Section 17.2.4.1. Illustration

In print media, shaded colour images can present a number of difficulties. In addition to the issue of cost, colour shifting, reproducibility and loss of detail in the half-toning process may lead to less than the desired result. Simple line art is an effective way to bypass many of these complications. Since the advent of printing in the middle ages, artists and scientists have explored the problems of creating illustrations within the limitations of the printing process. Over time, artists have built a vocabulary of outlines, hatched shading and varied textures to simplify and clearly portray an object. While the creation of such illustrations was time consuming and required considerable artistic talent, they effectively portrayed the observational science of the day. The advent of computers and computer graphics removed any requirement for skilled hand draftsmanship in the production of molecular representations, but did not solve all of the problems of good illustration. As mentioned above, prior to the widespread use of interactive computer graphics, molecular structures were often published as outline drawings of ball-and-stick models using programs such as ORTEP or PLUTO (Motherwell & Clegg, 1978). More recently, programs such as MOLSCRIPT (Kraulis, 1991) have re-established the popularity of line-art illustration in the molecular realm. A good ORTEP drawing usually took a great deal of preparation time in order to get the best representation and viewpoint to display the structure effectively. As the visual repertoire of molecular structure has expanded to a wide variety of shapes including ribbons, tubes and solvent-based surfaces, the challenge of automating the general illustration process has grown. A number of techniques have been developed in the computer-graphics community to generate images in the style of technical or artistic illustrations (Fig. 17.2.4.1). These approaches use lighting, depth information and geometry to produce black-and-white drawings with shapes defined by silhouette lines and cross-hatched shading, and details shown by a variety of textures. MOLSCRIPT has used some of these techniques for ribbon and ball-and-stick renderings. More general applications of these approaches to molecular illustration have also been described by Goodsell & Olson (1992).

Figure 17.2.4.1| top | pdf | Line-art molecular illustration. The figure on the left depicts the α-carbon backbone and molecular surface of the α subunit of haemoglobin (PDB code: 2hhb). Outlines define the shapes of the surfaces and tubes, and contour lines enhance their three-dimensionality. Hatch lines, normally used for shadows, are used here to darken the inside of the molecular surface. The figure on the right shows the interior of a human red blood cell (300 Å3), showing all molecules except water. The picture is drawn with outlines defining each molecule. Shadows and depth cuing are used to enhance the three-dimensional character of the image. Contour lines are not used. From Goodsell & Olson (1992).

A significant advantage of digital black-and-white illustration is the efficiency of representation. Since each picture element takes only a single bit of information (black or white), and since there are typically large areas that are of constant value, these images can be compressed, stored, transmitted and printed very efficiently. Thus, with the advent of electronic web publication, such illustrations represent an attractive alternative to full colour. These same characteristics represent significant advantages for the digital transmission and use of animated sequences as well.