Subject: Monitor Banding (Part 2 of 2)
Subject: Monitor Banding (Part 2 of 2)
- Subject: Subject: Monitor Banding (Part 2 of 2)
- From: "Tom Lianza" <email@hidden>
- Date: Thu, 20 Dec 2001 15:36:45 -0500
Non Parametric response of the monitor in dark regions
Most people on this list understand that displays behave in a non-linear
fashion that is often described by a term called gamma. This description
works very well for approximatley 7/8 of the useful range of the display and
the model fails miserably in the lower 1/8 of the working range of the
display. The required" boost" in this region will often exceed the range
that the look up table can provide . Vendors handle this in different ways.
Visual adjustment of this control is often hit or miss.
The problems in this area often have nothing to do with the calibration
device. It's the display adjustment that is a problem. This was a prime
factor in Sequel's decision to develop the Enable Cable to aid in automating
the display adjustment functions by addressing the DDC/2C compliant controls
within the monitor. The dark point is set based upon the desired gamma,
maximum luminance and knowledge of other factory parameters. The use of
this adjustment capability is extended to the RGB bias controls as well. The
RGB bias controls interact with the RGB gammas so it is necessary to iterate
these adjustments. These are adjustments that cannot happen using "PreCal"
sort of operations from the front panel, the on screen display perturbs the
display and it prevents reliable measurement of the dark regions. The
combination of these adjusment parameters and minimal manipulation of the
LUT's can acheive excellent color conformance( 1E* or less) down to 1% full
scale and 2 delta E visibility in the range below that. This technolgy is
available from LaCie, world wide. Within the US market a number of display
vendors are, or soon will be distributing this technolgy with their displays
aimed at imaging applications.
Other hardware problems:
The Graphics Cards shipped with the Macs have been an issue in a number of
areas. We recently found that the maximum acheivable luminance from the
same monitor on one Mac was 100 cd/m2 and when that monitor was moved to
another Mac, the maximum luminance was on the order of 75 cd/m2. The
difference was in the drive levels of the internal graphics card. Apple is a
great company, but their focus tends towards the full digital flat panel
market, so one can expect some lack of attention to detail in this area.
This reality has lead a number of major Motion Picture Studios to adapt the
Enable Cable/Calibration solution on every mission critical color display.
These folks understand that calibration and control involve careful
measurement and adjustment of each part of the process. The finest
calibration device or software in the world can't correct for a monitor or
hardware problem.
Monitor Vendors recognize that there are demanding situations that require
higher degrees of accuracy and adjustment than can be economically achieved
in the factory. They also realize that end users have specific adjustments
that may not be based upon recognized "standards" such as sRGB . To that
end, they are stepping up to the plate and offering technology that is
coupled to their displays to enhance the performance to a diverse group of
users. Now, if we could just get a graphics card vendor that cared about the
graphics market, like the old Radius and SuperMac guys....
Tom Lianza
Technical Director
Sequel Imaging Inc.
25 Nashua Rd.
Londonderry, NH 03053
Tom Lianza
Technical Director
Sequel Imaging Inc.
25 Nashua Rd.
Londonderry, NH 03053