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Internet remote-controlled optical correlator based on 256 × 256 FLC spatial light modulators
This content has been downloaded from IOPscience. Please scroll down to see the full text. 1999 J. Opt. A: Pure Appl. Opt. 1 307 (http://iopscience.iop.org/1464-4258/1/2/338) View the table of contents for this issue, or go to the journal homepage for more
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J. Opt. A: Pure Appl. Opt. 1 (1999) 307–309. Printed in the UK
PII: S1464-4258(99)97947-3
Internet remote-controlled optical correlator based on 256 × 256 FLC spatial light modulators ¨ Rolph Hey†, Bertrand Noharet and Henrik Sjoberg IOF, Institute of Optical Research, S-100 44 Stockholm, Sweden Received 11 September 1998, in final form 12 January 1999 Abstract. We present a compact optical correlator with Internet access. Users can remotely
download images and get the optically computed correlation results back on their monitor. Keywords: Optical pattern recognition, image processing, correlation, Internet
1. Introduction
There is a lot of work done nowadays in the field of optical pattern recognition and particularly on optical correlators, both in hardware developments and filter design. But only a few research groups have sufficient resources to enable them to work in parallel in both fields. In the frame of the ‘Swedish National Programme for Optical Information Processing’, we have developed an opto-electronic pattern recognition system based on an optical correlator. To enable university and industrial researchers to evaluate the technology and test their filters and algorithms, we present an Internet access to our correlator. 2. The correlator
The optical correlator that has been built at the Institute of Optical Research (IOF) (figure 1) is a compact correlator (21×28 cm2 footprint) based on binary reflective ferroelectric liquid crystal spatial light modulators (SLMs). It can process 256 × 256 pixel images at a maximum frame rate of 220 Hz (limited only by the CCD camera). The correlator can be used both as a VanderLugt correlator and as a joint transform correlator (switching from one configuration to the other does not exceed 15 minutes). As a first step, the software interface and the web pages have only been developed for the VanderLugt mode. 3. Internet remote control
Internet users can access the mainpage of our correlator at: http://www.iof.optics.kth.se/rolph%20project/correl0.html. As the correlator has to be switched on, the only available page to any non-registered user will be our demo page. Our registered users are supplied with an ID and password verification in order to gain access to the configuration pages. † E-mail address:
[email protected]
1464-4258/99/020307+03$19.50
© 1999 IOP Publishing Ltd
With this ID and password, registered users first access the FTP page, where they can remotely download their filters on our web server and then proceed to the set-up page, where they can choose: • Whether to pre-process the input images or not before correlation. • Which pre-processing to use (Sobel, Laplace, Roberts, Prewitt or custom). • Which type of binarization the input should have (level or percentage thresholding). • The binarization value, which should be between 0 and 255 for a level thresholding, and between 0 and 100 for the percentage thresholding. • The name of the input file. • The name of the filter file. As our SLMs are binary, all images have to be binarized before being processed by the correlator. Two methods of binarization are available: one with a fixed threshold and one with a histogram binarization (a certain percentage of the pixels are set to the upper value and the rest to the lower value). Moreover, it has been shown [1] that edge enhancement combined with binarization gives for certain types of images better correlation performances. Thus it is possible to edge-enhance the input image before binarization, by using a 3 × 3 kernel convolution (Sobel, Laplace, Roberts, Prewitt or a custom kernel). Once the set-up page is filled in and sent via Internet to our web server, the result is optically computed and sent back to the user (see figure 2 for simple schematic explanation). The web page on his screen will be automatically updated with the result as soon as it is available. 4. Results
An example of a typical result obtained with the correlator on real-world images is shown in figure 3 (result obtained without edge-enhancement). Thanks to its Internet interface, 307
R Hey et al
Figure 1. Picture of the correlator in VanderLugt mode.
Figure 2. Schematic explanation for the off-site correlation.
Figure 3. Experimental result from the compact correlator on real-world images.
the correlator has been successfully used by industrial researchers [2] at Saab Dynamics in J¨onk¨oping/Sweden 308
(300 km) and by university researchers from LSI/ENSPM in Marseille/France (3000 km).
Internet remote-controlled optical correlator
The Internet access makes it possible for our collaborators to test their developed filters and compare their simulated results with measured correlation peaks. Indeed, the results are dependant both on intrinsic coding constraints and on system noise.
Acknowledgment
5. Conclusion
References
We show a new way of collaboration between researchers in the field of optical pattern recognition between those developing optical set-ups and those developing filters, by sharing the hardware resources over the Internet. This type of collaboration makes it possible both to validate theoretical work on existing hardware and to validate hardware design by implementing complex filters. This type of approach has been demonstrated successfully at the Institute of Optical Research (Stockholm) in collaboration with researchers in Marseille and J¨onk¨oping.
Philippe R´efr´egier, from LSI/ENSPM (FRANCE), is acknowledged for having proposed the idea of sharing our correlator via the Internet.
[1] Sj¨oberg H, Noharet B, Wosinski L and Hey R 1998 A compact optical correlator: pre-processing and filter encoding strategies applied to images with varying illumination Opt. Eng. 37 1316–24 [2] Johansson J R and Rabelius D G 1998 Experimental results from fusion of binary correlation filters implemented on an optical correlator Proc. SPIE AeroSense
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