Adjusting the white luminance value for a CRT monitor is critical
to good calibration. In Step 4 we were advised to set the contrast
control to maximum. This step provides us with numerical feedback on
the actual luminance value of the monitor corresponding to the contrast
control setting. Many new monitors will have a maximum luminance value
well in excess of 100 cd/m2. Reducing
the contrast will reduce the White luminance value and is likely to be a lot
easier than ColorVision's instructions (see my notes on the following
Pre-calibration is the feature that sets PhotoCAL apart. With this
feature we can maximise our monitors colour rendering potential by
getting the colour temperature of the monitor to the desired target
value right at the outset of the process. This will mean that the
profile will NOT need to make any significant correction for white point colour
If the monitor allows separate adjustment of the RGB guns for
colour temperature pick the first option. This facility isn't
available on many low cost monitors, but the user should check anyway.
Typically we will find that the monitor has at the very least got presets
for 5000K, 6500K and 9300K. It would be rare to find a modern
monitor (at any price point) that didn't have some means of adjusting
the colour temperature.
If using profiling an LCD that has no controls for White Point, etc
(e.g. Apple LCD) choose "Has no colour
The process of measuring how the monitor
displays red, green, and blue is automatic and takes a few of minutes.
If the monitor allows individual adjustment of the RGB guns then
the dialog shown below will appear.
I use a Mitsubishi Diamond monitor and it has a continuously
adjustable colour temperature control therefore my monitor falls under
option 1. With Option 1 the monitor white point colour temperature is adjusted by
reducing the Red, Green or Blue guns until the 3 coloured bars lie
within the rectangle and the screen luminance
is between 85 and 95 cd/m2. Following
my advice at Step 6 the luminance value should already
have been at the desired value without any need to adjust the RGB guns
for anything other than the colour temperature.
The remaining steps are automatic; we just sit back and watch.
After a few minutes the user will be asked to name the new profile and that's
it, our monitor is now ready for use. Don't be tempted to readjust
the brightness or contrast, unless you intend to go through the whole
The remainder of this review relates to ColorVision's more up market
and equally more powerful software package called OptiCAL.
Part 2 - OptiCAL 3.x
aimed at the Professional means that OptiCAL is
intended to be even more accurate than PhotoCAL. It allows the user to
set target values for maximum and minimum luminance, gamma and colour
temperature. Using such an approach should be possible to
match a group of monitors to one standard. But bear in mind that the dimmest
monitor of the batch is the standard to which the others are matched.
I have used OptiCAL on my Mac and PC systems and am extremely happy with
the results obtained. Screen to print matches are good. On the downside OptiCAL is a bit more complex to use
than PhotoCAL. Note that the screen shots and instructions provided below
are specific to calibrating a CRT type display.
In addition to setting our own we can choose from a wide range of
predefined Targets and Curves, each of which describes
the gamma, colour temperature, maximum and minimum luminance levels.
Just so as we're clear what this means, the contrast control of the
monitor determines the white luminance, the brightness control the
black luminance and the colour controls the colour temperature. However, whereas with
PhotoCAL these aim points were
determined by ColorVision; OptiCAL allows the user to set them to any
value they like.
7 December 02
ColorVision have recently updated OptiCAL to version
3.7.x and as part of this update we find the process of
calibrating a CRT monitor has changed slightly. The changes to the
actual application are relatively minor but are still likely to cause
a fair amount of confusion, especially since the user documentation
doesn't really help in identifying the optimum calibration process.
I'll be honest and say that my initial attempts at calibrating a CRT
with this new version were an absolute disaster - so much so that I
almost gave up in disgust. Thankfully I didn't and after a few emails
to smarter folk than me I realised where I was making my mistake.
Rather than try and explain all the possible workflows I have revised
my earlier instructions and so concentrated upon the officially
recommended method of calibrating a CRT monitor.
Pre-calibration of a CRT monitor
The first step in optimising your monitor is Pre-calibration.
Pre-calibration is an optional (I still recommend that you do it) stage with OptiCAL.
To pre-calibrate the monitor we run a small application called PreCAL.
This application enables the user to set the monitor colour temperature to an exact value.
If the monitor is fitted with individual gun control we can also
preset the luminance value. Generally I aim for 90 cd/m2
(because the nice folk at ColorVision suggested it). Initial
indications suggested that I could easily have obtained a luminance
value in excess of 110 cd/m2. However, a lower value can be
achieved by adjusting two of the RGB guns or lowering the contrast control
(never go below 90%). Do NOT use PreCAL
with LCD type displays.
PreCAL - Accurately setting the
monitor colour temperature and luminance value - CRT ONLY!
Profiling a CRT Monitor
Once we open OptiCAL our first activity is to select the
appropriate display type, i.e. CRT or LCD (Step 1). Next we set
our Target values for Gamma and Whitepoint (Steps 2
and 3) - the
Black and White luminance values cannot be changed without first
changing OptiCAL from Standard to Precision mode.
The gamma (Step 2) should be set for 1.8 or 2.2 or whatever value you
prefer. Since we have already pre-calibrated the Whitepoint (Step 3) using
PreCAL we simply choose Native (do NOT be tempted to
choose anything else or you'll undo the PreCAL process). The checkbox
labelled "calibration enabled" should be checked! Once the
gamma and whitepoint values have been selected
we can begin the process of calibrating and characterising the
monitor. ALWAYS use the Calibrate (Step 4) button rather than the
menu options (this was were I came unstuck).
When configuring OptiCAL we have two basic choices, i.e. Precision
mode or Standard mode - the choices can be made by selecting
Preferences from the File Menu (OptiCAL menu in Mac OS X). Standard
requires that we set the screen brightness by eye as demonstrated in
the left hand screenshot below. Whereas with Precision mode we set
an luminance level and then use feedback from the Spyder to
fine-tune the monitor brightness. ColorVision recommend Standard
mode for most single monitor situations and this is now the route that
I recommend. It is much simpler and less likely to result in confusion
and erroneous results - honest!
Choosing between Standard and
Standard Mode (default)
With the Standard mode of calibration the remaining aspects
of the calibration process are fairly straight forward and require no
user intervention other than confirming the ICC profile name. Ideally
you should aim to recalibrate the display at least once per month.
The process of calibrating an LCD is virtually identical except
we choose LCD at Step 1. Since we should never use PreCAL with LCD's we
must define our Whitepoint value. For most LCD's it is better to leave
the Whitepoint at Native and let OptiCAL simply record the value
rather than attempt to adjust it to some pre-defined value.
OptiCAL also includes a useful set of tools that give the
user quite a bit of information on their monitor: -
Curves - This dialog window is used to display the uncalibrated state
of the monitor, the user selected Target value for Gamma, the
Correction applied to achieve the calibration, and the final
Calibration curve. This information provides feedback on the accuracy
of the calibration and its success in maximizing the range and
brightness of the display.
Looking at the actual curves shown below we can see that the right
most or lower curve relates to the native uncalibrated state of my
Mitsubishi monitor (native gamma of approx 2.2). The curve just to the
left is my target gamma (gamma 1.8) and the left most curve the
correction applied by OptiCAL so that my monitor gamma is corrected to
gamma 1.8. For the sake of clarity, the diagonal line equates to gamma
If we turn the Expert Mode ON in the
Preferences we can also use the curves dialog
window to fine tune the profile. This is achieved by adjusting the
control points, we can pick from one, three or nine points depending
upon how accurate we want to be.
Information - This dialog window provides the user with exact data on the
uncalibrated, target and calibrated monitor. Included is data for
display brightness, in Candelas; White Point (Colour Temperature); Phosphors; The Delta-E deviation of the calibrated monitor's
Colour Temperature, and the Delta-E deviation of the calibrated Red, Green and Blue Gamma
curves from the specified target value.
The documentation (Adobe Acrobat PDF) that comes with the most recent
versions of OptiCAL is only marginally better
than PhotoCAL and nowhere near as comprehensive as it once was.
Nearly 18 months on from writing the original review we find PhotoCAL and OptiCAL
at version x.7. PhotoCAL has certainly undergone a significant
face-lift and the wizard help messages are even more helpful than
earlier versions. OptiCAL has also undergone a face-lift but not on
the scale of PhotoCAL. In use both programs have been simplified and
reconfigured to enable calibration and profiling of LCD type displays.
As noted earlier the LCD version of PhotoCAL produced very satisfactory results
when calibrating an Apple 22" Cinema display I managed to borrow.
It was equally good with my own 23-inch Apple Cinema HD display.
Using either PhotoCAL or OptiCAL it will take about 5
to 10 minutes to calibrate and
profile CRT monitor from start to finish. This is comparable to most similar products, but on
the positive side is much faster than could be achieved using the
older MC-7 colorimeter. Since LCD's offer less scope for user
adjustment they are calibrated much quicker.
The Spyder/PhotoCAL monitor calibration and profiling
package is one to give serious
consideration too, especially if you're finding it difficult to get a
good screen to print match.
The additional features of OptiCAL will mainly benefit CRT
users working in a professional environment were colour accuracy
across multiple monitors is critical. The facility to set your own
target luminance levels is really quite neat, but probably unnecessary
for most users. I'm sure more expensive
packages offer a similar facility but none of the low end
alternatives, at least not that I'm aware off. OptiCAL also includes hooks for
other devices such as the Sequel Imaging unit, but I don't
think the Sequel unit is in the same league as the Spyder. The much more accurate and
expensive hardware device from X-Rite called the DTP92
can also be used with OptiCAL. In terms of profiling LCD the Spyder is
now competing head on with one of the industries giants - GretagMacbeth.
The LCD Spyder is MUCH less expensive than GretagMacbeth i1
but is it any more accurate? I think the Eye-One has the edge but like
many others I believe the Eye-One combined with OptiCAL would
make for a killer package, if only ColorVision were of a similar mind.
For more details on PhotoCAL, OptiCAL
and the Spyder visit ColorVision