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# Display Calibration and Measurement

LProf is an open source application that creates ICC profile for cameras, scanners and monitors.

# Display Calibration and Measurement Wizard

## Settings Page

The first page of the Display Calibration and Measurement Wizard is where users will setup the parameters used to calibrate their displays. These parameters include things like White point, Gamma and display brightness.

#### White Point

The white point can be set to one of three values. For most CRT users 6500K is the best setting. This is the standard white point for the sRGB standard. For those doing particularly color critical work a white point of 5000K might be a better setting for this. For users of LCD display either "Adopt native display WP" or 6500K are likely to be the best setting for this. "Adopt native display WP" will result in the largest dynamic range or gamut for LCD displays and most LCD displays have a backlight that is very close to 6500K. But this should be measured to confirm that the native white point of the display is not too far from 6500K, In most cases using a white point of 5000K with an LCD will have a significant impact on the dynamic range of the display and should be used with caution.

#### Gamma Type

This is where the gamma curve type is selected. There are three choices, generic, sRGB and L*. When you select a generic gamma you will be able to use the widgets in the Gamma Values group box to set the values of the gamma curve (see the next section for details). The sRGB gamma setting will result in the display being calibrated to have a gamma curve like that specified in the sRGB standard. The sRGB gamma curve may be a good general purpose calibration setting since most software and all web applications assume that the display is an sRGB device. The last choice is the L* gamma curve. This will give a perceptually uniform tone curve and this may be a good choice for those doing particularly color critical work.

#### Gamma Value

When a generic gamma curve is selected (see Gamma Type above) this group box is enabled and can be used to set the value of the gamma curve. If a generic gamma curve is used for most uses the correct selection is the default value which is 2.2. Some users might consider using a gamma value of 1.8 particularly if they are doing lots of work with black and white (monochrome) images. If you select the "User defined" radio button any gamma setting between 1.5 and 3.0 can be selected.

#### Sample Size

Use this to set the sample sizes used for doing calibration and profiling measurements. The larger the sample size the more accurate the results but the trade off is that measurements will take longer to do. For most users the default medium size is a good choice. But for those who are just starting out who are unsure of the process select the small size at first to make the process faster. The difference in the accuracy of the resulting calibration and profiles will be small.,

#### Display Type

Set tis according to the type of display you are calibrating and measuring for profiling.

#### Target Brightness

This allows you to set a target brightness for your display(s). Need to give users some info about how to go about deciding on how to set this. It should be based on the illumination level from the Ambient light measurement report.

#### Select Instrument

This combo box will contain a list of available measurement devices. Only devices that are suported by the meter library will be listed. Currently there are no filters applied to this list so devices that are not suitable for display calibration such as reflective spectrophotometers like those used for printer profiling will be listed. If you instrument(s) do not show up in this list then there is an issue with something on your machine that needs to be corrected such as not having access rights to the device. But in most cases devices will be listed even if there is an access issue. Instruments that are currently supported for display calibration and measurement are:

- GretagMacbeth Spectrolino

- X-Rite/GretagMacbeth EyeOne Pro

- X-Rite/GretagMacbeth EyeOne Display

- X-Rite/GretagMacbeth EyeOne Display 2

- X-Rite/GretagMacbeth EyeOne Display LT

- Various EyeOne Display OEM devices

- Colorvision Spyder 2

- X-Rite/Pantone Huey

- X-Rite DTP-92

- X-Rite DTP-94

#### Calibration reports

This button takes you to a dialog that will allow you to run various reports about the calibration state of your displays as well as an Ambient light report. See Calibration Reports for more information. This same button will appear on every page of the wizard and it will have the same function.

#### <Back Next>

These buttons will move you through the wizard pages.

### Adjust Controls Page

This page of the wizard will allow you to make adjustments to your display to adjust the white level, black level, white point and (if it is supported by your hardware) black point using the monitor controls with the help of your measurement device. In most cases these will need to be adjusted several times because these controls interact with each other. That is after you adjust one of these you may have to go back and adjust it again after adjusting other controls. This process normally takes about 5 minutes but the first time it will take a little longer since you will likely be making bigger adjustments (for subsequent calibrations your starting points will be closer to the correct values so you will be making smaller adjustments) and you will be getting used to how this works.

These adjustment can be made in any order and some adjustments may not be available for all devices and some of these may be disabled based on settings made in the Settings Page of this wizard. For CRTs you will use the "contrast" control to set your white level. For most LCD displays use the "brightness" control. On a CRT use the "brightness" control to set the black level. For most LCD displays you can not set the black level. Generally only very expensive CRTs have the ability to set the the black point. Those that can will have separate per channel RGB "brightness" controls and is some cases these are in the on screen display controls and can be somewhat difficult to find.
Once the adjustment type is selected the user will make sure that the wizard is located on the display that they wish to adjust and will then click on the "Make Adjustment" button. This will open the adjustment and measurement dialog which will use your measurement device to guide you through the adjustment process.

### Calibration Page

After you are satisfied with the adjustment of the display controls that were done on the Adjust Controls Page (see above) you can calibrate the display. Clicking the "Calibrate Display" button will bring up the adjustment and measurement dialog in calibration mode and will allow you to run a display calibration. This will take a set of measurements using your selected measurement device and use those measurements to calculate the new video card gamma tables. It then updates the actual video card gamma tables with these new settings and saves the calibration data in a file. The calibration file will be used when you create a profile to embed the calibration data into a "VCGT" tag data field in the profile. The data that is embedded into the profile can be used by a gamma loader such as xcalib to load the calibration data into you video card during system startup.

### Measurement Page

After the calibration step is finished you can move on to the Measurement Page to measure the calibrated display so that these measurements can be used to create a profile. Like the Calibration Page there is not much to do here other than to click the "Create Measurement Sheet" button which will bring up the adjustment and measurement dialog. Once the measurements have been completed you will press the "Finished" button and you will be taken back to the Monitor Profiler tab of the main LProf dialog. At that point you can create a profile using the calibration and measurement data created by this wizard.

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