Chinese traditional lacquerwares, ornamental objects decorated by multiple, composite layers of lacquers, are one of the most significant expressions of China art. Existing X-ray radiography and other detection technologies will cause irreparable damage to the lacquerware due to their high photon energy. Terahertz time-domain spectroscopic reflectometric imaging (THz-TDSRI) system being capable of highlight interfaces between layers in a stratigraphic buildup, could be a complementary technique for obtaining structural information about lacquered objects. In this study a Chinese lacquerware has been investigated by terahertz (THz) reflectometric imaging. The investigated lacquerware belongs to Palace Museum. The lacquerware is a decorative work made of a wood panel covered with several layers of lacquers to depict motifs. In order to detect lacquerware, the THz-TDSRI system was built by us. For imaging applications, the source of contrast is the optical density of materials and in reflection geometry the back-reflected THz pulse is analyzed for reflections originating from the various interfaces present between the various sample layers. The value of the electric field measured for each spatial coordinate (X, Y) of the scanned areas has been used for the bidimensional visualization of the lacquerware. The displaying method used in THz imaging application is pseudo coloring. Utilizing THz-TDSRI system, we observe non-invasively buried layers of the lacquerware, including faults in the wood layer, with the lacquerware was not injured. This shows that THz time-domain spectroscopic reflectometric imaging is a non-destructive inspection method for lacquer ware and has great potential in the future.
We analyzed the reasons why ZnTe generates terahertz echo. Based on the Gaussian beam, the terahertz signal with echo is produced by simulation. In this paper, the deconvolution algorithm is further improved. The linear assumption that sample absorption is proportional to frequency is abandoned. We studied the method of echo based on Echo State Network. Set 200 neural units in each layer of the network. We specify 250 rounds of training. To prevent the gradient from exploding, set the gradient threshold to 1. Specify an initial learning rate of 0.005. After 125 rounds of training, multiply it by a factor of 0.2 to reduce the learning rate. This method largely removes echo. But it has not been completely removed, and there is still less than 5% of the echo signal remaining. We consider the reason may be that the number of neurons, the number of iterations, weight setting and other parameters have yet to be optimized. Although this method does not completely remove the echo, but provides a new method for removing the echo. By optimizing parameters such as the number of neurons, the number of iterations, weight setting and increasing the amount of training data, this method is expected to become a new method for echo removal.
Terrorist attacks make the public safety issue becoming the focus of national attention. Passive terahertz security instrument can help overcomesome shortcomings with current security instruments. Terahertz wave has a strong penetrating power which can pass through clothes without harming human bodies and detected objects. However, in the lab experiments, we found that original terahertz imagesobtained by passive terahertz technique were often too vague to detect the objects of interest. Prior studies suggest that learning-based image super-resolution reconstruction(SRR) method can solve this problem. To our knowledge, we applied the learning-based image SRR method for the first time in single-frame passive terahertz image processing. Experimental results showed that the processed passive terahertz images wereclearer and easier to identify suspicious objects than the original images. We also compare our method with three conventional methods and our method show greater advantage over the other methods.
THz radiation can penetrate through many nonpolar dielectric materials and can be used for nondestructive/noninvasive sensing and imaging of targets under nonpolar, nonmetallic covers or containers. Thus using THz systems to "see through" concealing barriers (i.e. packaging, corrugated cardboard, clothing) has been proposed as a new security screening method. Objects that can be detected by THz include concealed weapons, explosives, and chemical agents under clothing. Passive THz imaging system can detect THz wave from human body without transmit any electromagnetic wave, and the suspicious objects will become visible because the THz wave is blocked by this items. We can find out whether or not someone is carrying dangerous objects through this image. In this paper, the THz image enhancement, segmentation and contour extraction algorithms were studied to achieve effective target image detection. First, the terahertz images are enhanced and their grayscales are stretched. Then we apply global threshold segmentation to extract the target, and finally the targets are marked on the image. Experimental results showed that the algorithm proposed in this paper can extract and mark targets effectively, so that people can identify suspicious objects under clothing quickly. The algorithm can significantly improve the usefulness of the terahertz security apparatus.
We presented a passive THz opto-mechnical scanning imaging method using a single detector and a trihedral scanning mirror. The system improved the imaging speed through employing two flapping mirrors. Also the trihedral scanning mirror and an ellipsoidal mirror were adopted. The parameters were set as follows: the best imaging distance was 2.2m with the image range of 1.6m（W）×1.6m（H）, the imaging time was 2s, and the resolution was 3cm. We imaged human body with different objects concealed under their clothes, such as buckle, ceramic chip, etc.
The passive detection is safe for passengers and operators as no radiation. Therefore, passive terahertz (THz) imaging can be applied to human body security check. Imaging in the THz band offers the unique property of being able to identify object through a range of materials. Therefore passive THz imaging is meaningful for security applications. This attribute has always been of interest to both the civil and military marks with applications. We took advantage of a single THz detector and a trihedral scanning mirror to propose another passive THz beam scanning imaging method. This method overcame the deficiencies of the serious decline in image quality due to the movement of the focused mirror. We exploited a THz scanning mirror with a trihedral scanning mirror and an ellipsoidal mirror to streamline the structure of the system and increase the scanning speed. Then the passive THz beam scanning imaging system was developed based on this method. The parameters were set as follows: the best imaging distance was 1.7m, the image height was 2m, the image width was 1m, the minimum imaging time of per frame was 8s, and the minimum resolution was 4cm. We imaged humans with different objects hidden under their clothes, such as fruit knife, belt buckle, mobile phone, screwdriver, bus cards, keys and other items. All the tested stuffs could be detected and recognized from the image.
As it is well-known, passive THz imaging devices have big potential for solution of the security problem. Nevertheless, one of the main problems, which take place on the way of using these devices, consists in the low image quality of developed passive THz camera. To change this situation, it is necessary to improve the engineering characteristics (resolution, sensitivity and so on) of the THz camera or to use computer processing of the image. In our opinion, the last issue is more preferable because it is more inexpensive. Below we illustrate possibility of suppression of the noise of the image captured by three THz passive camera developed in CNU (Beijing. China). After applying the computer processing of the image, its quality enhances many times. Achieved quality in many cases becomes enough for the detection of the object hidden under opaque clothes. We stress that the performance of developed computer code is enough high and does not restrict the performance of passive THz imaging device. The obtained results demonstrate the high efficiency of our approach for the detection of hidden objects and they are a very promising solution for the security problem. Nevertheless, developing the new spatial filter for treatment of the THz image remains a modern problem at present time.
Using the passive THz imaging system developed by the CNU-THz laboratory, we capture the passive THz image of
human body with forbidden objects hidden under opaque clothes. We demonstrate the possibility of significant
improving the quality of the image. Our approach bases on the application of spatial filters, developed by us for
computer treatment of passive THz imaging.
The THz imaging system is constructed with accordance to well known passive THz imaging principles and to the THz
quasi-optical theory. It contains a scanning mechanism, which has a detector approximately with 1200μm central
wavelength, a data acquisition card and a microcomputer. To get a clear imaging of object we apply a sequence of the
spatial filters to the image and spectral transforms of the image. The treatment of imaging from the passive THz device is
made by computer code. The performance time of treatment of the image, containing about 5000 pixels, is less than 0.1
To illustrate the efficiency of developed approach we detect the liquid explosive, knife, pistol and metal plate hidden
under opaque clothes. The results obtained demonstrate the high efficiency of our approach for the detection and
recognition of the hidden objects and are very promising for the real security application.
In order to improve the performance of grayscale image colorization based on color transfer, this paper proposes a novel
method by which pixels are matched accurately between images through region texture analysis using Gray Level
Co-occurrence Matrix (GLCM). This method consists of six steps: reference image selection, color space transformation,
grayscale linear transformation and compression, texture analysis using GLCM, pixel matching through texture value
comparison, and color value transfer between pixels. We applied this method to kinds of grayscale images, and they
gained natural color appearance like the reference images. Experimental results proved that this method is more effective
than conventional method in accurately transferring color to grayscale images.
Proc. SPIE. 6623, International Symposium on Photoelectronic Detection and Imaging 2007: Image Processing
KEYWORDS: Thermography, Image fusion, Infrared imaging, Digital signal processing, Detection and tracking algorithms, Image processing, Ultraviolet radiation, Night vision, Signal processing, RGB color model
To obtain a color night vision image, we proposed a color transfer algorithm in YUV color space based on the color
transfer algorithm in lαβ color space which Reinhard proposed. After rendering the simple statistics (means and
standard deviations) of the target image to the source image, the color appearance of the target image is transferred
to the source image. 2D chromatic histogram (UV histogram) which can help to find an appropriate target image is
established. Finally, we illustrated several examples of color transfer to multi-band fused images which are fused in
MIT fusion scheme. After a color fused image is obtained, the color transfer is executed to render the color
information of the target image to the fusion image. The final image could have a day-like color appearance.
Besides, the algorithm has less operation than which in lαβ color space because of less transform complexity. It can
be realized in real time in digital signal processors without color space transformation between RGB and YUV.
A color transfer scheme for visible and infrared images is presented. Two main procedures are included: image fusion
using steerable pyramid in YUV color space, color transfer based on local mean value of infrared image to enhance hot
contrast. Firstly, visible and infrared images are decomposed into 18 subband images with a 4-scale 4-oriatation
steerable pyramid that contains one highpass subands, one lowpass subband and sixteen bandpass subbands. In each
suband image, Y component of the fused image is formed by the pixels whose value is the larger one between the
visible and infrared images. The weighted subtracting operations between visible and infrared constitute the U and V
components. Then, during the process of color transfer, the local gray mean in the 5×5 window of the infrared image is
concerned. The V component that represents the difference between luminance(Y) and red color is increased by the
ratio of the local mean value to the global mean value. Therefore, the hot contrast of infrared is enhanced by rendering
hot targets intense red color. Test results show that, the image fusion with the 4-scale 4-oriatation steerable pyramid
multiples the paths to transfer the color and luminance of a target image into the fused images, thus, the transferred
images are much more colorful, and synchronously reserve the two image's advantage that the visible image is good at
situation awareness and the infrared image is superior in target detection.
A real-time color transfer system based on 3 pieces of multi-media DSP TM1300 for low-light level
visible(LLLV) and infrared(IR) images is built. Computing quantity is split among three TM13003. Two pieces of
TM1300 preprocess the dual-band images and calculate their mean and standard deviation respectively. The third
TM1300 executes fusion and color transfer in YUV space: Firstly the two preprocessed images are fused into one
primary color image(source image) in which hot targets present warm color, cold targets present cool color. Then the
mean and standard deviation of source images in Y, U, V components are deduced by preprocessed images pixel value
and their mean and standard deviation. Finally, the Y, U and V component of source image are scale by the variation ratio
of a day-time color image(target image) to the source image. The color and luminance distribution of the target image is
transferred into source image and makes it present a sort of day-time color appearance. Comparing to the usually used
l&agr;&bgr; space, color transfer in YUV space can avoid iterative color space transformation, logarithmic and exponential
calculation, and thus be effective in real-time realization while the color transferred results are acceptable.
A real-time 16-bit digital video grabber based on USB 2.0 protocol, thermal temperature measurement and dynamic analysis software are presented. One kind of 35 μm square pixel pitch's uncooled focal plane array thermal imaging module with 16-bit digital video output was selected. As long as being equipped with suitable camera lens, power supply and monitor, the module can be integrated as a thermal imaging system for observation, recognition, tracking and thermal images detection. Cypress Corp. CY7C68013 USB protocol chip is utilized. Main developments of video grabber are stressed on data transfer and logic control between imaging module and CY7C68013 with CPLD devices, and programming windows drivers based on Windriver. The measurement and dynamic analysis software involves not only traditional false color coding, point/line/area temperature analysis, but also several new functions: 1. Automatically mark and monitor the area when its temperature is higher than a setting threshold, and plot the curve of temperature histogram against time. 2. Monitor and plot the temperature movement versus time in manually setting points or area. 3. Database based on local area network convenient for sharing and managing data. Statistics form, curve plot, single-frame and sequence images can enter into database by manual operation or in term of some conditions set previously, such as files saving interval. Moreover, different functions are designed according to the authority of accessing local area network.