This simple program plays with some of the ideas from

• "Painterly Rendering with Curved Brush Strokes of Multiple Sizes" by Aaron Hertzman and
• "Processing Images and Video for an Impressionist Effect" by Peter Litwinowicz.

In these papers, the authors describe techniques for creating images with a hand-painted look from photographs.  These techniques involve aligning the digital brush strokes along edges from the original phtograph and then building up the final image in layers. Each layer uses a different sized brush to fill in the appropriate amount of detail.

ImagePainter can read and write PPM files and reinvent them in impressionist, expressionist, colorist wash, and pointillist styles using circle, line, and curved brush strokes. The user can tailor the effects of the algorithm by specifying thresholds, color jitter, color opacity, brush stroke size, and brush stroke shape.

The interface consists of a control window and corresponding image windows:

Above we see an impressionist rendition of an entraceway from Ibiza, Spain. In canvas settings, we can adjust the theshold and stroke overlap. The threshold helps determine how closely the final painting resembles the original photograph. A stroke overlap of 2.0 indicates that strokes will not overlap in a given layer while a stroke overlap of 0.0 will cause strokes to completely overlap. In the brushes settings, we can configure how many layers should be used to construct the final painting. In this example, we painted three layers where the brush for each layer is half the size of the previous brush. In the brush stroke settings, we have chosen curved brush strokes with no additional curvature, no color opacity, and a moderate minimum/maximum length.

Click on any of the images below to see them in more detail:

From left to right, top to bottom:

• A mountain scene in a modified pointilist style with red, blue, green color jittering.
• Lilies in an "expressionist" style
• Buckingham Palace in a hybrid style. *
• Derick Zoolander and Hansel in a hybrid impressionist style. To help conserve the detail in their faces, the stroke overlap was increased, the threshold was decreased, and the stroke lengths were decreased. Opacity was reduced as well.
• A mountain scene in a custom style. The strokes were configured not to overlap and the threshold was exagerrated to leave large empty spaces. The brush shape was also set to circle to enhance the effect.
• The sandman from Ibiza in a hybrid style. The default parameters for colorist wash were expanded to paint more layers with a smaller threshold. The brush type was also changed to circle. *
• Aline in London in a modified pointilist style. The opacity was increased while the value color jitter and stroke overlap was decreased.

Here is the source for this program.  To compile, you will need fltk 1.1.3 and openGL 1.2.