Skip to main content
  • Poster presentation
  • Open access
  • Published:

Boundary effects across filter spatial scales

Most saliency algorithms rely on a filter processing stage in which an image is analyzed using a bank of convolution kernels. When applying a convolution to an image, however, a region of pixels with thickness equal to one-half the kernel width at the image border is left undefined due to insufficient input (this undefined region is hereafter referred to as the boundary region). While the percentage of the output image falling within the boundary region is often kept small, this limits the spatial scale of filter which can be applied to the image. There is clear psychophysical evidence from visual search tasks that spatial scale can be used as a component of visual search, with differences in feature size, spatial frequency, and sub-component grouping [1]. Thus, handling filters with dimensions that are significant with respect to the image size is worthwhile if the spatial scale component of visual search is to be effectively incorporated, but this requires dealing with the resulting boundary region.

A large number of computational strategies have been developed over the years for dealing with the boundary region issue, including: image tiling/wrapping, image mirroring, image padding, filter truncation, and output truncation. Formal evaluations and comparisons of such strategies have not previously been performed. We provide such a comparison using visual search stimuli commonly utilized in human psychophysical experiments, as well as propose a novel method for incorporating information across multiple spatial scales with an output image defined up to the boundary region created by the smallest spatial scale.


  1. Wolfe Jeremy M: Visual Search. Attention. Edited by: Harold Pashler. 1998, Psychology Press

    Google Scholar 

Download references


Financial support was provided in part by the Natural Science and Engineering Research Council (NSERC) and the Canada Research Chairs Program.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Calden Wloka.

Rights and permissions

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver ( applies to the data made available in this article, unless otherwise stated.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Wloka, C., Bruce, N. & Tsotsos, J. Boundary effects across filter spatial scales. BMC Neurosci 15 (Suppl 1), P19 (2014).

Download citation

  • Published:

  • DOI: