像

  vtkImageLuminance 负责将一个 RGB彩色图像转换为一个单组分的灰度图像。映射公式为：

Luminance = 0.3xR + 0.59xG + 0.11xB

  式中R为输入图像的第一组分(红色)，G为第二组分(绿色)，B为第三组分(蓝色)。这个公式用于计算一个 RGB 颜色的亮度。该类的使用也比较简单，用户无须设置参数。代码如下：

vtkSmartPointer<vtkImageLuminance> luminanceFilter =
vtkSmartPointer<vtkImageLuminance>::New)
luminanceFilter->SetInputConnection(reader->GetOutputPort());
luminanceFilter->Update(0;

  上例读入一幅 RGB 彩色图像，通过 vtkImageLuminance 转换为灰度图像，执行结果如图所示。

#include <vtkAutoInit.h>
VTK_MODULE_INIT(vtkRenderingOpenGL2);// VTK was built with vtkRenderingOpenGL2
VTK_MODULE_INIT(vtkInteractionStyle);


#include <vtkSmartPointer.h>
#include <vtkImageData.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkInteractorStyleImage.h>
#include <vtkRenderer.h>
#include <vtkImageActor.h>
#include <vtkBMPReader.h>
#include <vtkImageLuminance.h>

//测试图像：../data/lena.bmp
int main(int argc, char* argv[])
{
	std::string sFile = "../data/lena.bmp";

	vtkSmartPointer<vtkBMPReader> reader =
		vtkSmartPointer<vtkBMPReader>::New();
	reader->SetFileName (sFile.c_str());
	reader->Update();

	vtkSmartPointer<vtkImageLuminance> luminanceFilter =
		vtkSmartPointer<vtkImageLuminance>::New();
	luminanceFilter->SetInputData(reader->GetOutput());
	luminanceFilter->Update();

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

	vtkSmartPointer<vtkImageActor> shiftscaleActor =
		vtkSmartPointer<vtkImageActor>::New();
	shiftscaleActor->SetInputData(luminanceFilter->GetOutput());

	double originalViewport[4] = {0.0, 0.0, 0.5, 1.0};
	double shiftscaleViewport[4] = {0.5, 0.0, 1.0, 1.0};

	vtkSmartPointer<vtkRenderer> originalRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	originalRenderer->SetViewport(originalViewport);
	originalRenderer->AddActor(originalActor);
	originalRenderer->ResetCamera();
	originalRenderer->SetBackground(1.0, 1.0, 1.0);

	vtkSmartPointer<vtkRenderer> shiftscaleRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	shiftscaleRenderer->SetViewport(shiftscaleViewport);
	shiftscaleRenderer->AddActor(shiftscaleActor);
	shiftscaleRenderer->ResetCamera();
	shiftscaleRenderer->SetBackground(1.0, 1.0, 1.0);

	vtkSmartPointer<vtkRenderWindow> renderWindow =
		vtkSmartPointer<vtkRenderWindow>::New();
	renderWindow->AddRenderer(originalRenderer);
	renderWindow->AddRenderer(shiftscaleRenderer);
	renderWindow->SetSize( 640, 320 );
	renderWindow->Render();
	renderWindow->SetWindowName("Color2GrayImageExample");

	vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
		vtkSmartPointer<vtkRenderWindowInteractor>::New();
	vtkSmartPointer<vtkInteractorStyleImage> style =
		vtkSmartPointer<vtkInteractorStyleImage>::New();

	renderWindowInteractor->SetInteractorStyle(style);
	renderWindowInteractor->SetRenderWindow(renderWindow);
	renderWindowInteractor->Initialize();

	renderWindowInteractor->Start();

	return EXIT_SUCCESS;
}

2、提取颜色分组

  VTK中利用 vtkImageExtractComponents可以方便地提取彩色图像的各个颜色组分。使用该类时只需要设置要提取的组分序号即可。下述代码演示了如何提取彩色图像的某个颜色组分。

  代码中定义了三个vtkImageExtractComponents 对象，分别用来提取红、绿和蓝色组分图像，函数 vtkImageExtractComponents::SetComponents)用来设置要提取的组分号，红、绿、蓝三色分别对应0、1和2。设置完毕，执行Update()即可得到各个组分的数据。其输出为vtkImageData，每一个颜色组分数据即是一个灰度图像。图5-17 为提取一幅彩色图像三个组分图像的结果。

#include <vtkAutoInit.h>
VTK_MODULE_INIT(vtkRenderingOpenGL2);// VTK was built with vtkRenderingOpenGL2
VTK_MODULE_INIT(vtkInteractionStyle);

#include <vtkImageData.h>
#include <vtkSmartPointer.h>
#include <vtkImageExtractComponents.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkInteractorStyleImage.h>
#include <vtkRenderer.h>
#include <vtkBMPReader.h>
#include <vtkImageActor.h>
 
//测试图像：../data/lena.bmp
int main(int argc, char* argv[])
{
	std::string sFile = "../data/lena.bmp";

	vtkSmartPointer<vtkBMPReader> reader =
		vtkSmartPointer<vtkBMPReader>::New();
	reader->SetFileName (sFile.c_str());
 
	vtkSmartPointer<vtkImageExtractComponents> extractRedFilter =
		vtkSmartPointer<vtkImageExtractComponents>::New();
	extractRedFilter->SetInputConnection(reader->GetOutputPort());
	extractRedFilter->SetComponents(0);
	extractRedFilter->Update();
 
	vtkSmartPointer<vtkImageExtractComponents> extractGreenFilter =
		vtkSmartPointer<vtkImageExtractComponents>::New();
	extractGreenFilter->SetInputConnection(reader->GetOutputPort());
	extractGreenFilter->SetComponents(1);
	extractGreenFilter->Update();
 
	vtkSmartPointer<vtkImageExtractComponents> extractBlueFilter =
		vtkSmartPointer<vtkImageExtractComponents>::New();
	extractBlueFilter->SetInputConnection(reader->GetOutputPort());
	extractBlueFilter->SetComponents(2);
	extractBlueFilter->Update();
 
	// Create actors
	vtkSmartPointer<vtkImageActor> inputActor =
		vtkSmartPointer<vtkImageActor>::New();
	inputActor->SetInputData(reader->GetOutput());
 
	vtkSmartPointer<vtkImageActor> redActor =
		vtkSmartPointer<vtkImageActor>::New();
	redActor->SetInputData(extractRedFilter->GetOutput());
 
	vtkSmartPointer<vtkImageActor> greenActor =
		vtkSmartPointer<vtkImageActor>::New();
	greenActor->SetInputData(extractGreenFilter->GetOutput());
 
	vtkSmartPointer<vtkImageActor> blueActor =
		vtkSmartPointer<vtkImageActor>::New();
	blueActor->SetInputData(extractBlueFilter->GetOutput());

	double inputViewport[4] = {0.0, 0.0, 0.25, 1.0};
	double redViewport[4] = {0.25, 0.0, 0.5, 1.0};
	double greenViewport[4] = {0.5, 0.0, 0.75, 1.0};
	double blueViewport[4] = {0.75, 0.0, 1.0, 1.0};

	vtkSmartPointer<vtkRenderer> inputRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	inputRenderer->SetViewport(inputViewport);
	inputRenderer->AddActor(inputActor);
	inputRenderer->ResetCamera();
	inputRenderer->SetBackground(1.0, 1.0, 1.0);
 
	vtkSmartPointer<vtkRenderer> redRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	redRenderer->SetViewport(redViewport);
	redRenderer->AddActor(redActor);
	redRenderer->ResetCamera();
	redRenderer->SetBackground(1.0, 1.0, 1.0);
 
	vtkSmartPointer<vtkRenderer> greenRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	greenRenderer->SetViewport(greenViewport);
	greenRenderer->AddActor(greenActor);
	greenRenderer->ResetCamera();
	greenRenderer->SetBackground(1.0, 1.0, 1.0);
 
	vtkSmartPointer<vtkRenderer> blueRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	blueRenderer->SetViewport(blueViewport);
	blueRenderer->AddActor(blueActor);
	blueRenderer->ResetCamera();
	blueRenderer->SetBackground(1.0, 1.0, 1.0);
 
	vtkSmartPointer<vtkRenderWindow> renderWindow =
		vtkSmartPointer<vtkRenderWindow>::New();
	renderWindow->AddRenderer(inputRenderer);
	renderWindow->AddRenderer(redRenderer);
	renderWindow->AddRenderer(greenRenderer);
	renderWindow->AddRenderer(blueRenderer);

	renderWindow->SetSize(1200, 300);
	renderWindow->Render();
	renderWindow->SetWindowName("ImageExtractComponentsExample");
 
	vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
		vtkSmartPointer<vtkRenderWindowInteractor>::New();
	vtkSmartPointer<vtkInteractorStyleImage> style =
		vtkSmartPointer<vtkInteractorStyleImage>::New();
 
	renderWindowInteractor->SetInteractorStyle(style);
	renderWindowInteractor->SetRenderWindow(renderWindow);
	renderWindowInteractor->Initialize();
	renderWindowInteractor->Start();

	return EXIT_SUCCESS;
}

3、图像彩色映射

  图像彩色映射的原理是:先生成一个颜色查找表，然后根据图像像素的一个标量值在颜色查找表中查找对应的颜色，并用新颜色值替代原来的像素值。VTK中以vtkImageMapToColors 实现图像彩色映射，以vtkLookUpTable生成颜色查找表。下述代码演示了如何进行彩色映射。

#include <vtkAutoInit.h>
VTK_MODULE_INIT(vtkRenderingOpenGL2);// VTK was built with vtkRenderingOpenGL2
VTK_MODULE_INIT(vtkInteractionStyle);

#include <vtkSmartPointer.h>
#include <vtkImageData.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkInteractorStyleImage.h>
#include <vtkRenderer.h>
#include <vtkImageActor.h>
#include <vtkJPEGReader.h>
#include <vtkImageLuminance.h>
#include <vtkLookupTable.h>
#include <vtkImageMapToColors.h>

//测试图像：../data/lena-gray.jpg
int main(int argc, char* argv[])
{
	vtkSmartPointer<vtkJPEGReader> reader =
		vtkSmartPointer<vtkJPEGReader>::New();
	reader->SetFileName ( "..\\data\\lena-gray.jpg" );

	vtkSmartPointer<vtkLookupTable> colorTable = 
		vtkSmartPointer<vtkLookupTable>::New(); 
	colorTable->SetRange( 0.0, 255.0 );
	colorTable->SetHueRange( 0.1, 0.5 );
	colorTable->SetValueRange( 0.6, 1.0 );
	colorTable->Build();

	vtkSmartPointer<vtkImageMapToColors> colorMap = 
		vtkSmartPointer<vtkImageMapToColors>::New();
	colorMap->SetInputConnection( reader->GetOutputPort() );
	colorMap->SetLookupTable( colorTable );
	colorMap->Update();

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

	vtkSmartPointer<vtkImageActor> shiftscaleActor =
		vtkSmartPointer<vtkImageActor>::New();
	shiftscaleActor->SetInputData(colorMap->GetOutput());

	double originalViewport[4] = {0.0, 0.0, 0.5, 1.0};
	double shiftscaleViewport[4] = {0.5, 0.0, 1.0, 1.0};

	vtkSmartPointer<vtkRenderer> originalRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	originalRenderer->SetViewport(originalViewport);
	originalRenderer->AddActor(originalActor);
	originalRenderer->ResetCamera();
	originalRenderer->SetBackground(1.0, 0.8, 1.0);

	vtkSmartPointer<vtkRenderer> shiftscaleRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	shiftscaleRenderer->SetViewport(shiftscaleViewport);
	shiftscaleRenderer->AddActor(shiftscaleActor);
	shiftscaleRenderer->ResetCamera();
	shiftscaleRenderer->SetBackground(1.0, 1.0, 0.8);

	vtkSmartPointer<vtkRenderWindow> renderWindow =
		vtkSmartPointer<vtkRenderWindow>::New();
	renderWindow->AddRenderer(originalRenderer);
	renderWindow->AddRenderer(shiftscaleRenderer);
	renderWindow->SetSize(900, 300);
	renderWindow->Render();
	renderWindow->SetWindowName("Gray2ColorImageExample");

	vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
		vtkSmartPointer<vtkRenderWindowInteractor>::New();
	vtkSmartPointer<vtkInteractorStyleImage> style =
		vtkSmartPointer<vtkInteractorStyleImage>::New();

	renderWindowInteractor->SetInteractorStyle(style);
	renderWindowInteractor->SetRenderWindow(renderWindow);
	renderWindowInteractor->Initialize();
	renderWindowInteractor->Start();

	return EXIT_SUCCESS;
}

4、颜色合成

  前面了解了如何提取彩色图像的各个颜色组分，VTK也支持将多个灰度图像合并成一个彩色图像。VTK 中的 vtkImageAppendComponents 类可用来合成彩色图像，其输入需要提供三个灰度图像。下面通过一个示例来演示 vtkImageAppendComponents 类的用法。

#include <vtkAutoInit.h>
VTK_MODULE_INIT(vtkRenderingOpenGL2);// VTK was built with vtkRenderingOpenGL2
VTK_MODULE_INIT(vtkInteractionStyle);

#include <vtkSmartPointer.h>
#include <vtkImageData.h>
#include <vtkImageAppendComponents.h>
#include <vtkImageCanvasSource2D.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkInteractorStyleImage.h>
#include <vtkRenderer.h>
#include <vtkJPEGReader.h>
#include <vtkImageActor.h>

int main(int, char *[])
{
	vtkSmartPointer<vtkImageCanvasSource2D> red =
		vtkSmartPointer<vtkImageCanvasSource2D>::New();
	red->SetScalarTypeToUnsignedChar();
	red->SetNumberOfScalarComponents(1);
	red->SetExtent(0, 100, 0, 100, 0, 0);
	red->SetDrawColor(0, 0, 0, 0);
	red->FillBox(0,100,0,100);
	red->SetDrawColor(255, 0, 0.0, 0.0);
	red->FillBox(20,40,20,40);
	red->Update();

	vtkSmartPointer<vtkImageCanvasSource2D> green =
		vtkSmartPointer<vtkImageCanvasSource2D>::New();
	green->SetScalarTypeToUnsignedChar();
	green->SetNumberOfScalarComponents(1);
	green->SetExtent(0, 100, 0, 100, 0, 0);
	green->SetDrawColor(0, 0, 0, 0);
	green->FillBox(0,100,0,100);
	green->SetDrawColor(255, 0, 0, 0);
	green->FillBox(30,50,30,50);
	green->Update();

	vtkSmartPointer<vtkImageCanvasSource2D> blue =
		vtkSmartPointer<vtkImageCanvasSource2D>::New();
	blue->SetScalarTypeToUnsignedChar();
	blue->SetNumberOfScalarComponents(1);
	blue->SetExtent(0, 100, 0, 100, 0, 0);
	blue->SetDrawColor(0, 0, 0, 0);
	blue->FillBox(0,100,0,100);
	blue->SetDrawColor(255, 0, 0, 0);
	blue->FillBox(40,60,40,60);
	blue->Update();

	vtkSmartPointer<vtkImageAppendComponents> appendFilter =
		vtkSmartPointer<vtkImageAppendComponents>::New();
	appendFilter->SetInputConnection(0, red->GetOutputPort());
	appendFilter->AddInputConnection(0, green->GetOutputPort());
	appendFilter->AddInputConnection(0, blue->GetOutputPort());
	appendFilter->Update();

	vtkSmartPointer<vtkImageActor> redActor =
		vtkSmartPointer<vtkImageActor>::New();
	redActor->SetInputData(red->GetOutput());

	vtkSmartPointer<vtkImageActor> greenActor =
		vtkSmartPointer<vtkImageActor>::New();
	greenActor->SetInputData(green->GetOutput());

	vtkSmartPointer<vtkImageActor> blueActor =
		vtkSmartPointer<vtkImageActor>::New();
	blueActor->SetInputData(blue->GetOutput());

	vtkSmartPointer<vtkImageActor> combinedActor =
		vtkSmartPointer<vtkImageActor>::New();
	combinedActor->SetInputData(appendFilter->GetOutput());

	// Define viewport ranges
	// (xmin, ymin, xmax, ymax)
	double redViewport[4] = {0.0, 0.0, 0.25, 1.0};
	double greenViewport[4] = {0.25, 0.0, 0.5, 1.0};
	double blueViewport[4] = {0.5, 0.0, 0.75, 1.0};
	double combinedViewport[4] = {0.75, 0.0, 1.0, 1.0};

	// Setup renderers
	vtkSmartPointer<vtkRenderer> redRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	redRenderer->SetViewport(redViewport);
	redRenderer->AddActor(redActor);
	redRenderer->ResetCamera();
	redRenderer->SetBackground(1.0, 1.0, 1.0);

	vtkSmartPointer<vtkRenderer> greenRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	greenRenderer->SetViewport(greenViewport);
	greenRenderer->AddActor(greenActor);
	greenRenderer->ResetCamera();
	greenRenderer->SetBackground(1.0, 1.0, 1.0);

	vtkSmartPointer<vtkRenderer> blueRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	blueRenderer->SetViewport(blueViewport);
	blueRenderer->AddActor(blueActor);
	blueRenderer->ResetCamera();
	blueRenderer->SetBackground(1.0, 1.0, 1.0);

	vtkSmartPointer<vtkRenderer> combinedRenderer =
		vtkSmartPointer<vtkRenderer>::New();
	combinedRenderer->SetViewport(combinedViewport);
	combinedRenderer->AddActor(combinedActor);
	combinedRenderer->ResetCamera();
	combinedRenderer->SetBackground(1.0, 1.0, 1.0);

	vtkSmartPointer<vtkRenderWindow> renderWindow =
		vtkSmartPointer<vtkRenderWindow>::New();
	renderWindow->AddRenderer(redRenderer);
	renderWindow->AddRenderer(greenRenderer);
	renderWindow->AddRenderer(blueRenderer);
	renderWindow->AddRenderer(combinedRenderer);
	renderWindow->SetSize(1200, 300);
	renderWindow->Render();
	renderWindow->SetWindowName("ImageAppendComponentsExample");

	vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
		vtkSmartPointer<vtkRenderWindowInteractor>::New();
	vtkSmartPointer<vtkInteractorStyleImage> style =
		vtkSmartPointer<vtkInteractorStyleImage>::New();

	renderWindowInteractor->SetInteractorStyle(style);
	renderWindowInteractor->SetRenderWindow(renderWindow);
	renderWindowInteractor->Initialize();
	renderWindowInteractor->Start();

	return EXIT_SUCCESS;
}

  上述代码先利用 vtkImageCanvasSource2D 定义了三个二值图像，每个图像中绘制了一个白色矩形，并且三个矩形有部分重叠;然后定义 vtkImageAppendComponents 对象，并将三个图像设置为 vtkImageAppendComponents 对象的输入来合成图像。合成的效果为三个图像中对应的三个像素点的像素值合成一个RGB像素值，如三个图像中第100 个像素的像素值分别为255、0和0，那么该点在输出图像中的像素值为(255,0,0)，显示为红色。