Subject: Monitor Banding . PART 1
Subject: Monitor Banding . PART 1
- Subject: Subject: Monitor Banding . PART 1
- From: "Tom Lianza" <email@hidden>
- Date: Thu, 20 Dec 2001 15:36:38 -0500
This message is the first of two parts :
Mr. Marchant comments on banding in the monitor image. Other folks have
recently complained about "plugged" shadows. These artifacst are real and
can be magnified by a number choices that end users often make. This is
particularly true for users on the Mac platform and I thought that I would
discuss these and talk about some solutions to these real problems. There
are a number of contributing factors to this artifact:
1. Quantization due to Look up tables
2. Non parametric response of the monitor in the dark regions.
3.Other Hardware problems.
Let's examine these details:
Quantization in the LUTS:
Nearly all graphic cards utilize 8 bit LUTS and DACS. The most common card
that the Mac User deals with is the card that ships with the platform.
Because the input and output resolutions are the same, any non-linear LUT
will result in a loss of output levels. Prior to the demise of Radius as a
graphic card vendor, Sequel and Radius worked together on an extended
resolution board (10 bit output dac) that addressed this problem. The
unfortunate financial problems at Radius prevented that card from ever
seeing the light of day, but our testing showed that when combined with
internal adjustment of display color temperature in the Press View, no
decernable or measureable artifacts could be seen in a display set to D50
gamma 1.8. There was also a marked improvement in displays that did not
have analog adjustment . Mr. Marchant did not describe his operating
environment, but the use of Gamma 1.8 that is so popular in the Mac market
place compounds this problem dramatically. Most of the monitors that we
have measured in our Lab have gammas that fall between 2.2 and 2.8 and this
value is a very strong function of the setting of the brightness control.
Given an 8 bit dac resolution and a gamma of 2.2, the base resoulution of
the system hovers between a Delta E* of .5 and .8. If a loaded lut results
in the loss of 2 counts in the mid tone, you will see a band in the
gradient. If an application is using the LUTS to simultaneously adjust
Color Temperature and adjust the display to relatively low gamma you will
definately see gradient issues.
More in Part II
Tom Lianza
Technical Director
Sequel Imaging Inc.
25 Nashua Rd.
Londonderry, NH 03053