Fired Cartridge Case Identification Using Optical Images and the Congruent Matching Cells (CMC) Method

Abstract

The Congruent Matching Cells (CMC) method for ballistics identification was invented at the National Institute of Standards and Technology (NIST). The CMC method is based on the correlation of pairs of small correlation cells instead of the correlation of entire images. Four identification parameters – TCCF, Tθ, Tx and Ty are proposed for identifying correlated cell pairs originating from the same firearm. The correlation conclusion (matching or non-matching) is determined by whether the number of CMC is ≥ 6. This method has been previously validated using a set of 780 pair-wise 3D topography images. However, most ballistic images stored in current local and national databases are in an optical intensity (grayscale) format. As a result, the reliability of applying the CMC method on optical intensity images is an important issue. In this paper, optical intensity images of breech face impressions captured on the same set of 40 cartridge cases are correlated and analyzed for the validation test of CMC method using optical images. This includes correlations of 63 pairs of matching images and 717 pairs of non-matching images under top ring lighting. Tests of the method do not produce any false identification (false positive) or false exclusion (false negative) results, which support the CMC method and the proposed identification criterion, C = 6, for firearm breech face identifications using optical intensity images.

Applying 3D measurements and computer matching algorithms to two firearm examination proficiency tests

“…In contrast, the ACCF calculation between entire surfaces is significantly affected by these dissimilar regions even if the rest of the surface matches very well. The CMC method has been successfully applied in various tests [15,16] and produced clear separation between the scores of known matching (KM) and known non-matching (KNM) samples making it a promising algorithm for ballistic evidence comparisons. The surfaces from Fig.…”

A Normalized Congruent Matching Area Method for the Correlation of Breech Face Impression Images

“…2. In our previous studies [4,5,7], the CMCs on KNM image pairs are most likely to appear at the edges of the breech face impression, as shown in Fig. 3.…”

“…The CMC method has been validated by different sets of topography measurements [4], by optical images [5], and by different correlation programs and statistical models [7]. Figure 2 shows the CMC distribution on KM image pair #19 vs. #20 (Fadul data set [10]) at different cell sizes.…”

A Fully Automatic Method for Comparing Cartridge Case Images,

“…The first step is to automatically select the breechface marks. In NIBIN and other research , this step is performed manually by adjusting a larger circle to pick out the primer region, and a smaller circle for the firing pin impression. Here, we select the breechface marks automatically by first finding the primer region and then removing the firing pin impression.…”

“…For researchers, both the continued and historical use of 2D imaging mean that the majority of data in local and national databases are in 2D, and it is essential for algorithms to be effective on these. Recent work on algorithms for 2D images includes a paper by NIST applying their Congruent Matching Cells method, originally developed for 3D topographies, to 2D , as well as work by Roth et al on images involving operational datasets taken from a police department, in addition to a data set of controlled test fires, as is usually used by researchers.…”