How to blend a gray and rgb image ?

Support
1

I want to blend a gray and rgb image.

Firstly, I have a image:

torgbGray = np.zeros(shape=[256, 256])
for i in range(256):
    for j in range(256):
        torgbGray[i, j] = i+j

Then, I convert this gray image to a rgb image by:

colorTable = vtk.vtkLookupTable()
colorTable.SetRange(100, 300)
colorTable.SetBelowRangeColor(0, 0, 0, 0)
colorTable.SetUseBelowRangeColor(True)
colorTable.SetAboveRangeColor(0, 0, 0, 0)
colorTable.SetUseAboveRangeColor(True)
colorTable.Build()

colorMap = vtk.vtkImageMapToColors()
colorMap.SetInputData(numpyToVTK(torgbGray))
colorMap.SetLookupTable(colorTable)
colorMap.Update()

The pixel of torgbGray would be transparent when the value is out of 100~300.

Then, I want to blend this colorMap with a gray image, for example the torgbGray.

The result is: torgbGray (left), colorMap (middle), blender result (right)

image
image487×528 13.8 KB

We can see that the torgbGray, colorMap is OK, but the blender result is wrong.

The whole code is:

import matplotlib.pyplot as plt
import vtkmodules.all as vtk
import numpy as np
from vtk.util.numpy_support import vtk_to_numpy, numpy_to_vtk

def numpyToVTK(data):
    if len(data.shape) == 2:
        data = data[:, :, np.newaxis]
    flat_data_array = data.transpose(2,1,0).flatten()
    vtk_data = numpy_to_vtk(num_array=flat_data_array, deep=True, array_type=vtk.VTK_UNSIGNED_SHORT)
    img = vtk.vtkImageData()
    img.GetPointData().SetScalars(vtk_data)
    img.SetDimensions(data.shape[0], data.shape[1], 1)
    return img

torgbGray = np.zeros(shape=[256, 256])
for i in range(256):
    for j in range(256):
        torgbGray[i, j] = i+j

grayImg = numpyToVTK(torgbGray)

colorTable = vtk.vtkLookupTable()
# colorTable.SetRange(torgbGray.min(), torgbGray.max())
colorTable.SetRange(100, 300)
colorTable.SetBelowRangeColor(0, 0, 0, 0)
colorTable.SetUseBelowRangeColor(True)
colorTable.SetAboveRangeColor(0, 0, 0, 0)
colorTable.SetUseAboveRangeColor(True)
colorTable.Build()

colorMap = vtk.vtkImageMapToColors()
colorMap.SetInputData(numpyToVTK(torgbGray))
colorMap.SetLookupTable(colorTable)
colorMap.Update()

windowLevelColor = vtk.vtkImageMapToWindowLevelColors()
windowLevelColor.SetInputData(grayImg)
windowLevelColor.Update()


grayImageActor = vtk.vtkImageActor()
grayImageActor.GetMapper().SetInputData(windowLevelColor.GetOutput())
grayRen = vtk.vtkRenderer()
grayRen.AddActor(grayImageActor)
grayRen.SetBackground(0.1, 0.2, 0.4)
grayRen.SetViewport(0, 0, 0.3, 1)

rgbImageActor = vtk.vtkImageActor()
rgbImageActor.GetMapper().SetInputData(colorMap.GetOutput())
rgbRen = vtk.vtkRenderer()
rgbRen.AddActor(rgbImageActor)
rgbRen.SetBackground(0.1, 0.2, 0.4)
rgbRen.SetViewport(0.3, 0, 0.6, 1)

image_blender = vtk.vtkImageBlend()
image_blender.AddInputData(colorMap.GetOutput())
image_blender.AddInputData(windowLevelColor.GetOutput())
image_blender.SetOpacity(1, 0.5)
image_blender.Update()

blenderImageActor = vtk.vtkImageActor()
blenderImageActor.GetMapper().SetInputData(image_blender.GetOutput())
blenderRen = vtk.vtkRenderer()
blenderRen.AddActor(blenderImageActor)
blenderRen.SetBackground(0.1, 0.2, 0.4)
blenderRen.SetViewport(0.6, 0, 1, 1)

renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(grayRen)
renWin.AddRenderer(rgbRen)
renWin.AddRenderer(blenderRen)
renWin.SetSize(400, 400)

iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)

renWin.Render()

iren.Start()

Any suggestion is appreciated~~~

2

For alpha blending, the ordering of the images is important. The image with the alpha must come after the other image:

image_blender.AddInputData(windowLevelColor.GetOutput())
image_blender.AddInputData(colorMap.GetOutput())

The math for alpha blending an overlay image [R1, G1, B1, A1] with a base image [R0, B0, G0] is:

  [R, G, B] = (1 - A1)*[R0, G0, B0]  + A1*[R1, G1, B1]
2 Likes
3

Thank you very much~~