Blurry Demo Reconstructions

[XiaoWang-Github]

Both the 2D and 3D Shepp Logan as well as microscopy demo reconstructions look blurry. See the attached images. Are the prior parameters set wrong?

[cabouman]

Xiao, the microscopy recon is always going to be a little blurry due to the limited data.
However, I agree that, on average, the recons tend to be a bit over regularized.
This is closely related to the issue #239, which recommends reducing "regularization" for the proximal map mode.

I propose we try two changes in the prerelease branch that address both problems consistently.
In auto_sigma_x we can change the scaling factor to 0.3 so that:

return_ 0.3 * auto_sigma_prior(sino, delta_channel, sharpness)

And in In auto_sigma_p we can change the scaling factor to 2.0 so that:

return 2.0 * auto_sigma_prior(sino, delta_channel, sharpness)

There could be some backward compatibility issues, but I think it's better to pull the bandaid off now.
If this is agreeable to everyone, I can make the changes, and then you can try running the new code to see if you like it better.

[XiaoWang-Github]

Sounds good!

[cabouman]

I had an extensive discussion with Jordan about this, and I'm talking to different people to formulate the best solution. This is a very small change, but it needs to be done very carefully.

[cabouman]

OK, my solution to this problem was just to increase the value of sharpness in the demos.
In the future, we may want to increase the default sharpness values in the code.