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.

本仓库包含2625枚发射后弹壳底火表面的膛面痕迹（breech face impressions）的高分辨形貌扫描数据。这批弹壳取自美国国防法医学中心（Defense Forensic Science Center, DFSC）埃姆斯实验室I期研究。本数据集作为基准数据集，用于开发并验证弹壳图像处理与比对算法。
弹壳表面的形貌图像采用Cadre Forensic™ TopMatch-3D大容量扫描仪采集，像素分辨率约为1.8微米（μm）。每张图像以二维数组（称为“表面矩阵”）的形式数字化存储，记录弹壳表面的相对深度值。每张表面矩阵连同拍摄参数元数据（包括图像尺寸、分辨率、采集者等）一并保存为x3p（XML 3D Surface Profile）格式文件。
此外，每张图像还附带一张尺寸相同的二维数组，称为“掩码（mask）”，对应图像上的人工标注区域。这些人工标注用于标记包含膛面痕迹的弹壳表面区域——这类痕迹与指纹类似，可用于识别发射该弹壳的枪械。
除原始全分辨率形貌图像外，本仓库的"sample_400_balanced"、"sample_400_balanced_afterAutoPreproc_masks"与"sample_400_balanced_preprocessed"文件夹中还提供了经过各类预处理步骤的图像版本。这些预处理操作旨在分离并增强图像中的膛面痕迹区域，例如利用x3p文件中保存的人工标注掩码，从整张图像中提取膛面痕迹所在的区域。
"code/"文件夹包含一段用R语言编写的可执行脚本"preProcess-scans.R"，可完整复现预处理后的扫描图像。
"validation"文件夹包含应用“一致性匹配单元（Congruent Matching Cells）”法（一种弹壳比对算法）的实验结果与可复现代码，同时还包含针对美国国家标准与技术研究院（NIST）标准参考材料#2461弹壳的比对实验结果。上述验证实验用于确保扫描与处理流程所生成的形貌扫描数据能够准确还原弹壳原始表面形貌。