[Python] allow reading render result pixel values directly

So after rendering an image using

bpy.ops.render.render()

the image bpy.data.images["Render Result"].pixels comes out blank

some threads suggested using a viewer node instead,

bpy.data.images["Viewer Node"].pixels works correctly but only when there's a blender GUI open! without GUI im getting a small 256x256 image

is this restriction still necessary ? ( blender.stackexchange.com/questions/69230/python-render-script-different-outcome-when-run-in-background/81240 )

workaround is to render to a temp exr then load it & read pixels from it