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Monitor Calibration & Profiling

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PhotoCAL and OptiCAL

By Ian Lyons

A Computer Darkroom Feature Preview

As most of us know by now Photoshop gets all of its information about the monitor from an ICC profile. Obviously the ICC profile must accurately describe "our" monitor before we can even begin to believe that what we see on the screen is accurate. However, in order that we can create such an ICC profile it is necessary for us to use the specialist tools designed for the purpose. Typically such tools will include purpose-designed hardware and/or software.

 

BACKGROUND

Since the introduction of the MC-7 colorimeter towards the end of 1999 ColorVision has become synonymous with high quality yet affordable monitor calibration and profiling. However, before getting down to discussing the hardware and software options available from ColorVision it's worth spending few moments reviewing why we should even bother to use them.

So what are these software and hardware tools actually doing? I'm sure your reply will be along the lines - "to calibrate the monitor, stupid". If that was your reply then I'm sorry to say you are only partially correct. Let me explain!

"Calibration" is actually the process of setting a device (in our case the monitor) to a known or fixed behaviour/state. One example being gamma 2.2 at a white point of 6500K. But that's it, calibrating the monitor doesn't say anything about the monitors "actual" capability in terms of what colours it can or cannot display. Every monitor is unique, so consistent colour from monitor-to-monitor cannot be achieved by calibration alone.

In order that we may determine a monitor's actual colour handling capability it is necessary to "Characterise" or "Profile" the monitor. To characterise the monitor we measure and record a range of colours. The data recorded is then saved as an ICC profile, which describes the colour capabilities of the monitor. Once we have characterised our monitor we can use it too its maximum potential.

Adobe provide a tool with Photoshop that enables the above processes to be carried out, and in the main many will find "Adobe Gamma" to be more than sufficient for their needs. Nevertheless, the human eye isn't exactly the most accurate measuring device, and is especially dependent upon stable ambient lighting conditions. A much better option would be to use software that allowed a hardware device to be used for measuring, and this is were ColorVision's PhotoCAL 2.x  and OptiCAL 3.x come in.

Monitor Spyder

The original monitor Spyder was announced at Seybold San Francisco in late August 2000 and was the replacement for very popular MC-7 colorimeter. The one I used for this review arrived in mid November 2000 and boy is it different from the MC-7 that I had already been using. Appearances mean little, although my first thoughts were, if this device works as well as it looks; then heaven help the opposition.

Spyder

The Spyder colorimeter is a LOT faster than its predecessor, and due to a completely redesigned underbelly (rubber skirt) it's supposedly no longer susceptible to the ingress of ambient light to the sensor window. The MC-7 worked best in a darkened room or when the sensor was covered during the measuring process. I think that even with the new design there may still be merit in doing this, there's really no point in taking chances. However, my own experience would suggest that the Spyder's susceptibility to light ingress is no worse than any other model of monitor calibrator I've used, and is certainly NOT the fault of the new design. From a technical standpoint the Spyder colorimeter uses 8 silicon photo detectors made up of 7 filtered sensors and 1 neutral luminance sensor. It uses the now common Universal Serial Bus (USB) so compatibility with most modern PC's and Mac's is assured.

One important point regarding the original Spyder is that it is not suitable for use with LCD type displays, however this has recently been rectified.

December 2001

A new version of the Spyder was announced by ColorVision at Seybold San Francisco in September 2001. This new Spyder unit has been designed for use with both CRT and LCD type displays. Both PhotoCAL and OptiCAL have been updated  to include the facilities required to calibrate LCD type displays. The screenshots used throughout this review have been updated to reflect the new software versions, however, as at time of writing this update I have not had the opportunity to evaluate the new Spyder.

May 2002

My new LCD type Spyder arrived April and after a few weeks testing it on both LCD (Apple Cinema display and CRT) I can report that ColorVision certainly seem to have cracked the LCD calibration nut. The new Spyder comes complete with a weighted hanger arranged specially designed to suspend the device over the face of the LCD. It is also worth pointing out that the filter attached to the underside of the Spyder MUST be removed when calibrating CRT type displays. This may appear to be a statement of the obvious, but sadly it appears not to have been obvious to some users.

 

Part 1 - PhotoCal 2.x

PhotoCal is the less expensive of the two monitor calibration/profiling packages available from ColorVision. The version discussed below includes the software and Spyder colorimeter at $174, although an LCD/CRT version can also be purchased at $284.

PhotoCAL is compatible with both the PC and Mac platforms. Users of Microsoft Windows 98/98SE/Me, 2000 and XP should find that it runs with out any problems.

The program itself is quite easy to install and runs via a simple wizard process, much like Adobe Gamma. Each stage is fully explained in the Wizard window and further instructions are provided in the form of a "PDF User Manual". Do make sure the Spyder colorimeter is connected before beginning the process of calibration and profiling.

The Spyder colorimeter is the key to making an accurate profile for the monitor. This device is quite compact and "sticks" to the face of the screen using three suction cups. The user should ensure that the surface of the monitor is cleaned before beginning calibration. The LCD version uses a special harness to suspend the Spyder over the face of the display and so avoids the suction cups damaging the surface.

The screenshots used below are based on the PC Windows version of PhotoCAL, but the process is virtually identical on the Mac. If there is any difference in operation I have not yet seen it. However, one thing to be careful of, make sure that you have disabled the Adobe Gamma  "Extension" on the Mac or remove Adobe Gamma Loader.Exe from the Windows Startup folder on the PC (use the Explorer search facility to search out instances of this file on Windows 2000 systems).

Introduction

Let me intro........................!

Step 1

Having introduced the LCD/CRT version of the Spyder ColorVision has also revamped PhotoCAL. On startup PhotoCAL 2.7 will ask the user to decide upon the monitor type, e.g. CRT or LCD. The screenshots used below are all based upon a conventional CRT type monitor. If the user makes the wrong selection the software will provide a warning to that effect upon carrying out the luminance measurements, of which more in a moment.

Monitor Type

Selecting the Monitor Type

Step 2

Having selected the appropriate type of monitor we begin the serious work of profiling it. Selecting the gamma is pretty simple, although we shouldn't assume that we must choose gamma 1.8 for a Mac and 2.2 for the PC. Read the user manual and screen tips for further information on choosing the optimum gamma. Mac users choosing gamma 2.2 will probably notice that the desktop and icons appear quite contrasty. If you're calibrating an Apple LCD type display I recommend that you choose 2.2 as this is closer to the Native gamma for Apple LCD's than 1.8.

 

Gamma

Step 3

In this step the user chooses their preferred colour temperature. Generally whether using a PC or Mac it's now common practice to use 6500K. This setting provides a slightly cooler or blue white than the old standard of 5000K. Apple LCD users should choose 6500K as this is the value to which most high-end LCD's have been preset.

Step 4

Adjust the CRT monitor contrast to its maximum value; however, be prepared to return to this step if the measured luminance value exceeds the optimum of 95 cd/m2. Actual measurement of the White luminance value takes place at Step 6 below. Setting the white luminance value too high will shorten the life of your CRT type monitor. With LCD type displays the white luminance value can be MUCH higher without any detrimental effect. Apple LCD displays only allow adjustment of the Brightness control which actually works like a Contrast control on CRT displays - set it to around 50% (Apple default value).

Contrast Setting

 

Step 5

As with Adobe Gamma it's still necessary to make your brightness control adjustment by eye. However, PhotoCAL uses 4 black patches, it's only when all four are just visible that you can tell the system is at the correct level of brightness. I have found this method far easier to work with than the method used by Adobe Gamma and certainly much easier than the methods employed in similar products.

Brightness Control

CRT Only - Adjusting the Black Luminance value

This step determines the Black luminance value and it's especially important with CRT's that it isn't set too low or high. Setting the black luminance level isn't so important if using an LCD type monitor; actually with many it isn't even possible.

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.

 

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