```python
import numpy as np
import py5_tools
import py5
def alter_image(msg: str, img: py5.Py5Image):
py5.println("PYTHON:", msg)
py5.println("PYTHON:", img)
img.load_np_pixels()
img.np_pixels[::2, ::2] = [255, 255, 0, 0]
img.update_np_pixels()
return img
py5_tools.register_processing_mode_key('test_transfer', alter_image)
py5_tools.register_processing_mode_key('np', np)
py5.run_sketch(jclassname='test.TestSketch')
```