Extracting information from EXR Files

Question

I am relatively new to computer vision and image processing. I have a single EXR file with 7 channels: 1-3 give me the RGB values, 4-6 give me the surface normals coded as RGB values and 7th channel contains depth information from the camera of the rendered image. I obtained this from the mitsuba renderer using the multi-channel plug-in.

I was wondering if there was any way to view these 7 channels separately. For eg. I would like an image showing only the depth values in grayscale. So far I haven't found a multi-channel EXR file viewer that does this for me. An example of what I'm talking about is shown in the link: https://www.mitsuba-renderer.org/devblog/wp-content/uploads/2014/02/multichannel.jpg

Really looking forward to any help. Thanks!!

Answer 1

I don't know any IDE-based tools that do this but a quick Python script should do the trick. I usually use Thijs Vogels' PyEXR to read the multi-channel EXR. Assuming your depth channel is called distance (which needs to be specified in your Mitsuba XML file under your hdrfilm), you can visualize it with the following code:

import pyexr

fp = pyexr.open('multichannel.exr')
img = fp.get('distance')
pyexr.write('distance.exr', img)