RE: OT: 16 bit editing myth or reality?
Well, Yves, I want to say that I think the simulation you did is of great value. It demonstrated that 16 bit editing provides a real benefit and quantified this benefit numerically. While it is possible to argue the relationship between these numbers and perceived image quality, I still think your approach is interesting. Thanks for sharing your results. gregory -----Original Message----- From: Yves Gauvreau [mailto:gauvreau-yves@cgocable.ca] Sent: Sunday, December 16, 2007 12:23 PM To: alt-photo-process-l@usask.ca Subject: 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 curve. 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 context. Regards Yves ----- 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 of > a > > > real world B&W image. Also the curve I use may not be > > > representative of > 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 both > 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 B&W > > > image and it may not be the same with a color image. > > > > > > I think we can safely say that this particular editing simulation shows > 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 to > come > > > to the same conclusion. > > If I understand your post correctly you didn't actually edit an image > in any > 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 does > 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 in > real software and examine the results, either visually or numerically. > > Don Bryant > > >
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