Shared Sampling for Real-Time Alpha Matting

Eduardo S. L. Gastal eslgastal@inf.ufrgs.br

and

Manuel M. Oliveira oliveira@inf.ufrgs.br

Instituto de Informática, UFRGS

Computer Graphics Forum.
Volume 29 (2010), Number 2, Proceedings of Eurographics 2010, pp. 575-584.

Contents

Image matting aims at extracting foreground elements from an image by means of color and opacity (alpha) estimation. While a lot of progress has been made in recent years on improving the accuracy of matting techniques, one common problem persisted: the low speed of matte computation. We present the first real-time matting technique for natural images and videos. Our technique is based on the observation that, for small neighborhoods, pixels tend to share similar attributes. Therefore, independently treating each pixel in the unknown regions of a trimap results in a lot of redundant work. We show how this computation can be significantly and safely reduced by means of a careful selection of pairs of background and foreground samples. Our technique achieves speedups of up to two orders of magnitude compared to previous ones, while producing high-quality alpha mattes. The quality of our results has been verified through an independent benchmark. The speed of our technique enables, for the first time, real-time alpha matting of videos, and has the potential to enable a new class of exciting applications.

Demo

Shared Matting demo for Linux 64-bit (2.7 MB) Version 1.0, December 2010.

NOTE: Download here a precompiled binary for libboost_program_options.so.1.40.0.

Material

Full paper (1.6 MB, 10 pages)

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Data

Below you can find intermediary results generated by our sample gathering and sample refinement steps. Each tgz archive contains the following images: expanded trimap, foreground color, background color, alpha value (including low-frequency alpha), confidence value and variance value. The original input images and trimaps are available from the alphamatting.com evaluation website.

doll

donkey

elephant

net

pineapple

plant

plasticbag

troll

GT04

Video

Images

Comparison of our technique (Shared Matting) against the state-of-the-art is available at the alphamatting.com evaluation website. The runtimes of our real-time matting technique for the images in this benchmark, using the most conservative trimaps, are as follows:

How does one processes pixels which do not find any foreground and/or background samples during the sample gathering?

Mark this pixel as "bad" and let it find a foreground/background sample pair by analyzing its neighboring pixels in the sample refinement step.

Citation

Eduardo S. L. Gastal and Manuel M. Oliveira. "Shared Sampling for Real-Time Alpha Matting". Computer Graphics Forum. Volume 29 (2010), Number 2, Proceedings of Eurographics 2010, pp. 575-584.

BibTeX

@article{GastalOliveira2010SharedMatting,
  author  = {Eduardo S. L. Gastal and Manuel M. Oliveira},
  title   = {Shared Sampling for Real-Time Alpha Matting},
  journal = {Computer Graphics Forum},
  volume  = {29},
  number  = {2},
  month   = {May},
  year    = {2010},
  pages   = {575-584},
  note    = {Proceedings of Eurographics}
}
  

Keywords

Alpha Matting, Compositing, Image processing, Video processing.

CNPq-Brazil fellowships # 200284/2009-6, and 305613/2007-3, and a PIBIC/CNPq/UFRGS fellowship.

Last updated: January 2017.