The Project Library provides a summary of all images. These are listed in a tree structure according to the image group they belong to, with one image per horizontal line. Image statistics are shown in columns, like in an Excel sheet; users can manually choose which parameters are displayed. The Project Library also displays a set of preview images for a selected image (a selected row in the table). These appear as thumbnails on the right of the table. To enable very fast display, small, pre-computed PNG preview files are displayed when the user manually browses through a large number of images, and enlarge to the original, full-resolution MRC file in full-screen display upon ‘double-clicking’. Different sets are available, depending on the mode in which Focus is run and the options selected. For example, the “Drift Overview” displays the 2D projected image stack and its FFT after drift correction, a drift trajectory plot, and the Thon ring fit.

A typical data collection session on a cryo-EM instrument results in thousands of image stacks, which can be organized and managed with Focus' Project Library. Images can be sorted according to each column of the library table and, thereby, ranked by specific parameters such as mean pixel value, defocus, CTF resolution fit, amount of drift in the stack, or iciness of the sample.

Sorting the Project Library by a specific parameter, allows a subset of images (image folders) to be selected based on specific image parameters (e.g., all images with too high defocus) by mouse-dragging. Selected images can then be moved to a different ‘image group’ folder (e.g., the TRASH folder) with one additional click. As TRASH is ranked as an image group, trashed image folders are not permanently deleted and can be moved to other groups at any time. Further, image folders can also be flagged with specific flag colors and sorted according to their flags. The Project Library allows scripts chosen by the user to be launched on a subset of images selected by mouse, flag or group, e.g., when a subset of images needs to be processed again using different parameter settings or algorithms.