clipka <ano### [at] anonymousorg> wrote:
> Am 22.03.2011 12:42, schrieb gregjohn:
> > In SEM work, it's not that 99.9% of PIXELS exist between GL64 and 192. Instead,
> > there's a distribution of electron counts (current?), and some bloke arbitrarily
> > decided to make 64 the min and 192 the max. Why didn't they decide to make it
> > like GL32 and 224?   I can say with some authority that failure to use the full
> > grey scale range in SEM work in in many cases cause one to lose information that
> > is present in the imaging conditions. I'm finding it annoying that people write
> > auto contrast brightness routines that throw away information.
>
> Leaving the brightest and darkest pixel values unused does have the
> advantage that even on poorly calibrated displays the brightest and
> darkest regions still show contrast. Keeping clear of the minimum &
> maximum representable values also has benefits when it comes to certain
> image processing, as some intermediate steps might otherwise
> over-/underflow. While these were probably bigger issues some decades
> ago, when calibrated displays were sparse and image processing was
> almost invariably done on bytes to conserve memory, tradition and
> backward compatibility may have preserved it to this date.
>
> Using a range from 64 to 191, rather than 32 to 223, has the advantage
> that you get exactly 128 (2^7) brightness levels. Computers love powers
> of 2.



Your statement about the best skiing photos would make for a fascinating
challenge. I would bet that the best ones still have very broad or bimodal
distributions, but on sunny days, the dark hump will be very small. It's not
<Nr,Ng,Nb> where *all* N's >>0.5.  A ski pole, black hat, or pine tree in the
corner of the photo.

[Later] From Flickr's "Most Interesting" "skiing" photos.
http://www.flickr.com/photos/52756285@N00/1390662667/
http://www.flickr.com/photos/firenzesca/2114824948/
Looking at these pics, they defintely have a (small) hump of very dark subject
matter in the histogram.  And these were among the lightest ones I could find.
As for "night" tag at Flickr, many had city lights (rgb>>0.5), and only a few
were all dark.

But as for your other point, finally, someone told me how "I'm missing
something!" ;) .  Monitor calibration could be the legacy, the historical reason
it may have sense to set up such a tradition at one time. In my shop, however, I
am the one guy (guy with the one type of job) who is most likely to do
post-processing of images, and I don't want to lose information.  Squeezing the
image range down to some arbitrary tight range is just always a bad idea. In the
small subset of cases where I'd end up pushing/ squeezing it myself, I could
very easily compress the range it later.  But you cannot uncompress to get back
the original.

Post a reply to this message