itk::ERROR: MultiMetricMultiResolutionRegistration on multi-channel image

ITK version 5.1.0
Python version 3.8.10

I'm trying to use SimpleITK on Python to do registration with histological images and mri images using this function

```python
def get_image_from_elastix_with_masks(fixed, moving):

elastixImageFilter = sitk.ElastixImageFilter()
for f in fixed:
elastixImageFilter.AddFixedImage(sitk.GetImageFromArray(f))

for m in moving:
elastixImageFilter.AddMovingImage(sitk.GetImageFromArray(m))

parameterMapVector = sitk.VectorOfParameterMap()

bspline_param = sitk.GetDefaultParameterMap("bspline")

parameterMapVector.append(bspline_param)
elastixImageFilter.SetParameterMap(parameterMapVector)
try:
elastixImageFilter.Execute()
except:
elastixImageFilter.LogToConsoleOn()
raise

return (
sitk.GetArrayFromImage(elastixImageFilter.GetResultImage())
)
```

However, I have the following error (whatever is the number of channels unless it's 1)

```
itk::ExceptionObject (0x7665910)
Location: "ElastixTemplate - Run()"
File: /home/tower/dev/build/Elastix/Components/Registrations/MultiMetricMultiResolutionRegistration/itkMultiMetricMultiResolutionImageRegistrationMethod.hxx
Line: 549
Description: itk::ERROR: MultiMetricMultiResolutionRegistration(0x75a66b0): The number of fixed image pyramids should be >= the number of fixed images

Error occurred during actual registration.
```

Would you have any idea about how to solve this issue ?