Monday, July 9, 2018

Non Photorealistic Rendering Software - The Watercolorist

"The Watercolorist" is software to watercolorize a photograph. "The Watercolorist" simulates/fakes wet-on-dry watercolor effects. See Non Photorealistic Rendering - Watercolor rendering (watercolorization) for the methodology that's behind it.

When you extract thewatercolorist-x64.rar, you should get something like this:

The directory "barn1024" shows you how to use the software. The "texture" directory contains the watercolor paper textures.

When you go into the directory "barn1024", you should see something like this:

The file called "thewatercoloris.bat" is the one you will double-click to run the software. It tells windows where the executable is. You need to edit the file so that the location of the executable is the correct one for your installation. I use notepad++ to edit text files but I am sure you can use notepad or wordpad with equal success.

The file "thewatercolorist_input.txt" is the input file for the software. It should look like this:


Line 1: input image. The input image should be the abstracted image called "abstracted_image_after_quantize.png" that comes from Non Photorealistic Rendering Software - The Cartoonist. You could also use "abstracted_image_after_oabf2.png" for a more wet-on-wet look if you prefer. It's quite possible to use something other than "The Cartoonist" to generate a good abstracted image. As a matter of fact, you should be able to use gimp or photoshop to get it.

Line 2: paper texture. I conveniently placed a few watercolor paper textures in the "texture" directory. You can use those or your own. There should be no spaces in the file name.

Line 3: paper texture beta (here, -2.0)

Line 4: turbulent flow beta (here, -4.0)

Line 5: edge darkening gradient convolution kernel size (here, 5)

Line 6: edge darkening beta (here, -4.0)

Line 7: output image (here, "watercolor_image.png"). There should be no spaces in the image name.

"The Watercolorist" simulates the following watercolor effects: watercolor paper texture (watercolor paint pigments have a tendency to deposit into the cavities of the paper), turbulent flow (in watercolors, there is a low frequency pigment density variation whenever waterlogged paint pigments are deposited on the paper), and edge darkening (paint pigments have a natural tendency to migrate to edges and deposit there in greater numbers). All those watercolor effects are simulated using the same technique: the current color is darkened/lightened according to a grayscale image that's supposed to represent pigment density. The higher the pigment density, the darker the color is going to be as more pigments get deposited onto the paper. The parameter "beta" (there is one for each watercolor effect) is used to scale that grayscale image so that the effect can be amplified/muted. The lower the beta, the more extreme the darkening/lightening will be.

"The Watercolorist" outputs images after each watercolor effect has been applied:
- image_after_paper_texture.png. This is the rendered image after the paper texture watercolor effect has been applied.
- image_after_turbulent_flow.png. This is the rendered image after the turbulent flow watercolor effect has been applied.
- image_after_edge_darkening.png. This is the rendered image after the edge darkening watercolor effect has been applied. It should the same as the output image by the way (here, watercolor_image.png).




"The Watercolorist" is free to download at Painting Software.

Source code: thewatercolorist on github.

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