Chapter 127 Determining the Identity
But even with fingerprints, identification and analysis are still very difficult.
One-third of the fingerprints left by the same finger have blurred edges and the ridges are squeezed together due to pressure.
Looking like five different fingerprints, this is the most difficult fingerprint that Lu Chuan has encountered so far.
This time, simple number-to-image transformation and image-to-number transformation cannot perform better preprocessing on fingerprints.
Therefore, Lu Chuan used a method that combines spatial domain algorithms and frequency domain algorithms.
In image enhancement technology, the frequency domain algorithm is a two-dimensional process that digitizes images, digitizing the image from a three-dimensional view into a two-dimensional number.
The technology used here is mainly basic methods such as Fourier transform.
Then use low-pass filtering to filter out the high-frequency signals, leaving only the low-frequency signals, so that the noise interference in the image can be removed.
At the same time, high-pass filtering must be used to remove low-frequency signals, because when the image starts from the center point and spreads to the edges, the frequency will gradually increase.
When it reaches the edge, the image frequency is the highest and the edge is the most blurry.
High-pass filtering can kick out low-frequency signal effects, thereby improving clarity around edges.
With the combination of the two, the processing of the airspace algorithm has achieved certain results.
However, because the image itself is too blurry, the image obtained only through frequency domain algorithm processing is not enough for subsequent matching.
After half an hour of processing, Lu Chuan continued to process the fingerprint image with the spatial algorithm.
The so-called frequency domain algorithm used by Lu Chuan operates on the gray value of the image.
This technology is divided into two types: point operation and neighborhood enhancement operation.
First of all, Lu Chuan used point arithmetic algorithm to correct, transform and histogram the gray scale.
The purpose of this operation is to make the image uniform, or to expand the dynamic range of the image and expand the contrast.
After that, Lu Chuan used the neighborhood enhancement algorithm to smooth or sharpen the image.
Many high-end mobile phones currently on the market actually have functions such as sharpening and grayscale adjustment.
But compared to what Lu Chuan did on his computer using professional PS paid software, the difference was as big as singing downstairs or firing shots upstairs.
The two are not of the same order of magnitude.
Lu Chuan had to go through this process for every fingerprint.
On average, the processing time for one fingerprint is almost an hour.
However, even so, Lu Chuan was still unable to use the full matching function of the fingerprint system after processing.
Because the number of labeled feature points is not enough.
The judicial effectiveness of fingerprint identification is related to the proficiency in feature point matching during the fingerprint identification and analysis process, and it is absolutely related.
If it is determined that there are less than 13 identical marking points, the fingerprint identification analysis will have no legal effect.
Of course, in this case, it does not mean that fingerprint identification analysis is useless.
Because as long as there are no clear similarities and differences, the identity of the suspect can actually be proved.
As long as the identity of the other party is determined, even if there is no fingerprint evidence, the police handling the case can always dig out other evidence.
As long as you can find people, everything else is easy.
Open the fingerprint comparison system, the second common comparison method in the system used by Lu Chuan.
Similarity comparison.
Five fingerprints meant that Lu Chuan had five chances.
The first fingerprint comparison was very unsatisfactory.
The system directly gives the failed comparison.
This means that this fingerprint has similarities and differences with all the fingerprints in the system, which means that the comparison has failed.
The second fingerprint still failed.
In front of the computer, Lu Chuan was not discouraged. If advanced fingerprint identification and analysis skills could not figure out this fingerprint, then there would probably be only a few people in the country who could figure out this fingerprint.
The third fingerprint comparison... failed again.
Looking at the last two fingerprints that had been preprocessed at hand, Lu Chuan took a deep breath.
Even if the five comparisons fail, it does not mean that there is no information about the other party in the fingerprint database.
Because these five fingerprints were so incomplete, after Lu Chuan performed pre-processing, the resulting fingerprints were quite different.
Therefore, if it fails, Lu Chuan has already made plans to preprocess the original fingerprints again.
While thinking, the data of the fourth fingerprint was also entered into the system.
The light blue aperture slowly rotates in the center of the screen, and the system data has begun to match. Didi didi.
Unlike the completely matching "ding" prompt sound, this time the system gave a continuous beep sound.
Lu Chuan perked up and looked at the screen carefully.
Similarity matching successful.
In the list, there were twenty-eight fingerprints lying there quietly, waiting for Lu Chuan to appreciate them one by one.
“Okay!”
Lu Chuan clasped his palms together, feeling very excited.
Fingerprint identification and analysis requires both technology and sometimes luck.
Or feel.
Having done fingerprint identification and analysis so many times, Lu Chuan knew very well that the first impression of fingerprint preprocessing was very important.
If the fingerprints processed for the first time are not matched successfully, the later the process is processed, the greater the distortion will be, and the less likely it is that the comparison will be successful.
Of course, this does not mean that the comparison will definitely be unsuccessful.
Kung Fu is not afraid of those who are determined. No matter how thick the iron pestle is, it will become thinner if it is rubbed too much.
No matter what happens, you can still vomit by rubbing it.
Twenty-eight similar fingerprints were sorted by the system according to the number of similar feature points.
Of course, this does not mean that the one ranked first is definitely the target fingerprint, the one ranked last may also be.
The key is that the original fingerprint was too badly damaged, only one third of the size, and blurred into an extremely distorted state.
Taking a deep breath, Lu Chuan started manually checking from the fingerprint ranked first.
This time, Lu Chuan did not just check with the pre-processed fingerprints.
The most important thing is to check it with the original fingerprint.
This is the difficulty of manually checking fingerprints. No matter how rubbish the original fingerprints are, the trace inspection police still have to sort out and compare them one by one.
Until obvious similarities and differences are found, the comparison is judged to have failed.
Or the similarities and differences have never been discovered and the identity is determined.
Twenty-eight fingerprints, the first fingerprint has a high degree of similarity, but it is also easy to find similarities and differences.
In less than five minutes, Lu Chuan discovered two obvious similarities and differences.
After marking, this fingerprint is goodbye.
Then came the second fingerprint. Lu Chuan followed the lines in the middle, sorted them out one by one, and then compared them with the original fingerprint.
This time the time was shorter, the battle was over in three minutes.
The third fingerprint...
Two minutes.
Then the fourth and fifth...
Just like a beauty pageant in a club, more than twenty destined female Bodhisattvas stand in a row, but who can save the guests from loneliness? If you have a soul, you can’t listen to the manager’s introduction.
Listening to his introduction, all of them have boundless magic power.
At this time, you should get rid of all distracting thoughts, start from the beginning, pick and see one by one.
Whether the hair is what you like, whether the advantages are prominent enough, whether the eyes are what you like, whether the slit of the skirt is in place...
Click!
Lu Chuan, who had compared the nineteenth fingerprint, seemed to have a flash of lightning in his mind.
The eyes light up and the mind becomes clear.
That means, it’s fate and it’s you!
For the nineteenth fingerprint, Lu Chuan stroked it in place from the beginning. After comparing the entire third of the fingerprints, no obvious similarities or differences were found.
Of course, this does not mean that the owner of this fingerprint must be the murderer.
After all, there is a one-third chance that a fingerprint is the same as someone else’s.
Although the probability is very small, it exists, and it cannot be used as judicial evidence to accuse the other party.
But in reality, one-third of the fingerprints can basically determine the identity of the other party.
As long as we are sure and find other evidence, it will be easier.
(End of this chapter)