A Look Into Photorealistic and Non-Photorealistic Rendering Margaux LeBlanc ‘15 Department of Computer Science, Colby College, Waterville, ME This term in Advanced Computer Graphics we have been exploring photorealist and non-photorealistic rendering. First I implemented Lindenmayer systems to represent the realistic growth of trees and flower. Lindenmayer systems can represent many natural phenomena such as snowflakes. Then I implemented an impressionist image filter that turned pictures into impressionist paintings. With my graphics engine I built this year in C I can create realistic or unrealistic photos of natural phenomena. Impressionist Filter Graphics Engine Capabilities: Scanline Fill Viewing Pipeline Visible Surface Algorithm- Z Buffer Bezier Curves and Surfaces Lighting Model Shading Model Keyframe Animation Lindenmayer Systems Image Filters- Edge detection, Impressionist, Gaussian Blur Based on a SIGGRAPH paper by Peter Litwinowicz in 1997 called “Processing Images and Video for An Impressionist Effect.” Lindenmayer Systems Start with a source image. This is operated on pixel by pixel Apply a Gaussian Blur to sort out unnecessary edges. Use Sobel Edge Detection to calculate the intensity gradient at each pixel. Lindenmayer systems are generated using a base case and applying a rule to it recursively: Base F Rule F F+F+ If I iterate 2 times over this set of rules we get the string output F+F+F+F+ which draws a square. I parsed all the strings in python and generated the images in C. To implement these systems in C I created a Turtle that kept track of position, orientation, and rotation so that the lines could be drawn in order. In one of the images you see that the tree has leaves, which are a special case. More special cases include changing colors, branching, parameterizing lengths and angles, and more. Align brush strokes with gradient field and clip strokes where edges occur. Color strokes according to the pixel color in the source image at the center of the stroke. Final image where strokes are drawn as ellipses with varying lengths and radii.