Re: filmscanners: Minolta DiMAGE Scan & Dimage 7 camera

[Arthur Entlich <artistic@ampsc.com>]

Walter Bushell wrote:


>> 
>> 
> 
> _____> AFAIk the cameras only support 8 bit output. Adjusting brightness
> color on 24 bit images does result in artifacts, one can up the bit depth
> for those resolutions to avoid the math problems, but still it's a
> restricted dmax. Then if we are having problems with CCDs in scanners just
> think of the problems in cameras.

This might be less of a problem than it appears.  Imagine you had a film 
which either had extremely wide exposure latitude, or could change ISO 
at will.  In effect, that is what the MOS/CCD sensors in a digital 
camera do.  They can move sensitivity levels within a wide range (much 
more than a couple of f-stops film can handle, with current film 
technology... Agfa and Kodak are working on new chemical techniques that 
could change this drastically)).  Digital sensors could even be set to 
decrease the exposure range, so that they compressed anything outside of 
their range.  Film can't do this, if you get over it's exposure range it 
simple blows out to Dmin and vice versa.

Photographic papers are even worse for this exposure latitude, which is 
why modern labs use digital enhancement techniques to improve prints 
from film.

If the exposure itself is "bang on center" within the sensitivity range 
of the sensors, then 8 bit/channel is probably al that is needed, as it 
is 16 million colors and hues, making for pretty much all the human eye 
can see.  The problem occurs when we squeeze this stuff up against one 
side or the other of the sensitivity range and then need to stretch it 
back out to fill that histogram space.  The we want all those extra 
levels to make smoother transitions to fix the loss of the color 
"resolution".

> 
> How long until the selection of lenses for digital cameras matches that of
> SLRs?   For this to happen, digital will have to get to good enough that
> the format can be frozen long enough for multiple lens types to be
> developed. 

I'm not sure this is a problem.  Nikon and others have camera bodies 
which have digital backs which otherwise accept 35mm SLR mounted lenses.

A 28-200 zoom, but at what quality level? Remember a lens used
> for digital work _must_ filter out all detail at less than half the
> sampling frequency to avoid aliasing.

Any filtering of this nature would not be done at the lens level.  A 
lens is an optical device, and the best thing it can do is accurately 
translate everything it sees to the sensitive/recording layer.  This is 
what all lenses strive toward.  If any type of resolution lowering were 
to be required it would be done via electronic means.  Keep in mind film 
also has a "sampling rate", although it is somewhat more randomized and 
right now, still finer than most electronic sensors made available for 
mere mortals.

Art