[ptx] exposure-blend 1.3

[JD Smith]

On Tue, 2006-07-25 at 07:24 +0100, Brian wrote:
> JD Smith wrote:
> >
> > Taking a few suggestion from early users (/backseat scripters ;), I've 
> > put  exposure-blend, the Gimp "script-fu" script suite for 3 exposure 
> > contrast blending, up at:
> >
> >  http://turtle.as.arizona.edu/jdsmith/exposure_blend.php
> >
> > This includes "edge protection" in the form of selective Gaussian 
> > smoothing, and a few other bug fixes and niceties.
> >
> > Enjoy,
> >
> > JD
> >
> >
> Looks interesting.  I wonder how effective it would be using a raw file 
> saved out as seperate images with -2, 0 and +2 exposure comenpsation?
> 
> Might be worthwhile trying that out.

I don't usually shoot RAW, but I've heard some reports that this works
at some level (though not usually as well as getting real exposures).
Might be simpler to convert RAW to 16bit and use one of the range
compression techniques, as Erik describes here:

http://wiki.panotools.org/RAW_dynamic_range_extraction

This includes links to a prescription for a full 16bit workflow.
Certainly for panoramas this would be easier than stitching 3 individual
panos from RAWs and combining later.

One misconception about RAW is it magically gives you higher dynamic
range.  While this is true at some level, most cameras already attempt
to compress much of the dynamic range output by the 12bit A/D
converters, to the 8bit JPG output.  You won't have quite the fidelity
at any given intensity, but in terms of the range of dark to bright,
roughly similar.  With raw, you can "shift the bits" to emphasize a
certain range of intensities, for instance more nuance in the shadows,
etc.  This lets you "open up" shadows without suffering as much from
banding and other numerical artifacts.  But it certainly isn't as if
in-camera RAW converters take the middle 8bits of the 12bit output and
throw the rest away (which would effectively give you that -2EV and +2EV
shot "for free" from a RAW shot, as compared to a JPG of the same).  

JD