Digital BW, The Print

> From: Steve Kale [mailto:stevekale@...]
>
> Unless I am mistaken the only way to do an ambient light check is
> as part of
> making a display profile and in that case it just gives the
> reading in terms
> of colour temp K and illumance lux.

Which software do you have? If you have Eye-One Share, there's a tool that
lets you measure incident light. I think it's under Evaluate (e) in the top
left corner, then Light, but my memory could be off. It lets you click the
button on the spectro to take a reading, and then examine its data in
various ways, including, if you want, storing the whole 36-band data in a
text file. But as long as you can get some sort of brightness out of it on a
linear scale, that's all you need. (I'm not at the computer that has all
this installed at the moment.)

> I am puzzled by this.  It's my minimum luminance that determines
> black level
> ie 0.4cd/m2.  This is a measure of the light emitted by the display when
> trying to not emit any light at all.  It is not affected (directly) by how
> bright my monitor can be ie the 270cd/m2. Haven't you just measured the
> dynamic range in density terms rather than the end points?

Yes.

> I guess I am
> interested in that but more interested in knowing the density
> equivalent of
> the black point. My LCD can obviously be a lot whiter than it is at the
> moment.  I have lowered the colour temp to D50. The key is what
> black can be
> represented.

Density is a logarithm of a ratio, normally the ratio of incident light to
reflected light. The only other thing you could take the ratio of is the
ratio of your room lights reflected off white paper, to the light emitted
and reflected from your black screen. I'm not sure that's meaningful.

The way I look at it is that the eye adapts to the display, just as it
adapts to room light, so that whatever your white point is becomes the
equivalent of paper white (as long as your screen brightness is something
reasonable). Just as changing the brightness your room lilghts doesn't make
a print look fundamentally different (over a reasonable range), the same
should be true of the monitor. I think the important monitor measurement
_is_ dynamic range, and that corresponds pretty directly to print density
range.

Of course, there is a small difference between the print density range and
the black density, because the paper white density isn't exactly zero.
However, many papers with optical brighteners probably have a negative
"density", emitting more visible light than struck it. I suppose you'd have
to take that into account for the most meaningful comparison. Using optical
brighteners can increase an image's contrast just as much as using a darker
black ink. And printing on gray paper can reduce it just as much as using a
weaker black ink, because what the eye/brain responds to is contrast range.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@...