returned a result with an exception set
```
# Optional context
## Current approach
The goal is to run a registration between two 3D objects as shown [here](https://discourse.itk.org/t/3d-image-registration-with-python-and-without-simpleitk/4773). There, @dzenanz set the image type into `itk.ImageRegistrationMethodv4`. The original data was created with
1. a numpy array
2. saved to a file and
3. read back with ~itk.imread
## Related posts
[Here](https://discourse.itk.org/t/image-type-for-an-itk-image-from-numpy-array/2348/2), I have seen that a `PyBuffer` can be used to specify the type of data for `GetImageFromArray` (which is the same as `image_from_array`).
```
ImageType = itk.Image[itk.RGBPixel[itk.UC], 3]
itk_image = itk.PyBuffer[ImageType].GetImageFromArray(np_image)
```
Also, [here](https://www.kitware.com/itk-python-image-pixel-types/), I found that image types can be casted
```
PixelType = itk.ctype(“unsigned char”)
image = itk.imread("input_filename.png", PixelType)
dimension = image.GetImageDimension()
InputImageType = type(image)
OutputPixelType = itk.ctype(“float”)
OutputImageType = itk.Image[OutputPixelType, dimension]
cast = itk.CastImageFilter[InputImageType, OutputImageType].New(image)
itk.imwrite(cast, "output_filename.png")
```
## Workaround
I have found that I can do this
```
fixed_image = itk.image_from_array(holder[0])
moving_image = itk.image_from_array(holder[-1])
# Set the data in the right format (casting)
fixed_castImageFilter = itk.CastImageFilter[
type(fixed_image), ImageType].New()
fixed_castImageFilter.SetInput(fixed_image)
moving_castImageFilter = itk.CastImageFilter[
type(moving_image), ImageType].New()
moving_castImageFilter.SetInput(moving_image)
```
followed by this
```
registration = itk.ImageRegistrationMethodv4[FixedImageType,MovingImageType].New(
FixedImage=fixed_castImageFilter,
MovingImage=moving_castImageFilter,
Metric=metric,
Optimizer=optimizer,
InitialTransform=initialTransform)
```
## System
Table 1: Python and ITK versions
| Python | 3.10.1 |
| ITK | 5.2.1 |
| Numpy | 1.21.5 |
| Scipy | 1.7.3 |
| Parabola\_(GNU/Linux) | 5.15.12-gnu-1 |
| gcc | 11.1.0 |
---
### Author:  [@phcerdan](https://discourse.itk.org/u/phcerdan)
#### Post date: [February 2, 2022, 8:03am UTC](https://discourse.itk.org/t/read-numpy-array-as-itk-itkimagepython-itkimagef3/4776/2 "2022-02-02T08:03:14Z")
Hi @edgar, the pixel type in numpy and itk has to match.
`float` in `itk` and `C and C++` languages is `np.float32`, `float` in python is usually equivalent to `double` in `C and C++`.
```auto
# Option 1
itk_image = itk.image_from_array(holder[0].astype(np.float32), ttype=(ImageType,))
```
You don’t need to specify the ttype. The following is equivalent and easier to read:
```auto
itk_image = itk.image_from_array(holder[0].astype(np.float32))
```
You are going to get bite by the shape of your holder, it seems to me that you are creating as a (x,y,z), but in python the standard is (z,y,x). ITK assume the standard when converting from/to numpy.
Check `itk_image.GetLargestPossibleRegion().GetSize()`, it is `itkSize3 ([3, 10, 10])`. ITK follows c convention: X, Y, Z, you are getting a X=3 image, that I bet is not what you expect.
To get the shape in Z = 3, your numpy holder should be: `np.zeros((series_length, 3, 10, 10))`
Hope it helps
---
### Author:  [@dzenanz](https://discourse.itk.org/u/dzenanz)
#### Post date: [February 2, 2022, 3:21pm UTC](https://discourse.itk.org/t/read-numpy-array-as-itk-itkimagepython-itkimagef3/4776/3 "2022-02-02T15:21:32Z")
@edgar, it looks like you could benefit from reading an up-to-date [getting started with ITK Python](https://itkpythonpackage.readthedocs.io/en/master/Quick_start_guide.html#filter-types). Your code could be significantly shortened and simplified.
Many of the examples have not been updated to the latest and greatest syntax. A possible exercise for you is to update one of the examples from functional to procedural syntax, and then [propose a PR](https://github.com/InsightSoftwareConsortium/ITKSphinxExamples/blob/master/Documentation/Contribute/ContributeWithGit.rst) with the changes.
---
### Author:  [@edgar](https://discourse.itk.org/u/edgar)
#### Post date: [February 2, 2022, 4:01pm UTC](https://discourse.itk.org/t/read-numpy-array-as-itk-itkimagepython-itkimagef3/4776/4 "2022-02-02T16:01:50Z")
This is great Pablo @phcerdan. Thank you very much.
Indeed, I was aware of the indexing situation, but I appreciate that you point it out.
---
### Author:  [@edgar](https://discourse.itk.org/u/edgar)
#### Post date: [February 2, 2022, 4:08pm UTC](https://discourse.itk.org/t/read-numpy-array-as-itk-itkimagepython-itkimagef3/4776/5 "2022-02-02T16:08:27Z")
Oh, ! did consult the [Getting started](https://itkpythonpackage.readthedocs.io/en/master/Quick_start_guide.html), but I could not find a way to convert my arrays. All of the examples dealt with reading files and that’s how I managed to deal with 2D.
Would it be fine if I paste my diff or my code over here or somewhere else? I try to stay away from M$oft. (I can create a repo on Codeberg, notabug, savannah or similar services).
Thank you very much for your advice.
---
### Author:  [@dzenanz](https://discourse.itk.org/u/dzenanz)
#### Post date: [February 2, 2022, 4:28pm UTC](https://discourse.itk.org/t/read-numpy-array-as-itk-itkimagepython-itkimagef3/4776/6 "2022-02-02T16:28:14Z")
If you dislike GitHub that much, you could attach a git diff file to a post here. And of course, tell us how to best attribute that contribution to you.
---
### Author:  [@edgar](https://discourse.itk.org/u/edgar)
#### Post date: [February 2, 2022, 4:41pm UTC](https://discourse.itk.org/t/read-numpy-array-as-itk-itkimagepython-itkimagef3/4776/7 "2022-02-02T16:41:04Z")
Hi @dzenanz. I really appreciate the flexibility. Don’t worry about the attribution. My biggest interest is the growth of free software. Let me take the chance to express my gratitude to you, KitWare and all who contribute to that goal 😃 . I will post my full solution shortly.
---
### Author:  [@edgar](https://discourse.itk.org/u/edgar)
#### Post date: [February 2, 2022, 5:23pm UTC](https://discourse.itk.org/t/read-numpy-array-as-itk-itkimagepython-itkimagef3/4776/8 "2022-02-02T17:23:34Z")
[0001-Simple-3D-registration-example-with-Python.patch](https://discourse.itk.org/uploads/short-url/nEyqJP1xbaecIanKsWUjubZgsIg.patch) (7.6 KB)
---
### Author:  [@dzenanz](https://discourse.itk.org/u/dzenanz)
#### Post date: [February 2, 2022, 10:41pm UTC](https://discourse.itk.org/t/read-numpy-array-as-itk-itkimagepython-itkimagef3/4776/9 "2022-02-02T22:41:37Z")
I now see that you put GPL3 into the file. To incorporate it into ITK examples, it needs to be licensed under Apache 2.0 only. Do you mind me removing GPL3 text?
---
### Author:  [@edgar](https://discourse.itk.org/u/edgar)
#### Post date: [February 2, 2022, 10:56pm UTC](https://discourse.itk.org/t/read-numpy-array-as-itk-itkimagepython-itkimagef3/4776/10 "2022-02-02T22:56:13Z")
Here you go 🙂
[0001-Simple-3D-registration-example-with-Python.patch](https://discourse.itk.org/uploads/short-url/uR2uxAPqKm4RpTA3se691QFzfrG.patch) (7.0 KB)
By the way, I am really interested in learning how to use ITK, and you mentioned that there is a newer syntax. Where can I learn about it? I am at the stage of creating little scripts to learn and test the software in terms of 3D registration. Thanks!
---
### Author:  [@dzenanz](https://discourse.itk.org/u/dzenanz)
#### Post date: [February 2, 2022, 11:05pm UTC](https://discourse.itk.org/t/read-numpy-array-as-itk-itkimagepython-itkimagef3/4776/11 "2022-02-02T23:05:39Z")
The new syntax is called _implicit_ or _procedural_ in the getting started guide. The old syntax is called _explicit_ or _functional_. You can see the differences on the example of [median filter](https://itkpythonpackage.readthedocs.io/en/master/Quick_start_guide.html#filter-types).
---
### Author:  [@edgar](https://discourse.itk.org/u/edgar)
#### Post date: [February 2, 2022, 11:12pm UTC](https://discourse.itk.org/t/read-numpy-array-as-itk-itkimagepython-itkimagef3/4776/12 "2022-02-02T23:12:56Z")
Thanks! I may ask some questions about it on another post.