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stacker:docs:faqlist [2020/10/13 18:00] rjlittlefield Added "noise getting added when I retouch" |
stacker:docs:faqlist [2020/10/13 18:11] rjlittlefield [simplify new explanation about noise in retouching] |
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| ===== Sometimes I see noise getting added when I retouch. Why is that? ===== | ===== Sometimes I see noise getting added when I retouch. Why is that? ===== | ||
| - | The PMax stacking operation always accumulates noise. This is because it is relentless about preserving the strongest "detail" at each pixel position, but at the pixel level it is almost totally unable to distinguish actual detail from random noise. The result is that the final PMax output contains, at each pixel position, the worst noise that appeared in any source frame at that pixel position. | + | This effect can occur when you retouch from a PMax output into a DMap output. As explained in [[:stacker:docs:faqlist#what_is_the_difference_between_pmax_and_dmap|another FAQ]], PMax output is generally noisier than DMap output. Often this difference is overlooked when you are looking at just one or the other, or even side-by-side. But when you retouch from PMax into DMap, the greater noise of PMax is carried over, and that's when it becomes obvious, seen against the quieter surrounding areas made by DMap. |
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| - | DMap, in contrast, does not accumulate noise. DMap output is either completely faithful to the source images (after adjustment for alignment and brightness variation, if any), or it has a little less noise than the source images due to weighted averaging in the transition zones between one source image and another. | + | |
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| - | The result is that PMax output is noisier than DMap output. Often this difference is overlooked when you are looking at just one or the other, or even side-by-side. But when you retouch from PMax into DMap, the greater noise of PMax is carried over, and that's when it becomes obvious, seen against the quieter surrounding areas made by DMap. | + | |
| There are a couple of ways to reduce this problem. First is to always shoot at the lowest possible ISO, so that your source images will have as little pixel noise as possible. Second is to retouch in the smallest possible areas, typically only where DMap has messed up the handling of front/back overlap between two focused parts of the subject. DMap will almost always give a better rendition of background and of foreground edges seen against unfocused background, so those areas usually should not be retouched from PMax. | There are a couple of ways to reduce this problem. First is to always shoot at the lowest possible ISO, so that your source images will have as little pixel noise as possible. Second is to retouch in the smallest possible areas, typically only where DMap has messed up the handling of front/back overlap between two focused parts of the subject. DMap will almost always give a better rendition of background and of foreground edges seen against unfocused background, so those areas usually should not be retouched from PMax. | ||