Topographic Scans of Breech Face Impressions on Cartridge Case Primers

This repository contains topographic scans of breech face impressions on the surface of 2,625 fired cartridge case primers. We obtained these cartridge cases from the Defense Forensic Science Center (DFSC) Ames Lab I study. We provide this data set as a benchmark to develop and validate cartridge case processing and comparison algorithms.

Topographic images of the cartridge case surfaces were taken using the Cadre Forensic (TM) TopMatch-3D High Capacity scanner at a resolution of approximately 1.8 micrometers ("microns") per pixel. Each image is digitally represented as a 2D array called a "surface matrix" containing the relative depth values of the cartridge case surface. Each surface matrix is saved along with metadata concerning the parameters under which the image was taken (including size, resolution, author, and others) to the x3p (XML 3D Surface Profile) file format. Additionally, each image is accompanied with a second 2D array of the same size called a "mask" representing manual annotations on the image. These manual annotations are intended to identify a region of the cartridge case surface containing "breech face impressions," which, analogous to a fingerprint, can be used to identify the firearm from which the cartridge case was fired.

Apart from the original, full resolution topographic images, versions of each image undergoing various pre-processing steps are also included in the "sample_400_balanced," "sample_400"balanced_afterAutoPreproc_masks," and "sample_400_balanced_preprocessed" folders. These pre-processing steps are intended to isolate and emphasize the breech face impressions in the image. For example, manual annotations saved in the x3p mask are used to extract the breech face impression region away from the rest of the image. The "code/" folder contains an executable script written in the R programming language called "preProcess-scans.R" that fully reproduces the pre-processed scans.

The "validation" folder contains results and reproducible code from applying a cartridge case comparison algorithm called the Congruent Matching Cells method. Additionally, the folder contains results from comparing NIST Standard Reference Material #2461 cartridge cases. These validations were performed to ensure that the scanning and processing procedures resulted in scans that accurately represent the original cartridge case surfaces.