Domingo Martín

Observer dependent deformations in illustration

Illustration has some visual characteristics that are very interesting yet also very difficult to obtain with a computer. Whilst the simulation of the tools used for painting and drawing is successful enough, expressive capabilities have not been developed to the same extent. The deformations of objects and space is a major element in the expressiveness of illustration. The use of Hierarchical Extended Non-Linear Transformations is presented as a powerful tool for obtaining such kind of expressivity.

Example-based stippling using a scale-dependent grayscale process

We present an example-based approach to synthesizing stipple illustrations for static 2D images that produces scale-dependent results appropriate for an intended spatial output size and resolution. We show how treating stippling as a grayscale process allows us to both produce on-screen output and to achieve stipple merging at medium tonal ranges. At the same time we can also produce images with high spatial and low color resolution for print reproduction. In addition, we discuss how to incorporate high-level illustration considerations into the stippling process based on discussions with and observations of a stipple artist. The implementation of the technique is based on a fast method for distributing dots using halftoning and can be used to create stipple images interactively.

Scale-dependent and example-based grayscale stippling

We present an example-based approach to synthesizing stipple illustrations for static 2D images that produces scale-dependent results appropriate for an intended spatial output size and resolution. We show how treating stippling as a grayscale process allows us to both produce on-screen output and to achieve stipple merging at medium tonal ranges. At the same time we can also produce images with high spatial and low color resolution for print reproduction. In addition, we discuss how to incorporate high-level illustration considerations into the stippling process based on discussions with and observations of a stipple artist. Also, certain features such as edges can be extracted and used to control the placement of dots to improve the result. The implementation of the technique is based on a fast method for distributing dots using halftoning and can be used to create stipple images interactively. We describe both a GPU implementation of the basic algorithm that creates stipple images in real-time for large images and an extended CPU method that allows a finer control of the output at interactive rates.

Scale-Dependent and Example-Based Stippling

We present an example-based approach to synthesizing stipple illustrations for static 2D images that produces scale-dependent results appropriate for an intended spatial output size and resolution. We show how treating stippling as a grayscale process allows us to both produce on-screen output and to achieve stipple merging at medium tonal ranges. At the same time we can also produce images with high spatial and low color resolution for print reproduction. In addition, we discuss how to incorporate high-level illustration considerations into the stippling process based on discussions with and observations of a stipple artist. Also, certain features such as edges can be extracted and used to control the placement of dots to improve the result. The implementation of the technique is based on a fast method for distributing dots using halftoning and can be used to create stipple images interactively. We describe both a GPU implementation of the basic algorithm that creates stipple images in real-time for large images and an extended CPU method that allows a finer control of the output at interactive rates.

Extended papers from NPAR 2010: Scale-dependent and example-based grayscale stippling

We present an example-based approach to synthesizing stipple illustrations for static 2D images that produces scale-dependent results appropriate for an intended spatial output size and resolution. We show how treating stippling as a grayscale process allows us to both produce on-screen output and to achieve stipple merging at medium tonal ranges. At the same time we can also produce images with high spatial and low color resolution for print reproduction. In addition, we discuss how to incorporate high-level illustration considerations into the stippling process based on discussions with and observations of a stipple artist. Also, certain features such as edges can be extracted and used to control the placement of dots to improve the result. The implementation of the technique is based on a fast method for distributing dots using halftoning and can be used to create stipple images interactively. We describe both a GPU implementation of the basic algorithm that creates stipple images in real-time for large images and an extended CPU method that allows a finer control of the output at interactive rates.

Rendering Silhouettes with Virtual Lights

We present a new method for obtaining non‐photorealistic images. These images have two main visual components: silhouettes and non‐realistic colouring. Silhouettes are lines that define the form of an object. They are used in classical animation and illustration as the main expressive components. In these applications, if it is necessary, colouring can be added once the drawings are made. For instance, generally, in illustration, colouring is flat and does not transmit volume information whilst silhouettes do it in an economical way. The proposed method is based on the Virtual Lights model, which allows us to use external components, the virtual lights, to define silhouettes. In this way, the designer is free to control where, when and how the silhouettes must appear. The method can be used with B‐rep geometric models.

Alhambra: a system for producing 2D animation

There is a great interest in producing computer animation that looks like 2D classic animation. The flat shading, silhouettes and inside contour lines are all visual characteristics that, joined to flexible expressiveness, constitute the basic elements of 2D animation. We have developed methods for obtaining the silhouettes and interior curves from polygonal models. Virtual lights is a new method for modeling the visualization of inside curves. The need for flexibility of the model is achieved by the use of hierarchical nonlinear transformations.

Flattening 3D objects using silhouettes

An important research area in non‐photorealistic rendering is the obtention of silhouettes. There are many methods to do this using 3D models and raster structures, but these are limited in their ability to create stylised silhouettes while maintaining complete flexibility. These limitations do not exist in illustration, as each element is plane and the interaction between them can be eliminated by locating each one in a different layer. This is the approach presented in this paper: a 3D model is flattened into plane elements ordered in space, which allows the silhouettes to be drawn with total flexibility.

A stochastic approach to simulate artists behaviour for automatic felt-tipped stippling

Nowadays, non-photorealistic rendering is an area in computer graphics that tries to simulate what artists do and the tools they use. Stippling illustrations with felt-tipped colour pen is not a commonly used technique by artists due to its complexity. In this paper we present a new method to simulate stippling illustrations with felt-tipped colour pen from a photograph or an image. This method infers a probability function with an expert system from some rules given by the artist and then simulates the behaviour of the artist when placing the dots on the illustration by means of a stochastic algorithm.

Silhouette detection in volumetric models based on a non-photorealistic illumination system

A basic step for many illustration techniques is the extraction of silhouettes and shape lines, in order to enhance the object shape visible to the observer. This paper presents a new and very fast method to obtain silhouettes and shape lines in non-photorealistic volume rendering processes, based on ray-tracing using an octree for optimization. This method consists of extracting contours based on image buffers acquired during the calculation of intersections in ray-tracing process with the model. These image buffers are then combined to produce silhouettes and shape lines from the model. A substantial improvement with regard to other silhouette extraction methods in volumes is that this method does not require the user to define thresholds; furthermore, it is not based on the z-buffer and thus does not depend on the precision of the latter. Neither the camera position nor the direction affect the performance of the algorithm. Finally, the algorithm detects silhouettes for objects which are inside other objects that are distinguished only by their hue.