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.
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.
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
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.