- Question to PI folks, why is this not the default in the BPP script?
Because the default of 500 maximum stars works perfectly in 99.9 percent cases. By setting the maximum alignment stars to zero you are selecting StarAlignment's automatic probe mode. This special mode is only intended for difficult cases, such as alignment of images with very different geometries, or mosaics with very little overlapping.
For normal image preprocessing tasks you should *never* need to change the default value of this parameter. If BatchPreprocessing is giving you alignment errors, typical causes are:
- In the case of CFA images, the
CFA Images option of the BPP has not been selected.
- Invalid master calibration frames. A common error is using a calibrated (bias-subtracted) master dark frame, since the BPP script expects the master dark to include the bias signal.
- Master frames generated by other applications, which in general are not compatible with our preprocessing tools.
- Extremely noisy light frames. In rare cases it may be necessary to use a nonzero noise reduction parameter (Image Registration section of BPP) to work with low-SNR images.
- Images with large amounts of strong cosmetic defects or bright artifacts can fool StarAlignment's star detection routines in very rare cases.
As a good starting point, I strongly recommend you watch the
videos about the BatchPreprocessing script on the
PixInsight Resources website. See also
Harry Page's video tutorials and
IP4AP video tutorials on introductory PixInsight topics.
On a side note, the current version of the BatchPreprocessing script is 1.37, released on July 14th. You should have received this version as a regular update to PixInsight 1.8.2.
