Research On Imaging System Of Remaining Information Of Fingerprint On Paper

With the rapid development of information technology, information security has been given increasing attention. The security departments, in particular, have attached greater importance to the document secrecy and they impose strict restrictions on the readers of the secret documents. This article elaborates on the testing principles and working procedures of the remaining trace on paper (mainly invisible fingerprints of sweat). Now the generally accepted method to handle and collect invisible fingerprints of sweat is by means of lime or ink powder. And the most proper way on such penetrating material carriers as paper and cardboard is steaming iodine approach. However all the above-mentioned methods will damage the testing samples on varying degrees. In order to keep the original testing samples intact, a new method is proposed to test and get image of the invisible of fingerprints of sweat. The new approach is to test the difference on resistance between the remaining trace in paper and non-remaining trace, and input the tested data into computer. This approach makes use of Visual C++6.0 to convert the tested data into image and the Visual C++ computing method to obtain a keener image. This approach also adopts the operations as threshold transform, gray-scale stretch,window transform, image smoothing, image sharpening, so that the processed image can meet the requirements of further division and identity.Chapter 1 mainly tells us about the whole plan demonstration and entire thinking of system. It also gives feasible analyze and item-study meaning.It elaborates on principle of data collection and correlation circuits in Chapter 2. Because the resistances between the remaining trace and non-remaining trace are different in paper, we can test remaining trace on paper by testing the resistance of invisible fingerprints of sweat. By voltage of sampling resistance RO12 is tested. Next the voltage signal which is magnified via linear amplifier. After converted to digital signal in A/D converter, the data is transmitted to PC. The data are deal with on PC. And the results are displayed on monitor and saved as image files (JPG or BMP format). We attain the examine trace aims. Evidently, the part of collecting data is required some sensitivities. So we consider the testing DC parameter. (01)Note: R1+R and R2+R are the paper resistances, R1 and R2 are the paper-changing resistances, Ro1 and Ro2 are the same sampling resistance.In fact: R>>R1, R2, Ro1, Ro2(1) When the sampling resistance uses the linear resistance Vi2,Ro1=Ro2=Ro, then: (02) (2) When the sampling resistance is non-linear resistance (03)Hence using non-linear resistance as sampling resistance is of advantage to testing. That is very important to improve display sensitivity. Researching non-linear sampling devices (circuit) and match preamplifier is the key to decide the equipment's display sensitivity .In fact the circuit design adopts constant current source circuit, driving source adopts ways of sin AC signal and DC signal. Sampling original data correspond with BMP format. But it is disturbed by the factors which are the humility uniform of system and paper, the uniformity of paper thickness and other outer interferences. This causes background noise very noisy. So it is essential to restrain the background signal and random noise mostly which can make it sure to renew aim information in high quality. Data need disposing necessarily. The information about invisible fingerprints of surest in Si district is seen as aim image. While the paper in Si district is seen as the image background .The paper's infirm of humidity and thickness maybe lead background signal to change too much. When this change approaches aim signal, it is disadvantage to discern aim signal. Now there is no suitable way to change paper thickness, so to restrain background noise only can uses the way of disposing data in most degree. The sampling of image signal lies in noise whic...