Black
Point
You
should see 4 separate tones in the
image above
You
should be able to distinguish between
the patches marked 0 and 10 in the
above sample (make sure you view them
with your eyes level to your monitor).
Patch 0 should be perfectly black,
matching the extreme borders of your
monitor, and patch 10 should be barely
visible. If you can not distinguish
any difference between patches 0 and
10 then your monitor is likely set
too dark. Adjust only the brightness
control of your monitor until it you
can just distinguish the difference
between patches 0 and 10 but try to
keep patch 0 as black as possible.
For the techies: advanced
techniques...
Everyone else can skip to the next
section...
When the black point is properly set,
an RGB value of #000000 or (0,0,0)
will appear as true black on your
monitor. Increase the RGB value slightly
and you should see a slight increase
in intensity. The non-scanned area
surrounding the displayed image is
an ideal reference for the black point.
The goal is to make display value
#000000 or (0,0,0) match the black
of the non-scanned border.
For adjustments to be accurate you
need to use consistent lighting when
viewing your monitor. The black point
for a brightly-lit room will be higher
than a dimly-lit room. After setting
room lights to your standard, minimize
any on-screen applications (including
your browser). If there are bright-colored
icons on your desktop, move them to
a folder and minimize the folder.
You can easily retrieve them later.
It is very important that your screen
be completely black.
Set the desktop background color to
black (0,0,0). To set the background
color in Windows, choose Start >
Settings > Control Panel, double-click
on Display, and click on the Appearance
tab. You can verify the RGB value
is (0,0,0) by double-clicking on the
color patch to view the Color Picker
dialog box.
Set brightness and contrast to 100%.
Adjust the vertical dimensions of
the screen so you can easily distinguish
the border between the scanned and
non-scanned areas. To make this adjustment,
shrink the view vertically, or move
the view up and down with your monitor
controls. This will expose the non-scanned
area. If you shrank the window 2"
from the top, then the border between
the scanned and non-scanned area should
be 2" down on your screen.
Decrease brightness until the the
scanned area blends with the non-scanned
area. If there is a dialog box for
monitor brightness, and it is distracting,
mask it so it doesn't interfere with
this step. Go back and forth until
you've identified the point where
the scanned area starts increasing
in intensity. Lock the setting when
the scanned area just starts to become
visible.
White
Point
You should see
4 separate colours in the image above
For
the techies: advanced techniques...
For everyone else - you're done!
You should be able to distinguish
between the 95% and 100% patches in
the above grayscale. If they appear
to be the same, then contrast is too
high, and highlights are blocked.
Most monitors work fine with contrast
set at 100%. If you find this too
bright, or highlights are blocked,
decrease contrast and recalibrate
the black point.
The sRGB standard specifies a color
temperature of 6500°. Most monitors
have provisions for setting color
temperature using on-screen menus.
You may find 6500° a bit warm.
Feel free to adjust this value so
that whites are white on your monitor.
Gamma
This whole section is pretty much
for the techies...
You must use software to make gamma
corrections. A change in gamma changes
the shape of the brightness curve
(see section on Theory). Most operating
systems support a Color Management
System (CMS) that allows you to control
display gamma. An exception is NT4.
If you're running NT4, you may want
to upgrade to Windows 2000 for better
color control. If you're using Adobe
Photoshop, you can adjust gamma using
Adobe Gamma. On a Windows computer,
click on Start > Settings >
Control Panel, and double-click on
the Adobe Gamma icon. De-select the
View Single Gamma Only checkbox, and
adjust each color individually. As
a double-check for Adobe Gamma, verify
that there is no color tint in the
following grayscale.
You can use the following chart to
determine monitor gamma for your system.
Stand ten feet from your monitor and
choose the patch that blends with
the background. For web use you'll
want a gamma of 2.2, the sRGB standard.
The sRGB color space also works well
for inkjet printers.
If gamma is around 2.5, you're viewing
the web through dark glasses. If gamma
is near 1.8, then images on the web
appear too bright. (Actually if you
gamma is 1.8 this is standard for
a Mac. If so, and if you're going
to be creating images for the web,
be sure to preview your work at a
gamma of 2.2. Otherwise, images that
look correct on your monitor, will
be too dark for the other 95% of the
world).
As a final pass in Adobe Gamma, select
View Single Gamma Only, and view this
chart while making minor adjustments.
As you move the gamma slider, you'll
see the display darken and lighten.
You are altering the look-up table
(LUT) that controls monitor display.
The RGB value of the smooth patches
remains the same, but they're interpreted
to a different brightness as you move
the slider.
