Digital BW, The Print

I had some time to think about this last night as I licked 100 pieces of
photorag trying to get them right side up  in the box that my 2 year
"helped" me with.  I has helped me clarify my thinking - hopefully it is not
just catching up with the rest of you.

1.  I now think you do need both density range and dynamic range to
characterise the tones in a print.  Clearly the blackest black is important
and the whitest white is important -- these are measured by their density
and the difference would be density range. Also the ability to render smooth
transitions from one tone to another across the density range is important
and this would be measured by Dynamic Range.

2.  I think dynamic ranges as Austin has described it to us is correct.  The
problem I was having was in assessing the minimum perceptible change value.

3.  The dynamic range is a characterisation of a system, not an attribute.
In the case of looking at a print I would suggest that the system is
comprised of the print, the incident light and, importantly, our eyes.  This
means that the minimum _perceptible_ change is what our eyes can
discriminate not quantum level stuff, or even microscopic changes like the
ink droplets or silver bits on paper.

This means that the dynamic range of a system measuring the density of a
print with a spectrophotometer will likely be different than the dynamic
range of the system using our eyes.

4. The dynamic range of my prints (using the piezo driver v5, and epson
1200, and MIS FS inks) has a maximum of:

-10log10((measured paper black density)-(measured paper white density)/256))

Since the originating image only contains 256 shades of grey this caps the
upper limit (ie smallest value of) on the minimum perceptible change.  If my
eyes can only perceive 100 shades of grey then the dynamic range is lower.
If my eyes can see 1000 shades of grey the dynamic range is still capped by
the 256 shades that the print originated in.

To assess whether a silver print has more or less dynamic range you would
have to use a "system" that can accurately discriminate as many distinct
tones as our eyes and see if either print reaches its discrimination limit
before the limit of our eyes is reached.

For me, this framework works well.  Does it make any sense to others?

Kevin Gulstene



On 3/28/02 8:28 PM, "Austin Franklin" <darkroom@...> wrote:

> 
>>> I do not see how you can directly "measure" the
>>> dynamic range of a print. Perhaps in electronics you can.
>> 
>> It seems simple to me.
>> 
>> You get the print driver to output the lightest continuous (yeah I know)
>> tone it is capable of short of not printing at all. You measure the
>> reflectance of that patch.
>> 
>> You measure the reflectance of the darkest tone it is capable of laying
>> down.
>> 
>> The dynamic range is the ratio between them, exactly as Kevin said.
> 
> That's not right.  That is the DENSITY range between the two, and is not the
> dynamic range.
> 
> Austin
> 
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