Work place: SFED/SEG/SEDA, Space Applications Centre, ISRO, Ahmedabad-India-380015
Research Interests: Models of Computation, Theory of Computation, Algorithm Design, Image Processing, Image Compression
Ashok Kumar, male, is a Scientist/Engineer at Space application Centre (ISRO). He completed his BE degree (Electronics and communication) from University of Rajasthan in 2007. He is currently involved in advance research and development activities for future electro-optical payloads at Sensor Front End Electronics Division (Sensor Development Area). His research interest includes VLSI design, image processing, computation photography etc. He has been awarded ―ISRO team excellence award-2009‖ for ―Miniaturized camera electronics development. He has published 9 papers in various international/national conferences and peer reviewed journals.
DOI: https://doi.org/10.5815/ijigsp.2016.02.08, Pub. Date: 8 Feb. 2016
In high radiometric resolution electro optical image payloads of remote sensing satellites, photon noise dominates SNR performance. Photon noise is input signal dependent and difficult to filter. This paper proposes a photon noise filtering technique for Ocean Color Monitor (OCM) images. Existing filtering techniques are meant for object detection and handles images with poor SNR. As OCM SNR is on higher side, custom sigma filter based denoising technique is developed. Proposed technique first converts photon noise to signal independent Gaussian noise. For this variance stabilization, Anscombe transform is used. Simulations are carried on various images. Proposed technique provides 20- 50% reduction in overall as well count-wise RMSE. FFT analysis shows significant reduction in noise. Proposed technique is of low complexity.[...] Read more.
DOI: https://doi.org/10.5815/ijieeb.2015.03.04, Pub. Date: 8 May 2015
ISRO's remote sensing continuity mission Resourcesat-II provided better radiometric performance as compared to Resourcesat-I. However, this improvement required implementation of onboard image compression techniques to maintain same transmission interface. In LISS-4 payload, prediction based DPCM technique with 10:7 compression ratio was implemented. Based on received data from this payload, some ringing artifacts were reported at high contrast targets, which degrade image quality significantly. However occurrences of such instances were very few. For future missions, efforts are made to develop an improved low complex image compression technique with better radiometry and lesser artifacts. Adaptive DPCM (ADPCM) technique provides better radiometric performance. This technique has been implemented onboard by other space agencies with their own proprietary algorithm. To maintain existing 10:7 compression ratio, novel ADPCM techniques with adaptive quantizers are developed. Developed ADPCM techniques are unique w.r.t. predictor and encoding. Developed techniques improve RMSE from 1.3 to 10 times depending on image contrast. Ringing artifacts are reduced to 1% from 38% with previous technique. Developed techniques are of low complexity and can be implemented in low end FPGA.[...] Read more.
DOI: https://doi.org/10.5815/ijigsp.2015.03.08, Pub. Date: 8 Feb. 2015
Future high resolution instrument planned by ISRO for space remote sensing will lead to higher data rates because of increase in resolution and dynamic range. Hence, image compression implementation becomes mandatory. Presently designed compression technique does not take account of imaging system noise like photon noise etc. This ignorance affects compression system performance. As a solution, this paper proposes MLG (Multi Linear Gain) operation prior to main compression system. With digital MLG operation, captured image can be optimally adjusted to systems noise. Proposed MLG operation improves compression ratio. Simulation results show 15-30% improvement in lossless compression ratio. However this improvement depends on MLG gains and corner points which can be driven by system SNR plot. MLG operation also helps in improving SNR at lower radiance input, when lossy JPEG2000 compression is used as main compression. Up to 1-6 dB SNR improvement is observed in simulations. Proposed MLG implementation is of very low complexity and planned to be used in future missions.[...] Read more.
DOI: https://doi.org/10.5815/ijitcs.2014.09.04, Pub. Date: 8 Aug. 2014
In satellite systems, large amount of high speed data is required to be transmitted from one system to another. Conventional parallel data transmission requires a large number of cables/interface-packages and results in large weight and volume. Parallel interface in a typical future camera system requires >8000 cables between camera electronics and data handling system. In addition, with increase in transmission rate, problems associated with crosstalk become more critical. One possible solution identified is serial interface, also termed as SERDES (SERializer/DESerializer) interface. A typical SERDES interface comprises of encoder/decoder, PLL, timing-control and multiplexer/de-multiplexer. Encoding of serial data solves high speed serial data transmission problems by incorporating clock embedding, DC balancing, sync info insertion and error detection. DC balancing also solves the issue of Inter-Symbol Interference (ISI). Available SERDES interface devices have limitations like poor reduction factor, no clock embedding or non-availability of space qualified part. Hence, an attempt is made to understand and implement SERDES encoder/decoder with a goal of indigenous SERDES ASIC development. Due to 12-bit input interface, a novel 12B/14B encoding technique is designed and developed. The developed technique preserves many good properties widely used 8B/10B encoding technique. FPGA simulation results achieved >50MSPS parallel rate which will lead to >700 Mpbs serial rate. Developed technique is very efficient and suitable for onboard implementation.[...] Read more.
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