Papers by Christos Grecos
Heuristic approaches for porting deep neural networks onto mobile devices
Real-Time Image Processing and Deep Learning 2021, 2021
Deep Neural Networks (DNNs) although promising for image processing, have significant computation... more Deep Neural Networks (DNNs) although promising for image processing, have significant computational complexity. This impedes implementation in resource-constrained systems. This paper presents effective heuristic approaches for porting DNNs onto mobile devices. Four sets of heuristics are studied: (1) heuristics based on the reuse of transferred weight matrices and weight pruning; (2) heuristics based on parameter reduction, network acceleration and non-tensor layer improvements; (3) a suite of heuristics for low power acceleration of DNNs based on dataflow, near memory and in-memory processing, transform schemes and analog based approaches; and (4) heuristics based on feature and feature map pruning utilizing cosine distances. These sets of heuristics achieve significant complexity, memory and power reductions with minimal reduction of accuracy across an assortment of state-of-the-art DNNs and applications.
<title>A fast eye detector using corners, color, and edges</title>
Real-Time Image Processing 2006, 2006
Eye detection plays a central role in an automatic face detection systems and it is also importan... more Eye detection plays a central role in an automatic face detection systems and it is also important for face recognition and face tracking. In this paper, we present a novel, unsupervised scheme for detecting eyes in skin patches based on our previous work. Working on the normalized RGB color space (NRGB ), we use a combination of corner identification, color and edges as heuristics for detecting eyes. Experimental results show that our scheme is very fast in the AR and Champion databases, while retaining very high detection rates.
A Fast Skin Colour Detector for Face Extraction
Storage and Retrieval for Image and Video Databases, 2003
Abstract: We consider skin color detection a preprocess forface detection, recognition and tracki... more Abstract: We consider skin color detection a preprocess forface detection, recognition and tracking. Our goal for is todesign a skin color detection algorithm in order to dramaticallyreduce the amount of data needed to be processed in later steps,while still providing acceptable performance.
Using MPEG-7 for shot based reduction of quality and rate fluctuations in H264 AVC
The Seventh Iasted International Conference on Visualization Imaging and Image Processing, Aug 9, 2007
Google, Inc. (search), Subscribe (Full Service), Register (Limited Service, Free), Login. Search:... more Google, Inc. (search), Subscribe (Full Service), Register (Limited Service, Free), Login. Search: The ACM Digital Library The Guide. ...
Robust multiple-initial-point prediction algorithm for fast motion estimation in the MPEG-2 standard
Opt Eng, 2005
We present a novel, computationally efficient and robust scheme for multiple-initial-point predic... more We present a novel, computationally efficient and robust scheme for multiple-initial-point predictors used in fast searches in the MPEG-2 standard. Extensive testing in a variety of video sequences with different motion characteristics clearly shows that it outperforms the center- and median-based predictors currently used by mean square error (MSE) reduction of 1.51, 5.25, and 3.62% for the diamond, the three-step, and the four-step searches and for the same bit rates as the standard.
Dual Smoothing for Marine Oil Spill Segmentation
IEEE Geoscience and Remote Sensing Letters, 2016
Low computational cost improvements of the rate-distortion performance in MPEG-2 rate control
Real-Time Imaging, 2003
Rate control in standards such as MPEG-2 or H263 plays an important role in controlling the compr... more Rate control in standards such as MPEG-2 or H263 plays an important role in controlling the compression rate and stabilizing the decoding and playback quality. In this paper, we combine the simplicity of the rate-distortion (R-D) predictive models with the improved R-D performance offered by the iterative approaches and we design effective rate control algorithms for low encoding delay and low complexity video compression. The proposed algorithms initially utilize the Lagrangian formulation in order to add a local R-D optimization component into the current rate control scheme of the standard. Subsequently, two online controllers are designed based on this local optimization scheme for adjusting the bit rate produced by the standard. Extensive experiments show improvements over the MPEG-2 scheme of 0.5–1dB per frame for a variety of test sequences when the same target bit rates are maintained.
Towards improved prediction accuracy in JPEG-LS
Opt Eng, 2002
Towards an improvement on prediction accuracy in JPEG-LS
Opt Eng, 2002
Among a context of three pixels, the present JPEG-LS produces predicted values based on whether a... more Among a context of three pixels, the present JPEG-LS produces predicted values based on whether a vertical edge or a horizontal edge is detected. When a diagonal edge exists, however, experiments and observation reveal that such a prediction will generate large predictive errors. By applying the triangle inequality to the analysis of predictive templates in JPEG-LS, we propose a diagonal-edge detection scheme to reduce the predictive error and hence provide an improvement on the prediction accuracy. Experiments are carried out to test the proposed scheme for a group of sample images. In comparison with the current JPEG-LS prediction, our scheme produces lower prediction errors, in terms of both MSE measurement and visual comparison of error images.
2006 Ph.D. Research in Microelectronics and Electronics, 2006
A new algorithm for fast mode decision in the H264 video coding standard is presented in this pap... more A new algorithm for fast mode decision in the H264 video coding standard is presented in this paper. The algorithm exploits mode grouping through moving averages of error cost functions for providing significant computational savings with similar Rate Distortion performance as compared to accepted standard contributions [3].
Reduced complexity Eye Detector for colour images using Harris Corners, Color heuristics and Edge maps
2006 Ph.D. Research in Microelectronics and Electronics, 2006
Eye detection plays a central role in automatic face detection systems and it is also important f... more Eye detection plays a central role in automatic face detection systems and it is also important for human-computer interaction and face tracking. In this paper, we present a novel, unsupervised scheme for detecting eyes in skin patches based on our previous work on skin patch detection (Chen and Grecos, 2005). Working on the normalized RGB color space (NRGB), we use a combination of corner identification, color and edges as heuristics for detecting eyes. Experimental results show that our scheme is very fast in the AR and Champion databases (average time 2.53 and 0.21 seconds per image respectively with un-optimized code), while retaining very high detection rates (100 and 89.5% correspondingly)
Journal of Real-Time Image Processing, 2013
Secure Media'' is dedicated to the areas of biometrics, surveillance, authentication and secure c... more Secure Media'' is dedicated to the areas of biometrics, surveillance, authentication and secure communications. The issue is oriented toward both theoretical and practical aspects and in the spirit of the journal, the emphasis is on the trade-offs necessary for achieving Real Time performance. This special issue contains eight contributions.
An improved rate control algorithm based on a novel shot detection scheme for the H.264/AVC standard
Journal of Real-Time Image Processing, 2008
An Eye Detector Based on Cues and Heuristics with a Good Accuracy/Complexity Trade-off
2008 NASA/ESA Conference on Adaptive Hardware and Systems, 2008
<title>A framework for fast mode decision in the H264 video coding standard</title>
Visual Communications and Image Processing 2006, 2006
Audiovisual Compression for Multimedia Services in Intelligent Environments
Studies in Computational Intelligence, 2008
Multimedia on Mobile Devices 2007 (Proceedings Volume)
A large number of recorded videos cannot be viewed on mobile devices (eg, PDAs or mobile phones) ... more A large number of recorded videos cannot be viewed on mobile devices (eg, PDAs or mobile phones) due to inappropriate screen resolutions or color depths of the displays. Recently, automatic transcoding algorithms have been introduced which facilitate the playback of previously recorded videos on new devices. One major challenge of transcoding is the preservation of the semantic content of the videos. Although much work was done on the adaptation of the image resolution, color adaptation of videos has not been addressed ...
Fast intra encoding decisions for high efficiency video coding standard
Journal of Real-Time Image Processing, 2014
Electronic Commerce Research, 2015
123 2 C. Grecos et al.
<title>Speeding up the optimization of the rate distortion performance in MPEG-2 video coding through quantizer loop parameterization</title>
Image and Video Communications and Processing 2003, 2003
A simple scheme for fast Rate Distortion optimization based on Lagrange multipliers is presented ... more A simple scheme for fast Rate Distortion optimization based on Lagrange multipliers is presented in this paper. It is based on the observation that for accurate target rates, the change of the multiplier alone may not have an effect for small step sizes. However, a combination of small step sizes alogn with appropriate quantizer loop parameterization may solve this problem thus result in in significant computaiotnal savings since only a portion of the Rate distortion characteristics need to be considered for optimization. Extensive experiments using quantizer loop parameterization reveal savings between 60.14 and 92.94% for the rate bounding case and between 56.48 and 91.01% for the bisection search for a wide variety of video sequences exhibiting different characteristics.
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Papers by Christos Grecos