Interpolation when resampling images

When applying a transformation to an image element or a labels element, or when rasterizing an image or labels, dask_image.ndinterp.affine_transform() is called (you can search this function to find the two occurrences in the code).

At the moment we use the following or equivalent code:

    if schema == Labels2DModel or schema == Labels3DModel:
        kwargs = {"prefilter": False, "order": 0}
    elif schema == Image2DModel or schema == Image3DModel:
        kwargs = {}
    else:
        raise ValueError(f"Unsupported schema {schema}")

to ensure that no interpolation is performed for labels, the result can be seen for instance here https://github.com/scverse/spatialdata/issues/165.

For images interpolation happens, an example of this is in the screenshot example. We may want to do one of the following:

1. expose kwargs to the user both for rasterize() and for BaseTransformation.transform()
2. don't do anything
3. use the same approach as for labels -> no interpolation, no antialiasing

• ...

When this is done we should update the test test_rasterize_raster(), which at the moment can't perform a pixel to pixel comparison (also because of this other issue https://github.com/scverse/spatialdata/issues/165).

Screenshot example.

This

becomes this (the offset is due to https://github.com/scverse/spatialdata/issues/165)

when doing a rasterization with the parameter target_unit_to_pixels = 2

Locate the two calls to dask_image.ndinterp.affine_transform() and inspect test_rasterize_raster(). First determine which interpolation policy is intended for images, including whether kwargs should be exposed or interpolation disabled; done means the chosen behavior is implemented for rasterize() and BaseTransformation.transform() and the test can perform a pixel-to-pixel comparison.