# Relation between vtkImageData WL and vtkImageActor WL
**URL:** https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934
**Category:** Support
**Created:** [April 1, 2020, 2:23pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934 "2020-04-01T14:23:59Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 1, 2020, 2:24pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/1 "2020-04-01T14:24:00Z")
What is the relation between _Window Level_ from **vtkImageData** and Window Level from **vtkImageActor**?
**vtkImageProperty** class has 2 members:
```
double ColorWindow;
double ColorLevel;
```
and they are initialized with **255** and **127.5** in constructor.
```
double dActorWindow = myImageActor->GetProperty()->GetColorWindow();
double dActorLevel = myImageActor->GetProperty()->GetColorLevel();
```
Fine.
**vtkImageData** window level values are taken _from DICOM tags_.
Let say that I have a DICOM series that has **80** as window and **30** as level. The pipeline put the data from **vtkImageData** into **vtkImageActor** in order to display 2d image.
When I display the initial window level value, in order to display the **original WL** , for **vtkImageActor** window **255** I should display the value as **80** , as **vtkImageData** said. When user change WL from the mouse, it change it on **vtkImageActor**. Let say that user increase with 5 window color. Because the **vtkImageActor** 255 means 80, when user increase **vtkImageActor** window color by 5, I display 85, right ? I hope you understand it:
`vtkImageData window color: 80 -> vtkImageActor window color: 255 -> display: 80;`
user increase vtkImageActor with 5.
` vtkImageActor window color: 300 -> display: 85;`
Well, I guess this approach is not correct, because with this calculation, when I have on my vtkImageActor W/L 400/50, my image looks more diffuse and darker like other 2d dicom viewers at the same WL. And I suspect that this calculation is wrong.
I can get here some image samples if need it.
My question is, how to convert correctly vtkImageActor window level regarding original vtkImageData ?
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 2, 2020, 8:49am UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/2 "2020-04-02T08:49:10Z")
How you compute/translate your vtkImageActor WL on your display ? Just a little hint/ help mean a lot for me !!! Thank you.
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 3, 2020, 2:06pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/3 "2020-04-03T14:06:03Z")
Is there any example of how to setup WL on vtkImageActor ? I’ve found nothing on VTK examples …
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 12, 2020, 4:56pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/4 "2020-04-12T16:56:13Z")
I think I have to include in my pipeline **vtkImageMapToWindowLevelColors** object. But I don’t know how. And I have seeked on internet, but I’ve found nothing …
can you tell me how to include this object in my pipeline ?
Thank you.
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 13, 2020, 9:03am UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/5 "2020-04-13T09:03:00Z")
I’ve found an example here: [https://lorensen.github.io/VTKExamples/site/Cxx/ImageProcessing/IdealHighPass/](https://lorensen.github.io/VTKExamples/site/Cxx/ImageProcessing/IdealHighPass/)
But after I put my **vtkImageMapToWindowLevelColors** into my pipeline, the WL values are still like before install this object in my pipeline.
---
### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [April 13, 2020, 4:36pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/6 "2020-04-13T16:36:35Z")
@flaviu2 All the window width/level values (for `vtkImageActor` and `vtkImageMapToWindowLevelColors`) should be in the range of the data type of your `vtkImageData`. You shouldn’t have the discrepancy as you mentioned.
Could you post your pipeline code?
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 13, 2020, 7:03pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/7 "2020-04-13T19:03:07Z")
Thank you @sankhesh, you are so kind ! I’ll prepare for you my pipeline listing. I’ll come back a little bit later. See you !
Flaviu.
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 14, 2020, 9:01am UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/8 "2020-04-14T09:01:37Z")
Here is my pipeline:
Input data: vtkDICOMReader -\> **vtkImageReslice** (named as _m\_pResliceAxial_)
View data: vtkImageActor -\> vtkImageMapToColors -\> **vtkImageReslice**
where _vtkImageMapToColors_, named as **m\_pColorAxial** is defined as:
```
// Create a greyscale lookup m_pLUTAxial
m_pLUTAxial->SetValueRange(0.0, 1.0); // from black to white
m_pLUTAxial->SetSaturationRange(0.0, 0.0); // no color saturation
m_pLUTAxial->SetRange(dLevel - 0.5 * dWindow, dLevel + 0.5 * dWindow); // image intensity range
m_pLUTAxial->SetHueRange(0, 1);
m_pLUTAxial->SetRampToLinear();
m_pLUTAxial->Build();
m_pColorAxial->SetLookupTable(m_pLUTAxial);
m_pColorAxial->SetInputConnection(m_pResliceAxial->GetOutputPort());
m_pColorAxial->SetOutputFormatToLuminance();
```
and
```
m_pImageActor->GetMapper()->SetInputConnection(m_pColorAxial->GetOutputPort());
```
where **dWindow** and **dLevel** is taken from DICOM tags (in this case is 80/35).
Is ok the presentation ? I mean is understandable ? Please tell me if I should give more details.
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 19, 2020, 11:33am UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/9 "2020-04-19T11:33:16Z")
I guess I identified the problem, but I don’t know how to solve it. The problem seem to be at setting **vtkLookupTable** for **vtkImageMapToColors** :
```
m_pLUTAxial->SetValueRange(0.0, 1.0); // from black to white
m_pLUTAxial->SetSaturationRange(0.0, 0.0); // no color saturation
m_pLUTAxial->SetRange(dLevel - 0.5 * dWindow, dLevel + 0.5 * dWindow); // image intensity range
m_pLUTAxial->SetHueRange(0, 1);
m_pLUTAxial->SetRampToLinear();
m_pLUTAxial->Build();
m_pColorAxial->SetOutputFormatToLuminance();
m_pColorAxial->SetLookupTable(m_pLUTAxial);
m_pColorAxial->SetInputConnection(m_pResliceAxial->GetOutputPort());
```
where **dWindow** and **dLevel** is coming from DICOM series. (In this case is 80/35).
_If I would not setup LUT for vtkImageMapToColors_, I mean comment this line:
`m_pColorAxial->SetLookupTable(m_pLUTAxial);`
the WL is correct any any WL value, but instead, I got this error:
```
ERROR: In D:\VTK\VTK-8.2.0\Imaging\Core\vtkImageMapToColors.cxx, line 154
vtkImageMapToColors (00000233F446F670): RequestInformation: No LookupTable was set but input data is not VTK_UNSIGNED_CHAR, therefore input can't be passed through!
```
So, how can I overcome this issue ? I am working on this from long time … ☹
---
### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [April 20, 2020, 2:55am UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/10 "2020-04-20T02:55:25Z")
> [@flaviu2](#):
>
> ```auto
> m_pColorAxial->SetOutputFormatToLuminance();
>
> ```
Setting the output format to a single channel would mean that the image mapper would also do a color lookup. If you want the `vtkImageMapToWindowLevelColors` to be your final color lookup, set the output format to RGB (or RGBA if you want translucency in the mapped colors).
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 20, 2020, 7:54am UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/11 "2020-04-20T07:54:57Z")
Here is the modification:
```
m_pLUTAxial->SetValueRange(0.0, 1.0); // from black to white
m_pLUTAxial->SetSaturationRange(0.0, 0.0); // no color saturation
m_pLUTAxial->SetRange(dLevel - 0.5 * dWindow, dLevel + 0.5 * dWindow); // image intensity range
m_pLUTAxial->SetHueRange(0, 1);
m_pLUTAxial->SetRampToLinear();
m_pLUTAxial->Build();
m_pColorAxial->SetOutputFormatToRGB(); // <-- modification
m_pColorAxial->SetLookupTable(m_pLUTAxial);
m_pColorAxial->SetInputConnection(m_pResliceAxial->GetOutputPort());
```
“where **dWindow** and **dLevel** is taken from DICOM tags (in this case is 80/35).”
These values are taken:
```
vtkDICOMMetaData* pMeta = m_pDICOMReader->GetMetaData();
const vtkDICOMValue& dWindow = pMeta->GetAttributeValue(DC::WindowWidth);
const vtkDICOMValue& dLevel = pMeta->GetAttributeValue(DC::WindowCenter);
```
Seem to behave the same way. At the **WL** like in dicom series, 80/35, my image look the same like in Radiant. But if I modify WL at 400/50, my image looks whiter than Radiant look at 400/50 WL.
---
### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [April 20, 2020, 2:11pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/12 "2020-04-20T14:11:19Z")
The lookup table could be saturating. What is the range you set on the lookup table? For testing, remove the following line:
> [@flaviu2](#):
>
> m\_pColorAxial-\>SetLookupTable(m\_pLUTAxial)
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 20, 2020, 2:40pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/13 "2020-04-20T14:40:33Z")
If I commented that line I got the following warning/error:
```
ERROR: In D:\VTK\VTK-8.2.0\Imaging\Core\vtkImageMapToColors.cxx, line 154
vtkImageMapToColors (000001FC9C3FE1D0): RequestInformation: No LookupTable was set but input data is not VTK_UNSIGNED_CHAR, therefore input can't be passed through!
```
I guess I cannot get out those line, would I ?
---
### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [April 20, 2020, 2:45pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/14 "2020-04-20T14:45:37Z")
I see. In that case, could you set the range of the lookup table to be the scalar range of the image data and not derived from the window and level tags?
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 20, 2020, 3:34pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/15 "2020-04-20T15:34:53Z")
I have tried:
```
double* dRange = m_pDICOMReader->GetOutput()->GetScalarRange();
```
and
```
m_pLUTAxial->SetValueRange(0.0, 1.0); // from black to white
m_pLUTAxial->SetSaturationRange(0.0, 0.0); // no color saturation
m_pLUTAxial->SetRange(dRange); // image intensity range
m_pLUTAxial->SetHueRange(0, 1);
m_pLUTAxial->SetRampToLinear();
m_pLUTAxial->Build();
m_pColorAxial->SetOutputFormatToRGBA();
m_pColorAxial->SetLookupTable(m_pLUTAxial);
m_pColorAxial->SetInputConnection(m_pResliceAxial->GetOutputPort());
```
The image are darker than in Radiant at the original WL, 80/35.
**dRange** has following values: 0.0 and 3913.0
---
### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [April 20, 2020, 4:31pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/16 "2020-04-20T16:31:56Z")
I am not sure what the difference could be. One suggestion - try loading your data in Slicer and see if the image looks different with the same window/level values. Slicer uses VTK for visualization and the pipeline is similar. If the image looks right in Slicer, maybe that could give you a clue as to what could be wrong with your code.
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 20, 2020, 6:40pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/17 "2020-04-20T18:40:38Z")
Is there a sure thing: if I didn’t apply LUT to my **vtkImageMapToColors** (_m\_pColorAxial_), my image looks and behave just like Radiant or 3dslicer. Once I included **vtkLookupTable** (_m\_pLUTAxial_), my image doesn’t look and behave exactly like Radiant or 3dslicer. And this issue drive me crazy for days …
---
### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [April 20, 2020, 8:22pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/18 "2020-04-20T20:22:07Z")
That means an issue with your lookup table. See the documentation here: [https://vtk.org/doc/nightly/html/classvtkImageMapToWindowLevelColors.html#details](https://vtk.org/doc/nightly/html/classvtkImageMapToWindowLevelColors.html#details)
---
### Author:  [@flaviu2](https://discourse.vtk.org/u/flaviu2)
#### Post date: [April 21, 2020, 8:33am UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/19 "2020-04-21T08:33:46Z")
I don’t have [vtkImageMapToWindowLevelColors](https://vtk.org/doc/nightly/html/classvtkImageMapToWindowLevelColors.html#details) into my pipeline … There is 2 questions: how should include it in my pipeline ? and, if I would include it, it solve my problem ?
---
### Author:  [@sankhesh](https://discourse.vtk.org/u/sankhesh)
#### Post date: [April 21, 2020, 2:36pm UTC](https://discourse.vtk.org/t/relation-between-vtkimagedata-wl-and-vtkimageactor-wl/2934/20 "2020-04-21T14:36:37Z")
Typically, the simplest image mapping pipeline would be something like this:
```cpp
vtkNew colors;
colors->SetInputConnection(reader->GetOutputPort());
// No need to set lookup table, unless you want a custom lookup table
// No need to set range, unless you want a limited range to be mapped
colors->SetWindow(window);
colors->SetLevel(level);
vtkNew actor;
actor->GetMapper()->SetInputConnection(colors->GetOutputPort());
```
For a detailed example, see [https://lorensen.github.io/VTKExamples/site/Cxx/Images/Transparency/](https://lorensen.github.io/VTKExamples/site/Cxx/Images/Transparency/).
You can replace `vtkImageMapToColors` with `vtkImageMapToWindowLevelColors` in that example to control window width/level of the displayed image.