Joseph Joby, Bhagatji Alpana, Singh Kehar
Photonics Group, Department of Physics, Indian Institute of Technology Delhi, New Delhi-16, India.
Appl Opt. 2010 Jan 20;49(3):471-8. doi: 10.1364/AO.49.000471.
Conventionally a holographic data storage system uses binary digital data as the input pages. We propose and demonstrate the use of a holographic data storage system for the purpose of invariant pattern recognition of gray-scale images. To improve the correlation accuracy for gray-scale images, we present a coding technique, phase Fourier transform (phase-FT) coding, to code a gray-scale image into a random and balanced digital binary image. In addition to the fact that a digital data page is obtained for incorporation into a holographic data storage system, this phase-FT coded image produces dc-free homogenized Fourier spectrum. This coded image can also be treated as an image for further processing, such as synthesis of distortion-invariant filters for invariant pattern recognition. A space-domain synthetic discriminant function (SDF) filter has been synthesized using these phase-FT coded images for rotation-invariant pattern recognition. Both simulation and experimental results are presented. The results show good correlation accuracy in comparison to correlation results obtained for SDF filter synthesized using the original gray-scale images themselves.
传统上，全息数据存储系统使用二进制数字数据作为输入页面。我们提出并演示了一种用于灰度图像不变模式识别的全息数据存储系统。为了提高灰度图像的相关精度，我们提出了一种编码技术，即相位傅里叶变换（phase-FT）编码，将灰度图像编码为随机且平衡的数字二进制图像。除了获得用于纳入全息数据存储系统的数字数据页面外，这种相位傅里叶变换编码图像还能产生无直流均匀化傅里叶频谱。这种编码图像也可被视为用于进一步处理的图像，例如合成用于不变模式识别的失真不变滤波器。利用这些相位傅里叶变换编码图像合成了一种空域合成判别函数（SDF）滤波器，用于旋转不变模式识别。给出了仿真和实验结果。结果表明，与使用原始灰度图像本身合成的SDF滤波器的相关结果相比，该方法具有良好的相关精度。
