I made a simple scene just to try to understand and fix the problem : it's just a teapot and a directional light. I applied a toon shader on the teapot, set the treshold angle to 20, and plugged a ramp with 3 tones in the base tonemap attribute. Everthing is fine. Then, if i start to add a bit of specular, then arnold draw an outline of the reflections. How can i prevent that ? I tried unchecking shader difference in the edge detection tab, switching between the 3 normal type modes, pluging an ai_utility node in mask color, plugging a ramp in the specular tonemap ... nothing worked. Any ideas ? Because on some of the images on the toon documentation page, they managed to get some specular reflections without the outlines.
No specular :
Specular weight : 0.1 :