ARTICLES: NPR categories – Part I: Pen-and-ink illustration

In our last article “Non-Photorealistic rendering (NPR)” we talked about NPR principles, motivations and categories.

Now, we will start a series of articles exploring each one of the NPR five categories. This article is about “Pen-and-ink illustration”.

Pen-and-ink

First of all, what are you talking about?

Ok, let’s start from the beginning. When we are talking about Pen-and-ink illustration we are talking about a render style which mimics the result created by traditional artists using Pen and ink techniques. For example:

pen_and_ink

 

I got it, but why should I consider Pen-and-ink illustration for my renders?

Winkenbach has published a complete paper on Pen-and-ink, you should read that, if you get excited about the subject.

Basically, two points: (1) it is ideal for outlines and (2) it reduces the necessity of complex expression tools and techniques – slightly different strokes can create several types of textures.

So, if you need to present something without losing audience’s attention in too many details, you should use this technique. In Winkenbach’s words: “Their simplicity provides an appealing crispness and directness.”

In another article, Vilanova says: “It is easier to copy, easier to reproduce in a book. It blends nicely with text, it has a linear quality since they use the same ink and paper. Its simplicity provides an appealing crispness and directness. There is also the possibility to give more emphasis in the important features.”

Do you agree? If so, let’s move forward to get some more information on it…

 

Fundamental principles

Pen-and-ink illustrations are based on three principles: Strokes, Tones/Textures and outline.

 Strokes: Stroke is the path created by the pen’s point when contacting the paper. It is the essential principle. Creating strokes can be tricky! Some highlights should be considered:

  • If stroke is too thin, you will have an appearance of a washed-out surface
  • If stroke is too rough, you can lose delicate details
  • Traditional artists need to pin and vary pen position when drawing a stroke. Keep it in mind
  • Variation of the stroke’s thickness will create a natural look.

Tones/Textures: Tone is the “amount of visible light reflected towards the observer from a point on a surface.” (WINKENBACH). In order to create the correct tone, consider these points:

  • Consider using lines evenly spaced and with almost the same weight.
  • In adjacent regions, try to keep same tone style.
  • Glass needs straight and crisp lines.
  • To mimic glare, remove details.
  • Old materials require sketchy look lines.
  • New materials require detailed lines.
  • Use impression to reduce the amount of textures in the entire drawing, focusing on specific parts of the surface.

Outline: Outline is not just the external boundary of a surface, but it is used to draw the essential parts of a surface, too. Pen-and-ink can create infinite combination of outline styles: varying thickness, angle, weight, etc… Some important tips provided by Winkenbach:

  • The quality of the outline stroke is important for conveying texture. For example, crisp straight lines are good for hard objects, while a greater variety of line quality is better for soft objects.
  • Thick outlines are used to suggest shadows,or to bring one objector part of an object forward in the scene. Thick line junctions are used to suggest darkness where objects overlap and to add “snappiness” to the illustration.
  • Outlines should become “haloed” and fade away where one object passes behind another object.
  • Outlines must be introduced where tones are omitted to convey shape.
  • Using “indication” for drawing outlines is just as important as for drawing tones.

Winkenbach presents in his article an entire algorithm concept to implement this technique. However, I encourage you to apply those principles in Blender Internal Render or in Blender Cycles. Do you think it is possible to produce something that mimics Pen-and-ink with the tools we have available? Try it out and show us.

Leo Pessoa Blendertoon!

 

References:

VILANOVA, Anna.  Non-Photorealistic Rendering. Available at <https://www.researchgate.net/profile/Amy_Gooch/publication/220695277_Non-photorealistic_rendering/links/0deec51b60866b7afd000000.pdf&gt; Accessed by 07-Aug-2017

WINKENBACH, Georges. SALESIN, David H. Computer-Generated Pen-and-Ink Illustration. Available at <https://maverick.inria.fr/Members/Cyril.Soler/DEA/NonPhotoRealisticRendering/Papers/p91-winkenbach.pdf >. Accessed by 26-Feb-2018

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