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| "Hot pixels" are pixels corresponding to image sensor elements that cannot adequately represent low light levels. "Good" elements put out very little current when they receive no light. "Hot" elements put out current even when they are in the dark. They show up as random bright spots in the images. They are a problem for high magnification macro images partly because, in order to increase depth of field, these images are often taken at small aperture settings. Moreover, the high magnification configuration spreads a limited amount of light coming off the subject over a relatively large area. The problem is exacerbated when image stacking is used to increase depth of field because the hot pixels show up in the final image in slightly different positions for each contributing image. What would be a single "noise" dot in a standalone image becomes a "trail" of dots in the image stack. A very good solution to this is to map these hot pixels and then remove their effect in software. This is done by taken a long exposure in total darkness. This image should be completely black. Instead it will have random (but repeatable) bright spots. The hot pixels in the image of a subject can then be removed by referring to the hot pixel map to determine which few spots should be filled in by adjoining data. This is MUCH more effective than trying to use noise removal software that will end up blurring the images. -------------------------------------- The experiment below shows how well the hot pixel mapping works by treating the map itself as an image from which the hot pixels should be removed. The images (both full image and cropped) look completely dark at normal brightness. EXTREME brightening shows some residual spots. This just illustrates that the software has a threshold when analyzing the map to determine which spots are too bright and should be fixed. |
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| 10 Images | Made with JAlbum & Chameleon | Help |