Chapter 47: Fingerprints on the Envelope (For 20230305143137924)

Lasers possess biological effects.

Light is a very special thing; even high school students know it possesses wave-particle duality.

Waves grant it energy.

Particles grant it impact.

Lasers of specific wavelengths can react with biological proteins; this is the principle behind laser fingerprint visualization.

In Lu Chuan's Intermediate Fingerprint Collection Skill Card, there is an analysis regarding the effectiveness of different laser wavelengths on fingerprint collection.

A laser light source with an output wavelength of 445±5 nanometers and an output power greater than 13 watts can non-destructively visualize fingerprints on paper.

Of course, fingerprints on leather or clothing can also be visualized using this method, though the corresponding laser wavelengths differ.

With the instrument, Lu Chuan quickly completed the collection of fingerprint information from the envelope.

However, this was not the end.

What the Economic Investigation Department needed were the fingerprint comparison results.

Lu Chuan felt quite excited.

Because the Primary Fingerprint Identification and Analysis skill rewarded by the system was finally being put to use.

Previously, whether in the South Suburb Arson Case or the Reservoir Corpse Case, although Lu Chuan had contributed greatly to fingerprint collection, he had essentially never participated in the comparison and analysis phase.

This time was different; from collection to analysis and identification, Lu Chuan would complete the entire process single-handedly.

*Ding!*

"Basic Task: Complete an excellent fingerprint identification and analysis to determine the identity of the fingerprint owner."

Although the fingerprints on the envelope had been visualized with the help of the variable-frequency laser spectrum analyzer, their completeness was not high.

Furthermore, among the thirty-nine fingerprints collected, many were overlapping.

What Lu Chuan needed to do now was to perform a comparative analysis on all the fingerprints to find their owners as effectively as possible.

The first step was preprocessing the fingerprints.

The prerequisite for fingerprint comparison is that the preprocessing must be done properly.

Fingerprint preprocessing involves many steps, and the requirements vary depending on the fingerprint.

Broadly speaking, fingerprint preprocessing can be divided into two categories: adjusting the fingerprint shape and marking fingerprint minutiae.

Shape adjustment is necessary because fingerprints extracted from different carriers differ in shape from normally collected fingerprints.

For example, the fingerprint left by a person's index finger on a flat surface is rounded and regular because it is not subject to external interference.

However, if the finger grips a water cup, the fingerprint will be affected by friction, causing slight deformation; additionally, because the cup is cylindrical, the fingerprint will extend along the shape of the cup.

A fingerprint collected this way would be an irregular long oval shape.

Preprocessing aims to minimize the influence of force and carrier shape on the fingerprint, thereby increasing the success rate of subsequent comparisons.

Marking minutiae is for the purpose of fingerprint recognition and comparison.

On any collected fingerprint, characteristic points such as ridge endings, bifurcations, and trifurcations can be marked on the patterns.

Fingerprint recognition utilizes these points to judge the similarities and differences between prints.

The Primary Fingerprint Identification and Analysis skill allowed Lu Chuan to handle fingerprint preprocessing with ease.

Compared to his previous experience with preprocessing, Lu Chuan felt it was incredibly smooth.

In front of the computer screen, a fingerprint was being magnified before his eyes.

Lu Chuan did not use complex drawing software to adjust the fingerprint; instead, he used the fingerprint adjustment software built into the automatic fingerprint comparison system.

In fact, many criminal investigators responsible for fingerprint comparison are reluctant to use the system's built-in software.

This is because the image adjustment software in the automatic fingerprint comparison system has limited functions and can only perform restricted adjustments.

Furthermore, the scope of adjustment is limited.

Lu Chuan was the exact opposite; all the experience instilled in him by the Primary Fingerprint Identification and Analysis skill was gained through the image processing software built into the fingerprint comparison system.

This had one major advantage: the legality of the comparison results was higher.

This involved the issue of the degree of fingerprint preprocessing.

Processing the shape of a fingerprint actually changes its size and the spacing of its ridges.

This is equivalent to indirectly changing the fingerprint's minutiae.

This is why, for the same fingerprint, some people can achieve a successful match after processing, while others cannot.

Ordinary image processing software has no restrictions, allowing for unlimited adjustments during preprocessing.

Therefore, many fingerprint comparisons require re-verification by two or even three people before a successful identification can be confirmed.

This re-verification is actually a judgment of the degree of deformation caused by preprocessing.

By using the drawing software built into the fingerprint comparison system, Lu Chuan had a higher probability of passing re-verification.

This was because the system itself restricted the degree of deformation allowed during processing.

At the computer, Lu Chuan's eyes were wide, his expression one of excitement.

Processing fingerprints was different from what most people imagined; it wasn't as simple as inputting a fingerprint image into the system and having it compared.

It was a task that required an extremely high level of meticulousness.

It was tedious, boring, and even agonizing.

Out of the thirty-nine fingerprints, Lu Chuan successfully completed twenty-seven.

The remaining twelve fingerprints, due to severe overlapping and too many breaks, could not be subjected to valuable preprocessing with his current skill level.

But twenty-seven fingerprints...

That was enough.

By the time the fingerprint preprocessing ended, it was already after four in the afternoon.

The remaining work was much simpler.

He just had to input the twenty-seven fingerprints into the system for automatic comparison.

Of course, a successful system match did not mean the fingerprint identification and analysis was a success.

Or rather, a failure of the system match did not necessarily mean the identification failed.

In the current criminal investigation system, the automatic fingerprint comparison system performs dissimilar comparisons based on the number of minutiae points.

Completely different fingerprints are excluded immediately—this is what is known as "idiot-proof comparison."

This is actually very fast; it is essentially a comparison of data.

The so-called "minutiae" are not just about marking a point and drawing a circle around it.

Instead, they must undergo certain calculations to present the angle and coordinate data of every characteristic point in the form of an axis.

Only then is the comparison performed within the system.

Within this data, there will inevitably be certain characteristic points of certain fingerprints that are identical.

The system will automatically list these fingerprints.

And based on the quantity of identical data, it will sort them from highest to lowest.

When all the data for all minutiae points are identical, it signifies a successful fingerprint match.

Leaving the system to run its comparison, Lu Chuan opened his phone.

Checking WeChat, he saw over a dozen unread messages.

Mom: "Your dad and I are going out for the National Day holiday, so you'll have to work overtime."

Ever since starting university, Lu Chuan had suddenly felt like he was someone who was "given a free top-up just for being a user."

In high school, he could eat whatever he wanted.

In university, he couldn't eat whatever he wanted.

Now that he was working, Lu Chuan didn't even dare to mention what he wanted to eat.

Dad: "Your mom wants to go out for the National Day holiday, do you want to accompany her?"

Lu Chuan grimaced and decisively deleted the message from Comrade Old Lu.

Me, accompany her?

Heh.

The remaining messages were mostly from classmates.

What caught Lu Chuan's eye was a message from three minutes ago.

"Thank you, Big Boss Silver for the tip of 20230305143137924! Wishing the Big Boss happiness as vast as the Eastern Sea and longevity as great as the Southern Mountains; may you be a groom every day and a bride every night!"

(End of Chapter)