Evaluation criteria.
\r\n\tBoth diagnosis and clinical manipulation of the patient with vasospasm is a unique and challenging situation. Multi-clinical approach is extremely mandatory. The patient must be treated in a center, which requires a experienced team with both neurological surgeons, interventional radiologists, neurologists and neuroanesthesiologists. Moreover, a well-equiped, isolated neurointensive care is needed for all patients suffering form subarachnoid hemorraghe.
\r\n\tIn their daily practice, both neurological surgeons, interventional radiologists, neurologists, neuroanesthesiologists, and even intensive care providers have to deal and challenge of vasospasm. Numerous studies relevant to pathophysiological mechanisms underlying vasospasm had been published, but we still know little about the exact mechanisms causing vasospasm. In the last decades of modern medical era, despite the technological developments concerning the neurological care of the patients with vasospasm, we still have no effective treatment and preventive care of this devastating entity.
\r\n\tThe aim of this book project is to provide in detailed knowledge to both physicians and scientists dealing with cerebral vasospasm. This book will attract interest of both students, residents, specialists and academics of neurological sciences.
The following text is a lecture given at the First Conference on Evolutionary Physiology, March 7, 1956. It was originally published in Russian, in the book Evolutsiya funktsii nervnoi sistemy (Evolution of Functions of the Nervous System), Leningrad, 1958, pp. 7–17. This text was written in the Soviet epoch and therefore it contains sometimes necessary “reverences” in the direction of communistic ideology.
The text was translated by Andrey Polyanovsky.
The question of evolutionary physiology as a discipline in its own right was raised only in our country. This may have a whole number of explanations. First of all, some outstanding scientists in our country followed the evolutionary line in studying one or another physiological issue. The necessity of the evolutionary approach in physiology was accentuated by I.P. Pavlov, I.M. Sechenov and N.E. Vvedensky. From them, we got not only statements, but also fundamental papers, which predetermined further development of the evolutionary trend in physiology. This especially concerns I.P. Pavlov’s studies of the higher nervous activity. I.P. Pavlov had good reasons to emphasize that studying conditioned reflexes is essentially studying reflexes in the process of their formation and development, in their beginnings and that, when studying a conditioned reflex activity, a researcher views the entire developmental continuum of reflex activity and, consequently, gets a chance to deduce from the history of conditioning the overall process of reflex activity formation during evolution. This has served a major impetus for physiologists in our country, rather than in any other, to choose the evolutionary road and to begin following the evolutionary principle.
Alongside the directions left by the coryphaei of experimental science, we have yet another, no less and may be even more important, explanation—the fact that all Soviet science is advancing under the guidance of the solely correct philosophical doctrine of dialectic materialism. The Marxist-Leninist doctrine obliges every researcher in the field of natural sciences to adhere to the principle that no one phenomenon can be understood without analyzing the history of its emergence, its development. It is the only historical method that enables correct understanding of the subject matter. Based on these two tenets—the requirements of the Marxist-Leninist philosophy and the directions by our great predecessors—we are approaching now the problems of evolutionary physiology.
It would be incorrect to say that wishes to study functions in their evolutionary history were not stated by other eminent physiologists. I remember that in 1908, the now late English physiologist Keith Lucas published his brochure entitled “Evolution of functions,” in which he expressed bitter regret that the evolutionary principle, which proved to be extremely fruitful and widely used in morphological sciences,* was almost of no use in physiology. K. Lucas stated some considerations on the necessity of following the evolutionary principle in physiological studies and, furthermore, pointed out the difficulties physiologists encounter if they attempt to approach a study of the function from the viewpoint of its emergence and origin. In any case, our Soviet physiology can be presently characterized exactly as physiology imbued with the evolutionary principle. Nevertheless, the question does arise on whether it is enough for individual researchers working in the field of physiology simply to adhere to evolutionary theory, to reckon with evolutionary theory, to try applying the historic approach to solving one or another problem or to seek a new discipline entitled “evolutionary physiology” to appear and develop as an independent discipline within the system of physiological studies and biological sciences.
I can afford asserting that the time has come not simply for the evolutionary principle to become a guiding force in furthering physiological studies but for the independent discipline, evolutionary physiology, to arise as a result of the progress achieved by physiological science in general.
I must say that morphologists already pointed out the necessity of establishing evolutionary physiology along with evolutionary morphology. These statements belong to late A.N. Severtsov, who emphasized that it is time for physiologists to address the evolutionary matters and to found evolutionary physiology along with evolutionary morphology. The term “evolutionary physiology,” still unknown in other countries, is our term, our proposition to single out evolutionary physiology as a discipline in its own right along with evolutionary morphology, evolutionary histology and evolutionary biochemistry.
I have to remind that in this case it is definitely not about tearing evolutionary physiology as an independent discipline from the rest of physiology. Not at all! We should consider it as a new, present-day stage in the development of physiology because evolutionary physiology can in no way be constructed in isolation from the rest of physiology. It should make maximum use of all that abundant material, which was obtained both by classical (medical) physiology and by general physiology, zoophysiology, comparative physiology and embryophysiology—all those branches of physiology that have been elaborated until now and have achieved enormous success. Evolutionary physiology should use all this material. It is a product of, a superstructure over, those physiological studies that are in progress now. But this does not deprive it of the right to put forward its own questions, to pose them as a leading line, and to select the material that helps solve the evolutionary problem.
What should be the tasks of evolutionary physiology? It seems to me that the two pivotal lines should underlie evolutionary physiology. K. Lucas grieved that there were no studies of the evolution of functions, and of course, the evolution of functions must be the first pivot of evolutionary physiology. We should strive to consider any function subjected to experimental investigation in terms of the history of its formation: how one or another function is formed in the process of evolution, how the intertwining of separate functions led to certain changes in each of them, resulting in the representation of each given function in certain animals exactly this way and not otherwise. This is the question of studying the evolution of functions.
Another question is whether evolutionary physiology should and could be confined to studying the evolution of functions. I do not think so. The second, no less and may be even more important task of evolutionary physiology, is supposed to be functional evolution, that is, a verification of evolutionary physiology on the basis not of morphological material and morphological methods but physiological studies.
A study of the evolution of functions will provide a certain material and open up a new avenue toward understanding why the evolutionary process was running this way, but not otherwise, and what the mainstream of the evolutionary process was in terms of the evolution of functions.
It may appear that these are one and the same. But essentially it is not true, indeed. Functional evolution is a higher stage of evolutionary physiology as compared to studying the evolution of functions. In one case, we simply track the historical developmental path of some functional relationships, while in another case we approach the understanding of what the evolutionary process is and how it formed, why the evolutionary process was running exactly this way being based on those functional rearrangements that were arising in living organisms.
Proceeding now to more specific tasks that underlie both main pivots of evolutionary physiology, we must pose a question: is it enough to study the developmental path of various functional relationships in different representatives of the animal kingdom we are dealing with, taking into account the history of the formation of these functions, or should we also set ourselves the task of elucidating the mechanisms of the evolution of functions, those specific conditions and motives that directed the process of development along one or another way? In other words, should we also study the significance of the individual factors that determined the course of evolution?
In this respect, we certainly have to reckon with the basic tenet of our science and Marxist-Leninist philosophy that organism and its environment make up a single, indivisible and interrelated whole. With this in mind and considering that the entire process of the development of different functional relationships ran in a certain environmental context, everchanging, ever affecting living organisms, it becomes clear that no one function could form and undergo any changes otherwise than under the influence of and depending on those environmental impacts that it was permanently exposed to. So, the task of studying the evolution of functions involves not only the elucidation of the course of development, developmental pattern, succession of events, but also establishing the interdependence of these events as well as the causative dependence of all changes and transformations on the environmental factors that affect living beings. We have to reckon both with the internal factors coming from the organism itself, in the form of an interaction of its separate parts, and the external factors.
As regards the problem of functional evolution, this is a much more complicated matter. Here we need to foresee the issue of what further development is supposed to be, how we could imagine the further transformation of individual functions and whole organisms under the effect of those environmental changes that are occurring right now, before our eyes, and that may become determinative for further development of functional relationships. These issues are not only of theoretical significance. Of course, their theoretical significance is quite clear to everyone and requires no proof, but I have to remind that the conditions, under which the organisms are living at present, change substantially every day. Enormous success of science and technology, that we are witnessing now and that resulted from great progress humankind has achieved in its evolution, creates by itself new living conditions, sometimes so different from the normal that they may prove to be determinative for further development of life on Earth. From this viewpoint, we have to admit that evolutionary physiology, in the sense I have stated above, is not only a theoretical but also a strictly practical science in the sense of considering all those conditions, under which we are living now and will be living in the near future, in the light of those influences that these conditions may have on the existing organisms and their offspring, be it of human beings or the animal world.
The question arises: what methods should evolutionary physiology use to embrace the tasks I have just talked about?
Over many years, I and my fellow workers have been adhering to the viewpoint that correct understanding of the evolution of functions and mechanisms underlying evolutionary changes in functions is attainable provided that one and the same researcher uses simultaneously four methods, basically different but leading to the same goal.
The first way, as is clear to everyone, is certainly comparative physiology—the use of comparative physiological material in order to understand how different phyletic lines evolved under different living conditions and how the same functions developed becoming more sophisticated or, quite the contrary, dropping out in some phyletic lines depending on the specific living conditions. The question then arises as to how one and the same function undergoes changes under different conditions and, on the other hand, how the initially different functional relationships converge leading to one and the same ultimate result under the influence of environmental factors.
Evolutionary physiology should definitely be based on the ready material of comparative physiology and zoophysiology, but on the other hand, it should develop on its own, artificially selecting those animal samples and conditions that are of special interest from the viewpoint of the evolution of functions. Here, perhaps, we have to run counter to the views of some evolutionists. We believe that it is necessary to distinguish between three disciplines. The first is zoophysiology, that is, descriptive physiology of individual animal species, an extremely important science, which is of great theoretical and even greater practical significance. We need to know all forms of life represented now on Earth. Another thing is comparative physiology, which chooses from the huge material of zoophysiology only certain objects and issues that allow a comparison and elucidation of certain regularities. Yet more special and, at the same time, complex demands are made by evolutionary physiology, which not simply compares what occurs under different living conditions but uses the experimental method to understand how these functions formed.
The second way is the use of ontogenetic development, that is, studying functions not in phylogenesis but ontogenesis. Here there is less of the ready material, and we need to strain every nerve to reinforce this aspect of physiological studies because at present ontogenetic physiology is developed relatively poorly. We should try to embrace both the embryonic and postnatal stages of development and find out when the rudiments of different functions begin to show up, at what stage and how the function of those structures that pre-existed and developed independently changes depending on the formation of different morphological structures. This particularly concerns those tissues and organs that fall at a certain age during their development under the influence of the nervous system and endocrine factors. As a result of these effects, endocrine and neural, the developmental course itself undergoes substantial changes, and we should understand how the development would proceed without the interference of certain endocrine factors and the determinative influence of the nervous system on the development of endocrine organs as well as, vice versa, the effect of endocrine organs on the variability of the nervous system. With regard for all these features we should approach ontogenetic physiology to make it a tool for studying the evolution of functions.
Still, additional possibilities open up in front of us—the use of clinical material. I must say that it was not without reason that the issues of evolutionary physiology were raised by physicians, not biologists. This seems to be a paradox, but it is not true, and this is because clinical studies led to the idea that in certain cases some symptoms represent echoes of what had happened at earlier developmental stages, that in some cases of pathology, we deal with echoes of the evolutionary process, with reverting to those functional states that characterize the earlier developmental periods.
Of course, it is particularly easy to draw a comparison between clinical symptoms of different diseases and those phenomena that we observe during ontogenesis, but phylogenesis also reveals a lot in this respect.
Directly related to the use of the clinical material is the use of special experimental methods. These methods boil down to an artificial disconnection of individual organs and tissues from their controlling mechanisms, a disconnection inside the controlling mechanisms themselves, inside the nervous system, and a disconnection of some lower levels from the higher ones. Then follows an observation of changes that occur both in the lower parts of the nervous system depending on the loss of regulatory influences from the higher parts and, vice versa, in the higher parts as a result of the loss of those afferentations that arrive from the lower parts. In this respect, we are particularly lucky because we can afford carrying out any experimental transections in animals providing thereby new conditions for functioning of organs, tissues and parts of the central nervous system and endocrine apparatuses, which change their regulatory function under the influence of these disconnections. Hence, we can compare these data with the results of clinical pathology and those of comparative and ontogenetic physiology.
Based on these four methods of investigation, it is possible to get an idea of how the evolutionary process was proceeding and how functions were changing during their development. As a result, not only factual relationships (not merely descriptive though) would be established, but to a large extent it would be also possible to unravel the mechanisms of interaction and, hence, to a certain extent, resolve causal relationships as well. Still, that is not all. Experiments allow a special analysis of the effect of external factors. Now we have got an extremely abundant experience in the sense that modern science and technology have made it possible to generate such forms of energy that were unknown or unattainable previously. At present, they can be generated, detected, recorded and quantitatively evaluated. It is increasingly often that we are learning about the existence of those forms of energy that we have been unaware of before.
While throughout its evolutionary and historical development and until recently humankind was aware of only a limited number of energies that affected it naturally, over the last decades we have learnt that many types of energies represented in nature are much wider than we thought. Yet recently, ultrasounds seemed to be something artificially produced by people, but now it is turning out that during the evolutionary process not only were they generated by different animals but also served as means of signaling being perceived and evaluated in the same way as we perceive sound frequencies in the narrow range of audibility. Likewise, radio waves discovered by our compatriot Popov and being widely used in television and radio turn out to be generated by the Sun as well; the Sun’s rays, that we assessed previously only in terms of their energy, contain also electromagnetic oscillations of those frequencies, wavelengths, that we use in radio engineering. So that over millions and billions of years during the evolutionary process, animal and human organisms were exposed to these electromagnetic waves, and it is only now, over just the last three decades, that we have come to grips with studying ultrahigh frequencies and applying them in ambulances and clinics for treatment, diagnostics, and so on. Nevertheless, they did exist in nature and affected all of us.
So far, we studied experimentally the effect of these ultrahigh frequencies for pure pragmatic purposes—their application in technology, medicine, and so on. Now they are becoming one of the possible factors of evolution, and we should set to studying ultrasound frequencies, electromagnetic waves and ultraviolet radiation not only in terms of their impact on individual functions and organisms but also in terms of their possible role in the evolutionary process. Thereby, we should look into the influence they may have on future generations.
If we investigate varied types of energies that we receive in their natural form and that we can now generate artificially, graduate, record and evaluate quantitatively, if we find out how they are reflected in the development of different functions, then we will obtain an enormous material for understanding not only the developmental course of functions and the history of the emergence of functional relationships but also their dependence on the environmental factors. Thus, we are arriving at a proposition that evolutionary physiology, as we understand it, should encompass a wide range of studies. It will certainly be interwoven with classical, applied and comparative physiology but anyway underlain with an endeavor to comprehend the causal dependence of the developmental course of functions on the external and internal factors, to understand those major lines, along which the evolution of functions is running and which jointly led the evolutionary process to proceed exactly in the way it did, and finally, to understand the diversity of pathways the evolutionary process may proceed along depending on those conditions that will be created on our planet. Here are the main tasks and main methods of evolutionary physiology.
However, the question arises whether the abovementioned exhausts the matter. Of course not. The basic principle, which underlies the evolutionary doctrine and studies carried out by the coryphaei of our physiological science, especially I.P. Pavlov’s, is that organisms undergo the process of continuous adaptation to the environment. Therefore, it is not enough just to understand what specifically, and under what influence, is happening. We should clarify the adaptive role of the evolution of functions, understand how life was preserved and how it assumes various forms depending on the adaptation of a living being to new conditions under the influence of the external and internal environmental factors. We ought to understand which conditions are disastrous and which prove to be surmounted or secured by certain adaptations.
Elucidation of a number of adaptive mechanisms, adaptive changes in functions should again be one of the major tasks of evolutionary physiology. In this sense, evolutionary physiology will be not only a theoretical, but also strictly practical, science, since it will lead to results, which will enable us to influence the course of evolution in the future. It is quite important for medicine and zootechnics.
Especially hard questions arise when we approach a study of the human organism. We know well that the human organism at a certain stage of evolutionary development stopped to be only a biological being and became a social being. Interrelationships among people led to the establishment of certain social relations. The latter resulted from a kind of leap, or what may seem to be a leap, because some of our immediate predecessors perished and are now inaccessible for being studied. But in any case, the fact is that humankind rose above the rest of the animal world and in many respects surpassed it, creating new forms of activity as well as new forms of relationships with the environment. Man to a certain extent became the master of nature, at least of some of its aspects; he can consciously control it being expected to intensify his activity in this direction. Humans entered into certain relationships that are lacking in other animals. Man is not only a biological, but a social being, and this, on the one hand, relates to his nervous system development and transition to other forms of existence, but, on the other hand, these new forms of existence and interaction prove to be a powerful factor, which influences the course of changes in the structure and functions of an organism.
From this viewpoint, the historical period of the human existence certainly represents an extremely important stage in the evolutionary process, and evolutionary physiology should not digress from this point.
Recently, it seemed that the relationships among people, who created social living conditions and stay under the influence of these social factors, should serve a borderline, at which a physiologist must stop. However, proceeding from the I.P. Pavlov’s doctrine and Marxist-Leninist theory, we can afford asserting that physiology must not stop here. The whole human organism with all its manifestations should become a subject of physiological investigation.
This does not mean that we should reject the existence of psychology and some other humanities. Quite the contrary, our task is to tie physiological studies to psychological as closely as possible in order to understand those physiological mechanisms that provided humans with the potential to turn from pure biological beings to simultaneously biological and social beings, to understand those physiological mechanisms that provided the possibility of interrelationships among people and thereby made this possibility a factor consciously directing the development of our progeny.
If we abandon this task, then both medicine in its major part, pedagogy and art will be absolutely cut off, ejected from natural sciences and left beyond the scope of natural-scientific investigation. This is not to be understood as an attempt to account for all social relations in terms of natural sciences. Of course, this would be incorrect, but providing a physiological basis for them should be our goal. No doubt, an exclusively important role in this respect was played by the I.P. Pavlov’s doctrine about two signaling systems. If it were not for the two signaling systems, if the second signaling system were not superstructured over the first signaling system common to the animal kingdom, if those multiform influences that we widely use in fostering our children and interrelating with each other were not established, then we would have been ignorant of functional interconnections in the human organism and its relationship with the environment.
From this viewpoint, the aspiration for studying the human higher nervous activity during its formation and development is supposed to be the acme of evolutionary physiology. A comparison of the human and animal organisms shows a striking divergence in their developmental paths from the first hours of life.
When studying the postnatal development of animals and comparing it with that of human organisms, we see how considerably the range of possibilities for the nervous system development expands under the influence of the second signaling system, while the biological processes themselves become largely subjected to the influence of the second signaling system.
This stage of the evolutionary physiology formation should certainly interest us first of all, because it leads to the cognition of humankind while representing a junction between natural and social factors, which determine the development of human personality and its activity.
This is how I and a narrow circle of my fellow workers envision the tasks and methods of evolutionary physiology. I know that many of the abovementioned propositions are far from being new as they are recognized and being used for a long time. May be much of the said will prove to be worded unsatisfactorily. Anyway, underestimation of some of the points I have afforded to draw your attention to might have an unfavorable effect on the progress of evolutionary physiology.
Evolutionary physiology, as stated above, is supposed to be pivotal to independent research. It demands to enlist a number of experimental methods from physiologists, biochemists, morphologists and psychologists to create by joint efforts a science that would complement evolutionary morphology and, at the same time, provide a clear and comprehensive understanding of how the interrelationships among people and nature as well as among people themselves first formed and then altered during evolution under the effect of historic conditions. Simultaneously, such a high goal will be promoting the resolution of a whole number of practical tasks, because all our efforts to comprehend the causal dependence among functions of an organism as well as between the effect of external factors and activity of an organism will be a means of practical assistance to the population of our motherland and the whole world in defending against some adverse factors, which are present in nature, which we generate artificially and which expand their use. Without the knowledge of their role, we may prove to be helpless in combating pernicious influences. Such a science, essentially theoretical and being of profound practical importance, should become the goal of evolutionary physiologists.
I reiterate that nowhere are the interests of theory and practice interwoven that closely as in evolutionary physiology. Not only will we be aware of how to struggle against the influence of some external factors on an organism but will obtain an enormous material to extend the range of our theoretical ideas from analyzing those conditions, under which the work is in progress at various scientific and manufacturing institutions. This unity of theory and practice should always underlie our approach to a problem and be a guiding star, allowing us not to shut ourselves off from the life practice and not to be afraid that one or another experimental path has a character of applied science. There is neither a theoretical nor practical science, there is a single science and there must be a single science. Practice must help theory and vice versa.
The fast multimedia technology development and network communications makes ultrahigh-definition (HD) and HD video contents widely used in our daily life. This fast jump to use high video resolutions in which many provide some problems in terms of memory storage cost and transmission bandwidth gives birth to the new high efficiency video coding (HEVC) [1, 2]. HEVC is developed in 2013 by the joint collaborative team on video coding (ISO/IEC) Moving Picture Experts Group (MPEG) and the International ITU-T Video Coding Experts Group (VCEG). It is urbanized to overcome the enormous amount of UHD video contents. Compared to the earlier H.264/AVC [3] standard and at the identical visual quality, HEVC guarantees a high encoding performance, reaching 50% of bitrate [4]. Facing to this immense huge encoding performance, a huge computational complexity is obtained. Motion estimation (ME) represents the large part of encoding process that occupies around 70% of the total time of inter prediction, as Jungho [5] indicates in Figure 1.
\nEncoding time distribution.
This large consumption is principally due to the new hierarchy of the block coding based on coding tree units (CTU). This new concept is analog to macroblocks in the earlier standard of compression. Each picture frame is divided into square forms, called coding units (CUs) [6], where 64 × 64 represents the maximum size, and recursively subdivided into 8 × 8 blocks. Prediction and transform blocks (PUs and TUs) are in each CU, where PU represents the principal unit in the ME process.
\nFigure 2 shows the CTU tree structure in the HEVC standard where LCU represents the large coding unit and SCU represents the small coding unit.
\nCTU tree structure in the HEVC standard.
When reducing the time essential for the search algorithm, the ME computational complexity will be automatically reduced. Furthermore, when using different fast mode decision algorithms based on early termination, the ME computational complexity will be reduced, which primes to the entire HEVC execution time reduction.
\nIt is within this context that this article presents a fast encoding algorithm principally based on the early skip detection (ESD), the coded block flag (CBF) fast method (CFM), and the early CU termination (ECU) modes [7, 8, 9] to decrease the HEVC encoding complexity.
\nThe remainder of this paper is structured as follows: the next section details some works on the HEVC fast motion estimation algorithms. Section 3 provided an overview of the motion estimation algorithm. Section 4 highlights the proposed fast configuration for the HEVC encoder. Experimental results for the fast HEVC configuration compared to the results obtained with the original HM16.2 reference software [10] are discussed in Section 5. Finally, in Section 6, conclusions and some prospects are given.
\nAiming to optimize the HEVC encoder complexity, several works have been proposed to reduce the test zonal search (TZS) motion estimation algorithm. Some works are interested in hardware solutions, and others are focused on software optimizations.
\nIn [11], using sequential and parallel techniques, two hardware diamond architectures for HEVC video coding are proposed. These architectures achieve an encoding in full HD at 30 frames per second using a Virtex-7 field programmable gate array (FPGA) design.
\nAuthors in [12] have proposed a hardware parallel sum of absolute difference (SAD) design for gray-scale images to reduce motion estimation time for block size of 4 × 4 pixels. A multiplier is exploited for addition as a partial product reduction (PPR). Results obtained on Virtex-2 Xilinx FPGA show that the maximum frequency obtained is 133.2 MHz for 4 × 4 block size. Nalluri et al., in [13, 14], have proposed two other SAD architectures on FPGA Xilinx Virtex without and with parallelism. The proposed parallel architecture has accelerated the SAD calculation by 3.9× compared to the serial SAD architecture. In [15], authors have proposed two implementations of the SAD and SSD algorithms using NVIDIA GeForce GTX480 with CUDA language in order to reduce the ME run-time. The proposed architecture saved about 32% of encoding time for class E video sequences with nonsignificant degradation in the PSNR and the bitrate.
\nRegarding software solutions, the 8-point square and the 8-point diamond have been replaced by Nalluri et al. [16] with a 6-point hexagonal in the TZS ME algorithm, and 50% in encoding time is saved without degradation in bitrate and PSNR. To replace the TZS algorithm, in [17, 18], authors proposed small diamond pattern search (SDPS), large diamond pattern search (LDPS), and horizontal diamond search (HDS). Experiments using HM8.0 showed that these algorithms allow a reduction of 49% of motion estimation calculation time with nonsignificant increase in bitrate and slight degradation in video quality.
\nIn [19], Liquan et al. have proposed a fast mode decision algorithm by skipping some depths. The proposed work allows saving about 21.5% of encoding time with a slight bitrate increase and a negligible efficiency loss coding. The algorithm proposed by Qin [20] uses the ECU algorithm according to an adaptive MSE threshold value. This work ensures time saving without degradation in the quality. Podder [21] has also proposed an interesting software method to reduce the ME time. Based on human visual features (HVF), an efficient decision of the appropriate block partitioning mode has been obtained. This work allows saving 41.44% of the execution time for SCVS video sequences. In the work published in [22], a fast HEVC ME based on DS and three fast mode decisions, ECU, ESD, and CBF modes, have been presented. Simulation results show a reduction of 56.75% in the complexity of HEVC in terms of execution time, accompanied with slight degradation in video quality and bitrate, when comparing the HM.16.2 executed on an Intel® Core TM i7–3770 @3.4 GHz processor. Authors in [22] have tested just one sequence from each class with just two quantification parameters (QPs), QP = 22 and 37, to evaluate the use of the fast modes.
\nBy analyzing all these previous works, we can note that using fast mode decision algorithms represents an interesting technique in order to reduce the HEVC computational complexity.
\nTZ Search algorithm, used in HEVC ME process (Figure 3), includes four distinct main stages in order to determine the best motion vector.
\nMotion estimation process.
These stages, which are the motion vector prediction (MVP), the first search performed with a pattern of square or diamond forms, the refinement, and the raster search, are described in the next subsections.
\nTo compute the corresponding block’s median predictor, the TZS algorithm uses the up predictor, the upper right predictor, and the left predictor (Figure 4).
\nMV adjacent of a current PU.
The median computation is done via the following equation.
\nThe first search is performed by the determination of the search pattern and the “searchrange.” As it is detailed in Figure 5(a) and (b), the main goal of this stage is to localize the search window via a pattern of square or a diamond forms.
\nDiamond/square search pattern. (a) Diamond search pattern stride length equal to 4. (b) Square search pattern stride length equal to 4.
Thus, these two search patterns are referred to the eight points for each round. The distance corresponding to the minimum distortion point is saved in the “BestDistance” variable. Currently, diamond search pattern is used as default, but the square pattern search can also be used by modifying the HEVC configuration file through the “Diamondsearch” variable.
\nThis step consists of choosing the distance which corresponds to the greatest matched point from the previous search. Three cases according to this distance denoted as “BestDistance” are summarized as follows:
The process is stopped when “BestDistance” = 0.
A refinement is needed when 1 < “BestDistance” < iRaster.
In the configuration file, “iRaster” represents a changeable variable not to be overdone.
BestDistance > iRaster is agreed correctly; a raster scan is achieved using the iRaster value as the length step. If difference obtained from the starting station to the MV from the first level is besides large, this step is preceded. This step is computed on the entire search window.
Figure 6 shows an example of a full search algorithm with iRaster which is equal to 4.
\nRaster search pattern when iRaster = 4.
The refinement is performed when the distance of the motion vector previously obtained is different to 0. There are mainly two refinement types:
Raster refinement
The best point obtained from the previous steps corresponds to the start point of the star refinement. It can be performed using a diamond or a square pattern with distances ranging from “search range” to one. In each iteration, the distance is divided by 2, and when the distance will be equal to one, two adjacent point searches are performed, and then the process is stopped.
Star refinement
In this step, the selected point obtained from the previous steps corresponds to the start point of the star refinement. In each iteration, the distance is divided by two, and when the distance will be equal to one, two adjacent point searches are applied to determine the best estimated MV which gives the minimum of SAD (Figure 7).
\nThe used TZSearch algorithm.
Several fast decision mode algorithms are in this effort aiming to speed up the ME process. Firstly, diamond search pattern is utilized to decrease the encoder computational complexity. Some configurations are also set, such as the early CU termination (ECU), the early skip detection (ESD), and the coded block flag (CBF) in which fast decision mode algorithms are adopted in HEVC video coding. These proposed fast algorithms were given bellow.
\nThis algorithm is used when switching from a depth p to the next p + 1. As Figure 8 showed, if skip is the best current CU prediction mode, the sub-tree calculations can be skipped [23]. Thus, good mode is determined with rate distortion (RD) calculation cost [24]. The minimal RD cost relates to the skip mode that caused the stop of the partitioning [25].
\nAlgorithm of early CU termination.
Several works show that the most chosen mode was the skip [25]. This clarifies the detail that an excessive enhancement is obtained when the skip mode recognition is anticipated. This mode induces a better encoder performance since it denotes a block code deprived of residual information.
\nThe early skip detection signifies a modest verification of the two-variance motion skip conditions (CBF and differential motion vector (DMV)). As shown in Figure 9, this verification is performed after determining the best inter 2 N × 2 N. Before checking the skip mode, the current CU performs two inter 2 N × 2 N modes (advanced motion vector prediction called AMVP and merge mode). The DMV and CBF are checked when the minimum RD cost is induced by the mode selection. When CBF is equivalent to zero and the best mode inter 2 N × 2 N DMV is equal to (0, 0), the skip mode is the best mode of current CU. Consequently, the residual modes of PU are not examined anymore [8].
\nEarly skip detection algorithm.
The coded fast method (CFM) detects the best mode of a prediction unit [7]. As shown in Figure 10, for each PU mode belonging to a CU, the RD cost is calculated.
\nAlgorithm of coded block flag fast method.
An evaluation of the different coefficients, CBF for the luminance and the two chrominances, is performed. When all transform coefficients (CBF_Y, CBF_U, and CBF_V) are equal to zero [9], all remaining modes will not be tested.
\nThe performance evaluation of this work is effectuated with a random access (RA) configuration through the HM 16.2 reference test model, exploiting the fast mode decision algorithms ECU, ESD, and CBF, previously detailed. To appraise the fast implementation, a comparison of HEVC encoding time, bitrate, and PSNR with the original is effectuated, where a search range is 64. Sixty-four also is the CU maximal size and CU partition depth maximal equals four. An Intel® Core TM i7–3770 @ 3.4 GHz is used in this work with Windows 8 OS platform.
\nThe four resolutions tested are to the four classes (class D (416 × 240), class C (832 × 480), class B (1920 × 1080), and class A (2560 × 1600)) [26]. For each video sequence, 50 is the encoded frame number used. To evaluate results, eight sequences recommended by the JCT-VC [26], each one with four quantification parameters (QP) 22, 27, 32, and 37, are used.
\nTo evaluate this work, we used the formula detailed in Table 1.
\nCriteria | \nDescription | \nFormula | \n
---|---|---|
ΔT (%) | \nEncoding time speedup | \n\n\n | \n
ΔPSNR (dB) | \nPSNR loss | \n\n\n | \n
ΔBR (%) | \nBitrate increase | \n\n\n | \n
Evaluation criteria.
Where: Bitrateoriginal, PSNRoriginal and Toriginal represent bitrate, video quality, and encoding time of the original algorithm, respectively and Bitrateproposed, PSNRproposed and Tproposed, BitRateProposed represent bitrate, video quality, and encoding time of the proposed algorithm, respectively.
Table 2 specifies the results obtained when using the proposed fast HEVC configuration compared to the original one.
\nClass | \nSequences | \nQP | \nΔT(%) | \nΔPSNR (dB) | \nΔBR(%) | \n
---|---|---|---|---|---|
Class A 2560 × 1600 | \nPeopleOnStreet | \n22 | \n−25.04 | \n−0.040 | \n−0.470 | \n
27 | \n−28.37 | \n−0.100 | \n−0.006 | \n||
32 | \n−39.44 | \n−0.187 | \n−1.086 | \n||
37 | \n−49.69 | \n−0.030 | \n−2.182 | \n||
Traffic | \n22 | \n−47.27 | \n−0.103 | \n−0.018 | \n|
27 | \n−62.04 | \n−0.128 | \n−0.017 | \n||
32 | \n−71.83 | \n−0.180 | \n−0.027 | \n||
37 | \n−79.40 | \n−0.194 | \n−0.024 | \n||
Average class A | \n−50.385 | \n−0.123 | \n−0.478 | \n||
Class B 1920 × 1080 | \nBQTerrace | \n22 | \n−29.91 | \n−0.060 | \n−1.180 | \n
27 | \n−60.27 | \n−0.086 | \n−0.022 | \n||
32 | \n−76.67 | \n−0.081 | \n−0.021 | \n||
37 | \n−84.51 | \n−0.067 | \n−2.000 | \n||
BasketballDrive | \n22 | \n−32.15 | \n−0.015 | \n−0.004 | \n|
27 | \n−45.23 | \n−0.026 | \n−0.157 | \n||
32 | \n−54.85 | \n−0.059 | \n−0.640 | \n||
37 | \n−63.82 | \n−0.084 | \n−0.009 | \n||
Average class B | \n−55.926 | \n−0.059 | \n−0.504 | \n||
Class C 832 × 480 | \nRaceHorses | \n22 | \n−11.45 | \n−0.029 | \n−1.430 | \n
27 | \n−22.79 | \n−0.073 | \n−0.005 | \n||
32 | \n−35.24 | \n−0.166 | \n−0.010 | \n||
37 | \n−44.10 | \n−0.230 | \n−2.138 | \n||
PartyScene | \n22 | \n−19.90 | \n−0.040 | \n−0.002 | \n|
27 | \n−35.13 | \n−0.115 | \n−0.009 | \n||
32 | \n−47.93 | \n−0.168 | \n−0.016 | \n||
37 | \n−58.59 | \n−0.194 | \n−0.027 | \n||
Average class C | \n−34.400 | \n−0.126 | \n−0.454 | \n||
Class D 416 × 240 | \nBQSquare | \n22 | \n−34.64 | \n−0.075 | \n−0.870 | \n
27 | \n−54.78 | \n−0.137 | \n−0.016 | \n||
32 | \n−66.90 | \n−0.156 | \n−0.012 | \n||
37 | \n−75.35 | \n−0.137 | \n−0.810 | \n||
BlowingBubbles | \n22 | \n−17.81 | \n−0.070 | \n−0.005 | \n|
27 | \n−28.62 | \n−0.110 | \n−0.005 | \n||
32 | \n−40.05 | \n−0.134 | \n−0.015 | \n||
37 | \n−52.46 | \n−0.115 | \n−0.012 | \n||
Average class D | \n−46.326 | \n−0.116 | \n−0.218 | \n||
Average | \n−46.759 | \n−0.106 | \n−0.416 | \n
Performance evaluation of the proposed algorithm compared to the original one.
The proposed algorithm shows a time saving of up to 46.759% on average compared to the original algorithm. The speedup attains 84.51% of encoding time for BQTerrace video for QP 37. In fact, the time saving is more important for some videos such as Traffic, BQSquare, and BQTerrace sequences ranging from 57.91 to 65.135%. This is due to the motion slowness in these sequences. Indeed, for videos containing low motion activities [18], the improvement is more significant. With the highest resolution, traffic video is characterized by intensive movement of objects against a stationary background. Concerning BQSquare, this video having fast motion is often coded by the bi-predictive mode, as it is the best prediction mode.
\nDefiantly for sequences with high activity, such as BlowingBubbles, RaceHorses, and PeopleOnStreet, the time saving is only around 34.73 and 28.38%. The worst case is for the motion-filled and dynamic RaceHorses video, which records horse racing. Many great frequency details are in this video, since horsetail is regularly expensive to encode.
\nThe time saving is visible with 49% for BasketballDrive sequence. This video contains a high contrast and high motion activities. The background has a rather similar texture.
\nNot only the encoding time was saved but also the bitrate which is justified by the negative values in the table, ranging from 0.002 to −2.182% for PartyScene and PeopleOnStreet with QP equal to 22 and 37, respectively. Regarding the quality of video, the PSNR deprivation is from −0.015 to −0.23 dB for BasketballDrive and RaceHorses with QP equal to 22 and 37, respectively.
\nIn average, the fast HEVC configuration induces a nonsignificant poverty in terms of video quality, around 0.106 dB, with a decrease of 0.416% in the bitrate that is a very interesting point in terms of increasing the compression performance.
\nFigure 11 shows the curves of rate distortion (RD) of HEVC original algorithm and the fast one, for two sequences for each class: PeopleOnStreet and Traffic from class A (2560 × 1600), BQTerrace and BasketballDrive from class B (1920 × 1080), PartyScene and BasketballDrive from class C (832 × 480), and BlowingBubbles and BQSquare from class D (416 × 240). This can also be checked in Table 2. The sequences are taken at QPs 22, 27, 32, and 37.
\nRD curve comparison of our algorithm versus the original one.
Four QP parameters are presented in all curves; horizontal axes on (kbps) represent the bitrate where the vertical one on (dB) represents the PSNR.
\nFigure 11 shows that all RD curves are overlaid [27]. In fact, the proposed changes have insignificant impairments on bitrate and PSNR. For lower QP values, the degradation is more significant. Experimental results prove that the fast configuration gives better performances than the original one, given that it offers a significant time saving, without any influence on the quality and the bitrate.
\nFurther, for all tested sequences, an important speedup is obtained for bigger QPs. Figure 12 evaluates the time saving in average by varying from 22 to 37. We note that the time saving increases in proportion to QP. In average, for higher QP, equal to 37, the run-time decreases by 63.5%. This decline is justified by the choice of the skip mode for bigger QP values [25].
\nCurves of time saving for all videos coded through random access configuration with QP from 22 to 37.
Table 3 summarizes the performances of the proposed work compared to different previous algorithms.
\n\n | Kibeya [17] | \nLiquan [19] | \nQin [20] | \n||||||
---|---|---|---|---|---|---|---|---|---|
\n | ΔPSNR (dB) | \nΔBR (%) | \nΔT (%) | \nΔPSNR (dB) | \nΔBR (%) | \nΔT (%) | \nΔPSNR (dB) | \nΔBR (%) | \nΔT (%) | \n
Class A | \n−0.052 | \n1.08 | \n30.67 | \n— | \n— | \n— | \n0.1% | \n— | \n−22.4 | \n
Class B | \n−0.013 | \n0.29 | \n45.37 | \n−0.020 | \n0.834 | \n−34.00 | \n0.3% | \n— | \n−28.4 | \n
Class C | \n−0.011 | \n0.53 | \n20.86 | \n−0.045 | \n1.225 | \n−16.50 | \n0.2% | \n— | \n−23.0 | \n
Class D | \n−0.008 | \n0.26 | \n6.9 | \n−0.040 | \n1.060 | \n−13. 50 | \n0.2% | \n— | \n−17.0 | \n
Average | \n−0.0105 | \n0.54 | \n25.95 | \n−0.035 | \n1.039 | \n−21.33 | \n0.2% | \n— | \n−22.7 | \n
\n | Podder [21] | \nProposed fast algorithm | \n\n | \n | \n | ||||
\n | ΔPSNR (dB) | \nΔBR (%) | \nΔT (%) | \nΔPSNR (dB) | \nΔBR (%) | \nΔT (%) | \n\n | \n | \n |
Class A | \n— | \n— | \n−41.9 | \n−0.123 | \n−0.478 | \n−50.384 | \n\n | \n | \n |
Class B | \n— | \n— | \n−34.37 | \n−0.059 | \n−0.504 | \n−55.926 | \n\n | \n | \n |
Class C | \n— | \n— | \n−42.92 | \n−0.126 | \n−0.454 | \n−34.400 | \n\n | \n | \n |
Class D | \n— | \n— | \n−46.57 | \n−0.116 | \n−0.218 | \n−46.326 | \n\n | \n | \n |
Average | \n— | \n— | \n−41.44 | \n−0.106 | \n−0.416 | \n−46.759 | \n\n | \n | \n |
Proposed algorithm compared to previous works.
Compared to [17], the proposed work was more competent in terms of bitrate and saving time. In fact, [17] allows saving about 25.95% of encoding time with a slight bitrate. This algorithm was based on large diamond search pattern as an algorithm for motion estimation implemented on HM8.0. Concerning Liquan [19], its algorithm consists of skipping some detailed depths used in the preceding frames. This work allows saving about 21.5% of encoding time with a slight bitrate. Qin [20] implemented an algorithm established on the ECU according to a MSE adaptive threshold value. A time saving without degradation in the quality is obtained in this work. Another interesting method was presented by Podder et al. [21], where human visual features (HVF) are used for the selection of appropriate block partitioning modes. This work offered 41.44% reduction in terms of time for the standard class video sequences (SCVS).
\nHEVC induces an important progress in terms of video quality, in particular for high video resolutions. Nevertheless, this recital is combined with a bigger computational complexity which tremendously increases the encoding time. Motion estimation module using the quadtree structure represents the mainly strong process that is a conduit to the augmentation of the HEVC computational complication. In this paper to decrease this computational complexity, one fast configuration was presented to optimize the ME process by using CU partitioning fast mode decision algorithm and a diamond search. A reduction of 46.75% in the encoding time is obtained without inducing a significant degradation in encoding performance in terms of video quality or bitrate.
\nAs perspectives, additional optimizations will be also implemented to reduce the encoder complexity via digital platform for video processing.
\nWe will also exploit the fast configuration detailed in this paper for the new compression standard Joint Video Exploration Team (JVET) [28, 29].
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\\n\\nWe are currently in the process of collecting sponsorship. If you have any ideas or would like to help sponsor this ambitious program, we’d love to hear from you. Contact Dr. Anke Beck at anke@intechopen.com.
\n\nAll of our IntechOpen sponsors are in good company! The research in past IntechOpen books and chapters have been funded by:
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