Coherent and digital image enhancement, their basic differences and constraints

Television image enhancement has long been accomplished by using analog circuits to operate on the analog television signal and thereby emphasize both horizontal and vertical transitions. Now it is feasible to perform comparable image enhancement by digital techniques operating in real time on a pulse-code-modulated NTSC television signal. Several algorithms have been developed to generate vertical and horizontal video details from PCM NTSC television signals encoded at a 10.7-MHz rate (three times the color subcarrier frequency) and at a 14.3-MHz rate (four time the subcarrier frequency). Practical design concepts are presented to implement digital image enhancers. In addition to ensuring the stability, accuracy and reliability that are the usual advantages of digital systems, digital image enhancement will enable video processing techniques to be used that can actually be performed best by digital means. In particular, more nearly optimum coring or “crispening” circuits will be possible and the detail signals will be easily programmable, which may permit automatic adaptive enhancement.

Digital enhancement of video images for NDT

Screening mammography continues to play a key role in the early diagnosis of non-palpable breast cancer. Approximately 5% of patients will have lesions on their mammograms that appear neither clearly benign nor malignant. The proper management of these patients is not well defined. In this study, the mammograms of 64 women who underwent breast biopsy were reviewed. After the initial review, the mammograms were reevaluated using a personal computer driven digital conversion and enhancement system. The majority of indeterminate lesions were assigned a determinate diagnosis by enhancing the areas of abnormality through enlargement, contrast adjustment, and brightness adjustment. The radiologists were able to maintain baseline sensitivity and specificity throughout this process. In contrast, enhancement of lesions initially assigned a diagnosis of characteristically benign or malignant demonstrated no advantage over plain film mammography. These findings suggest a role for the selective use of digital mammography and enhancement techniques.

Polarization dependent loss (PDL) causes imbalanced optical signal to noise ratio (OSNR) of the two polarizations, thus remains one of the major bottlenecks for next-generation polarization-division-multiplexed (PDM) coherent optical transmission systems. In this paper, we investigate Pairwise Coding for adaptive PDL mitigation in PDM coherent optical systems. By pre-coding across two polarizations, the PDL-induced performance degradation can be largely mitigated without any coding overhead. We present details of the coding and de-coding design, and also derive the analytical symbol/bit error rate of the Polarization Pairwise Coding scheme, which can be used to predict the performance gain as well as for optimal rotation angle calculation. Simulation results verify that Pairwise Coding achieves substantial system performance gains over a wide range of PDL values. Compared with other digital coding techniques, Polarization Pairwise Coding shows improved performance than Walsh-Hadamard transform since it maximizes the coordinate diversity; and also Pairwise Coding is computationally much simpler to decode compared with the Golden and Silver Codes, therefore is practical for current 100-Gb/s and future 400-Gb/s and 1-Tb/s digital coherent transceivers.

Characteristics of the lesions in digital mammography images will be more clear after image enhancement, which can increase the detection rate of early breast cancer. This paper proposes a modified unsharp masking approach based on an improved high-pass filter. Experimental result of digital mammography image enhancement proves that the proposed method can effectively extrude the edges of lesions and at the same time can suppress the noises in uniform background areas.

Digital image enhancement with DStretch®: Is complexity always necessary for efficiency?

Digital image enhancement techniques provide a multitude of choices for improving the visual quality of diagnostic images. Appropriate choice of such techniques is greatly influenced by the imaging modality, task at hand and viewing conditions. This sequence of two articles will provide an overview of underlying concepts, along with algorithms commonly used for radiographic image enhancement. The first article focuses on spatial domain techniques for radiographic image enhancement, with particular reference to point processing methods, histogram modification and unsharp masking.

Diabetic Retinopathy (DR) is a vision loss impairment due to complications arising from the diabetic condition and affects the retina and resulting pathologies can be monitored by analysing the colour fundus image. However, in retinal fundus images, the contrast between the retinal vasculature and the background is very low and varies within the image making visualisation and analysis of small retinal vasculatures difficult. Therefore, enhancement of the fundus image is important to provide the best visualization of the retinal blood vessels. Fluorescein angiogram overcomes this imaging problem but it is invasive and leads to other physiological problems. In this research work, a non-invasive digital image enhancement technique called RETICA has been developed that overcomes the problem of varied and low contrast in fundus images. RETICA first normalises the varied contrast using a Retinex based method that separates the illumination from the reflectance part of the image followed by ICA that forms the original retinal pigment makeup namely the macular, haemoglobin and melanin retinal pigment. The haemoglobin image exhibits the highest contrast for retinal vessels. Results based on a dataset of 13 fundus images show that RETICA successfully normalises the low and varied contrast and enhances the retinal vessels. It achieved a better average contrast improvement factor of up to 5.56 compared to the invasive FFA with 5.34. This improvement in contrast reduces the need for fluorescein angiogram in DR assessment.

The digital contour enhancement techniques of infrared image are discussed. Emphasis is laid the thermal spread compensation method. On the basis of describing the theory of the method, the model is suggested. The concrete project based on the model for realizing digital contour enhancement of the infrared thermal image is put forward, and some test results are shown.

Theory of Optical Communications. Fiber Devices for Optical Communication Systems. Integrated Devices for Optical Communication Systems. Direct Detection Optical Communication Systems. Coherent Systems: Structure and Ideal Performance. Performance Degradation Sources in Coherent Optical Systems. Multilevel Coherent Optical Systems. Multichannel Optical Systems. Present--Day Systems Implementations. Appendices. Index.

DIGITAL CONTOUR ENHANCEMENT OF INFRARED IMAGE

The introduction of white light in several fields of optics such as interferometry, diffraction and optical testing, has produced many valuable contributions that frequently have led to optical techniques of present application. The use of white light in optical processing also allows to extend the capabilities of this field by including new operations and applications, besides other advantages related the reduction of noise. White light processors are able to encode through different wavelengths distinct types of information. The display of information using several wavelengths or spectral bands is specially adequated in images addressed to human observers or other colour sensitive receivers, since these receivers can take advantage of the high sensitivity of the human eye to small changes of colour. In this way different pseudocolour techniques addressed to enhance through colour distinct types of information have been recently developed . The parallel white light processors could be used to process images for direct analysis or could serve as preprocessor which derives colour encoded texture information for further processing by digital, optical or other techniques. On the other hand white light processors enable direct enhancement and restoration of colour images. Images with poor colour saturation due to inadequate illumination or registration conditions can be enhanced by spatial filtering. Also, images with spatially invariant degradations such as defocusing and chromatism, can be restored in white light by optical or digital techniques.

The study focuses on the use of digital enhancement techniques and remote sensing tools, such as LANDSAT-7 (ETM) satellite data, for mapping different types of rocks (lithology) in the southwest region of Taiz, Yemen. The study area is approximately 273.km2. In this work, the various digital enhancement techniques were utilized to improve the ETM images for the mapping of rock units. These techniques included atmospheric and geometric changes, colour composition techniques, and contrast stretching. The seven bands of the ETM were used to create 147 different coloured images, with red (R), green (G), and blue (B) representing any three-band combination. Based on the images’ capacity to distinguish between various rock units, their interpretive components, and the region’s prior geological map, these images were compared to one another. The outcome reveals that the top photographs were the coloured ones from 4/5/2, 6/5/4, 4/3/5, 4/2/6, 6/4/7, 4/1/7, and 6/4/5. By following the lines of the four distinct rock units—granite, syenite, trachyte, and ignimbrite units—four maps were produced using these photos. These maps and the geological map’s same units (previous map) were compared based on the size. The result of this comparison shows the sizes of the syenite, trachyte and ignimbrite units were higher the sizes of the same unites of the geological map. This is because, some parts of these units were not mapped in the previous map. Whereas, the size of the granite unit from images was lower than the same unit of the geological map. This is because, the different rock units were mapped as a granite unit in the previous map. Moreover, three new rock units were identified in this work and not existed in the previous geological map. This work represents an important advance in the fields of geology and remote sensing through the introduction of a new method for mapping rock units from Landsat-7 ETM images. These findings can be useful to geologists, environmental scientists, and policy makers by providing them with more insight into geological formations-a rather vital thing to know in resource management, environmental monitoring, and planning in areas of similar geological settings.

In recent years, with the development of digital technology, digital image processing has been widely and deeply applied in the field of computer graphics. Digital image processing system is a complex real-time system, it from the camera, fax machine and other scanning equipment to obtain image information, after digital transformation, digital image information coding, filtering, enhancement, recovery, compression, storage and other processing, finally generate visual image. This design uses TMS320C6748 as the core processor of the system, SAA7113 as the video decoding chip of the system, CPLD as the sampling controller, DDR2 chip as the external expansion memory. The ROM expansion uses NAND flash memory chip. On the basis of hardware design, combined with software algorithm to complete image processing. The system can be used in information communication, image recognition, news scene and other fields of image processing and transmission. This paper analyzes the hardware structure and data processing algorithm of the system in detail. The experimental results show that the system can not only obtain higher compression ratio, but also reduce the distortion of the reconstructed image. The image processing system has certain practicability.

This paper describes a new approach to adaptive digital halftoning with the least squares model-based (LSMB) method. A framework is presented for the adaptive control of smoothness and sharpness of the halftone patterns according to local image characteristics. The proposed method employs explicit, quantitative models of the human visual system represented as 2D linear filters (eye filters). In contrast with the standard LSMB method where the single eye filter is employed uniformly over the image, the model parameters are controlled according to local image characteristics for each pixel. Because of the adaptive selection of eye filters for the pixels, image enhancement is incorporated into the halftoning process. Effectiveness of the proposed approach is demonstrated through experiments using real data compared with the error-diffusion algorithm and the standard LSMB method.