my 2ct:
- underexposure + digital exposure correction is terrible wrt noise
- i think our highlight reconstruction (this is about hardware clipped
pixels in the input) has some problems currently, if i find some time i
want to fix this.
j.
On Fri, Jun 7, 2013 at 11:34 AM, Rob Z. Smith <rzsm...@nhbc.co.uk> wrote:
> Surely the best thing to do is to just shoot normally, expose properly
> and, if the Nikon base curve is excessively boosting highlights, use a
> different curve. I certainly wouldn't want to go around underexposing my
> shots just to suit a particular raw development tool whether this is dt or
> not.
>
> You might try one of the Pentax curves I use, they don't seem to ever
> cause this problem for me. I assume that the Nikon curve was constructed
> to mimic as far as possible the appearance of jpegs straight out of the
> camera and that involved some sort of bright tone lift. If you aren't
> worried about 'exact' match of jpeg and 'out of the box' processed raw
> files there seems nothing wrong with just using a curve that doesn't have
> effects you don't want.
>
> Rgds,
> Rob.
>
> -----Original Message-----
> From: Chris Siebenmann [mailto:c...@cs.toronto.edu]
> Sent: 06 June 2013 17:18
> To: David Vincent-Jones
> Cc: darktable-users@lists.sourceforge.net
> Subject: Re: [Darktable-users] Best way to recover highlights that are
> blown in processing?
>
> | Something that I now find that is more effective is the use of the
> | channel-mixer along with blentif. I also am using the lightness tab to
> | select the brightest pixels and then I pull the red values slightly
> | back which gives the blue values a chance to be seen.
> |
> | I have however become a lot more cognicent of the problem during the
> | shooting session in an effort not to have to deal with this situation
> | later on.
>
> As far as I can see the only real way to deal with this during the
> shooting session is to underexpose significantly[*], unless I'm missing
> something. The current state of affairs really seems to be that bright but
> unclipped highlights will be shoved into over-exposure by darktable's base
> curves (and sometimes other processing); to avoid this you must avoid
> bright highlights in the RAW, ergo underexposure.
>
> (It is easy enough to see this happen by turning on overexposure markers
> and then flipping back and forth in the initial history stack between
> 'sharpen' and 'base curve'. The difference in my sample NEF is quite
> striking.)
>
> If I had a suitable step wedge test chart, I would actually do the
> experiment to find the first stop of highlights that darktable's Nikon base
> curves push into blown highlights. Someone familiar with the code and the
> base curves wouldn't even need to do any tests. My guess is that the
> important thing to know is the L level that is effectively blown; base
> curves themselves are relatively readable in src/iop/basecurve.c.
>
> - cks
> [*: here I mean 'underexpose well beyond the point needed to avoid
> hard clipping'.]
>
>
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