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John Park avatar image
John Park asked ·

Why does the width scaling values under 0.4 (in aiToon Shader) affects opacity?

I want to render my obj with a very thin line, but it seems that the edge width scaling value under 0.4 is rendered in gray color. Even on the Arnold website, where it explains how the edge width scaling works, shows that the color is faded out.


How do I render a thin black line with its full opacity in Arnold?


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Mads Drøschler avatar image
Mads Drøschler answered ·

You can inject a reverse distance to camera width and control the actual width in the distance so it "looks" like something, but you will be injecting thicker lines proportionally to the objects distance to camera.

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Alan King avatar image
Alan King answered ·

Hello John,

What I think is going on is that arnold is using a technique for very thin edges and contours that is similar to min_pixel_width on curves shapes (you can read about the technique here). The aiToon effect has a hard-coded minimum width of 0.5 pixels, which means that anything below that width will be clamped to a half pixel width, but become proportionally less visible as the width decreases. This was added to the toon shader to avoid aliasing artifacts like the dotted or jagged edges that you can see in the tips of the curves here:

In any case, as the width of the edge becomes thinner, it is expected that it would have less of an impact on the pixel's color. What would you rather expect to happen instead?


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