U of S | Mailing List Archive | alt-photo-process-l | Re: OT: 16 bit editing myth or reality?

Re: OT: 16 bit editing myth or reality?

Hi Don,

My goal was simply to verify for my own benefit, if it was better to apply a
gamma correction on 8 bit or 16 bit data and see if the benefit if any was
significant or not. Maybe I should have said this better from the start and
I can only apologize for not doing so.

If you look at the histogram of a "real world" image you would see in many
cases or on average, a form that is very similar to what is called a normal
distribution. An histogram of a normaly distributed set of values as most of
its value near the center (the mean) and it decrease smoothly towards the
extremes on both sides equaly. This curve, made by drawing a smoothed line
at the top of each bin of an histogram, is often refered to as the bell

For my simulation a used a program called R freely available at
http://www.r-project.org/ . To make a long story short, using R I generated
a set of values having an histogram similar to a real world image. But as
Ryuji pointed out, my editing simulation was rather simplistic and I agree
with him on this.

The fact that I didn't use Photoshop for this is irrelevent because the
mathematical function I used would have been exactly the same in whatever
image editing program. I use mostly Picture Window Pro for my editing and it
as a gamma correction transform in its toolbox but I don't know if PS as the
same function available. With PS like software it easy to forget that all
the editing we apply to an image is actually realised by some mathematical
transform of the data.

I think Ryuji also said it much better then I could how a truly "scientific"
evaluation of this subject should be done to account for real world image
editing. This is not what I tried to do as I explained above.

I hope this clarification will be helpfull to put all this into the proper


----- Original Message -----
From: "Don Bryant" <dsbryant@bellsouth.net>
To: <alt-photo-process-l@usask.ca>
Sent: Saturday, December 15, 2007 7:42 PM
Subject: RE: OT: 16 bit editing myth or reality?

> Yves,
> > > Conclusion:
> > >
> > > Though I started with random numbers which mean the data is not a real
> > > image, I took great care to use numbers that would be representative
> a
> > > real world B&W image. Also the curve I use may not be representative
> an
> > > actual transformation one would use on a real image but it is actually
> an
> > > inverse gamma transformation and this type of transform is used
> practically
> > > all the time in color managed environment. I think we can say that
> the
> > > data and the curve are representative of actual editing that could be
> done
> > > on real world images though this particular data set is similar to a
> > > image and it may not be the same with a color image.
> > >
> > > I think we can safely say that this particular editing simulation
> that
> > > we would benefit from working in 16 bit mode.
> > >
> > > But I remind you that other types of editing may or may not allow us
> come
> > > to the same conclusion.
> If I understand your post correctly you didn't actually edit an image in
> type of image editing software. That being the case how can we draw any
> conclusions relative to real world image editing based on your simulation?
> Or to put it another way, how do you know what an image editing program
> to real image data and thus how can you arrive at that conclusion with any
> reliability?
> I think the most useful way to approach this problem is to use real data
> real software and examine the results, either visually or numerically.
> Don Bryant