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EP-4736133-A1 - METHOD FOR PROCESSING A TEST IMAGE, COMPUTER DEVICE AND COMPUTER PROGRAM ASSOCIATED THEREWITH

EP4736133A1EP 4736133 A1EP4736133 A1EP 4736133A1EP-4736133-A1

Abstract

The invention relates to a method for processing a test image showing a plurality of latent fingerprints, which method comprises the following steps of: - generating (E102), using a neural network, a semantic segmentation map comprising, for each block of a plurality of blocks of the test image, a score indicative of a probability of existence of a latent fingerprint passing through the block, - generating (E104) a binary map estimating, for each block of the plurality of blocks, whether or not the block shows a latent fingerprint portion, - detecting (E106) a plurality of instances of latent fingerprints from the binary map, - for each instance of the plurality of instances, obtaining (E108) an aggregated score by aggregating the scores associated with the blocks of the plurality of blocks that belong to the instance, - obtaining (E110) a restricted plurality of instances by restricting the plurality of instances to each instance whose aggregated score is greater than a threshold.

Inventors

  • MABYALAHT, Guy
  • KAZDAGHLI, LAURENT SEMY

Assignees

  • Idemia Public Security France

Dates

Publication Date
20260506
Application Date
20240515

Claims (10)

  1. [Claim 1] A method of processing a proof image showing a plurality of latent prints, the method comprising the following steps implemented by a computing device (1): - generation (El 02) by a neural network of a semantic segmentation map from the test image, the semantic segmentation map comprising, for each block forming part of a plurality of blocks of the test image, a score associated with the block indicative of a probability of existence in the test image of a latent imprint passing through the block, - generation (El 04) of a binary map from the semantic segmentation map, the binary map estimating, for each block of the plurality of blocks of the test image, whether or not the block shows a part of a latent fingerprint, - detection (E106) of a plurality of latent fingerprint instances from the binary map, - for each instance of the plurality of instances, obtaining (El 09) an aggregated score from the semantic segmentation map, the aggregated score being obtained by aggregating the scores associated with the blocks of the plurality of blocks of the test image which belong to said instance, - obtaining (El 10) a restricted plurality of instances by restricting the plurality of instances to each instance whose aggregate score is greater than a predetermined threshold.
  2. [Claim 2] A method of processing a proof image according to the preceding claim, wherein the aggregated score of an instance is the average of the scores associated with the blocks of the plurality of blocks of the proof image which show a portion of the latent fingerprint of said detected instance.
  3. [Claim 3] A method of processing a proof image according to any preceding claim, wherein the step (El 06) of detecting a plurality of latent fingerprint instances comprises a substep (SE106 2) of applying a watershed segmentation to the binary map by means of a sliding window.
  4. [Claim 4] A method of processing a proof image according to any preceding claim, wherein the step (El 06) of detecting a plurality of latent fingerprint instances comprises a substep (SE106 6) of applying an analysis by components related to another binary map obtained from the binary map.
  5. [Claim 5] Method for processing a proof image according to the preceding claim, in which the step (E106) of detecting a plurality of latent print instances further comprises the following sub-step (SE106_4): - obtaining the other binary map by eroding the binary map through an erosion window having a predetermined surface, to eliminate the blocks of the proof image which show a latent print portion having a surface less than the predetermined surface.
  6. [Claim 6] A method of processing a proof image according to any one of the preceding claims, the method comprising, between the step (E106) of detecting a plurality of latent fingerprint instances and the step (E109), for each instance of the plurality of instances, of obtaining an aggregated score, a step (E108) of reducing the plurality of instances comprising the following sub-steps: - for each instance of the plurality of instances, definition (SE108 2) of a detection box, the detection box being the smallest rectangular box which entirely contains said instance, - deletion (SE108_4) of an instance of the plurality of instances if its detection box is included in a detection box of another instance of said plurality of instances, - merging (SE108 6) a first instance and a second instance of the plurality of instances if the intersection of a detection box of the first instance and a detection box of the second instance is greater than a predefined fraction of the union of said detection boxes of the first instance and detection box of the second instance.
  7. [Claim 7] A method of processing a proof image according to any one of the preceding claims, the method further comprising an identification step (El 12) in which at least one latent fingerprint instance of the restricted plurality of instances is individually compared to a reference fingerprint, to verify a correspondence between each latent fingerprint of the at least one latent fingerprint instance and the reference fingerprint.
  8. [Claim 8] A computer program comprising code instructions for executing the method according to any preceding claim when these instructions are executed by the computer.
  9. [Claim 9] A computer-readable storage medium storing computer-executable instructions for carrying out the method of any one of claims 1 to 7.
  10. [Claim 10] A computing device (1) for processing a proof image showing a plurality of latent prints, the computing device (1) being configured to: - generating by a neural network a semantic segmentation map from the test image, the semantic segmentation map comprising, for each block forming part of a plurality of blocks of the test image, a score associated with the block indicative of a probability of existence in the test image of a latent fingerprint passing through the block, - generating a binary map from the semantic segmentation map, the binary map estimating, for each block of the plurality of blocks of the test image, whether or not the block shows a latent fingerprint portion, - detect a plurality of latent fingerprint instances from the binary map, - obtaining for each instance of the plurality of instances, an aggregated score from the semantic segmentation map, the aggregated score being obtained by aggregating the scores associated with the blocks of the plurality of blocks of the test image which belong to said instance, - obtain a restricted plurality of instances by restricting the plurality of instances to each instance whose aggregate score is greater than a predetermined threshold.

Description

Description Title of the invention: Method for processing a test image, associated computer device and computer program. [0001] The invention relates to a method for processing a proof image showing a plurality of latent prints. The invention also relates to a computer device and an associated computer program. [0002] Methods are known for identifying or authenticating an individual using his or her papillary prints, for example a fingerprint and/or a palm print and/or a plantar print, these methods comprising the following steps. Conventionally, a test image showing a test papillary print of an individual is acquired, and this image is compared with a reference image showing a reference papillary print, to verify a correspondence between the test papillary print and the reference papillary print. If such a correspondence is found, then it is considered that the individual has previously been enrolled. [0003] In a police investigation context, it is possible to use as a test image a photograph of one or more papillary traces left on a support by the affixing of an area of the skin presenting papillary ridges. This photograph is typically acquired by a generic device, that is to say a device not specifically dedicated to the acquisition of papillary prints. [0004] A papillary trace appearing in an image of this type is commonly called a "latent" print and can be assimilated to a papillary print. [0005] Comparing a reference image showing a reference papillary print, to a test image showing several latent prints, degrades the performance of the identification and authentication methods, typically the false negative rate and/or the false positive rate. [0006] To remedy this, it is known to manually dissociate the latent prints from the proof image, that is to say to instantiate the latent prints from the proof image, to allow their individual processing by the identification and authentication methods. [0007] This dissociation is carried out manually by a specialist and proves to be inefficient for large quantities of test images. [0008] The paper “Automatic Latent Fingerprint Segmentation” Dinh-Luan Nguyen, Kai Cao and Anil K. Jain, arXiv: 1804.09650v2 describes the use of neural networks that perform instance-based segmentation of a fingerprint and the ability to thus process a test image showing a plurality of latent fingerprints to dissociate the latent fingerprints from said test image. However, instance segmentation neural networks are complex to implement and particularly costly in terms of computation time and memory space. [0009] Additionally, a test image may show multiple types of fingerprints, typically one or more latent fingerprints, and one or more latent palmprints. [0010] To overcome these drawbacks, the present invention proposes, according to a first aspect, a method for processing a test image showing a plurality of latent prints, the method comprising the following steps implemented by a computer device: - generation by a neural network of a semantic segmentation map from the test image, the semantic segmentation map comprising, for each block forming part of a plurality of blocks of the test image, a score associated with the block indicative of a probability of existence in the test image of a latent fingerprint passing through the block, - generating a binary map from the semantic segmentation map, the binary map estimating, for each block of the plurality of blocks of the test image, whether or not the block shows a latent fingerprint portion, - detection of a plurality of latent fingerprint instances from the binary map, - for each instance of the plurality of instances, obtaining an aggregated score from the semantic segmentation map, the aggregated score being obtained by aggregating the scores associated with the blocks of the plurality of blocks of the test image which belong to said instance, - obtaining a restricted plurality of instances by restricting the plurality of instances to each instance whose aggregate score is greater than a predetermined threshold. [0011] According to advantageous and non-limiting characteristics: - the aggregated score of an instance is the average of the scores associated with the blocks of the plurality of blocks of the test image which show a part of the latent fingerprint of said detected instance; - the step of detecting a plurality of latent fingerprint instances comprises a sub-step of applying a watershed segmentation to the binary map by means of a sliding window; - the step of detecting a plurality of instances of latent fingerprints comprises a sub-step of applying a related component analysis to another binary map obtained from the binary map; - the step of detecting a plurality of latent fingerprint instances further comprises the following substep: obtaining the other binary map by eroding the binary map through an erosion window having a predetermined surface, to eliminate blocks from the proof image which show a latent print portio