Liquid Rescale

Image resizing for most cases today works directly on pixel level irrespective of the content. A first step to not distort the information is to keep the aspect ratio the same. However this too is not very good, specially if the content of focus in the image was small to begin with, thus making it even smaller. Liquid rescale is an awesome technique for content-aware image resizing and the publication can be found here. The video below demonstrates its applications, and also quickly explains the main concept.

The idea behind this is astonishingly simple. Instead of removing a straight column (row) of pixels to reduce the width (height), a so-called vertical (horizontal) seam is removed. The seam is a connected path of low energy pixels in the image. Thus, removing a seam does not alter the high energy content, which is usually semantically useful.

An image is analyzed and seams are ordered from low to high energy. The seams with lowest energy are removed first for reducing the size of the image, and subsequent seams are removed to reach the desired image size. The image can also be expanded by adding in extra pixels in these seam locations with values as the average of the neighbours. The video below throws light on how these seams look and shows nice applications.

A Gimp plugin can be found here and imagemagick incorporates it in here.

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