Re: [APML] Histograms

[Matt BenDaniel <matt@starmatt.com>]

Alan,

The "picket fence" is a problem. It means that the smoothness of the image 
will be compromised.

You want to scan most kinds of color film at 2000 DPI. Use the full-depth 
mode (e.g. 16-bits per channel).

When you bring the image into PS, crop off the edges if necessary. Look at 
the histogram. If it is clipped, you need to figure out what happened 
during scanning, correct it and rescan.

Then use PS levels to spread the histogram to the edges. Also adjust the 
gamma to put the "hump" about 1/4 from the left side.

Once you've finished the above levels adjustment you can switch to 8-bit 
mode without significant loss. If you use layers for further adjustments 
(e.g. curves, hue/sat, etc), you probably won't see the "picket fence" again.

My advice is to use layers as much as possible and save the image in PSD 
format.

I believe that certain members of this list are over-enamoured with 16-bit 
processing. I contend that one does not experience material loss in 8-bit 
mode, as long as you know how to configure the histogram correctly before 
switching into 8-bit mode and as long as you use layers. You have to switch 
to 8-bit mode to use layers. Layers have such overwhelming advantages, that 
the benefits eclipse any slight losses. I believe that anyone who truly 
understands how to use layers will never want to do without them. With 
layers, you can out-process non-layers-users in less than half the time.

You would not believe the raw images I have been able to clean with layers. 
For example, http://world.std.com/~mattb/gallery/astro/naneb.html looked 
completely hopeless at the start (I think due to bad hypering and/or 
humidity) . But it cleaned up nicely. S&T published that image and I got 
paid for it. I'd be willing to share the raw data with anyone who wants to 
try to process that image, and especially to anyone who believes they can 
succeed without layers.

Matt

At 12:20 PM 4/29/2002, Alan Voetsch wrote:
>Hey all,
>
> > > As I've been playing around with Photoshop stuff:
> > > contrast/brightness; hue/saturation; color
> > balance;
> > > levels; and curves, I've noticed the histogram
> > changes
> > > from what looks like the silhouette of a hill, to
> > > something that looks like a picket fence if the
> > pieces
> > > of wood were placed about an inch apart and viewed
> > > from about thirty feet away. In other words, lots
> > of
> > > steep, narrow spikes. The images are improving,
> > but is
> > > this what I want?
>
>I wanted to re-post this question I asked yesterday.
>Some background info: even though we have a SS4000,
>the negs in question were only scanned at 600dpi. Is
>what I described above a direct result of the scan
>resolution? Or is it more directly related to the
>pre-scan dialog? My problem right now is that the
>scanner is in (for everyones convenience) a more
>centrally located position and I'm not sure what the
>scan settings were. I do plan on re-scanning within a
>week.
>
>Thanks,
>Alan
>
>
>
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--
Matt BenDaniel
matt@starmatt.com
http://starmatt.com


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