Mosaic Construction with StarAlignment: Two-Frame Mosaic of the M31 Region

In this video we show the construction of a wide-field mosaic of the Andromeda Galaxy region with the StarAlignment tool in PixInsight 1.6.1. We apply StarAlignment in mosaic generation mode with automatic frame adaptation, surface splines registration model, and bicubic spline pixel interpolation. Finally, we use the generated registration mask to verify the accuracy of registration by visual inspection of the overlapping area between mosaic frames.

This mosaic is a difficult case for two reasons. On one hand, the overlapping between frames is relatively small. The overlapped area is about 100 pixels tall, while each image is 4000x2700 pixels approximately. In addition, field curvature affects each frame with opposite sign on the overlapped area. This leads to geometrical distortions that challenge the star matching routines in StarAlignment. Surface splines (also known as thin plates), and an increased tolerance of the RANSAC star matching algorithm, play key roles in this example to correct for all of these distortions accurately.

The automatic frame adaptation routine has been improved in PixInsight 1.6.1. Frame adaptation computes a linear function that is applied to equalize background and signal levels between adjacent mosaic frames, yielding a seamless mosaic. A precondition to generate seamless mosaics is the rigorous flat fielding of all mosaic frames. In this example, the achieved result is really excellent thanks to an exquisite calibration of the raw images.

The images have been acquired by Jordi Gallego with a Takahashi FSQ-106 telescope and a STL-11000 CCD camera. Jordi has kindly given us permission to use his images in this video tutorial.

Category:

Science & Technology

Tags:

• PixInsight
• astrophotography
• mosaic generation
• image registration