Trees and Colored Edge Detection Chris Burnham Department of Computer Science, Colby College, Waterville, ME Colored Edge Detection L-System Trees L-Systems are a way to generate images using text. A base string of characters is then iteratively replaced by a set of rules to create a final string. Using rules the string is then drawn into the image using a turtle that gets its commands from a string. My L-systems use a 3-D turtle that For my non-photorealist section I implemented a edge detection algorithm with a twist. As edge detection usually runs in either a single color band or on a grey scaled image I ran mine on all three color bands and then built a final image using all three. The edge starts by applying a Gaussian Blur to the image which I have demonstrated on one of my trees shown to the left. The next step was to look at the color gradient for all the pixels this step is shown the right. After this using the gradient direction and strength I thinned all of the edges found to where the greatest change was. Finally I separated out my potential edges into three groups by a strength threshold. If a edge was very strong then it was definitely an edge. Also if a edge was weak enough we know that it is not an edge so we drop it. Finally for middle strength potential edges we only keep them if they are connected to a strong edge. Because we need these weak edges to extend out even if the majority of them is weak the algorithm that looks at them must be recursively written. Once we have looked at the edges like this we produce the image to the right. Finally I ran my algorithm in each of draws cylinders and spheres. It supports branching, decreasing sizes of both cylinder length and width, and probabilistic rules. The images to the right demonstrates the system’s ability to draw L-systems in 3-dimensions. The shapes drawn are known as the Hilbert Curve. What makes the Hilbert Curve interesting is that it is a space filling curve. What this means is that the L-system is run for more iterations it will continue to fill up with boxes and if you were to put a integer vertex at every corner eventually every possible 3-dimensional integer coordinates would be reached. The top drawing demonstrates a earlier iteration but after the pattern has emerged, while the bottom image is of a later iteration. Down at the bottom is a L-system I call the Wandering String, which I designed to demonstrate my systems ability to generate L-systems with probabilistic rules. Each of the images is the same L-system which has the ability to move in many different direction and to grow to different lengths. Blured Gradiant Thinned Gradient Edges Edges the three color bands. If a edge is detected in a color band then that color band receives a 255 color value in that band otherwise it receives a 0 in that color band. The image to the right demonstrates its output on my example tree picture. All the other images at bottom of the page are my tri color edge detection running real world photos. Hilbert Curves Finally to the right are my trees which is what this project was building towards. Each of the trees is generated by the same L-system which I designed to look like a tree. It features thinning branches both as you move up the tree as well as out on a limb. The same is true for branch length but to a different degree. Also as it grows branches can die off. You will also note that the trunk has the ability to grow different amounts before My Computer and a Board Tri Colored Edges the first branch. Sunset Love Wandering String Trees