Addition of Image Quality Metrics

[lauramurgatroyd]

Description

In @RasmiaKulan's project we applied the following image quality metrics to reconstructions with FBP and iterative:

Signal to noise ratio (SNR):

• this requires an ROI in a dataset
• calculates the mean divided by the standard deviation in the ROI
• Note: we already have PSNR - do we want to have both?

Contrast to noise ratio (CNR):

• this requires two different ROIs to compare the contrast between
• Calculates [mean(ROI1) - mean (ROI 2) ]/ stdev ROI2
• There are other methods of calculating this so which one to implement is to be discussed

L2-Norm-Error:

• takes two different images or ROIs in two different images
• this is an assessment of the difference in pixel values
• L2Norm(image1-image2)/L2Norm(image2)

We could add these image quality metrics into CIL, where we currently have some existing metrics:

CIL/Wrappers/Python/cil/utilities/quality_measures.py

Line 4 in 4f6e3cf

# Licensed under the Apache License, Version 2.0 (the "License");

Some of the existing metrics, such as PSNR already exist in skimage.metrics so we could potentially make use of this instead and remove them from CIL https://scikit-image.org/docs/stable/api/skimage.metrics.html

[lauramurgatroyd]

Also related: #1836