Backprojection Example

[garrettwrong]

We received a request for a tutorial demonstrating backprojection. I do not believe this requires any new application code at this time, just added documentation.

This could be accomplished by refreshing an existing tutorial or creating a new one. I suspect the intended application is to accompany teaching about projection-backprojection, the slice theorem, etc. IE example code that is functionally equivalent to the classic graphic from Yoel and Amit's paper:

[janden]

Might be easier to visualize with the sinogram capability (#1095)? Visualizing regular volumes in 3D is hard – visualizing backprojected images is even harder.

[janden]

Also, could you give a reference to the paper? I'm not sure I've seen this figure before, actually.

[garrettwrong]

https://www.researchgate.net/publication/250918146_A_Fourier-based_Approach_for_Iterative_3D_Reconstruction_from_Cryo-EM_Images?_tp=eyJjb250ZXh0Ijp7ImZpcnN0UGFnZSI6Il9kaXJlY3QiLCJwYWdlIjoiX2RpcmVjdCJ9fQ

[ajrzepiela]

I am also very interested in the backprojection tutorial. Without it ready, could you point me to which modules I should start looking at to see how it works in Aspire? Thanks for tips.

[garrettwrong]

Hi, given an image source, the method performing just backprojection is im_backward found here.

You can see how it is used in the mean volume estimation code. Starting with zero'd volume, the code slices a batch of images, backprojects them, then accumulates that batch of backprojections into the volume.