I'm running Blender 2.79:
/path/to/blender -b empty.blend -P script.py
With script.py:
import numpy as np
import bpy
x, y = 100, 100
print("rendering")
bpy.ops.render.render()
res = bpy.data.images['Viewer Node']
print(len(res.pixels[:]), x*y*4)
arr = np.array(res.pixels[:]).reshape((y, x, 4))
empty.blend is a simple scene (camera+cube+light) with render settings at 100px by 100px @ 100%, with compositing nodes:
I get an error because res.pixels[:] has length 262144 (= 256 * 256 * 4) when it should be 40000 (= 100 * 100 * 4). Moreover, res.pixels[:] is all zeros.
If I run Blender without -b, it works.
