  This article discusses the detection of inorganic gunshot residue (iGSR)
particles through scanning electron microscopy with energy dispersive X-ray
spectrometer (SEM/EDS) in the discovery step. We calculated the probability
that all characteristic inorganic gunshot residue particles (iGSR) go
undetected and their dependence on the image pixel resolution setup. We built
and validated a iGSR particle detection model that relates particle size with
equipment registers, and we applied it to 1,174 samples analyzed by a forensic
science laboratory. Our results indicate that the probability of missing all
characteristic iGSR particles is below 5% for pixel sizes below $0.32 \mu
m^{2}$. These values indicate that pixel sizes as great as the double in area
that is commonly used in laboratory casework, $0.16 \mu m^{2}$, are effective
for an initial scanning of a sample as it yields good rates of detection of
characteristic particles, which might exponentially reduce laboratory workload.

Signal Processing;Image and Video Processing;Data Analysis, Statistics and Probability;Instrumentation and Detectors