At 10:17 AM 1/17/01 +1100, Julian wrote:
>At 04:42 17/01/01, Rafe wrote:
>>It's not too difficult to make intelligent
>>"composites" from multiple passes of a slide
>>or negative -- provided the scanner and driver
>>have good registration from pass to pass.
>
>Rafe thanks - I do this sort of thing regularly (shows I am not good at
>taking flat, well-lit shots!). The problem I was discussing arises when
>you get blooming from one scanner exposure to another - then it becomes
>difficult if not impossible to combine them satisfactorily using these
>techniques. The difficulty is that the blooming extends over a small
>"dark" area of the hi-exposure scan that is therefore not covered
>satisfactorily by that scan, but it is also not covered satisfactorily by
>the low- exposure scan (still too dark). You get horrible edges, whether
>you use the manual masking that you describe, or a kind of semi-automatic
>masking such as using one of the image exposures (inverted) as the mask.
>(the last technique was described here some time ago, but I have found
>doing it manually to be better in general).
I've never had good luck with this method when
the layer masks had sharp edges, or were based
on (for example) thresholding/blurring/otherwise
processing the original, or one of the color
channels. When I try that, the edges and the
images themselves tend to look artificial.
(I think this is what those $200 masking plugins
are good for... )
The only layer mask that works in these cases
is one with a smooth linear gradient, to blend
from one exposure to the other (eg., foreground
to background.) Hence my analogy to the
graduated-ND filter -- which, when you think of
it, should have been used in the first place.
Granted, there's a limited range of photos on
which this technique is based, but the situation
comes up now and then in landscape photos.
The layer mask just needs a smooth transition
over the appropriate region of the photo. The
gradient should be "hard" enough to achieve the
desired effect, but not so hard as to be noticeable.
The "manual" part of this method is simply
deciding where to place the gradient, and how
wide to make it.
rafe b.
