Akira Shiozaki

Biometric Verification Using Keystroke Motion and Key Press Timing for ATM User Authentication

We propose a biometric verification method using biometric feature in keystroke operation for ATM (automatic teller machine) user authentication. In the proposed method, ATM user authentication is performed by using the 10 types of biometric feature of hand-shape which are extracted from keystroke motion in ATM operation. Moreover, we calculate the similarity between current ATM operator and genuine user in consideration of key-press timing. The proposed method can improve the safety of the present situation without special additional operation, physical load and psychological burden

Hand Region Extraction by Background Subtraction with Renewable Background for Hand Gesture Recognition

In order to realize high-precision hand gesture recognition, it is necessary that hand region is extracted correctly from moving image. In this paper, we propose a new hand region extraction method by using background subtraction algorithm. In the proposed method, we introduce the renewal of background image according to the situation of input image. In comparison with the conventional method, our method is able to extract hand region more accurately and more efficiently. Moreover, the proposed method has been applied to hand region extraction for Japanese sign language, and its validity has been confirmed

Digital watermarking method for tamper detection and recovery of JPEG images

Digital watermarking is a technique that embeds additional data into digital contents so that the distortion by embedding them is imperceptible, where the additional data are called watermark. One of the applications of digital watermarking is tamper detection and recovery. The digital watermarking methods for tamper detection and recovery can detect the tampered region in a tampered image and recover it. In this application, the digital watermarking methods solve the problem that digital contents can be tampered so that the falsification is not detected. In this manuscript, we propose a new method for tamper detection and recovery of JPEG images by using a RS code. The proposed method embeds the check symbols corresponding to an information-reduced original image into the LSBs of the quantized DCT coefficients in a JPEG image directly. Therefore the method completely extracts the embedded data from watermarked JPEG images. We investigated the performance of the proposed method in view of the image quality and the ability of tamper detection and recovery. The experiments of the image quality confirmed the imperceptibility of watermarked images and images used for recovery. The experiments of the ability of tamper detection and recovery confirmed the maximum size of recoverable tampered region and the difficulty of undetectable falsification.

Reversible Watermarking Method for JPEG Images

In this letter, we propose a simple reversible watermarking method for JPEG images using the characteristics of JPEG compression. The method embeds a watermark into a JPEG image, and it extracts the watermark from the watermarked JPEG image and at the same time can recover the watermarked JPEG image to an original unwatermarked JPEG image. Moreover we investigate the number of embeddable blocks, the quality of watermarked images, and the increase of file-size by embedding a watermark.

Multichannel audio watermarking method by multiple embedding

The objective of this work is to increase the capacity of watermark information in the audio watermarking method based on amplitude modification. We increase the capacity of watermark information by embedding multiple watermarks in the different levels of audio data independently. Moreover, we aim to improve the sound quality by modifying the scaling curve of the conventional method.

Multi-Layer Audio Watermarking Based on Amplitude Modification

In the conventional method proposed by W.N.Lie et al., it is difficult to satisfy both the capacity of watermark information and the robustness to MP3 compression. The objective of this work is to increase the capacity of watermark information in the audio watermarking based on low-frequency amplitude modification. We increase the capacity of watermark information by embedding multiple watermarks in individual layers. In the proposed method, it has plural data channels, so it is possible to embed watermark information by selecting the proper data channel according to the capacity of data or extraction accuracy.

An audio watermarking method by using automatic music transcription information

The objective of this work is to embed watermark information into digital audio data as the deterioration of sound quality is not perceivable to human ears. Hence, we consider that watermark information is embedded in the consonance to melody line or bass line. Generally, unison, octave, perfect fifth and perfect fourth are called consonance and human ears can hardly feel annoyed for consonance. Hence, we focus on perfect fifth and perfect fourth in the consonance. For decision of embedding positions, we need to estimate tone pitches, and we use spectrogram analysis as a technique of automatic music transcription. We embed watermark information with perfect fifth or perfect fourth of consonance from the pitch which is estimated by spectrogram analysis, and we aim at good sound quality of watermarked audio signal without sense of discomfort. Therefore, we propose an audio watermarking method by using automatic music transcription information.

Digital watermarking method warranting the lower limit of image quality of watermarked images

We propose a digital watermarking method warranting the lower limit of the image quality of watermarked images. The proposed method controls the degradation of a watermarked image by using a lower limit image. The lower limit image means the image of the worst quality that users can permit. The proposed method accepts any lower limit image and does not require it at extraction. Therefore lower limit images can be decided flexibly. In this paper, we introduce 2-dimensional human visual MTF model as an example of obtaining lower limit images. Also we use JPEG-compressed images of quality 75% and 50% as lower limit images. We investigate the performance of the proposed method by experiments. Moreover we compare the proposed method using three types of lower limit images with the existing method in view of the tradeoff between PSNR and the robustness against JPEG compression.

Evaluation of the accuracy of CT numbers in statistical correction of nonlinearity for polychromatic X-ray CT projection data

The CT number is theoretically independent of the number of incident photons and the thickness of a subject. However, when noise is added, the CT number becomes dependent on the number of incident photons because of the nonlinearity of the logarithm operation, and so the accuracy of the CT number is degraded, especially in a photon-starved state. The inconsistency of the CT number due to nonlinearity generates an intense streak artifact in a reconstructed image. We have theoretically clarified the statistical characteristics of both the nonlinearity of the logarithm transform and the non-zero/non-negative restriction in the logarithm operation. Moreover, we have formulated a correction method for such nonlinearity according to the statistical distribution of noise, and we carried out computer simulations for monochromatic X-ray beams. However, the applicability to polychromatic-energy photons has not been confirmed. The artifacts induced by the beam-hardening effect, which occurs when incident beams are polychromatic, remarkably deteriorate the accuracy of the CT number. In this paper, we quantitatively evaluate the improvement of the quality of reconstructed images by our correction method by using a numerical experiment when incident beams are polychromatic. The experimental results show that there is less influence on spatial resolution and that the CT number is hardly dependent on the number of incident photons for a polychromatic beam as well as a monochromatic beam. Moreover, the results suggest the possibility that the same image quality is obtained at a much lower exposure level than the clinical exposure level of low-dose CT.

Correction Method of Nonlinearity Due to Logarithm Operation for X-Ray CT Projection Data with Noise in Photon-Starved State

In the acquisition of projection data of X-ray CT, logarithm operation is indispensable. But noise distribution is nonlinearly projected by the logarithm operation, and this deteriorates the precision of CT number. This influence becomes particularly remarkable when only a few photons are caught with a detector. It generates a strong streak artifact (SA) in a reconstructed image. Previously we have clarified the influence of the nonlinearity by statistical analysis and proposed a correction method for such nonlinearity. However, there is a problem that the compensation for clamp processing cannot be performed and that the suppression of SA is not enough in photon shortage state. In this paper, we propose a new technique for correcting the nonlinearity due to logarithm operation for noisy data by combining the previously presented method and an adaptive filtering method. The technique performs an adaptive filtering only when the number of captured photons is very few. Moreover we quantitatively evaluate the influence of noise on the reconstructed image in the proposed method by the experiment using numerical phantoms. The experimental results show that there is less influence on spatial resolution despite suppressing SA effectively and that CT number are hardly dependent on the number of the incident photons.