Paul De Ley & Wim Bert - February 11th 2003

Video Capture and Editing: Discussion

This section is an expanded web version of the following paper:
De Ley, P., and W. Bert. Submitted. Video Capture and Editing as a tool for the storage, distribution and illustration of morphological characters of nematodes. Journal of Nematology 34: 296-302.

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Summary
Introduction
Material and Methods
Results
Applications
Conclusions
References
Glossary
 

Basic strengths and weaknesses of VCE

Despite the limited resolution and some technical flaws, the tested configurations were easy to use and yielded finished clips that were of acceptable image quality and file size. Compared to film-based still photography, VCE was in all respects faster, more versatile and more forgiving. Firstly, no film development was required, so the captured clip could be checked instantaneously for flaws, and retaken if necessary. Secondly, while it was very easy to obtain still images from a clip, it was rather difficult and time-consuming to photograph a continuous series of focusing levels ÷ all the more so because it was not possible to check the result on the spot. Thirdly, the video cameras had a much broader tolerance for low light conditions and/or slight movements of the specimen. Although both situations did affect image quality, fuzziness or graininess of the image became a problem much less quickly than with still photography on film. Thus, it was quite difficult to obtain a good series of still photographs of a freshly dissected gonad, because the temporary mount still allowed for some movement of the specimen due to muscular contractions and plasmolysis. By comparison, the VCE system immediately yielded a good series of images of the same specimen (Fig. 4).

Digital still photography has many advantages over its film-based counterpart, in that it matches or even exceeds the level of resolution, while bypassing the development step. Digital still cameras are also rapidly becoming more affordable and more compatible with microcomputers, and more advanced models are increasingly combining still photography with video functions (albeit at reduced resolution and frame rate).

Compared to digital stills, analog video capture is limited in terms of resolution attainable with existing cameras, but on the other hand it provides a distinct advantage with respect to multifocal recording. Not only does this allow capture of a series of focal planes in one quick operation, but it also results in files that retain this focal series as a single object, without necessarily using more disk space than a single high-resolution digital still image. VCE and digital still photography are therefore complementary rather than competing approaches: the latter is to be preferred when resolution is critical, while the former is more appropriate for reproducing the focusing action of a microscope, thereby translating three-dimensional topologies into a series of two-dimensional optical sections.

Undoubtedly, the distinction between digital stills and analog video clips will disappear quickly if technological developments continue along current lines. Digital video cameras are now becoming available, as well as video capture cards that accept digital input (such as the tested DV500 capture card). Within the next few years, we can therefore expect prices to drop and equipment to develop sufficiently rapidly to allow the use of completely digital VCE configurations. In terms of computer hardware, the process will become more and more efficient with the continued development of larger computer memory chips, larger hard disks, faster processors, faster internet connections, more efficient codecs and more powerful video editors.

Another relevant technological development, is image capture and digital enhancement resulting in still images with Extended Depth of Field (EDF, see Tucker et al., 1999), i.e. a much greater range of focus than allowed for by standard optics. This approach holds great promise for the production of single still images containing contrast-rich and focused structures occurring at different levels, but as far as known to us, inexpensive systems are not yet available on the market, and we are not aware of any examples where EDF has already been applied to nematodes or other transparent invertebrates. One problem could be that heavily sclerotized structures like buccal capsules and stylets will blot out over- or underlying structures. Also, a VCE clip preserves structural clues to angle of view and position of a specimen, whereas an EDF image combines information from multiple standard focal planes into a single omnifocal plane. In the case of nematodes, this could mean that a clear single EDF image could be obtained of a nematode lip region in sublateral view, with both amphids in focus, but without any remaining clue allowing distinction between a dorso-sublateral and a ventro-lateral angle of view. Practical application to nematode specimens will show whether these concerns are important or not, and to what extent EDF can be combined with VCE and other types of microscopy imaging.

A last useful comparison that needs to be be made, concerns the performance and uses of VCE as compared to Confocal Laser Scanning Microscopy (CLSM, see e.g. Czymmek et al., 1994; Donaldson & Lausberg, 1998). The latter approach has many advantages, in that it e.g. significantly enhances resolution, as well as relying on software capable of measuring distances and constructing three-dimensional models. We have not yet tested our configurations in the context of automated biometric analyses, as the emphasis of the approach outlined here is on the recording and representation of morphology itself, rather than on subsequent biomathematical applications. Nevertheless, it is presumably possible to expand our hardware and software to incorporate three-dimensional imaging functions (see e.g. Omasa & Kouda, 1998).

As a trade-off for the benefits, it should also be noted that CLSM systems are significantly more expensive, and alter the properties of the microscope itself in ways that make its use rather different from routine practice in nematology, so that for most nematologists it is not a realistic option to convert their research microscope into a CLSM system. By comparison, adding the various components of a VCE system can be done at a much lower cost and with greater ease, without modifying the basic properties of the microscope itself.
 


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