I have a couple of images in a python script that I want to add together. Here is a rough example of what I want to do. All the image variables are of the type bpy.types.Image:

final_image = bpy.ops.image.new(name="lightmap.png", width=1024, height=1024)

#This line does not work
final_image = lightmap_direct + lightmap_indirect + lightmap_emissive

So my question is if there is an easy way to add these images together. I am mainly interested in the add blend mode, though others modes are also interesting.

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    $\begingroup$ The + operator isn't overloaded to do that. What exactly would the + symbolize? Additive? or mix? It can be done using bpy alone but it's more involved than your example.. $\endgroup$
    – zeffii
    Oct 25, 2015 at 12:47

1 Answer 1


Blender comes bundled with numpy. Image references have a property called .pixels which you can turn into a numpy array of the same dimensions. Numpy does use overloaded operators for array math. The initial setup aside, you'll see it is quite close to what you were trying.

import math
import numpy as np

import bpy

def np_array_from_image(img_name):
    img = bpy.data.images[img_name]
    return np.array(img.pixels[:])

pixelsA = np_array_from_image('A')
pixelsB = np_array_from_image('B')
pixelsC = np_array_from_image('C')
pixelsD = (pixelsA + pixelsB + pixelsC) / 3

image_D = bpy.data.images['D']
image_D.pixels = pixelsD.tolist()

# then click in the UV editor / to update the view..to see the pixels of `D` updated

Maybe this will give enough insight, and push towards learning some numpy.

This does 'mix' btw..

enter image description here

I'm not sure about the algorithm for add.. (below shown using material rgb mix nodes)

enter image description here

it's not as simple as a+b+c. maybe something like adding the smallest value of each array:

# add smallest element values
interim_1 = np.minimum(pixelsA, pixelsB)
pixelsD = np.minimum(interim_1, pixelsC)

producing this:

enter image description here

  • $\begingroup$ Just out of interest: Why fortran is doing the math? $\endgroup$
    – p2or
    Oct 25, 2015 at 13:09
  • $\begingroup$ I've edited the answer. It may not be executed in Fortran, most likely straight in C. Both execute much faster than Python, and are the reason numpy is chosen for fast computations using a python higher level language as a 'director'. $\endgroup$
    – zeffii
    Oct 25, 2015 at 13:13
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    $\begingroup$ see: stackoverflow.com/questions/8385602/… $\endgroup$
    – zeffii
    Oct 25, 2015 at 13:14
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    $\begingroup$ Interesting, nice to know that numpy is a built-in module now. Thanks zeffii! $\endgroup$
    – p2or
    Oct 25, 2015 at 13:33
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    $\begingroup$ Nice, also did not know that numpy was built in! About the "add" thing, I have three lightmaps (direct, indirect, emitted). Adding the rgb values, at least i think, should give the correct result in that case. Anyhow, good answer. $\endgroup$ Oct 25, 2015 at 14:08

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