Plant Identification
Page 33
The Chicago Field Museum used to make and sell bound ‘micro-herbaria’, or sets of photocopies of herbarium specimens reduced to 66 per cent (see http://fm2.field museum.org/plantguides/microherbaria.asp) as field reference material. More recently, they have started to use scanners to produce colour versions of the same. Either way, this clearly represents a cheap and convenient way to make a basic field guide; they even sell their micro-herbaria on the internet in volumes at ten specimens per US$1.
See Table 8.1 for a summary of the pros and cons of photocopies or scans. One of the most frustrating problems is that the leaves to be scanned have to be flat and are limited in size to the glass plate of the copier or scanner, although they can be reduced or enlarged from this size.
Limbe field trials of photocopied plants
Photocopies of herbarium specimens were compared in the Limbe field trials (see Case study 8.1) and performed similarly to most other formats in the accuracy trials, although
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respondents did not rate them very highly for other attributes. The addition of the simple textual key made a slight but significant improvement to their accuracy, possibly because although some details are visible from a photocopy, others (which may be implicit in a key) are not.
Photocopies can provide a cheap, relatively light replacement for real leaves. There is little need to laminate the pages since photocopies (unlike cheaper inkjet inks) are fairly water resistant and new copies can be made easily anyway. However, it is not much harder to photograph leaves, and the potential benefits of ease of arrangement of digitized images in a document may well outweigh the speed of photocopying.
Photocopies suffer many of the same limitations as real plants – for instance, only small to medium-sized leaves are suitable; other plant parts are not.
In many cases, people reproduce guides by photocopying; so if you want to encourage this, it is worth checking how well your illustrations of another type come out when photocopied.
X-rays
X-ray photography, or radiography, of leaves produces high-quality black-and-white images of venation patterns that surpass line drawings and conventional photography for accuracy and detail. They are cheap and quick to produce, but require specialist equipment that may only be available in hospitals or industrial laboratories. There are few published examples, notably Christophel and Hyland (1993) and Hyland et al (1998). The example in Figure 8.1 shows a portion of a leaf of Cola. It was taken with an X-ray machine used to test seed viability. The radiograph was scanned using a desktop scanner equipped with a transparency hood.
Results of field trials of X-rays
X-rays of leaf specimens, as an additional detail with line drawings, were compared for usability, accuracy and saleability on the field trials in Cameroon (see Case study 8.1). In a way, this became a test of the usability of leaf venation as a character for identification, and the X-rays did not improve the accuracy of identification of line drawings in the trials, nor were they particularly liked by the respondents. While veins are, in some cases, like fingerprints of the plant and provide subtle identification hints, they are hard to match correctly; as highlighted by our respondents, other characters such as hairs and colour are not only often equally or more important, but also more easily recognized in the field and not visible on X-ray images.
If you have the equipment, X-ray images represent an easy way of providing accurate images of venation pattern and leaf shape. However, the venation that is visible in the field can be made more simply with a digital camera. There are very few circumstances when it is worth considering X-ray pictures in tropical plant field guides. In the unlikely event that your only access to illustrative tools is a friend in a local seed-testing centre, then experimentation may be worthwhile. If your users have technical jobs that requires them to identify fragments of leaves – for instance, those used in nesting material – or poisons eaten by livestock, then a library of X-ray images of candidate species can be recommended. Finally, X-ray pictures can be very beautiful abstractions of leaves, and for this reason they might find a place in a more artistic or aesthetic type of field guide.
Illustration 199
Film photography and photographs, in general
Increasing numbers of colour photographic guides are attractive, affordable and useful, and can be produced on modest budgets (see, for example, Gardner et al, 2000; Hawthorne et al, 2005). There are many books and courses, and much experience in photography, so we will not cover general aspects here. Many of the principles of basic camera technique that are especially applicable to plant photography apply whether you are using film or a digital camera (see Box 8.5).
Until recently, in order to obtain good-quality photographs, the only viable solution was to use slide film (transparencies), which is expensive and deteriorates after some time in the tropics. While it may still be the best way to take the highest-quality photographs – for instance, for posters and art exhibitions – the days of the superiority of slide film for small photographs in reasonably priced books is over. Nowadays, it is often impossible to see the differences between the best digital photographs from those made in traditional ways. There are some remarkable photographic field guides where the photographer used slide film (see Box 2.1, page 17). However, these often required massive and generally unrealistic financial subsidies. Today, digital photography stands to increase the viability of similar initiatives (see Box 8.6).
Slides can be used as the basis for public talks with less expensive equipment than required to project computer images. Many (although a rapidly declining number) institutions may have slide projectors, but no equipment for projecting digital images. The main reasons for using slides will soon be inertia to change and a heritage of old slide libraries. Slides might be returned from the developers with disappointing results, by which time the field trip or opportunity for taking pictures is long past: at best, one can never be sure how accurate subtle colours have been rendered, and these subtleties are important for bark slash, for instance. Digital cameras of adequate quality are declining rapidly in price and the recurrent costs (mainly batteries, hopefully rechargeable ones) are lower than film. In most cases, scanned images of your slides are not likely to be as high quality (colour accuracy and resolution) as the originals, especially if they have not been treated with absolute care. We therefore strongly advise field guide makers to use a digital camera.
Many readers may have access to an archive of historical images. The best advice we can give for these is that you scan them into digital format early on in your field guide project. Early digitization of slide libraries will considerably facilitate the demonstration and discussion of plans for field guides and, in conjunction with a good image database (see Box 8.8), will help to highlight priorities for new imagery.
The main problem for printing photographs – whether for final publication or, more acutely, for draft versions (see Chapter 9) – is the expense of high-quality colour printing, relative to black and white. At least now it is cheaper and more practical than it was, with an A4 photo sheet costing around US$1 (see Box 8.7).
Photo guide trials
Photographic guide materials of various types were evaluated in Ghana, Grenada and Cameroon (see Case study 8.1). In all cases, photographs were at least as accurate as any other format, and users rated the format very highly, whether photographs of fresh leaves in Cameroon, photographs of whole tree characters in Ghana or for general photographs of plants in Grenada. They are also one of the fastest formats to create and can be made without employing an artist. However, the medium is up to four times as
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BOX 8.5 SOME BRIEF NOTES ON HOW TO CONTROL YOUR CAMERA Even if you are inclined to set your camera to ‘Auto exposure, auto focus’, there will be times when you will only get good results by manual control. The following key points should be known to all photographers to get the best out of your camera:
•
Read a guide to photography to help you understand exposure, depth of focus and so on.
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Make sure that the blur due to motion in the subject or vibration of the machine is minimized by keeping a high shutter speed or using a tripod. Shutter speeds below 1/125 may well lead to blurring, except with a tripod or flash.
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You will benefit from a tripod if you are taking many pictures of tree bases in the forest.
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Use depth of focus (DOF) to control whether details at a broad range of distances from the lens are in focus (high DOF), or whether a sharper picture is taken of a specific point or plane (low DOF). High DOF is obtained by a narrow aperture (small gap to let light in), which obliges the shutter speed to be slower.
•
On a digital camera, at least, slight underexposure is preferable to slight overexposure.
It is usually possible to enhance the former to reveal details in the shadows, whereas
‘burnt-out pictures’ will often have nothing retrievable from the highlights.
•
In the tropics, use an ultraviolet (UV) filter if you taking pictures in the open. Ultraviolet light causes slight fogging or overexposure and loss of contrast. You can also compensate for this by setting your camera’s automatic exposure over-ride to reduce exposure by one ‘F. Stop’. This may be indicated by ‘–1’.
•
Use flash sparingly, but try and find natural light patches in the forest. If you do use a flash, beware that the camera-based flash will make bark textures, mild fluting, etc., look more flat and featureless due to loss of shadows.
•
You can compensate even on some digital cameras for low light by increasing the ‘film speed (ASA or ‘DIN setting’). This will inevitably lead to a grainier or (on digital) more speckled or ‘noisier’ picture; but that may be preferable to using the flash.
•
Try to ensure a neutral background – for example, black is often best. Take a non-shiny black cloth to the forest with you and, where the ground is rarely flat, a small blackboard as well.
•
Make sure that you buy a camera with a close macro lens. Of the cheaper models, the Nikon Coolpix 4500 and similar models have generally been the best for this.
Furthermore, invest in a small LED ring light (not a ring flash): capturing rainforest details without one can be very tiresome, and the internal flash does not work well up close.
•
Beware of subtle yellow and other pale shades in bark and flowers. They frequently become overexposed to glaring white if you set your exposure to automatic, especially if the flash is deployed.
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Study other field guides to work out what subjects, views and composition rules work best.
expensive to print as monochrome images. Respondents were unwilling to pay four times as much for published photographic field guides, even though they prefered them, and line drawings were often just as accurate for appropriate subjects.
Illustration 201
BOX 8.6 PHOTOGRAPHY AND THE FORESTRY RESEARCH
PROGRAMME PHOTO GUIDES
During the early part of the Forestry Research Programme (FRP) Field Guide Project (see Case study 8.1), we started using existing photographic equipment to develop photo libraries for guides in these countries. These images were scanned onto Kodak Photo-CDs, and have subsequently been included into our digital photo library. Soon after, the Nikon Coolpix 990/5 digital camera came on the market, so after some experimentation, and considering the inconvenience of slide film, we decided to use this as the main means of photography. It made the capture of tropical plant imagery several times easier, and some types of image that were infamously difficult to take with slide film (for example, yellow bark slashes with a flash) were reasonably easy through trial and error, changing the flash intensity or shutter controls.
Special or enhanced imagery
One of the options opened up by digital handling of imagery is that it is possible to enhance the images – for example, to make a more usable contrast or more healthy green colour – or to modify your photographs more substantially to more diagram-like images. In Figure 8.5 we show two of many possible ways in which venation, outlines and other key features of your leaf can be prepared for monochrome printing with a little practice in a cheap digital editing package. Remember when manipulating images like this to take and maintain copies of the original photographs in colour.
BOX 8.7 EQUIPMENT FOR A DIGITAL PHOTO GUIDE
The resources needed to produce a guide are modest, compared to standard film photography:
•
a good digital camera with several 256 megabyte (MB) or larger memory chips and at least 5 megapixel capability;
•
rechargeable batteries for as many days as your field trips require, or camps or bases with electricity;
•
a laptop computer (or stand-alone hard drive) with appropriate software (see Box 8.8) and a memory chip reader;
•
a robust external hard disk (at least for back-up) capable of holding about 1 to 2MB
times the number of photographs to be captured (before perhaps downloading to a desktop computer) – 40 gigabyte (GB) portable hard drives recommended;
•
a black matt cloth, large enough to back the largest compound leaf you will need to show;
•
an external flash for the camera is often useful, as is a tripod, for taking tree bole pictures in the forest;
•
specimen collection and normal field work equipment.
BRAHMS (http://herbaria.plants.ox.ac.uk/bol/home/) and Thumbs Plus (www.cerious.com) software can be used to help you organize and rename your photos and link them to relevant specimen information.
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(a) Original photo
(b) Sharpened (image,
(c) De-saturated (image,
filter); add contrast
adjust colours)
(image, adjust colours)
(d) Edge detection (filter,
(e) Sharpened and
(f) Anti-aliased (image
edge detection, ‘Man-
smoothed, then colours
filter-edge process)
Hildreth, crossed’)
inverted
(g) Contrast increased
(h) Trace by outline
(i) Detail of (h)
(image, adjust colours)
(Corel-Trace)
Note: A Diospyros mannii leaf photo was obtained by holding the specimen up to the light and photographing it with a Nikon Coolpix macro lens, showing scalariform venation. Various digital manipulations using basic view/edit options in Thumbs Plus are shown. Figures 8.5 (a)–(g) above refer to Thumbs Plus menu options (www.cerious.com). Similar functions are available in all image-editing packages. Figure 8.5 (h) is performed in the Corel-Trace package, allowing the image to be enlarged indefinitely without introducing ‘aliasing’ (stepped diagonals). See also Figure 6.2, page 135.
Source: William Hawthorne
Figure 8.5 Making an image that can substitute for a line drawing from a digital photograph
Illustration 203
Botanical illustration
Drawings
Drawings have traditionally been the most important medium for botanical illustration, and for this reason many botanists are familiar and comfortable with the use of them in field guides. Most botanical works include some of them. There are still circumstances when drawings are to be recommended in field guides even if they are being reduced in importance by advances in printing and photography.
One of the main problems is the availability and cost of a specialist artist. One of us (Rosemary Wise) has much experience of training complete amateurs to create drawings, and perfectly usable drawings can be produced by more than half of the global population with a few weeks of practice and a few days’ trai
ning, so why not think about trying yourself? Some basic pointers to creating your own botanical artwork are included on our website (http://herbaria.plants.ox.ac.uk/VFH).
Costs and practicality
When considering the costs of drawings, think about the convenience of drawing from herbarium specimens. Most of your plants will likely be found together, hopefully largely correctly named, in a dried and pressed state in a herbarium. This also applies if you want to take photographs or photocopy the same specimens.
In contrast, to make most use of your camera for a field guide, you should be out in the field photographing fresh plants and many more parts than seen in the herbarium.
Travel costs vary – perhaps you are lucky and they are insignificant because your forest is next door. But in some cases, for large-ranging field guides covering many rare plants, illustrations based on herbarium specimens may be your only option for financial reasons. For a large print run of a cheaper monochrome guide, it will also be worth investing in line drawings.
Results of trials with drawings
We compared drawings with other media in our FRP tests in Grenada and Cameroon (see Case study 8.1). We also have experience of the pros and cons of drawings related to Ghanaian trees, as we have witnessed many years’ use of Field Guide to the Forest Trees of Ghana, with all circa 700 species drawn (Hawthorne, 1990), and the more recent The Woody Plants of Western African Forests: A Guide to the Forest Trees, Shrubs and Lianes from Senegal to Ghana, with 2600 drawings (Hawthorne and Jongkind, 2006; see Case study 8.2). In general, non-technical audiences do not rate drawings very highly for beauty or usability; indeed, in some circumstances, they produce slightly less accurate answers with them. In most cases, though, the distaste is not matched by a significant loss of accuracy. These issues do not, in general, apply to technical users, however, who are more likely to appreciate the simplicity, efficiency or parsimony inher-ent in a good drawing, and understand and use the artistic conventions that have evolved over centuries of botanical illustration.