# vtkImageData: SetScalarComponentFromDouble do not change GetScalarRange
**URL:** https://discourse.vtk.org/t/vtkimagedata-setscalarcomponentfromdouble-do-not-change-getscalarrange/9703
**Category:** Support
**Created:** [October 31, 2022, 2:41am UTC](https://discourse.vtk.org/t/vtkimagedata-setscalarcomponentfromdouble-do-not-change-getscalarrange/9703 "2022-10-31T02:41:41Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@zhang-qiang-github](https://discourse.vtk.org/u/zhang-qiang-github)
#### Post date: [October 31, 2022, 2:41am UTC](https://discourse.vtk.org/t/vtkimagedata-setscalarcomponentfromdouble-do-not-change-getscalarrange/9703/1 "2022-10-31T02:41:41Z")
For a `vtkImageData`, I want to modify the scalar using `SetScalarComponentFromDouble`. But, I find the `GetScalarRange` do not return the correct result after `SetScalarComponentFromDouble`.
My test code is:
```auto
import vtkmodules.all as vtk
img = vtk.vtkImageData()
img.SetDimensions(100, 100, 1)
img.AllocateScalars(vtk.VTK_DOUBLE, 1)
for i in range(100):
for j in range(100):
img.SetScalarComponentFromDouble(i, j, 0, 0, i+j)
range1 = img.GetScalarRange()
print('range1: ', range1)
img.SetScalarComponentFromDouble(0, 0, 0, 0, 1000)
img.Modified()
range2 = img.GetScalarRange()
print('range2: ', range2)
```
The `range2` is the same with `range1` (0~198) even `img.SetScalarComponentFromDouble(0, 0, 0, 0, 1000)`.
After look at the c++ code, I find that the `range` do not computer after `SetScalarComponentFromDouble`. For `vtkDataArray`, the `GetRange` explain that:
```auto
The range is computed and then cached, and will not be re-computed on subsequent calls to GetRange().
```
How can I force it to re-compute range?
---
### Author:  [@zhang-qiang-github](https://discourse.vtk.org/u/zhang-qiang-github)
#### Post date: [October 31, 2022, 3:32am UTC](https://discourse.vtk.org/t/vtkimagedata-setscalarcomponentfromdouble-do-not-change-getscalarrange/9703/2 "2022-10-31T03:32:20Z")
The explanation of `vtkDataArray::ComputeRange` said: “Call ClearRange to force a recomputation if it is needed.”
1. I can not find `ClearRange` method in `vtk`.
2. How to call `ClearRange` in `vtkImageData`?
---
### Author:  [@dgobbi](https://discourse.vtk.org/u/dgobbi)
#### Post date: [October 31, 2022, 4:18pm UTC](https://discourse.vtk.org/t/vtkimagedata-setscalarcomponentfromdouble-do-not-change-getscalarrange/9703/3 "2022-10-31T16:18:32Z")
The `ClearRange()` method doesn’t exist in VTK anymore (I’m not sure when it was removed).
But to answer your original question, instead of `img.Modified()`, call the following:
```python
img.GetPointData().GetScalars().Modified()
```
To see why, consider how `SetScalarComponentFromDouble()` is implemented in vtkImageData.cxx:
```nohighlight
vtkIdType index = this->GetScalarIndex(x, y, z);
vtkDataArray* scalars = this->GetPointData()->GetScalars();
scalars->SetComponent(index, comp);
```
The `Set` method is being called on the `vtkDataArray` object.