Pixel Value Differencing Research Articles

A high quality steganographic method with pixel-value differencing and modulus function

In this paper, we shall propose a new image steganographic technique capable of producing a secret-embedded image that is totally indistinguishable from the original image by the human eye. In addition, our new method avoids the falling-off-boundary problem by using pixel-value differencing and the modulus function. First, we derive a difference value from two consecutive pixels by utilizing the pixel-value differencing technique (PVD). The hiding capacity of the two consecutive pixels depends on the difference value. In other words, the smoother area is, the less secret data can be hidden; on the contrary, the more edges an area has, the more secret data can be embedded. This way, the stego-image quality degradation is more imperceptible to the human eye. Second, the remainder of the two consecutive pixels can be computed by using the modulus operation, and then secret data can be embedded into the two pixels by modifying their remainder. In our scheme, there is an optimal approach to alter the remainder so as to greatly reduce the image distortion caused by the hiding of the secret data. The values of the two consecutive pixels are scarcely changed after the embedding of the secret message by the proposed optimal alteration algorithm. Experimental results have also demonstrated that the proposed scheme is secure against the RS detection attack.

Digitizing radiographic films: a simple way to evaluate indirect digital images

Objectives:This study applied a simple method to evaluate the performance of three digital devices (two scanners and one digital camera) using the reproducibility of pixel values attributed to the same radiographic image.Methods:Using the same capture parameters, a radiographic image was repeatedly digitized in order to determine the variability of pixel values given to the image throughout the digitization process. One coefficient value was obtained and was called pixel value reproducibility.Results:A significant difference in pixel values was observed among the three devices for the digitized images (ANOVA, p<0.00001). There was significant pixel value variability at the same digitization conditions for one scanner and the digital camera.Conclusions:Digital devices may assign pixel values differently in consecutive digitization depending on the optical density of the radiographic image and the equipment. The pixel value reproducibility was not satisfactory as tested for two devices. It is maybe advisable knowing the digitization variations regarding pixel values whenever using digital radiography images in longitudinal clinical examinations.

312 LUTEAL MORPHOMETRIC PARAMETERS AND SONOGRAPHIC ECHOTEXTURE DURING LUTEOGENESIS PERIOD IN PREGNANT GOATS

Sonographic echotexture is an important parameter for corpora lutea (CL) evaluation, since it is related to variations on vascularization and histological features of CL and, consequently, to steroidogenesis. The aim of this study was to evaluate the luteal dynamics and pixel value during the early luteogenic period in goats. Nuliparous Toggenburg females (n = 18) with an average age of 8 months, weight of 33.52 � 5.58 kg, and body condition score of 3.5 � 0.33 (1 to 5 scale) were used. Ovarian sonographic evaluations were performed daily for 21 days after natural estrus, using a portable ultrasound device (Aloka SSD 500, Aloka Co., Ltd., Tokyo, Japan) equipped with an adapted linear rectal 5-MHz probe. CL and cavity areas were measured at their largest diameter. CL area minus the cavity area was considered luteal tissue. Images were digitalized in .TIFF format, at a 1500 � 1125 resolution, using a video capture board (Pinnacle DC10, Pinnacle Systems, Mountain View, CA, USA). Images recovered on Days 6, 8, 10, and 12 of the estrous cycle were analyzed using a custom software (Quantpro�). Each image dot (pixel) received a numeric value ranging from 0 (black) to 255 (white). Representative elementary area (REA) of 5625 pixels (0.31 cm2) was defined in the luteal tissue (proposed by Van den Bygaarty et al. 1999 Can. J. Soil Sci. 7, 149–160). Due to the possibility of early luteal regression, only data from pregnant animals (14/18, 77.8%) were used. Follicle diameter, CL area, and cavity were analyzed by ANOVA, and differences among means were evaluated by Tukey's test. Correlations were established by Pearson's correlation method. Results are presented as means � SEM. Mean diameter of ovulatory follicle was 0.75 � 0.01 cm. There was no significant correlation (P &gt; 0.05) between ovulatory follicle diameter and CL area. CL were first visualized on Day 5.68 � 0.37 after the estrus, with a mean area of 0.56 � 0.05 cm2, and progressively increased in size (P &lt; 0.001) until Day 12, reaching a maximum area of 1.18 � 0.06 cm2. A significant (P &lt; 0.05) pixel value increase was observed from Days 6 to 12 of the cycle (42.79 � 5.06a; 47.90 � 4.51ab; 48.33 � 4.21b; and 52.95 � 4.65b, respectively, values with the same superscript not being significantly different). There was a significant positive correlation (R = 0.54, P &lt; 0.0001) between luteal tissue area and pixel value during the luteogenesis period. In single ovulating goats (10/14; 71.42%), the mean time for the first CL visualization was lower (4.71 � 0.15 v. 6.78 � 0.89 days; P &lt; 0.01) and the area of the CL on Day 12 was larger (1.32 � 0.04 v. 1.03 � 0.15 cm2; P &lt; 0.01) than in goats with two or more ovulations, but there was no difference in luteal pixel value (52.32 � 3.19 v. 53.75 � 3.90; P &gt; 0.05). The presence of luteal cavities was observed in 89.47% (17/19) of the CLs on the first day of visualization, with a mean size of 0.30 � 0.05 cm2, representing 45.31% of the total CL area and difficult echotexture analysis. These cavities progressively regressed (P &lt; 0.01) until Day 11 of the cycle, with an area less than 0.1 cm2. These results show that pixel values are correlated to CL development in goats, suggesting an association between CL echotexture and steroidogenic function.

Reproducibility of pixel values for two photostimulable phosphor plates in consecutive standardized scannings

The objective of the present study was to determine the reproducibility of the pixel values obtained with the Digora system (Soredex, Finland). Exposures were standardized, with variation in exposure and scanning time of two photostimulable phosphor plates containing a stepwedge image. The smallest variation in pixel values ranged from 50 to 75%, with the widest variations being observed in less dense steps. A significant difference in pixel values was observed in terms of X-ray exposure and scanning times and between the two plates themselves (ANOVA, p < 0.01). Using the present methodology, the reproducibility of pixel values was not satisfactory for the tested white photostimulable plates. This wide variation in digitalization might be influenced by the amount of X-rays that sensitized the plates. It may be important to establish the reproducibility of the pixel values in quantitative studies using digital image.

New edge detection method for high-resolution SAR images

A new edge detection method combining the scanning window central edge (SWCE) detector and an improved active contour model is proposed. The method first emploies the SWCE detector based on the difference of area pixel value means to perform an optimal edge detection, and then proposes an improved active contour model with modified energy functions to refine the location of the edges. The initial nodes of the improved active contour model are automatically found from the vectorised results of the SWCE detector. Tests on simulated speckled images and real airborne SAR images show that the combined method can benefit from the advantages of the both techniques and get satisfactory edge detection and localization abilities at the same time.

Low-dose ECG-gated 64-slices helical CT angiography of the chest: evaluation of image quality in 105 patients

The purpose of this study was to evaluate image quality of low-dose electrocardiogram (ECG)-gated multislice helical computed tomography (CT) angiograms of the chest. One hundred and five consecutive patients with a regular sinus rhythm (72 men; 33 women) underwent ECG-gated CT angiographic examination of the chest without administration of beta blockers using the following parameters: (a) collimation 32 x 0.6 mm with z-flying focal spot for the acquisition of 64 overlapping 0.6-mm slices, rotation time 0.33 s, pitch 0.3; (b) 120 kV, 200 mAs; (c) use of two dose modulation systems, including adjustment of the mAs setting to the patient's size and anatomical shape and an ECG-controlled tube current. Subjective and objective image quality was evaluated by two radiologists in consensus on 3-mm-thick scans reconstructed at 55% of the response rate (RR) interval. The population and protocol characteristics included: (a) a mean [+/-standard deviation (SD)] body mass index (BMI) of 24.47 (+/-4.64); (b) a mean (+/-SD) heart rate of 72.04 (+/-15.76) bpm; (c) a mean (+/-SD) scanning time of 18.3 (+/-2.73) s; (d) a mean (+/-SD) dose-length product (DLP) value of 260.57 (+/-83.67) mGy/cm; (e) an estimated average effective dose of 4.95 (+/-1.59) mSv. Subjective noise was depicted in a total of nine examinations (8.5%), always rated as mild. Objective noise was assessed by measuring the standard deviation of pixel values in a homogeneous region of interest within the trachea and descending aorta; SD was 15.91 HU in the trachea and 22.16 HU in the descending aorta, with no significant difference in the mean value of the standard deviations between the four categories of BMI except for obese patients, who had a higher mean SD within the aorta. Interpolation artefacts were depicted in 22 patients, with a mean heart rate significantly lower than that of patients without interpolation artifacts, rated as mild in 11 patients and severe in 11 patients. The severity of interpolation artefacts was significantly linked to a low heart rate in affected patients. The overall image quality of CT scans was rated as diagnostic in 94 patients (89.5%) while 11 examinations (10.5%) were found to be partially nondiagnostic owing to the cyclic presence of severe interpolation artefacts, which can be compensated for by additional reconstructions at a different temporal window. In these cases, interpolation artefacts could have been avoided by reducing the pitch from 0.3 to 0.2 at the expense of increased patient dose. Low-dose ECG-gated CT angiograms of the chest can be obtained in routine clinical practice with 64-slice CT technology without altering the diagnostic value of CT scans.

Image steganographic scheme based on pixel-value differencing and LSB replacement methods

In order to improve the capacity of the hidden secret data and to provide an imperceptible stego-image quality, a novel steganographic method based on least-significant-bit (LSB) replacement and pixel-value differencing (PVD) method is presented. First, a different value from two consecutive pixels by utilising the PVD method is obtained. A small difference value can be located on a smooth area and the large one is located on an edged area. In the smooth areas, the secret data is hidden into the cover image by LSB method while using the PVD method in the edged areas. Because the range width is variable, and the area in which the secret data is concealed by LSB or PVD method are hard to guess, the security level is the same as that of a single using the PVD method of the proposed method. From the experimental results, compared with the PVD method being used alone, the proposed method can hide a much larger information and maintains a good visual quality of stego-image.

대용량 소포영상에서 관심영역 고속추출 방법에 관한 연구

본 문은 고속으로 이송되는 컨베이어 벨트 환경에서 획득된 대용량 소포 영상에서 다양한 관심영역(ROI：Region of Interest)을 고속 추출할 수 있는 방법을 제안한다. 제안된 방법의 친 번째 단계에서는 영상을 32<TEX>${\times}$</TEX>32 픽셀 크기의 마스크로 나누고 그 중 내부 픽셀의 최대값과 최소값의 차이값이 최저 동적 입계값보다 큰 경우에 1차 후보로 검출한다. 두 번째 단계에서는 1차 후보 마스크를 다시 8<TEX>${\times}$</TEX>8크기의 서브마스크로 나누고 적셀 값의 편차(deviation)을 기준으로 최저 임계값보다 큰 마스크만 남김으로서 불필요한 영역을 제거한다. 이러한 전처리 과정을 거쳐 1차원 바코드, 2차원 바코드, 소포의 외형 경계, 레이블 및 문자와 같은 소포의 정보가 기록되어 있는 영역(ROI)을 제외한 나머지 영역을 제거한다. 후처리 과정에서는 위의 ROI 중 2차원 바코드 영역만을 추출하기 위해서 각각의 ROI에 대하여 기준축을 생성한 결과를 이용하여 각각의 영역을 검증하였다. 이와 같은 방법으로 실험한 결과 대용량 소포영상에서 약 200msec 이내에 다양한 ROI를 추출하였으며 100%의 정확도로 2차원 바코드 영역을 지정할 수 있음을 확인하였다. In this paper, we propose a sequence of method which extrats ROIs(Region of Interests) rapidly from the parcel image of large size. In the proposed method, original image is spilt into the small masks, and the meaningful masks, the ROIs, are extracted by two criterions sequentially The first criterion is difference of pixel value between Inner points, and the second is deviation of it. After processing, some informational ROIs-the areas of bar code, characters, label and the outline of object-are acquired. Using diagonal axis of each ROI and the feature of various 2D bar code, the area of 2D bar code can be extracted from the ROIs. From an experiment using above methods, various ROIs are extracted less than 200msec from large-size parcel image, and 2D bar code region is selected by the accuracy of 100％.

Vulnerability of pixel-value differencing steganography to histogram analysis and modification for enhanced security

The pixel-value differencing (PVD) steganography can embed a large amount of secret bits into a still image with high imperceptibility as it makes use of the characteristics of human vision sensitivity. However, a loophole exists in the PVD method. Unusual steps in the histogram of pixel differences reveal the presence of a secret message. An analyst can even estimate the length of hidden bits from the histogram. To enhance security, a modified scheme is proposed which avoids occurrence of the above-mentioned steps in the pixel difference histogram while preserving the advantage of low visual distortion of the PVD. The histogram-based steganalysis is therefore defeated.

A steganographic method for images by pixel-value differencing

A new and efficient steganographic method for embedding secret messages into a gray-valued cover image is proposed. In the process of embedding a secret message, a cover image is partitioned into non-overlapping blocks of two consecutive pixels. A difference value is calculated from the values of the two pixels in each block. All possible difference values are classified into a number of ranges. The selection of the range intervals is based on the characteristics of human vision’s sensitivity to gray value variations from smoothness to contrast. The difference value then is replaced by a new value to embed the value of a sub-stream of the secret message. The number of bits which can be embedded in a pixel pair is decided by the width of the range that the difference value belongs to. The method is designed in such a way that the modification is never out of the range interval. This method provides an easy way to produce a more imperceptible result than those yielded by simple least-significant-bit replacement methods. The embedded secret message can be extracted from the resulting stego-image without referencing the original cover image. Moreover, a pseudo-random mechanism may be used to achieve secrecy protection. Experimental results show the feasibility of the proposed method. Dual statistics attacks were also conducted to collect related data to show the security of the method.

A de-blocking algorithm and a blockiness metric for highly compressed images

Blockiness is a typical artifact in reconstructed images that have been coded by a block-based discrete cosine transform (BDCT). In highly compressed images and video, the blocking artifacts are easily noticeable as the discontinuities between relatively homogeneous regions. Many current noniterative de-blocking algorithms attempt to remove the blocking artifacts by smoothing a few pixels around the block boundaries; however, the results are not satisfactory, especially at very low bit rates. We propose a de-blocking algorithm based on the number of connected blocks in a relatively homogeneous region, the magnitude of abrupt changes between neighboring blocks, and the quantization step size of DCT coefficients. Due to its adaptability, the proposed algorithm can smooth out the blocking artifacts while keeping the strong edges and texture areas untouched. Since this algorithm is noniterative and only identifies those block pairs that actually need de-blocking, its computation cost is low. In addition, we have developed a new metric to measure the blocking artifacts in images. Through analyzing the 2N-point (N is the block size) one-dimensional DCT coefficients of the two neighboring blocks with blocking artifacts, we show that all of the even DCT coefficients of the combined 2N points are zeros (except frequency k=0). The odd DCT coefficients are proportional to the pixel value difference between these two blocks with their magnitudes almost inversely proportional to frequency k. We selected the first DCT coefficient (frequency k=1) as an indicator for the strength of blocking artifacts in the reconstructed images. For the postprocessed images, we used a weighted summation of the squared first DCT coefficient to measure their blocking artifacts. Experimental results demonstrate that our proposed de-blocking algorithm produces better results than other methods, both visually and quantitatively, while the proposed blocking artifact metric is more consistent with subjective evaluation than the peak signal-to-noise ratio.

Diffusion MRI and spectroscopy in Rasmussen's encephalitis.

The purpose of this study was to evaluate the diffusion MRI and proton MR spectroscopy findings in a rare disorder, Rasmussen's encephalitis. Diffusion MRI studies of 3 cases of Rasmussen's encephalitis were performed using the echo-planar trace sequence (TR=5700 ms, TE=139.03 ms). The gradient-echo diffusion sequence, PSIF (TR=21.6 ms, TE=5 ms), which is a reverse FISP sequence, and proton MR spectroscopy (TR=1500 ms, TE=40 ms) were applied in two patients. The trace sequence revealed high apparent diffusion coefficient values at the diseased regions (1.21+/-0.13 x 10(-3) mm2/s), compared with normal parenchymal values in 12 control cases (0.84+/-0.09 x 10(-3) mm2/s), indicating increased motion of water molecules (disintegration of the tissue) in these regions. The PSIF sequence revealed pixel value differences between the two hemispheres. Proton MR spectroscopy revealed decreased N-acetyl aspartate peaks, compared with five control cases.

Measurement of Root Mean Square Granularity of X-ray Films Using a Commercial Film Scanner

Root mean square granularity of films are generally measured using a microdensito-meter, although it is costly and not easily available. To solve the cost problem, we tried to use an inexpensive commercial film scanner. Films with different densities were prepared and the relationship between densities by a diffuse densitometer and pixel values by a film scanner was obtained. We found that a linear relationship exists between rms granularity and a corrected standard deviation of pixel value that is available as an index granularity.

Noise reduction in PET attenuation correction using non-linear Gaussian filters

In a PET study, shortening of transmission scan time is highly desired for improving patient comfort and increasing scanner throughput. It necessitates a method that reduces statistical noise in attenuation correction factors (ACFs). The authors have evaluated non-linear Gaussian (NLG) filtering for smoothing transmission images reconstructed with filtered back-projection instead of using iterative reconstruction and segmentation methods. The NLG filtering operation is a variation of local weighted averaging in a neighborhood around a pixel, which weights are determined according to both distance in location and difference in pixel value. Several filtering steps with different NLG parameters can effectively reduce noise without losing structural information. The NLG smoothed transmission images are then forward projected to generate ACFs. Results with phantom and patient data suggested that the NLG filtering method is useful for attenuation correction using count-limited transmission data for both brain and whole-body PET studies.

Near-lossless image compression techniques

Predictive and multiresolution techniques for near-lossless image compression based on the criterion of maximum allowable deviation of pixel values are investigated. A procedure for near-lossless compression using a modification of lossless predictive coding techniques to satisfy the specified tolerance is described. Simulation results with modified versions of two of the best lossless predictive coding techniques known, CALIC and JPEG-LS, are provided. Application of lossless coding based on reversible transforms in conjunction with prequantization is shown to be inferior to predictive techniques for near-lossless compression. A partial embedding two-layer scheme is proposed in which an embedded multiresolution coder generates a lossy base layer, and a simple but effective context-based lossless coder codes the difference between the original image and the lossy reconstruction. Results show that this lossy plus near-lossless technique yields compression ratios close to those obtained with predictive techniques, while providing the feature of a partially embedded bit-stream.

Blocking artifacts reduction in image compression with block boundary discontinuity criterion

This paper proposes a novel blocking artifacts reduction method based on the notion that the blocking artifacts are caused by heavy accuracy loss of transform coefficients in the quantization process. We define the block boundary discontinuity measure as the sum of the squared differences of pixel values along the block boundary. The proposed method compensates for selected transform coefficients so that the resultant image has a minimum block boundary discontinuity. The proposed method does not require a particular transform domain where the compensation should take place; therefore, an appropriate transform domain can be selected at the user's discretion. In the experiments, the scheme is applied to DCT-based compressed images to show its performance.