# Cross GLCM

Cross GLCM is when I & J for GLCM is taken from separate images, yielding statistical relationships between images

## Usage

Use Cross GLCM on an image like so.

```pycon
>>> from glcm_cupy import GLCMCross
>>> import numpy as np
>>> from PIL import Image
>>> ar = np.asarray(Image.open("image.jpg"))
>>> ar.shape
(1080, 1920, 3)
>>> g = GLCMCross(...).run(ar)
>>> g.shape
(1080, 1920, 3, 6)
```

Last dimension of ``g`` is the GLCM Features.

To retrieve a GLCM Feature:

```pycon
>>> from glcm_cupy import CONTRAST
>>> g[..., CONTRAST].shape
```

Consider ``glcm_cross`` if not reusing ``GLCMCross()``

```pycon
>>> from glcm_cupy import glcm
>>> g = glcm_cross(ar, ...)
```

## Selecting and Retrieving Combinations

In each ``GLCMCross()`` instance, is a ``ix_combos`` property to specify combinations

In a 3 channel image, the following will only cross indices, 0 with 1, 1 with 2, **skipping** 0 with 2

```pycon
>>> from glcm_cupy import glcm
>>> g = GLCMCross(..., ix_combos=[[0, 1], [1, 2]]).run(ar)
>>> g.shape
(1080, 1920, 2, 6)
```

``g[:,:,0,:]`` retrieves 0 cross 1, ``g[:,:,1,:]`` retrieves 1 cross 2.

## Default Combinations

By default, ``ix_combos is None``, uses all possible combinations. After ``run(...)``, ``ix_combos`` will be populated
with combinations used. Thus, you can retrieve the default ordering of the 3rd dimension.

The combinations uses the ordering of ``itertools.combinations(range(CHANNELS), 2)``.

```{warning}

When using ``glcm_cross``, you can't retrieve the generated order.
However, you may use ``itertools.combinations`` to indirectly yield it.
```