Graphics, Imaging, and Games Lab

This is the final post concerning my undergraduate honours project (course code COMP 4905) for Fall 2016.

It was an interesting project to work on, for several reasons:

I extended my superpixel filtering module so that it accepts an arbitrary input image representing pixel scores. Lighter pixels (lightness in the CIE L*a*b* colour space) are interpreted as more strongly preferring stippled rendering, whereas darker pixels are interpreted as more strongly preferring smooth rendering. The filter determines the average lightness value within each superpixel. Finally, it performs Otsu thresholding on the average lightness values to classify superpixels into two groups: Those which will be stippled, and those which will be rendered with smoothed colours only.

Consequently, I was free to experiment with a wide variety of methods for selecting superpixels for stippling or smooth rendering, without having to implement these methods.

As is evident in my last post, colour images are far more attractive in general than greyscale images.

Consequently, I adjusted the process for blending stipples with superpixels to incorporate colour channels as well as the CIE L*a*b* lightness channel.

Having implemented structure preserving stippling [1] and SLIC [2], I can now explore using the two techniques together.

In the full image stylization process, areas with high-frequency texture will be approximated by stipples, whereas areas with lower-frequency texture will be approximated by closed shapes. To create the closed shapes and decide how the image is to be divided into regions, each containing pixels with similar properties, I need an image segmentation algorithm.

For now, I have chosen Simple Linear Iterative Clustering (SLIC) [1] as the segmentation algorithm. SLIC is efficient and produces regions which adhere well to edges in the image. Moreover, it is not overly difficult to implement.

Following up on my previous post. I am pleased to provide some stippling results from a debugged implementation.

I have tentatively replicated the stippling algorithm of Dr. Hua Li and Dr. David Mould described here.

The implementation of the algorithm itself was straight-forward. I am grateful that the method was so clearly described in the article.

During the previous week, I expanded the functionality of the small Qt-based graphical application that will serve as the environment for image processing algorithms.

This and the following blog posts describe my undergraduate honours project (course code COMP 4905) for Fall 2016.

Earlier this month I gave a tech talk to the undergraduate society here at Carleton.  These are my slides: