The content on this blog represents my personal exploration of computational image processing techniques and is entirely separate from my professional work. This is not AI or generative AI. All opinions, experiments, and analyses are my own.
The techniques discussed here are presented for educational and research purposes only. While I strive for accuracy, this is a space for experimentation and discussion at the forefront of forensic image analysis, not a substitute for peer-reviewed research or certified forensic methodology, even though these emerging techniques are generating more accurate results than many traditional methods.
The Setup
There are some things that stay quiet for a very long time, waiting for someone to finally understand their language. It feels a bit like finding a letter that was never meant to be read, but now that I have seen it, I cannot look away. I wanted to use every tool I have to find the light still hidden in those shadows, to show that even the smallest spark from the past refuses to be completely extinguished.
The Chemical Chain of Decay
Aged blood detection relies on the fact that hemoglobin goes through a predictable degradation chain, with each stage featuring distinct light absorption signatures:
- Fresh Blood: Contains oxyhemoglobin with strong absorption peaks at roughly 415nm (the Soret band), 540nm, and 577nm.
- The First Shift: Within hours, it deoxygenates, shifting the 540nm and 577nm doublet into a single broad absorption around 555nm.
- Oxidation: Over days to weeks, it oxidizes to methemoglobin, revealing a distinct peak at roughly 630nm that fresh blood lacks.
- Archival Age: Over months to years, it degrades into hemichrome and hematin. These highly stable end products cause the Soret band to shift drastically from 415nm down toward 405nm.
Algorithmic Detection Indices
To detect this sample, the script computes several specific indices that target these aged spectral signatures rather than fresh ones:
- NDBI (580nm vs 630nm ratio): Fresh blood absorbs at 580nm but not 630nm, while aged blood absorbs at both, isolating the methemoglobin peak.
- Soret Ratio (415nm vs 630nm): This catches the relative shift between the two major absorption features as the sample ages.
- Met Index (630nm / 540nm): This directly measures the methemoglobin concentration relative to the other forms.
Bridging Algorithms and Optical Hardware
While my MST and MAMBA models are incredible at hyperspectral reconstruction (turning 3 RGB channels into 31 spectral bands), there is a computational catch. These models are often trained on natural scenes and have never seen aged hemoglobin spectra. Left alone, the algorithm might hallucinate a spectral shape that looks plausible but is physically wrong.
To solve this and capture serious forensic data, the neural network must be ground truthed using actual narrowband measurements. To build this pipeline, I used reference data captured by a NoIR dual camera setup equipped with specific bandpass filters, particularly a 630nm filter, to physically isolate the methemoglobin peak and verify the physics.
The Final False Color Visualization
By anchoring the reconstructed datacube with real narrowband filter data, the pipeline performs a flawless spectral classification. The false color gradient (the glowing "Inferno" scale seen here) is the visual map of those indices at work. The bright yellow "stars" represent dense, fossilized clusters of hemichrome and hematin, while the sweeping purple to orange background maps the physical drying gradient of the original serum.