Calculating how much light gets through steel mesh (commonly used to make cages) I have expanded steel mesh that I use to make garden cages:



I would like to know how much sunlight the mesh lets through.

I think I need to calculate the area of the mesh's negative space. And then from there I could calculate a percentage of sunlight that is let through.

How can I calculate how much light would get through?
Crop the ruler and binarize:



Then count the white pixels and divide by the sum of white and black to find:

$0.592548$

In Mathematica:

pixels = Flatten[
   ImageData[
     Binarize[
      ImageTake[mesh, {140, 664}, {1, 892}]]]];
N@Count[pixels, 1]/(Count[pixels, 0] + Count[pixels, 1])


$0.592548$

People wanted a different threshold:
I can use Geographic Information Systems (GIS) software to plot and calculate the area of the negative space:


Crop the image down to a more manageable size (in Microsoft Paint).
In GIS software, draw a rectangle around the image to get it's area.
Draw polygons in the negative space.



  Area of image  = 147542 units
  
  Area of negative space = 92907 units



Calculate the percentage of negative space:



  92907 / 147542 = 62.97%




Therefore, approximately 63% of light would get through this mesh.