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[Author] Takahiro YAMAMOTO(3hit)

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  • Method of Spread Spectrum Watermarking Using Quantization Index Modulation for Cropped Images

    Takahiro YAMAMOTO  Masaki KAWAMURA  

     
    PAPER-Data Engineering, Web Information Systems

      Pubricized:
    2015/04/16
      Vol:
    E98-D No:7
      Page(s):
    1306-1315

    We propose a method of spread spectrum digital watermarking with quantization index modulation (QIM) and evaluate the method on the basis of IHC evaluation criteria. The spread spectrum technique can make watermarks robust by using spread codes. Since watermarks can have redundancy, messages can be decoded from a degraded stego-image. Under IHC evaluation criteria, it is necessary to decode the messages without the original image. To do so, we propose a method in which watermarks are generated by using the spread spectrum technique and are embedded by QIM. QIM is an embedding method that can decode without an original image. The IHC evaluation criteria include JPEG compression and cropping as attacks. JPEG compression is lossy compression. Therefore, errors occur in watermarks. Since watermarks in stego-images are out of synchronization due to cropping, the position of embedded watermarks may be unclear. Detecting this position is needed while decoding. Therefore, both error correction and synchronization are required for digital watermarking methods. As countermeasures against cropping, the original image is divided into segments to embed watermarks. Moreover, each segment is divided into 8×8 pixel blocks. A watermark is embedded into a DCT coefficient in a block by QIM. To synchronize in decoding, the proposed method uses the correlation between watermarks and spread codes. After synchronization, watermarks are extracted by QIM, and then, messages are estimated from the watermarks. The proposed method was evaluated on the basis of the IHC evaluation criteria. The PSNR had to be higher than 30 dB. Ten 1920×1080 rectangular regions were cropped from each stego-image, and 200-bit messages were decoded from these regions. Their BERs were calculated to assess the tolerance. As a result, the BERs were less than 1.0%, and the average PSNR was 46.70 dB. Therefore, our method achieved a high image quality when using the IHC evaluation criteria. In addition, the proposed method was also evaluated by using StirMark 4.0. As a result, we found that our method has robustness for not only JPEG compression and cropping but also additional noise and Gaussian filtering. Moreover, the method has an advantage in that detection time is small since the synchronization is processed in 8×8 pixel blocks.

  • Tailored Optical Frequency Comb Block Generation Using InP-Based Mach-Zehnder Modulator

    Takahiro YAMAMOTO  Takeaki SAIKAI  Eiichi YAMADA  Hiroshi YASAKA  

     
    BRIEF PAPER-Lasers, Quantum Electronics

      Vol:
    E97-C No:3
      Page(s):
    222-224

    A reduction in the intensity deviation of a nine-channel optical frequency comb block (OFCB) is demonstrated, by adopting an asymmetric differential drive method for an InP-based dual drive Mach-Zehnder modulator. The generation of a tailored OFCB with an intensity deviation of less than 0.8dB is confirmed by using the modulator.

  • A Systematic Methodology for Design and Worst-Case Error Analysis of Approximate Array Multipliers

    Takahiro YAMAMOTO  Ittetsu TANIGUCHI  Hiroyuki TOMIYAMA  Shigeru YAMASHITA  Yuko HARA-AZUMI  

     
    LETTER

      Vol:
    E100-A No:7
      Page(s):
    1496-1499

    Approximate computing is considered as a promising approach to design of power- or area-efficient digital circuits. This paper proposes a systematic methodology for design and worst-case accuracy analysis of approximate array multipliers. Our methodology systematically designs a series of approximate array multipliers with different area, delay, power and accuracy characteristics so that an LSI designer can select the one which best fits to the requirements of her/his applications. Our experiments explore the trade-offs among area, delay, power and accuracy of the approximate multipliers.