clipka escreveu:
> "Thomas de Groot" <tDOTdegroot@interDOTnlANOTHERDOTnet> wrote:
>> That overlaying of images intrigues me. It is merging of two or more images
>> in a paint program isn't it? What is used in that case? Averaging?
> 
> I geuss I'd do it with *POV* - because (a) it allows for best-quality input,
> using HDR file format, and (b) I know for sure that it will use the maximum
> possible precision for computation - using an orthographic scene process; and
> yes, that would be plain averaging. Which is exactly what each instance of
> mcpov does anyways for all of its iterations (although that's done even at
> float precision; but when parallelizing mcpov runs, we're probably talking
> about just 4 or 8 shots that finally need to be mixed).
> 
> One thing to pay attention to would be to take runtime differences into account
> appropriately. For example, if three threads had been running for 4 hours each,
> and another render was started 2 hours later and consequently ran only 2 hours,
> I'd give that 2-hour shot a lower weight.
> 
> 
> If using Photoshop instead, there's two possibilities to go; both involve just
> plain normal layer combination, with some transparency to the layers:
> 
> (a) process the shots in pairs, giving the lower layer full opacity and the
> higher one 50%. If, say, you had shots A, B, C, D, E, F, G and H, you'd first


> 
> (b) stack all the shots; give the lowest layer 100% opacity, the next higher one
> 50%, the next higher one 33%, then 25%, 20%, 17%, and so on. Merge to a single
> shot.
> 
> I have no idea which of these approaches would leave you with the least loss. I
> guess (a), but it depends on how Photoshop does things internally. If for
> example it stays in the 8 bit integer domain for its computations, (b) is
> obviously crap; but if it uses floating-point math (or at least 16-bit
> arithmetics) during any "merge layers" operation, but converts back to 8-bit
> after such an operation, you're definitely better off with (b).
> 
> In any case, Photoshop can never do as good as POV.
> 
> 
> Additionally, with POV you can stay in the linear domain (speaking of gamma
> here) throughout the whole process before outputting the final results; I don't
> know whether Photoshop takes gamma issues into account when merging images. This
> will probably not be an issue when images are low-noise already, but if you
> still have some deal of graininess it may make a difference.
> 
> Note however that when working with linear output from the actual renders, you
> *do* want to use HDR, otherwise you'll lose a lot of detail in dark parts of
> the shot.
> 
> 

Yes, what he said.  Just took the words right out of my mouth. ;)

-- 
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