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Re: filmscanners: Goals in adjusting scans?



On Sat, 31 Mar 2001 10:12:13 -0800  JimD (rasterdogs@home.com) wrote:

> 
> The more I scan images with my ss4000 the more I realize
> how much I need to learn.

You are not wrong. 
 
> Should I be setting white and black points in the
> scanning software(Vuescan, insight, SilverFast...whatever)
> to get a full spread histogram when I open the image in
> photoshop and look at the histogram there?

Yes, unless you are scanning to 16bit/ch files, in which case do a rough 
adjustment in VS, then tweak in PS.

With 8bit, you don't have much scope for adjustments after acquisition, so 
should get as close as possible to the final, desired result. The reason is 
that with 8 bits, you get rounding errors during successive mathematical 
operations on the data. This destroys precision of colour and tonal value - eg 
241.35 gets rounded to 241, which then gets modified perhaps to 235.68 which 
gets rounded to 236. Do that a few times and you can end up with only an 
approximation to what the value would have been if you had more bits. 

So: working in 16bits is much preferable.
 
> Since I'm scanning mainly to make color prints on a 1270
> should the file output from the scanner yield a histogram
> range from a black of 0 to a white of 255 or will I get better results 
> aiming for black of ~6 and white of ~244? I know I can adjust
> curves/levels in PS to set this but wonder it is better to
> do so with the scanner controls prior to changing the image
> in PS?

It really depends on the image (subject tonal range) and your intention. For 
full-range pics, usually I find it best to just clip the shadows a little, 
whilst allowing some headroom at the white point end.

> I've been using Vuescan and outputting 16 bit files to
> Photoshop, that does seem to give a smoother histogram
> once I've made initial changes and converted to 8 bit.
> Is there a downside to this approach?

Nope, just time and effort.

Regards 

Tony Sleep
http://www.halftone.co.uk - Online portfolio & exhibit; + film scanner info & 
comparisons




 




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