Criteria for High Dynamic Range (HDR) Imaging of Photomicrographs (2009)

2009:159:Brown, Zipperer

Microscope, Vol 57:2, p.59-62

Abstract:

Not so long ago, film cameras were used to collect images of microscopic and macroscopic items for documentation. The usual procedure was to load the camera with film, set the camera on a tripod, copy stand or microscope to begin the photo documentation process. Exposures were taken at the “best” exposure setting using a light meter with a gray card or a suitable region in the microscopic field of view. Exposures above and below this “best” setting were also collected in case there were features of interest that were not well exposed at the “best” exposure setting.

By using this exposure bracketing technique, images with suitable contrast and detail were routinely collected. With the tripod and copy stand, lighting was controlled by flash or by flood lights that were adjusted to provide the even illumination for the item of interest. Shooting items outdoors on a cloudy day was also an excellent alternative, especially when using film balanced for daylight. Even illumination was especially important when using the microscope.

Until camera sensors can be improved and manufactured to capture a greater dynamic range than is presently available, HDR images will provide a means to recover some of the contrast that is discarded by today’s digital cameras. A quick internet search on HDR will return a range of articles, books and software that can be explored to educate and excite even the most accomplished digital photomicrographers! All you need is the software (many versions can be used on a trial basis at no cost), a reflected light stereomicroscope using brightfield or darkfield illumination, and a rigid mounting so each image exposure is in the exact position as the last.



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