Re: HP Dreamcolor uniformity issues
Re: HP Dreamcolor uniformity issues
- Subject: Re: HP Dreamcolor uniformity issues
- From: Richard Wagner <email@hidden>
- Date: Fri, 13 Mar 2009 13:16:07 -0700
On Mar 12, 2009,Darren Sheppard <email@hidden> wrote:
Currently got the uniformity problem with the HP DreamColor display ;
First display had mild unevenness that got steadily worse over a month
or so. Contacted HP and another display was sent overnight,
unfortunately this one was worse than the first. Contacted HP again
and another display sent over night, even worse.
All the displays have a manufacture date of June 08 and the two
replacement displays were refurbs. We are fighting with HP to get a
brand new replacement instead of a refurb. Makes me think that a lot
of the displays with the June 08 date are of poor quality control.
The first panel I received also had a significant lack of uniformity
across the screen when viewing a neutral gray window (or white,
or...). The right side had an obvious magenta color cast, and the
left side, a green cast. There was significant falloff in the lower
left corner. I received a replacement panel within a day or two
(they actually sent two panels by mistake), and fortunately the
second panel does not have this problem. I certainly would not
consider the first panel acceptable for professional photographers,
color correctors, proofing, etc. Our current panel was manufactured
in August 2008.
I also agree that while the software performs the basic functions of
calibration and profiling adequately (I think!), is relatively weak
in other features that we have come to expect. It does not seem
likely that a SDK will be released to 3rd party developers, so we're
stuck with the ($350) add-on HP software and customized colorimeter.
What is particularly irksome to me is that the software provides no
means to verify that the target values were achieved, or how far off
the actual values are after calibration and profiling. I don't have
the numbers handy, but I used an Eye-One Pro and a trial version of
BasICColor Display (to run the verification routine) and the
luminance and white points were significantly different from the
target values. This likely makes little difference in most day to
day use, but I like the confidence factor of knowing that a monitor
is performing as I think it is, vs. the "trust me" approach. Others
may disagree, and I don't know if this omission was intentional or
not. Currently, there is no presentation of the actual luminance,
the minimum (black) luminance, color temperature, or gamma, and it is
not possible to track previous results as can be done with current
versions of Match, ColorEyes Display, or BasICColor Display. There is
also no feedback given on the video card LUT. In fact, there is no
way for the user to verify anything about the calibration or
profiling process using the HP / X-Rite colorimeter.
I have learned more about the display since first purchasing it, and
some of this information might be of interest to others on this List
because it may affect expectations, both of the display itself and of
the software.
Here are my notes on what I've learned to date:
The data path on this display is quite different from any other
display. Unlike many of the displays that we are used to working
with, this display does not have a typical LUT structure and it was
not aimed at the typical graphic arts professional or photographer.
The display does not have traditional RGB gains. The display has an
adjustable color space and this puts some rather stiff constraints on
the use of lookup tables. The display has a built in matrix shaper
lut configuration. This consists of an input lut, 3X3 hardware
multiplier and an output lut as well as a scalable white point. The
first look up table, must, by definition be the canonical transfer
function of the color space. If it is not, the 3/x3 multiply will
introduce large color errors due to the non-linearity. The white
point setting is a function both of the matrix multiply and the
backlight adjustment. There is no independent control of backlight
RGB. The multiplying matrix is a trim factor for white and it sets
the primary mapping. The second LUT must correct the display color
drift and it must, again by definition, be the inverse of the display
optical transfer function. While certain preferences for display
calibration software may exist, the typical functions that many
desire cannot easily be employed in this display pipeline. For
example, if you wanted L* mapping in the display, you would have to
make sure your graphics card generated the output in L* form. This
means you would be putting a LUT in front of a LUT. You would
quantize your output to the display. The calibration / profiling
application features that some people desire that are found in the
other apps that use RGB gains and LUTs are not really implementable
in this display. One desirable addition to the display pipeline would
have been an offset to lower the display contrast ratio.
All that being said, we have found it to be an outstanding monitor
for color work. The wide gamut is very useful - just don't look at
the Mac OS X interface elements too long or you'll think you've been
given mind-altering drugs - the colors really pop from the screen.
This monitor really ups the ante in "what you see is what you print"
color editing. We have had zero problems with this particular panel
since receiving it in mid-November 2008 and we're very pleased with
it, in all respects.
--Rich Wagner
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