Digital BW, The Print

Hi Paul


> From: "Paul D. DeRocco" <pderocco@...>
> 
> I'm assuming you have the Eye-One Pro spectro.

Yes I do

>You should be able to use the
> ambient light measurement tool in the Eye-One Share program as a light
> meter. Since Paul wants you to measure the combination of the light emitted
> from the screen and the light reflected by the screen, I think it will be
> necessary to leave the diffuser off, and point the opening at the black and
> white areas of the screen from sufficient distance not to block the source
> of reflections. In other words, use it as a spot meter, rather than an
> incident light meter. This should work fine, because the Eye-One has a nice
> narrow acceptance angle.

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.
> 
>> Someone out there must be able to convert 0.4cd/m2 into a density figure.
>> That's my black point.
> 
> Density is just a base ten logarithm of the reflectance. The only reasonable
> way to convert a monitor's brightness range to a density figure is to divide
> the white luminance by the black luminance and take the logarithm. If you
> actually get a 400:1 range, that would correspond to a density of 2.6. If
> reflections reduce that to, say, 100:1, that would be like a density of 2.0.
> 
> Of course, reflections don't just reduce the apparent density of the blacks,
> they distract by reflecting actual unrelated images of things. So a
> measurement that shows that the monitor with your shirt reflected off it has
> a black luminance of 2.7cd/m^2 doesn't mean that it has the same subjective
> effect as a monitor that actually has a 100:1 contrast range in a pitch
> black room.
> 


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?  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.  One test might be to somehow set the colour management between
file and display to absolute (?) and key in L figures for equivalent
densities into a swatch programme like Eye One Share and note at which point
they don't get any darker?



(BTW if you have ever watched someone tune a plasma display for a home
theatre environment it is very interesting.  Most plasma and LCD displays
are way too bright off the showroom floor.  Why?  Because they are
calibrated for the sales pitch rather than actual use.  Sales floors
typically have enormous ambient light levels and so the sets have their
brightness or more correctly their black level turned all the way up.  If
you want a plasma display which will work well in a relatively controlled
environment choose one with greater "contrast" - actually greater dynamic
range (white point divided by black point) rather than "brightness".  The
first thing you'll do when you get it home is to drive the black point
substantially lower.)