[Leica] Re: resolution vs. dynamic range for slide scanners

[Pascal <cyberdog@ibm.net>]

On 05-08-1998 13:01 Alexey Merz wrote:

>While high resolution will improve dynamic range for very small areas of
>highlight or shadow, dynamic range is NOT solely a function of resolution, 
>and the Dmax for a given detection system is not resolution dependant.

On 05-08-1998 15:29 John Chapman wrote:

>Alex Merz wrote that dynamic range was more important than resolution
>per se. Dynamic range is completely dependent on the resolution you scan
>at that is a given.

Thanks to all who responded to my original question about advice on slide 
scanners. It was very enlightening as I am a novice in this field.
Please forgive me, but I would like to ask something which is not 
entirely clear.

Scanning resolution of course depends on the purpose. It is obvious than 
requirements for pre-press are different from those for web publishing. 
For the latter, resolution is not that important since there is in any 
case the screen display limitation (around 72 dpi), and since primary 
importance goes towards shorter download times. Therefore you will have 
to scan at limited resolution and find an optimum quality/size level, in 
order to keep the file as small as possible without loosing too much 
detail.

But how does this relate to the question of dynamic range? On face value, 
a slide scanner with the highest dynamic range would have the preference. 
Presently in the sub 2000 USD price range, this is the Nikon SuperScan 
LS-2000 with a range of 3.6. By comparison, the entry-level model, the 
Coolscan III (LS-20) has a range of 3.0.

Now, what is the exact relation between optical resolution and dynamic 
range?
Take both Nikon scanners, they have the same optical resolution of 2700 
dpi, but there is clearly a difference in dynamic range (30 bit scans for 
Coolscan LS-20 and 36 bit scans for the LS-2000). This probably means 
there is less detail in darker, shadowed areas on slides and negatives 
for the Coolscan LS-20. It is obvious that such detail would be noticed 
at optimum resolution, but what about lower resolutions?
Suppose you are scanning for web publishing purposes, and you limit your 
resolution at 72 or 150 dpi. Two questions:
- - Would this limitation in resolution have an effect on dynamic range, or 
is dynamic range independent on the resolution setting?
- - Would the difference in dynamic range between the two scanners be 
noticeable at that kind of low resolution, and if no, from what level of 
resolution would you see the difference?

In other words, I don't doubt that the Nikon SuperScan LS-2000 is clearly 
the better of the two, but if you limit yourself to web publishing (I am 
not into pre-press), would you obtain lesser quality with the cheaper 
entry-level Coolscan LS-20?

Thanks for an insight.
Greetings,

Pascal

- --------------------------------------------------------
Check out: http://members.xoom.com/cyberplace/
- -------------------------------------------------------
Who else than Leica could make a camera like the R8 ?
With that unique design and above all: that ergonomics.
Nikon ? Canon ? Nobody but Leica !
- -------------------------------------------------------
<<< PGP public key available on request >>>