CSE 557 Computer Graphics Grail

Fall 2004

Project One

Impressionist painting

Project 1: Impressionist

Assigned: Thursday, September 2, 2004
Due: Thursday, September 16, 2004
Artifact Due: Monday, September 20, 2004

Project Description

Impressionist is an interactive program that creates pictures that look like impressionistic paintings. It is based on a paper and a program by Paul Haeberli.

To create an impressionistic picture, the user loads an existing image and paints a seqence of "brush strokes" onto a blank pixel canvas. These brush strokes pick up color from the original image, giving the look of a painting. To see some samples that were generated with the sample solution, click here.

Project Objective

You will add the functionality to a skeleton version of the Impressionist program, which we will provide. The purpose of this project is to give you experience working with image manipulation, OpenGL primitives, user-interface design, and image processing.

Getting Started

In either case, you'll definitely want to take a look at the FLTK documentation and the OpenGL Red Book.

Explanation of the Skeleton Program

The skeleton program we provide does very little. It allows you to load the original image (which must be a 24-bit uncompressed BMP file), and save the painted version. Brush selection is done via a modeless dialog ("File/Brushes..."). There is one brush implemented (points) and a slider for controlling the brush size.

Required Extensions

You must add the following features to the Impressionist program:
  1. Implement 5 different brush types: a single line, a brush consisting of multiple scattered lines (think scratches), a brush consisting of multiple scattered points (think spraycan), (filled) circles, and scattered (filled) circles (think polkadots).
  2. Add sliders to control various brush attributes. You need to include sliders for the line thickness, brush angle, and alpha (opacity), in addition to the existing brush size slider. Feel free to add any other sliders that you feel might be helpful to the project.
  3. Add the ability to control the brush direction (angle). The stroke direction should be controlled four different ways: using a slider value, using the right mouse button to drag out a direction line, using the direction of the cursor movement, and using directions that are perpendicular to the gradient of the image. For information about calculating the gradient of an image, look here. You can use a radio box to allow the user to select which method to use.
There will be a sample solution posted soon. Your implementations of brush strokes, brush direction controls, etc. do not have to behave exactly the same as the sample solution, but they should demonstrate the same functionality.

Project Artifact

When you are done with this project, you will create a project "artifact" to show off the features of your program. For the Impressionist artifact, you will create an impressionistic painting from an image of your choice. We will then create a gallery of all the paintings on the course web page. Please note that you are not allowed to use other people's programs or sample solutions for your artifacts.

Bells and Whistles

Here is a list of suggestions for extending the program. You are encouraged to come up with your own extensions. We're always interested in seeing new, unanticipated ways to use this program!

[whistle] To give your paintings more variety, add some additional brush types to the program. These brush strokes should be substantially different from those you are required to implement. You will get one whistle for each new brush.


[whistle] When using your program, you currently can't see what part of the original image you're painting. Extend the program so that when you're making a brush stroke, a marker appears on the original image showing where you're painting.


[bell+whistle] A different solution to the problem of not being able to see where you're painting is to show a dimmed version of the painting on the canvas. Add a slider that allows the user to fade in or fade out the original image beneath the user's brush strokes on the canvas. (Beware, this bell and whistle is more difficult than it looks).


[bell+whistle] To make your painting more interesting, add "alpha-mapped" brush strokes. In other words, allow the user to load a bitmap representing a brush stroke. This bitmap would contain an alpha value at each position. Then when this brush is used to draw, a single color would be selected from the image, all pixels in the brush bitmap would be set to this RGB color (without changing the alpha value), and this partially transparent bitmap would be painted on the canvas. A new color would be used each time the brush is drawn.


[bell+whistle] It can be time-consuming to paint an image manually. Add a feature so that a whole painting can be created automatically. The user should only have to specify a brush type, size, and angle to use. Then the program should automatically paint brush strokes over the entire image, using a randomized brush order and varying the brush attributes slightly as it goes (to increase realism).


[bell+whistle] At times, you may want the brush strokes to follow the gradient of a different image than the base image. Add a button(s) that will cause the direction of brush strokes to be automatically determined from a user specified image.


[bell+whistle] The "accuracy" of the painting can be also be improved by clipping long brush strokes to edges in the image. Allow the user to load a black-and-white image that represents the edges in the picture. Then add a checkbox so that the user can turn on edge-clipping, which will automatically clip brush strokes at edges in the image.


[bell] Add the ability to apply a convolution kernel (filter) to either the original image or the original image and store the result in the painted image. See this discussion of image processing to understand what you need to be able to do. You should also build an appropriate UI for the kernel interface. You should be able to change the kernel size in both x and y separately. You should support at least a 3x3 kernel. Some code for this is already present in the skeleton, but the UI element is not. You should also be able to support a preview window, which you render to before rendering to the paint window.

[bell] [bell] Use the image processing techniques described in class to automatically find the edges in the base image. Once you have found the edges, add a button to the user interface that will allow the user to select whether or not the brush strokes should be clipped to the edges in the picture.


[bell] [bell] Implement a multiresolution automatic painting technique. See Painterly Styles for Expressive Rendering.


[bell] [bell] Implement a curved brush that follows the image gradient. See Painterly Styles for Expressive Rendering.


[bell] [bell] [bell] Design a brush that can be used to stretch and pull the image as if it were rubber. See Alex Warp.


[bell] [bell] [bell] [bell] Extend the Impressionist program to work with video. The user should be able to load a series of images from a video and set up some initial parameters, and the program should automatically generate an impressionistic version of the video. The video should exhibit temporal coherency.


Related References