Computer Vision and Image Processing Techniques for Mobile Applications

Camera phones have penetrated every corner of society and have become a focal point for communications. In our research we extend the traditional use of such devices to help bridge the gap between physical and digital worlds. Their combined image acquisition, processing, storage, and communication capabilities in a compact, portable device make them an ideal platform for embedding computer vision and image processing capabilities in the pursuit of new mobile applications. This dissertation is presented as a series of computer vision and image processing techniques together with their applications on the mobile device. We have developed a set of techniques for ego-motion estimation, enhancement, feature extraction, perspective correction, object detection, and document retrieval that serve as a basis for such applications. Our applications include a dynamic video barcode that can transfer significant amounts of information visually, a document retrieval system that can retrieve documents from low resolution snapshots, and a series of applications for the users with visual disabilities such as a currency reader. Solutions for mobile devices require a fundamentally different approach than traditional vision techniques that run on traditional computers, so we consider user-device interaction and the fact that these algorithms must execute in a resource constrained environment. For each problem we perform both theoretical and empirical analysis in an attempt to optimize performance and usability. The thesis makes contributions related to efficient implementation of image processing and computer vision techniques, analysis of information theory, feature extraction and analysis of low quality images, and device usability

SECURE DATA TRANSMISSION USING BARCODE MODULATION METHOD FOR MOBILE DEVICES

In this study, a new approach for data modulation in 2-D barcodes is introduced, and its performance is evaluated in comparison to other standard methods of barcode modulation. In this new approach, orthogonal frequency-division multiplexing (OFDM) modulation is used together with differential phase shift keying (DPSK) over adjacent frequency domain elements. A barcode can be transferred from one mobile to another by capturing images. But the relative movements during capture can induce motion-blur distortions in the captured image. This problem can be solved by using orthogonal frequency division multiplexing (OFDM) modulation along with differential phase shift keying (DPSK). In this technique, a large number of closely spaced orthogonal sub-carriers carry the data on several parallel data streams or channels. The sub-carriers are modulated with any of the conventional modulation technique. Here DPSK modulation is used to modulate the sub-carriers. The modulation is performed in the message which is encoded as the barcode. The barcode is captured and then fast Fourier transform (FFT) is applied onto the decoded message. Then, original message is retrieved by performing demodulation. Since data is stored in phase difference, adjacent elements are less affected by the motion blur distortions

An Optical Design Configuration for Wireless Data Transmission

The concept of 2D barcodes is of great relevance for use in wireless data transmission between handheld electronic devices. In a typical setup, any file on a cell phone for example can be transferred to a second cell phone through a series of images on the LCD which are then captured and decoded through the camera of the second cell phone. In this research, a new approach for data modulation in 2D barcodes is introduced, and its performance is evaluated in comparison to other standard methods of barcode modulation. In the proposed method, Orthogonal Frequency Division Multiplexing (OFDM) modulation is used together with Differential Phase Shift Keying (DPSK) over adjacent frequency domain elements to modulate intensity of individual pixels. It is shown that the bit error rate performance of the proposed system is superior to the current state of the art in various scenarios. A specific aim of this study is to establish a system that is proven tolerant to camera motion, picture blur and light leakage within neighboring pixels of an LCD. Furthermore, intensity modulation requires the input signal used to modulate a light source to be positive, which requires the addition of a dc bias. In the meantime, the high crest factor of OFDM requires a lower modulation index to limit clipping distortion. These two factors result in poor power efficiency in radio over fiber applications in which signal bandwidth is generally much less than the carrier frequency. In this study, it is shown that clipping a bipolar radio frequency signal at zero level, when it has a carrier frequency sufficiently higher than its bandwidth, results in negligible distortion in the pass band and most of the distortion power is concentrated in the baseband. Consequently, with less power provided to the optical carrier, higher power efficiencies and better receiver sensitivity will result. Finally, a more efficient optical integrated system is introduced to implement the proposed intensity modulation method which is optimized for radio over fiber applications