Browsing by Author "Santos, Joao M."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Compression of medical images using MRP with bi-directional prediction and histogram packingPublication . Santos, Joao M.; Guarda, Andre F.R.; Cruz, Luís A. da Silva; Rodrigues, Nuno M. M.; Faria, Sergio M. M. deMedical imaging technology has become essential for the improvement of medical practice. This led to advances in the technology, namely in image sampling resolutions, pixel bit-depth and inter slice resolution. Additionally, common use of medical images, the life expectancy of patients and legal restrictions led to increasing storage costs. Therefore, efficient compression of medical image data is in high demand, for archiving and transmission. In this work we propose to improve the compression efficiency of the Minimum Rate Predictors lossless encoder, by adding bi-directional prediction support and a histogram packing technique. The results show that the proposed method presents a higher compression efficiency than state-of-the-art HEVC encoder. The compression efficiency is improved by 20%, on average, when compared to HEVC and by 46.1% when compared with the original MRP algorithm.
- Disparity compensation of light fields for improved efficiency in 4D transform-based encodersPublication . Santos, Joao M.; Thomaz, Lucas A.; Assuncao, Pedro A. A.; Cruz, Luis A. da Silva; Tavora, Luis M. N.; Faria, Sergio M. M. deEfficient light field en coders take advantage of the inherent 4D data structures to achieve high compression performance. This is accomplished by exploiting the redundancy of co-located pixels in different sub-aperture images (SAIs) through prediction and/or transform schemes to find a m ore compact representation of the signal. However, in image regions with higher disparity between SAIs, such scheme's performance tends to decrease, thus reducing the compression efficiency. This paper introduces a reversible pre-processing algorithm for disparity compensation that operates on the SAI domain of light field data. The proposed method contributes to improve the transform efficiency of the encoder, since the disparity-compensated data presents higher correlation between co-located image blocks. The experimental results show significant improvements in the compression performance of 4D light fields, achieving Bjontegaard delta rate gains of about 44% on average for MuLE codec using the 4D discrete cosine transform, when encoding High Density Camera Arrays (HDCA) light field images.
- Lossless light-field compression using reversible colour transformationsPublication . Santos, Joao M.; Pedro A. A. Assuncao; Cruz, Luis A. da Silva; Luís Távora; Fonseca-Pinto, Rui; Sergio M. M. FariaRecent advances in Light Field acquisition and rendering are pushing research efforts towards increasingly efficient methods to encode this particular type of data. Light Field image compression is of the utmost importance, not only due to the large amount of data required for its representation but also due to quality requirements of many applications and computational photography methods. This paper presents a research study about the impact of reversible colour transformations and alternative data arrangements in Light Field lossless coding. The experimental results indicate that the RCT reversible transform consistently achieves the highest compression performance across all data arrangements and lossless encoders. In particular, the best results are obtained with MRP when encoding the stack of sub-aperture images using a spiral scan order, achieving 6.41 bpp, on average.