Join GitHub today
GitHub is home to over 28 million developers working together to host and review code, manage projects, and build software together.Sign up
spider - align ap sr
The main part of the procedure brings two objects into register. This is achieved by alternating shift and rotational alignment until the relative change of position is smaller than 0.5 pixels. After alignment of all the objects (which constitutes one iteration step of the procedure) the global average is centered using the low-pass filtered disc of the same size as the object and alignment parameters for all the images are modified accordingly. Iterations are repeated until stable alignment is reached (see above).
There are only few parameters to choose (fig. 1). Input particles should have positive contrast, i.e. objects should be bright on the dark background. You have to decide the limits of integration for the rotational search (in terms of inside and outside rings). The outer radius has to correspond to the particle size. To avoid oversampling (and thus the relatively large error of interpolation) an inner radius of 5 px was found to be sufficient for all practical purposes.
When the protocol is finished you may click on the Analyze Results button. The produced output are the final total average and a stack of aligned particles (Fig. 2).