Why Crop Early?

[Mark de Regt]

I have always waited until all masters are aligned, and I'm essentially done with processing, before cropping.  Cropping earlier seems to me to result in more loss of data, as the aligned masters will not overlap completely.

The PI tutorial directs us to crop each master before aligning.  Is there any reason for this?

Thanks.

[Juan Conejero]

Cropping earlier seems to me to result in more loss of data, as the aligned masters will not overlap completely.

You are absolutely right. Never crop any frames before alignment. However, once you have aligned and combined all the components of your image, cropping black borders and similar artifacts may help statistics computations.

The PI tutorial directs us to crop each master before aligning.

What tutorial?

[Mark de Regt]

What tutorial?

  Warren's tutorial.  It's talking about cropping the individual masters (e.g., the Luminance master).  My question is that if I crop all four or five masters before aligning them, making my color combine and adding my various luminance layers, I think I often will have to crop more off the LRGB image, and more than if I had held off cropping until after the LRGB combine.

[Warhen]

Mark, I think Juan would agree in recommending aligning ALL subframes to one reference image, once (i.e. HaLRGB to a reference L). When integrated separately of course, that results in 4/5 masters already aligned to one another. Using the power of DynamicCrop, we can effectively trim them at the start of postprocessing, maintaining precise alignment. As Juan says- subsequent steps (DBE/BN/ColCal, etc.) should work better without the black borders in the calculations. Just take the time to get the crops right. Otherwise, we're degrading the quality of our masters doing multiple alignments (i.e. master to master).