I have done the same analysis for run18 data.

Here is PCA components.

This is the difference between the original image and the reconstructed image with various numbers of components for a visit (113513).

In this case, 1 or 4 components are preferable.

When the data from run18 and run19 are combined, the PCA components will become this.

In this case, ~3 components may be needed.

However, there is a case we cannot reconstruct the image properly even if we use more components.

This visit is not used for the calculation of PCA.

I'm trying to use all the data from previous runs. I have selected 5 frames each from the previous 5 runs (run12 20230719, run14 20231216, run16 20240502, run18 20240825, run19 20241017), for a total of 25 frames. Then I did the PCA analysis. However, as shown in the figure showing the first 20 PCA components, I'm not sure yet what's happening. Components 11, 12, and 15 look more important than 6-10. Residual CRs or some other features may contribute to components 6-10 but I need more investigation to confirm.

The following figure shows how StDev of residual images for each dark frame varies as a function of the number of PCA components used. The frames with the same color were taken on the same night. As can be seen, except for the first few components, each PCA component affects only the data taken on a specific night and seems to trace noise-level details. Something seems to be wrong. ???

I have analyzed the dark data taken during the January 2025 commissioning run (run20). Specifically I have used the following visits. 

{20250123: [119786, 119792, 119790, 119787, 119789],
 20250125: [120106, 120112, 120111, 120105, 120093],
 20250127: [120581, 120579, 120580],
 20250128: [120727, 120726, 120721, 120723, 120722]}

Only two PCA components are significant, with the first component explaining 99.8% of the variance. This suggests that the amplifier glow is stable within each run. While applying just the first component is sufficient, the second component can also be included. Despite applying the RepairTask on each frame and using the Robust PCA algorithm to isolate a low-rank matrix from noisy features (in this case, cosmic rays), some cosmic ray contamination remains. To include the second PCA component for dark subtraction, Robert's new cosmic ray remover may need to be applied.