Despite alignment worked well on series of “not so different” images, new alignment algorithm is more robust and reliable. It is able to properly align images with very significant mutual shift and rotation and also image series captured before and after GEM pier swap (images rotated by 180 degrees) can be properly aligned using new SIPS v3.8.

Certain SIPS tools (e.g. Blink Images or Combine Images) not only determine mutual position of individual frames, but also create a transformed (not only shifted, but also rotated) version of every image in series to display them on exactly the same position. So, after alignment, Blink tool shows sequence of frames with perfectly steady stars and Combine tool creates sum of images with centroids of matching stars on the very same coordinates. Algorithm creating the transformed version of images was also improved to create new image with better sub-pixel precision and at the same time to preserve all features of the original image, like dynamic range, star flux (sum of values in individual star pixels) etc.

Photometry tool

The new alignment algorithm affected also the Photometry tool, when a series of images with very significant mutual offsets were processed. Photometry in SIPS v3.8 now works more reliably on such series.

Photometry report was slightly updated:

• Star metadata now includes star name and coordinates determined by SIPS, not only catalog coordinates.

• Star metadata lines contain informations not only for VAR, but also for all used CMPx and CHK stars.

Photometry relied on image names to sort individual frames in the series. This is why previous SIPS versions failed to display light curves properly in the unlikely situation, when order of image names did not correspond to the order of exposure date/time. New v3.8 sorts images according to time of exposure when adding individual frames to the list box, so image name is no longer relevant and light curve is always displayed correctly.

Bug fixes

A few minor bugs were fixed in v3.8:

• Beginning with version 3.7, the Context camera tool remembers the selected sub-frame and binning to provide always the same view when SIPS is started. However, this feature caused problems when context camera was meanwhile switched for another one with different resolution. Version 3.8 handles such situation by adjusting these parameters to fit newly connected camera.

• The image resample function (invoked from the Image Transform or New Images Transform tools) did not work properly when resampling in the x axis remained 1 (other resampling worked ok).

• One of the previous SIPS harmed the ability of the user to cancel the process of series alignment, executed in many background threads. New v3.8 fixes this problem and running alignment can be canceled by the user.

SIPS is a freeware and can be downloaded from the Download section of this web site.