Digital BW, The Print

On Jan 4, 2009, at 11:24:48 AM, "Jon Cone" <jon@...> wrote:

This parallels a discussion in progress on the Piezography list. What
you did when calibrating your two LCDs was not to calibrate your two
LCDs but to calibrate the video board of your computer because that is
what EyeOne and CV Spyder, etc do.
___
Hi Jon,

Well, its one part of what they do... They start by doing any possible 
hardware calibration at the display, then move on the VLUT 
adjustments, and of course create a profile defining the result when 
they are done.


Your video board when it is not
calibrated has the ability to output 256red x 256green x 256 blue
output levels to produce 16.7 million colors.
___
Raw color, maximum number of values, but uncorrected... like printing 
without color management...

In order to render
grayscale without banding you need all those levels...
___
In order to get nice smooth grays on screen, you should certainly 
minimize the adjustments you make at the videocard level... none of 
this effects the print, only the screen view, but its nice to not have 
excessive banding on screen, as it interferes with seeing your 
image...


What calibration does is to reduce the output levels of the video
board in order to realize the targets of color temperature,
brightness, etc...
___
No, first it does any adjustment that is possible at the hardware 
controls level, which is certainly how "brightness" is adjusted in 
virtually all cases. Color temp adjustment, for displays have RGB 
Gains controls, are also done at the display hardware control level. 
If Gains are not available, and you do not choose Native as your 
whitepoint, and you do not have a display with LUT capabilities in the 
display, then yes, the final choice is that the VLUTs in the videocard 
are adjusted for this, as is gray balance.
and saves this as a vLUT which loads when you
startup your computer. Think of the vLUT as three curves being applied
to your video board...

Calibrator displays like the Eizo CG series have an on-board hardware
engine that produces billions of colors.
___
Which is why users are instructed to set the Whitepoint and Gamma at 
the display LUT level on such high end graphics displays first, in 
advance of running third party display calibration software; or to use 
software that does both. This could mean running a display 
manufacturer's software once, to generally define gamma and 
whitepoint, then running a third party product such as Spyder3Elite 
every few weeks, on the high end graphics display and your other 
displays as well (the specialty software for such displays does not 
typically play well with other displays or calibrated multiple display 
setups). Or it might mean simply running the manufacturer's display 
software once in a while, if your needs are simpler. Or it might mean 
using a specialty product such as ColorEyes to control the internal 
LUTs on the display, as well as doing your general profiling of all 
displays.


The order of priority that calibration products use is: set display 
hardware controls to optimal adjustments first (where available), set 
display LUTs to any further corrections next, (if available), set 
videocard LUTs to any remaining needed corrections, and finally, 
define the end result in an ICC profile. Displays not having hardware 
controls or internal LUTs should be targeted to Whitepoint and Gamma 
values reasonably close to their native values, to avoid visible 
banding caused by moving them too far with videocard VLUT corrections. 
Those with such controls can afford to be adjusted somewhat somewhat 
more widely. The new Apple 24 inch LED Cinema Display, for instance, 
has neither hardware controls (beyond backlight control for 
brightness) nor internal LUTs; but since its native gamma and 
whitepoint are close to desired values, it calibrates nicely without 
them, and at a price below displays with internal LUTs.

Once videocards and OSes have a functioning high bit pathway from the 
card to the display, this will all become moot, and the desirable 
features of internal LUTs will be equally functional at the videocard 
LUTs, ending the whole problem of proprietary access to internal LUTs 
and the communication issues that ensue, and eliminating most needs 
for displays with internal LUTs.

Please feel free to repost to your other list...
--
C. David Tobie
WW Product Technology Manager
Digital Imaging & Home Theater
Datacolor
CDTobie@...
www.datacolor.com/spyder3


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