Re: filmscanners: LED Illumination for Film Scanners

[Arthur Entlich <artistic@ampsc.com>]

Tony Sleep wrote:

> On Wed, 20 Jun 2001 21:59:33 -0400  Austin Franklin 
> (darkroom@ix.netcom.com) wrote:
> 
> 
>> It's entirely different.  Incandescent lamps used for such are diffuse 
>> and
>> are not near as focused as LEDs.  Using commercially available standard
>> parts, you need individual LEDs because you need three colors.
> 
> 
> Bah, small minded Luddites abound ;-) Of course the real advance will be 
> to use high-intensity TFT panels as a scanner lightsource, strobing RGB 
> sequentially and <GET THIS> self-masking in a closed-loop with the CCD. A 
> calibration prescan will allow user and/or automated control of curves, to 
> attenuate or boost TFT pixel brightness on an individual basis, thereby 
> ensuring maximum shadow detail (all kept above the noise floor), 
> unblowable highlights, balancing of bright areas like skies at scan time, 
> and an OD range of about 12.6 <g>

Gee, 'big' minds seem to think alike.  I was actually looking into this 
myself.  I think the problem is that the TFT display doesn't provide the 
light source, just the color, so you are still having to provide a good 
constant color light source (cold cathode, I suppose).  Also, those LCD 
panels do have problems with color accuracy (which is why no one does 
color managed work with a LCD panel) and also there are still failed 
"pixels", something one would like to avoid in mission critical 
applications like scanning.

By the way, some of the index prints that are made by photo labs which 
come with APS rolls, for instance, use a negative digital mask made from 
a color LCD screen contact printed onto the photo paper.  Resolution is 
not great, but its an ingenious idea, IMHO.

> 
> A shame TFT doesn't have room for IR, but I'm sure that can be fixed. 

I suspect this could be accomplished through using two different light 
sources.

> 
> Interested scanner manufacturers should forward large bundles of used $50 
> notes to me ASAP <g>

Now, don't tell me you've given up on Euros already!

Art