The Drop Matrix Matcher (DMM) is a software application that helps to find similar patterns in images. The software can detect all regions in an image where it finds a great similarity with a given pattern. This means in effect the detected regions can vary in brightness or variance.

Usage

In the DMM software you can upload a certain pattern or even choose any region of an uploaded image as pattern. Then you upload an image in which you want to search for the pattern. With the DMM software you can view the regions on that image which looks similar to the pattern. In addition there is a controller element to adjust how similar the region has to be to the pattern to be detected (degree of similiarity).

Aside from that you can even filter the image to get only one of the three printing colors (cyan, magenta, yellow) represented in the image. For further examination you can also change the brightness and contrast both in the image and in the pattern. Besides it is possible to search for the same pattern in another image and compare the results.

Method

For the similiarity computation a global and local brightness invariant and variance invariant template matching algorithm is used.

Forensic Use Case

The DMM software was developed to support the manual inspection of forensic ink-jet printed documents at the forensic science laboratory (KTU Tübingen, Germany). Documents printed with ink-jet printers are not easy to reproduce. This means that not every drop is exactly at the same position when printing the same source two times. But if you want to prove a certain document was printed from a certain printer, reproducibility is desirable. Although not every drop position is reproducible, usually you can find some drop patterns that are arranged in a similar way.

The developed DMM detects (matchs) reproducible patterns (drop matrix) in several prints. This helps to identify the ink-jet printer of a printed document (counterfeit banknote, identity card, contract etc.) and thus can help to expose a culprit (counterfeiter etc.). The procedure “matching the drop matrices” gave the software the name.

Other Use Cases

The software can be used for any template matching application, where you need to find similar patterns with the need of brightness and variance invariance.

Forensic example

Using the Drop Matrix Matcher Software

In this case, it is possible to use the Drop Matrix Matcher Software (DMM). The following screenshots depicts how the DMM can be used to find a selected Drop Matrix of the reference print in the questioned print of the counterfeit banknote.

Detecting the same Drop Matrix on two prints

Detecting the same Drop Matrix multiple times in one print

The Drop Matrix Matcher Software (DMM) can also be used to detect the same drop matrix at different positions on one print.