I think that you can start understanding the

intuitive subject of depth, which is the disparity map from two cameras (stereovision) by exploiting epipolar geometry , those are keywords in the field, that you can search by . Disparity refers to the distance between two corresponding points in the left and right image of a stereo pair. Try to check this link https://stackoverflow.com/questions/7337323/what-is-the-definition-of-a-disparity-map

and this: https://towardsdatascience.com/depth-estimation-1-basics-and-intuition-86f2c9538cd1

If you like the math, you can check the fundamentals of multi-view geometry here: http://www.epixea.com/research/multi-view-coding-thesisch3.html

Otherwise if you are technically interested, there are a lot of tutorials on matlab, opencv: one of them https://docs.opencv.org/master/dd/d53/tutorial_py_depthmap.html

Have a look at the attached items for you review : https://towardsdatascience.com/depth-estimation-1-basics-and-intuition-86f2c9538cd1 http://www.epixea.com/research/multi-view-coding-thesisch3.html

https://medium.com/beyondminds/depth-estimation-cad24b0099f

https://www.intechopen.com/books/coding-theory/efficient-depth-estimation-using-sparse-stereo-vision-with-other-perception-techniques

There are many methods a few are here:

https://openaccess.thecvf.com/content_ICCV_2019/papers/Garg_Learning_Single_Camera_Depth_Estimation_Using_Dual-Pixels_ICCV_2019_paper.pdf

Chapter Efficient Depth Estimation Using Sparse Stereo-Vision with O...

https://ieeexplore.ieee.org/abstract/document/5457420