Atelier Bonryu(E)
zone plate photography
Laboratory: Zone Plate Photography
Taking Zone Plate Photographs
- HDR Zone Plate Photograph -
Well-finished sharp zone plate photograph: As described previously an image of an object and its halo, and also a fog due to an ambient light are all projected in a zone plate photograph. Because of existence of the background light a zone plate photograph becomes blurred and a misunderstanding that a zone plate photograph is always extremely soft arises from this fact. We described a method to remove the fog covering a zone plate photograph by adjusting the level of a photograph taken by a digital camera in order to make use of the high resolving power hidden under the background light and make it sharp. By this process the zone plate photograph becomes sharp without loosing the attractive feature of a zone plate, i.e., a halo. However, this procedure reduces an effective dynamic range considerably and the photograph becomes rather dark.
HDR (High Dynamic Range) photograph: Human eyes can perceive lights over a very wide range of brightness. On the other hand, in the case of a camera the dynamic range is limited within a narrower range because of the performances of a sensor, a memory, an electric circuit, a monitor and so on. For this reason the photogenic object itself and the image of the object taken by a camera, sometimes, give considerably different impressions each other. This problem is solved in principle by making a camera with higher dynamic range and look at the taken photograph by using a monitor with a higher dynamic range. But to solve this problem in this way is very difficult or impossible to realize. By the way, HDRI (high dynamic range imaging) technique becomes popular recently, which is a method to take several shots of the same object by changing exposures (bracketing) and make a high dynamic range photograph by combining these bracketed photographs. Of course, as the dynamic range of the resulting photograph is higher than a usual dynamic range of a monitor, the range of levels of the photograph are compressed so that they are mapped within the usual dynamic range of the monitor (tone mapping). For this purpose there are a lot of softwares are available, such as Photomatix Pro, CinePaint, HDRtist, qtpfsgui, and so on.
Pseudo-HDR: Though an HDR photograph is created by combining several photographs with different exposures, there is a simplified process to create a pseudo-HDR photograph. In this simplified process several photographs duplicated from an original photograph are combined into one “HDR” photograph by interpreting the exposure of each duplicated photograph different (Photomatix Pro, etc.) or only a single shot is used as an “HDR” photograph though it is a LDR (low dynamic range) photograph (HDRtist, etc.). Basically, a pseudo-HDR photograph is made only by mapping the brightness levels of the above single photograph so that local contrasts in a highlight and in a shadow are enhanced at the cost of reducing the global contrast. In this case, of course, the dynamic range is not really expanded but detailed structures in the shadow or the highlight which are not visible in the original picture become clear in the processed one.
HDR zone plate photograph: The following left zone plate photographs are those of which we adjusted levels as described in the previous page but detailed structure of shadows and highlights of these are not well distinguishable. We applied the pseudo-HDR process to them and the right photographs are obtained. As the bracketing is not necessary for this method we used the already existing photographs for this process. Though the optimization of the process has not been carried out we got rather satisfactory photographs where structures in shadows and highlights are considerably clearly expressed.
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