Digital BW, The Print

Oh, I wasn't trying to dispute your methodology regarding defects, just to
illustrate the more basic concept of histogram movement. Obviously,
increasing contrast generally also increases the contrast of the noise,
which is going to accentuate any defects. That's going to be a limiting
factor regardless of what bit-depth you work in, because the noise is part
of your data. All the more reason to concentrate on good exposures and good
scans, to get the data right in the first place.

I'm not sure how you could isolate the effects of noise from those of
histogram movement, or what you would do about it if you could.

-Jason

-----Original Message-----
From: Todd Flashner [mailto:tflash@...]
Sent: Tuesday, August 14, 2001 2:44 PM
To: DigitalBlackandWhiteThePrint@yahoogroups.com
Subject: Re: [Digital BW] Re: Image Histograms Destroyed


Jason,

I don't disagree with anything you are saying, but I mean that even in in an
analog scenario, contrast and density reveals inherent flaws.

So, assuming my experiment is a flawed one, how else might one test to
determine if what they don't like in their image is a function of a broken
histogram, vs, bad data, which is merely being exposed as such?

Todd

> Increasing contrast (which I find is what I'm doing most of the time) is
the
> thing that kills the histogram, because you are stretching a smaller range
> of values into a larger range. Decreasing contrast shouldn't really cause
> any problems. Here's an easy experiment that illustrates it: open a new
> blank image in Photoshop and use the gradient tool to create a gradient
from
> pure black to pure white across the image. The histogram should be
> relatively smooth. Now use the levels tool to reduce the contrast so the
> gradient goes from, say, 60% gray to 40% gray. The histogram will be
> squashed into the middle, but should still be as smooth as before. Now use
> the levels again to reverse it back to a black to white gradient. The
> histogram will have huge gaps, and there should be obvious banding in the
> image.
>
> Of course, as others have said, all this histogram worship has been a bit
> overblown. It all depends on the image. Not all images will have smooth
> histograms -- an image of black and white stripes for instance -- and the
> only thing that really matters is how the print looks. That being said,
> getting a handle on the principles at work has finally helped me
understand
> why I was getting posterization in some of my images, and switching to a
> 16bit workflow has helped me solve those problems.
>
> -Jason
>
> -----Original Message-----
> From: Todd Flashner [mailto:tflash@...]
> Sent: Tuesday, August 14, 2001 1:55 PM
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Subject: Re: [Digital BW] Re: Image Histograms Destroyed
>
> I assume when you fatigue the the shy it's is through darkening
> it, and/or adding contrast. This always seems to expose defects in film
and
> scans for me. If you were to apply an equal move in the opposite direction
> instead, i.e., lightening it how would it look? Heck, lets really test
> it....


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