QVIEW: software for rapid selection of particles from digital electron micrographs.

The QVIEW image-processing software package provides a graphical user interface for interactive and rapid selection of particles from digital electron micrographs. This package was developed to facilitate the selection of elliptical, hydrophobic, and aggregating particles, which present complications for other particle selection packages. Speed improvements have been attained by using the fast graphics routines available in the Tc1/Tk toolkit and by separating the time consuming image-processing procedures from the interactive selection steps. The software is based on C++ and Tc1/Tk, both of which are readily available on many computer platforms. Processing features include removal of oversaturated pixels, planar subtraction using three or more background regions, exclusion of unwanted density such as nearby particles, and application of a circular or elliptical mask. Particles, along with their corresponding background and exclude regions, may be selected interactively from multiple digital micrographs, and the selection parameters are saved in a disk file for later processing. C shell processing scripts are easily modified and customized for specific applications. In summary, this software package enables the user-friendly, rapid selection of particles suitable for input into three-dimensional reconstruction packages.