Cameras are not perfect: two defects are:
A recent paper by Tom Mertens, Jan Kautz and Frank Van Reeth ``Exposure Fusion'' (see the link under enfuse below) describes a new method which solves both problems. In brief, the method selects ``good'' pixels from each image according to three factors:
The 6 bracketed images of Figure 1 where taken with a Canon EOS 5D with 15mm Fisheye lens at f16 and shutter speeds of 1/4000, 1/1000, 1/250, 1/60, 1/15, and 1/4 using a tripod. None of the images is any good by itself. Putting them though enfuse gives Figure 2; this result is as good as any I have obtained using HDR methods and is much faster- just a few seconds of processing.
As discussed in my previous article (Digit 36), the creation of spherical panoramas requires exposure blending; for this reason the panoramic software hugin now incorporates enfuse. Because hugin can also align images, it can be used to fuse hand-held bracketed shots. Figure 3 shows three bracketed exposures taken with a hand-held Canon 5D with a EF24-105mm f/4L IS USM lens used at 105mm. The first (average) exposure lacks detail in the white cloud and in the dark shadow; the second (2 stops under) exposure has a nice cloud and the third (2 stops over) has detail in the shadow. They can be aligned and fused within hugin by using the following steps:
But enfuse can do more than exposure blending; the fact that it uses contrast as a fusion criterion means that images can be blended to achieve enhanced depth of field. Figure 5 shows two of three images taken in natural lighting with a Canon EOS 5D with a 100mm macro lens at f20 and a shutter speed of 0.3. The first image was manually focused on the petal tip and the second on the inside. Thus the first image is sharp at the tip but the stamen is blurred whereas the second image is blurred at the tip but the stamen is sharp.
These images can be fused using hugin in the same way as for Figure 4; but with two difference arising from the differing fields of view:
The result of applying this method to aligned images is given in Figure 6; the image appears to have a larger depth of field in that all parts of the petal and stamen are now in focus.
Further information is available on the web:
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