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The Aided Eye - What is Different About Scientific Images?, A Challenging Variety

photography imaging radiation information

DAVID MALIN
Anglo-Australian Observatory, RMIT University

Scientific photography may be described as many things by different people and consequently this section has tried to tease out the many threads that make up its rich tapestry.

Scientific photography’s beginnings can be traced to the beginning of science itself.

The invention of the telescope and the microscope occurred at about the same time, 400 years ago. Together, these technologies extended human vision and human imagination, laying the foundation for modern science. However, no mere description could communicate the unexpected worlds that Galileo and Leeuwenhoek discovered. It was their drawings of the mountains of the moon and astonishing variety of life in a drop of water that captured the imagination of the literate few and spread the idea that there was more to the universe than was visible to the unaided eye. These discoveries changed man’s perceptions of life, the universe, and everything contained in it.

Photography made its debut 240 years later, extending human vision much further, and in many unexpected directions. As it matured, photography made many new branches of science and technology possible. Images of science now grace the pages of popular magazines and are seen on television and the Internet, opening the eyes of billions to the excitement of discovery, learning, and the hidden beauty of the world.

What is Different About Scientific Images?

Scientific photography might be considered to be more a state of mind, than a single technology. It is the motivation behind the picture that differentiates an image of science from an everyday photograph. Two pictures might look identical, but the scientific photograph will carry with it some information, perhaps a record of where, when, how, or why it was made and maybe something about what it shows. Better still, it will have a dimension, a calibration, a context, and a description. If it does not carry at least some of this detail, it is just another picture. The inclusion of data implies that the image was deliberately made to convey information, rather than an impression. A scientific picture will only spawn a thousand words if it is seeded with a few of its own.

Only one of the senses, vision, is able to absorb the essence of an image. Images can be made of places and things that man can never hope to see directly, and at wavelengths that the human vision system cannot detect with our senses. Most photographic images are made with electromagnetic (EM) radiation, the form of radiant energy that includes light. The spectrum of EM is enormous, ranging from highly energetic gamma rays with wavelengths of atomic dimensions to radio waves hundreds of kilometers from crest to crest (10 -14 to 10 6 m). Visible radiation is located in between X-rays and radio waves, with the rainbow hues of nature occupying a very tiny part (4 × 10 -7 to 7 × 10 -7 m) of the spectrum between the ultraviolet and infrared.

As might be expected, much of this range is beyond normal imaging detectors like photographic film or the charge-coupled device (CCD). No matter how it is detected, the radiation carries with it information about the origins of the radiation itself and of its interactions with matter on the way to detection. A major role of scientific imaging is to transform information generated by almost any wavelength—interacting with an object of any size, at any distance, and in all four dimen-sions—into something two-dimensional that we can see. As a consequence, a scientific photograph may be presented to the eye as a conventional-looking picture, but it also may contain information that has been captured by a detector quite unlike the eye or film, manipulated in ways that the brain cannot match and finally emerging with colors and contrasts that never existed in reality.

Of course, this is the broadest view of all possibilities, and many images of science are made with familiar equipment and materials. However, irrespective of its origins, no image can ever be totally objective, not even a scientific image made with objectivity in mind. Someone has to decide what manipulations and adjustments are necessary to create the final output, when to capture the image, and how to present the end result. A practical knowledge of how the information is influenced by the disparate sequences of collection, detection, data handling, and transmission are essential skills for a scientific photographer. The creator of the image has to understand each of these steps to convey and interpret the information it contains. Scientific photography is thus not simply everyday picture-making of a scientific subject, although it may be in some daily application.

The terms detector, output, information, and transmission are used here quite deliberately because a scientific image is not just a photographic representation, but rather it is data, and is thus subject to the same concepts of attenuation, noise, and distortion as any other data-set. That does not mean that pictures made for a scientific purpose need to be so burdened with information that they are visually uninteresting. Indeed they are much more effective if they are good to look at, but aesthetics must never compromise the underlying science.

A Challenging Variety

Scientific photography embraces an enormous range of disciplines, and a wide variety of skills that, at first glance, do not seem to have much connection with imaging. However, the science part of scientific photography allows us to think of it in a way that is not normal in the more traditional branches of image making. We can thus divide the subject into several overlapping domains.

These domains often deal with the interaction of EM radiation with the object of interest as an entity in its own right, such as the study of a virus, a butterfly, or a planet. This interaction might involve the absorption, reflection, polarization, diffraction, or scattering of the incident energy and the resulting image as formed by a microscope, camera, or telescope, or collected by a satellite and returned to earth as a radio transmission. Many such images are necessarily made in natural light but others demand special lighting skills, optics, or access to aircraft or even rocketry.

In some cases the objects of interest emit their own radiation naturally (a galaxy or a firefly) or under stimulation from other radiation (a gaseous nebula or a fluorescent microbe). With self-luminous specimens, the distribution, nature, and intensity of the emitted radiation is of interest; often this radiation is weak. Consequently, exposure times are long, which presents capture challenges as well.

Sometimes (as in astronomy) there is no control over the lighting and placement of the objects of interest and photography requires one to make the best of what nature offers. Elsewhere, as in optical and electron microscopy, the preparation of the specimen is the essence of the technique, and recording it is more of a formality. Often the researcher, preparer, and photographer are the same person. Another role of scientific imaging is to reveal places that are too remote to be seen directly or that are otherwise inaccessible, such as the deepest ocean, the brain, or the far side of the moon. Here the photographer may be a remotely controlled submarine, a radiographer, an astronaut, or a satellite. While the earth’s surface is where we live, the photography of it from space has provided new insights into the nature of processes on and under the surface, especially meteorology, oceanography, geology, and even demography.

Photography also possesses a unique ability to compress, reverse, and expand time, so we must consider the temporal domain of imaging as well. This is mainly evident in time-lapse and high-speed photography. Also, the travel time of light is finite, so in astronomy distant things are seen as they were long ago, and the most distant things are seen as they were near the beginning of time itself. Here, photography, or its digital equivalent, is a component of a time machine.

In addition to direct imaging with various kinds of optics, pictures can be built from data that exist in another physical domain, such as Fourier space, as a hologram, or as a stream of data as in scanning electron microscope image. Some of these activities are so specialized that they are not mentioned in this section. But specialized methods involving unexpected wavelengths and exotic imaging techniques can quickly become part of the mainstream, such as ultrasonic imaging of the unborn and magnetic resonance imaging of living tissue. This last imaging technique involves radio waves, strong magnetic fields, and Fourier image reconstruction techniques over an extended time. The image recording itself is almost automatic, but the underlying physics of the imaging process is fascinating.

Where there is an interesting application such as this we will mention it. However, if we have omitted your specialty we apologize. Once upon a time it was possible for one person to know something about most aspects of scientific photography. This is no longer true.

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