Data Content

The Visible Cement Data Set is organized into distinct subsets for each experiment performed at the ESRF in September, 2000. Each distinct data set is comprised of a set of files that provide the raw data, a text-based description, 2-D and 3-D images of the microstructure, and movie files containing animated views of the microstructure. Details on each of these are as follows:

• raw data files- each raw datafile contains a 512 x 1024 x 1024 volume of data comprising either the top or bottom half of the complete microstructure. These files have been rescaled with a data resolution of one byte per data element, each element thus having a value (greylevel) between 0 and 255. The initial data provided by the ESRF was at a data resolution of four bytes (floating-point) per data element, with a proportionately higher greylevel resolution. All initial indications are that the reduced 0-255 greylevel range is adequate for reliably distinguishing features (phases) in the data sets. In both the raw data files available on the web site and the initial data files supplied by the ESRF, the right-most index varies the fastest in the file. That is the first 1024 data elements in the file correspond to the first row (left to right) of 3-D data and the first 1024 x 1024 data elements correspond to the first slice (back to front) of the 512 slices comprising the (half, top to bottom) data set.

• description- a text-based description provides details on the material being observed for each data set, including the date and hour that the sample was actually imaged at the ESRF facility.

• 2-D slice images (JPEG format)- generally, 3 or more complete 1024 x 1024 2-D images are produced representing the top, middle, and bottom slices of a 300 pixel thick subsection of the 3-D microstructure (see Figure 2 for an example). These images were used to determine the best region from which to extract the 300 voxel by 300 voxel by 300 voxel subvolumes used in the fly-through animations, generally avoiding regions that contained processing flaws or imaging artifacts.

• 3-D image subvolume- a 300 voxel by 300 voxel by 300 voxel subvolume was selected from each data set and stored in a one byte per voxel data file.

• movie files (QuickTime compatible format)- for each 300³ subvolume, a fly-through animation has been created. For this, each of the 300 2-D slices are viewed in sequence, giving the illusion that one is flying through the microstructure.

  

Figure 2: 2-D image (1024 pixels by 1024 pixels) of slice 151 for unhydrated cement powder. Bright grey particles are unhydrated cement and dark grey is air-filled porosity. Greylevel bar at bottom of image indicates greylevel intensity variation from 0 (left) to 255 (right). The diameter of all slices is approximately 1 mm.