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Contd.

 

Step 6

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 screenshot).

 

White Luminance

CRT Only

 

Step 7

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 temperature.

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 controls".

 

Colour Temperature

 

Step 8

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.

 

Fine Tuning Colour Temperature

CRT Only

 

Concluding steps

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 process again.

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

Obviously being 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.

 

Precalibration

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.

 

OptiCal

 

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).

 

Note:

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!

 

Image

Choosing between Standard and Precision Mode

 

Image Image

Standard Mode (default)

Precision Mode

 

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.

Extra Features

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 1.0.

 

OptiCal Curves

 

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.

 

OptiCal Info

 

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.

CONCLUSIONS

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 Monitor 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 at http://www.colorvision.com

 

 

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