Idiot's Guide to Manual Display Calibration

LightSpace CMS can be used for manual Display Calibration, using any display's in-built Colour Management System (CMS) controls to accurately calibrate the display as far as is possible with the display's provided controls.

Manual Calibration can be performed with the Free LightSpace DPS version of LightSpace CMS.

Using this guide it should be possible to get accurate results from LightSpace CMS without having to fully understand the software, although it is highly recommended to learn the full software as there are many, many additional capabilities not covered by this guide.


An Overview Guide to Manual Display Calibration

Display Calibration

LightSpace CMS takes a very open 'free-flow- approach to calibration, without the need to adhere to rigid pre-set structures or workflows.

Instead, LightSpace CMS provides a tool-box of features that can be used in different ways to best perform accurate manual display calibration.

Please Note: Manual Display Calibration can be performed via the Free LightSpace DPS version of LightSpace CMS, and a suitable probe.


Why Calibrate?

The real requirement for display calibration is actually very obvious, as without it you will never be seeing images as the production team, specifically the DoP, intends. This is true for both displays used on film and TV productions, as well as for the home consumer.

Therefore, display calibration is required so that the viewed images match as closely as possible the colour standards expected by the images being viewed, as such video standards define how an image should look on any given screen when accurately matched to the given standard.

Unfortunately, nearly all displays are provided with very poor 'factory' calibration out of the box, especially home TVs which tend to come with over saturated colours, widely inaccurate gamma and colour temperature, and incorrect black and white levels, with such settings aimed at 'looking pretty' in the TV show-room.

'Showroom' settings are anything but 'accurate', and demand the TV be accurately calibrated before any images will look as intended.

Beyond this, many TVs have what are claimed as 'professional' calibration pre-sets, such as ISF or THX. Unfortunately such settings should be considered as nothing more than 'marketing gimmicks', as rarely are they accurate at all. At best, they are just 'less wrong'.


What to Calibrate?

What can be manually calibrated actually depends on the manual controls provided by the display manufacturer. Often, these controls are next to useless, and the only real approach available for accurate calibration is to 'turn off' (or null) just about all the manual controls, and turn to an external 3D LUT box to provide the most accurate calibration possible.

If you are serious about calibration the only truly viable option is to turn off all the display's internal Colour Management Systems, and use a 3D LUT for all calibration. No display's manual calibration capabilities come close to this level of accuracy.

But, for the sake of this guide, we will assume the display in question has good internal manual CMS controls, and provide a step-by-step overview to the 'best-practice' approach for manual display calibration.

With this acceptance, there are six major calibration steps to be taken:

Black & White levels
Peak White
Best 'Picture Mode'
Gamma
Grey Scale/White Balance
Gamut/Colour

While the above list is fairly simple, it will be necessary to re-visit most entries for a second, or even third time, after checking the other entries. For example, the Black & White levels will need to be re-verified after the best Picture Mode' has been found - but you really need to set the black and white levels before evaluating the display's different Picture Modes, as incorrect black & white levels will make a Picture Modes look wrong...

It is imperative to understand that such a 'repetitive' and 'circular' approach to manual calibration is a requirement due to to the way just about all manual TV calibration controls work.


Manual Display Controls

The actual controls that will be used during manual display calibration will vary depending on what is provided by the specific display being calibrated. Knowing what controls are available, and what they are used for is a critical step in gaining accurate final calibration.

It is also important to note that many displays have very poor controls, to the point that some controls do not work as expected (including wrong control labeling, incorrect functionality, and just plain poor design!). It really is key to know if the display in question has controls that operate as expected, or not.

Picture Mode
Picture Mode selects different display-wide settings, on-top of which the other display controls work (often with different controls active or not, depending on the Picture Mode selected). For accurate display calibration the need is to find the mode that is the least inaccurate. This is usually 'Movie' or 'Cinema' mode, which contrary to their names is actually closer to a the correct colour and gamma calibration for TV's, and has nothing to do with trying to emulate Cinema imagery. Additionally, when selecting these modes many home TVs provide additional manual controls, as described below. If a User Mode is available, that is often the best to select, as it provides the best 'blank canvas' with which to work, with the best selection of additional manual controls.

Colour Profile
Colour Profile options (or Picture Options, or similar names) on some displays are usually a sub-set of Picture Mode, and provides yet another level of 'options'. As with Picture Mode, the best setting to chose is often 'User' or 'Custom'. But, it is always best to verify each mode with direct profiling.

Backlight
Backlight, where available (usually on LCD displays, not Plasmas or OLED) controls the overall illumination level used for the screen, and can be used to set the overall 'brightness' of the screen. The control will affect both peak white and minimum black, with more effect on white. Unlike Brightness and Contrast controls there is little chance of 'clipping'. The primary function of the Backlight control is to enable Peak White to be set, in conjunction with the Contrast control.

Iris
projectors often have an Iris control (and possible bulb power) which is equivalent to 'Backlight' on an LCD display, and should be used in a similar way.

A second function of Backlight is to move between 'Night' and 'Daylight' settings, if you cannot accurately control the viewing environment (limit daylight contamination). Changing the Backlight setting can usually be performed without (badly) affecting other settings.

Brightness
Brightness controls the point at which black detail on the screen becomes clipped or crushed if set low, or if set too high will cause blacks to look grey and washed-out.

Contrast
Contrast controls the point at which white detail on the screen clips or crushes if set too high, and will make whites appear dim, grey and washed-out if set too low. Contrast needs to be set in conjunction with Backlight where available, and on displays without a Backlight is used to set the peak white value directly.

Sharpness
While Sharpness has no direct effect on calibration, it does have a perceived effect if set incorrectly. Usually, incorrect means set to a too high value, causing 'ringing' artefacts around image edge transitions.

Colour
Colour usually controls the colour saturation within the display's fixed gamut. That means it will increase the saturation colours that are within the display's gamut, but will have little or even no effect on colours at the gamut edge. Colour should be set to maintain internal gamut colour saturation accuracy, and not to try to extend the display's maximum gamut.

Tint
Tint is often a very simple colour ratio balance, usually altering the ratio of green to red, making one colour more prevalent compared to the other. With most modern displays this should be left at 'null'.

Hue
Hue can be present as an alternative to Tint, and changes the overall screen colour based on a vector rotation. As with Tint, this should be left null if better CMS controls are available. On some displays the 'Hue' control is just a 'Tint' control, again just altering the ratio of green to red.

Tone
Tone, or Colour Temperature, is usually a simple set of presets ranging from Cool, to Warm 1, and Warm 2. The correct setting is the one that sets the white point colour temperature closest to the desired standard. Warm 2 is usually closest.

Gamma
Gamma controls are often a simple selection of presets, meaning the closest value to the desired target should be used, or a slider with relative values. The offered presets are often not the same as the suggested value they are labeled with, so the result must be profiled (measured) for verification.

Many displays, especially those that are selected by users looking for decent image display capabilities, have additional 'Advanced Settings'. Theses controls usually include more accurate CMS (Colour Management System) capabilities, but may also included some of the controls listed above.

White Balance
White Balance sets the grey scale neutrality (colour temperature), often via 2 point or 10 point controls, depending on the display. 2 point allows for the colour temperature to be set individually for low brightness levels and higher ones. 10 point provides for control in 10% steps throughout the brightness range.

With multiple point White Balance you can often use the controls as 'fine' adjustments for Gamma, as changing the RGB values for each 'point' by the same amount, positive or negative, will change the relative luminance of the selected point, so altering gamma at that point.

RGB Bias & Gain
On many displays White Balance is controlled by settings called RGB Bias, Offset, Cuts, or similar for the low-end, and RGB Gain, Drive, or similar for highlight control. Such controls work as for 2 Point White Balance.

Gamma
Some displays - very few - offer an advanced Multi-Point Gamma control, which can be used to finely tune the overall gamma response of the display.

Colour Space
Colour Space provides control of the display's gamut, within the limits of the screen's capabilities. The only option we are interested in is 'Custom', as this allows the user to set the colour space as accurately as possible to the desired colour space standard. This is often via controls for RGB primary as well CMY secondary colours.

Having secondary CMY controls goes against standard display calibration colour science, as secondary CMY colours should be a simple and direct calculation from the primary colours, and shows the poor colour management inherent in most home TVs.

Most home TVs also have a plethora of additional modes/controls that must be disabled for accurate display calibration. Such modes include:

Dynamic Contrast
Advanced Contrast
Black Tone
Black Correction
Advanced Contrast Enhancement
Auto Light Limiter
Live Colour
Dynamic Colour
And many, many more...

Such modes, if active, will defeat any and all attempts at accurate display calibration.


The Toolbox

The tools required for Manual Display Calibration are basically the same as for 3D LUT calibration, as the initial steps are essentially the same.

LightSpace DPS
The free LightSpace DPS version of LightSpace CMS can be used for all the manual display calibration steps outlined within this guide.

Probe
A probe is required to measure values from the display, enabling the correct manual settings to be made. The cheapest probe we recommend is the i1 Display Pro OEM RevB, especially when you consider the actual level of accuracy possible with Manual Display Calibration.

Patch Generator
Patch Generation is required to enable known stimulus colours to be sent to the display being calibrated, enabling the probe to take readings and allow LightSpace DPS to compare the measured values with the actual target vales for the required colour space. For most calibration work the HDMI output from the LightSpace CMS laptop is perfect from this, as it enables Closed-Loop (the probe and patch generator are both under LightSpace CMS control) measurements. More information can be read on the Direct HDMI for Display Profiling page.

If it is desired to use an external Patch Generator, and a purchased license for LightSpace CMS is being used, LightSpace CMS is compatible with many different systems, from the IS-Mini, to Resolve, Scratch, and Mistika, as well as the Lumagen and Prisma LUT Boxes, DVDO Test Patch Generator, and madVR HTPC system, plus many others. See the Tips & Tricks pages for more info.

Calibration Test Patterns
Test Patterns are used for two distinct applications. The primary use is to enable the manual setting of display controls, for black and white levels for example. The second application is to enable controls that are not directly colour related to be set - such as 'Sharpness'.

Calibration Discs
Calibration Discs can be used as an alternative to patch generator, specifically with the DIP mode (Display Independent Profiling)capability of LightSpace CMS, which enables the calibration disc to automatically play the correct colour patches as required for LightSpace CMS profiling, as well as providing a plethora of alternative Test Pattern images. We recommend the use of Ted's LightSpace CMS Calibration Disc.


Initial Display Setup

With the required tools at the ready it's time to start the Display Calibration process. This guide will focus on the basic requirements, but any competent individual will quickly understand that there are additional possibilities that can be utilised to enhance the whole calibration procedure. There are additional User Guides that can be reviewed to advance user knowledge.


Pre-Calibration Profile

Before embarking on any calibration workflow it is a good procedure to first profile the display to assess its present calibration status. With LightSpace CMS this is simple to perform using the system's Quick Profiling capabilities, and will help define the areas of manual display control that need particular focus.

  • Start LightSpace CMS, navigate to 'Tools/Discoverable Probes' and select the correct probe.
  • Connect the probe.
  • Allow 20 to 30 minutes probe warm-up time.
  • Start the display, and again leave for 20 to 30 minutes warm-up time.
    (To shorten warm-up times it is possible to run dummy profile sequences.)
  • Open the 'Calibration Interface' window, and follow any on-screen instruction for probe calibration, if needed.
  • Select 'Probe Options' and set the required parameters for the probe and display combination.
    (Review the Profiling User Manual for more information on Probe Options.)

Direct HDMI

  • Using Extended Desktop enables LightSpace CMS to run on the laptop screen, and the Patch Sequence run on the display to be calibrated.
    (It's a good idea to also set the laptop Desktop Background to black.)
  • Double click the small 'Patch Window' to open the free-floating patch window, and drag to the Extended Desktop, which is the display to be calibrated.
    (A double click on the free-floating patch window will remove the window border.)
  • Set the patch windows to the desired size, and place the probe as required to read the patch location.
    (Patch size and probe location - contact or non-contact - depends on the display technology being profiled, usually contact for LCDs, non-contact for displays that heat up substantially, such as Plasmas and OLEDs, and also non-contact for projectors. Set 'Extra Delay Time' if the display requires 'settling' time between patch changes - Plasmas for example.)
  • Set the Target Min & Max Luminance values for the display using the 'Options' menu - either manually or automatically via the Update button - and select the target Colour Space from the drop-down menu on the main Calibration Interface window.
    (The Min & Max Y values do not 'need' to be set at this point - as they can be changed at any time - but they set the Target Values, and are the basis for the reported Y accuracy during measurements, and so will affect the reported Delta-E values when performing Manual Measurements.)
    (For initial profiling these should be set manually to the ideal values for the display to be profiled - such as 0.05 Nits Min, and 100 Nits Max, as is defined ideal for a Grade-1 professional display.)

Min Max Luminance

Probe Matching

Probe Matching is a technique used to 'calibrate' one probe and display combination to another probe, on the same display. This means faster and cheaper filter based probes can be matched to slower and more expensive spectrometers, increasing the profile accuracy, while benefiting from the filter probe's speed and better black level reading.

  • Attach the first probe, selecting standard probe parameters as required
    (As this will ba a Tri-stimulus probe use the probe's 'default' matrix pre-set, not a display specific one as you are building your own 'matrix')
  • If using the LightSpace inbuilt patch generator, enter a matrix name and press 'OK'
    (Use a name that includes the display and probe details)
  • Place the probe on the patch window and press 'Measure'
  • The patch window will cycle R, G, B and W patches, and save the probe/display matrix data
  • Change the probe to the second (Spectro) probe, and repeat the process
    (Be aware Spectro's do not use matrix pre-sets)
  • If using a separate patch window, not controlled via LightSpace, use the RGBW 'Update' buttons in-turn
    (Each patch colour needs to be a value of 240 to match the LightSpace patches)
  • Enter a name for matrix when prompted
    (Use a name that includes the display and probe details)
  • With the probe placed on a patch of the matching colour press 'Measure' to take a measurement
  • When White is measured the Luma value will be updated too
  • Alternatively, manually enter the xy values, remembering the Luma value too when reading White
    (As with direct LightSpace matching, the colour patches MUST be based on 240 data, NOT 255)
  • Select the Reference Probe/Display matrix from the lower drop-down menu
  • Select the Active (in-use) Probe/Display matrix from the upper drop-down menu
  • All measurements will now be 'corrected' using the Probe/Display matching function
    (You must always use the Tri-stimulus probe's 'default' matrix pre-set, as used when performing the probe matching!)

See the Probes - User Guide for further information.

  • From within the 'Calibration Interface' window select 'Profile' from under 'Quick Profiling'.
  • Select 'Closed Loop Mode', and 'Primary & Secondary' from the drop-down list.
  • Press 'Start', and enter a profile name, such as 'Pre_Calibration', in the pop-up window, and click OK.
    (Another pop-up window will appear with a 30 second countdown, providing time for room lights to be turned-off, etc. For immediate profiling press the provided OK button.)
  • The patch window will run through the selected Patch Sequence, plotting the results on the various graphs, and show the patch target values and the actual measured results while profiling, including showing each measurement accuracy via the 'Zoom' widget window.
  • During profiling the 'Active Measurement' values show the perfect 'Target' values for the patch colour displayed, and the 'Actual' values as measured from the display, based on the user set Luminance value and selected Colour Space.

Ted's LightSpace CMS Calibration Disc

To use Ted's LightSpace CMS Calibration Disc for a Quick Profile you will need to know the Maximum time taken for the reading of dark patches.
(The only way to verify the actual timings required for DIP Mode is to 'time' the duration any given probe/display combination requires when measuring dark patch colours - not just black, but dark R, G, and B patches. The longest time, plus one second, must be used as the time for all patches in DIP Mode. To take such time duration measurements use the live 'Measure' mode with colour patches displayed manually via whatever source is connected to the display to be profiled.)
(Here are instructions for measuring probe read times using the 'Meter Time per Patch Finder Chapter' of Ted's Calibration Dics.)

Then simply set the disc to the correct Quick Profile chapter for Primary and Secondary patches, and from within LightSpace's 'Calibration Interface' window select 'Profile', then select 'DIP Mode', and also 'Primary & Secondary' from the drop-down list.

To start the profile sequence press 'Play' on the Blu-Ray player, and the last 'OK' button on LightSpace (shown when the 30 second timer is counting down) at the same time. Both the Blu-Ray and LightSpace CMS will run 'in sync'.

  • To evaluate the profile data further, select 'Manage', and from the Manage Colour Spaces library window select and 'Display' the profile.
  • 'Display' via the Manage Colour Spaces library has additional options that help evaluate the display profile data. Looking at the above image the option for 'Gamut Triangle Level' has been used to show that the display has a wider gamut (specifically in blue) at RGB stimulus level 166, 166, 166, compared to level 255, 255, 255, as shown in the initial graph.
    (The various 'Filters' can be used to view specific colour measurement data, as well as the Luminance Min/Max and contrast ratio being shown.)
  • Additionally, any point within the CIE diagram can be double-clicked to show further detail on the selected point

Point Select

  • The various graphs also show the full display set-up, including Gamut, Gamma, RGB Separation, RGB Balance, Grey Scale Delta-E, and full Delta-E Distribution.
  • From the 'Display' graph window the 'Export PDF' button can be used to generate a report with all the profile data included.
    (If using the Free LightSpace DPS version it is a good idea to use this at this stage, as closing LightSpace DPS will lose any and all profile data collected.)
  • If desired, a second or even third Quick profile can be performed using different Quick Profile options, such as a 'Gamut Sweep' or 'Memory Colours' selected from the Quick Profile drop-down list, enabling further display evaluation.

Calibration Quick profile Menu

Having performed Quick Profiles, the results can be assessed by comparing the plotted data against the ideal target points. In most cases incorrect calibration will be easy to see as the plotted points will vary from the colour space targets. The Delta-E graphs are really of little use at this stage, as unless the display is close to accurate the errors will just be huge!


Display Issues
Bad Gamut

Bad Gamut can be inaccurate colours, smaller than target Gamma, or as above, obvious 'Gamut roll-back'. Unfortunately, such 'roll-back' issues show very poor display internal colour management, and would take 3D LUT calibration to fix.

Bad Gamma

Bad Gamma can be just the wrong value compared to the target, or more obvious 'Dynamic Gamma' controls being turned on, as in the above graph, which need to be turn off if at all possible. If the effect is the result of ABL (Automated Brightness Limiting), which can't be turned off, as smaller patch size will be required.

Bad RGB Separation

Bad RGB Separation shows issues with the independence of the display's colour channels, with cross-coupling of the red, green, and blue colour channels such that when an input colour change that should affect only a single colour channel also causes changes within the other colour channels.

Bad RGB Balance

Bad RGB Balance will show that the Grey Scale has colour contamination, and/or that the colour temperature is not accurate to the target colour space.

Any errors within the profile graphs shows inaccurate calibration, and helps define the areas of the display that need looking at, from turning off Display Modes that cause serious issues, to using the Manual Controls to provided better calibrated accuracy.


Manual Display Calibration

With the Pre-Calibration data available and saved as a PDF report, the inaccuracies of the display can be assessed and the various display modes and settings reconfigured to correct for the errors.


Set Black & White levels

The first Manual Calibration settings to be set and verified are the relative Black & White clipping levels of the display. This can be performed using the downloadable Light Illusion CalImages from the Light Illusion website, or via Ted's fantastic LightSpace CMS Calibration Disc.

Whichever source you use, the process is much the same. Display the BrightnessCal and ContrastCal (or similar) images on the display to be calibrated, and adjust the manual controls as required to limit clipping/crushing.

As before, we will initially assume you are using the Direct HDMI connection from the LightSpace CMS laptop, using Extended Desktop mode to display the patches and CalImages on the display being calibrated. Using this technique the EDID data will re-scale the images to be the correct TV Legal range - 16-235 (64-940), meaning there will be no 'below black' or 'above white' bars as used from Ted's Disc source, as outlined below.

BrightnessCal Brightness
ContrastCal Contrast
  • With the BrightnessCal image displayed via a suitable graphics program (xnView is ideal for this, as it can display the images full-screen, with no borders or other visible text/info), use the display's Brightness control to set the image such that all patches are 'JUST' visible, with the darkest top left black patch more a 'feeling' of being visible, than really visible.
  • With the ContrastCal image displayed, use the display's Contrast control to set the image such that all patches are again 'JUST' visible, with the brightest white patch more a 'feeling' of being visible, than really visible.

For more information on understanding Black and White level issues, and the use of direct HDMI from the LightSpace laptop see Data vs. Legal TV Levels, and Direct HDMI.

Displays with 'Strange' Brightness/Contrast Controls

Some displays have Brightness/Contrast (and possibly Backlight) controls that do not function as expected, with Brightness acting more like Backlight, and Contrast just setting the peak clipping levels at any white level, with no direct 'Black Level' control.

With such display the aim is still the same - to get the best Blacks Level, with the correct White Level, with no clipping at peak white (Black clipping being uncontrollable).

Ted's LightSpace CMS Calibration Disc

  • If using a Ted's Calibration Disc for Black Level setup with flashing bars, via a Blu-Ray player, the Brightness control should be set to a point where the 'Below Black (2-15) and Reference Black (16) flashing bars are not visible, but the Above Black (17 and higher) to be visible.
  • Using Ted's Disc for White Level setup is similar, with the Contrast control being set to a point where the 'Reference White' (235) flashing bar and below are visible. While commercial Blu-Ray discs do not go above 235, there are some demonstration videos from reference disk sources that can include Super White. In that case adjust the contrast until your see the last 253 bar barely flashing.
  • The correct shade for the flashing bars is always neutral grey, with no colour shades(see 'Grey Scale Balance' later).
Brightness
Contrast

On some home TVs the way the Contrast control functions prevents Super White levels from being clipped, regardless how bright the TV is made. On such TVs just concentrate on getting the correct Peak White value, and ignore Super White clipping.

TV Legal Black and White Level Setup

There is a lot of confusion regarding the correct setup for Black and White Levels, based specifically on the concept of Super White (or Whiter Than White - WTW) signals that can go beyond the TV Legal level of 235 8 bit (940 in 10 bit). With Black Levels it seems to fairly well understood that home TVs should be set to 'clip' at 16 (64).

While in the world of production and post-production many cameras and post-systems can have valid image data beyond and below TV Legal levels (black and white), there are (presently) no consumer sources that ever contain valid content that is below 16 (64), or above 235 (940), so calibrating a home TV to 'allow' for Super White is just limiting the display unnecessarily, with no 'image' benefit at all - in fact, the exact opposite.


Data Range Black and White Levels

With displays that are not expecting TV Legal input sources, such as 'computer monitors', the correct Black and White levels will depend on the source in use - often 0-255 (0-1023) - but, depending on the sources in use, may be 16-235 (64-940).

For on-set & post-production displays the correct 'calibration' for Black and White levels will depend on the workflow in use, which many indeed be Full Range data signals, or TV Legal. It is imperative the the correct workflow, and therefore expected Black and White levels, are known and understood before calibration commences.

Set Peak White

With the Black and White levels set using the 'CalImages', the next step is to set the set the Peak Luminance of 100% white to the desired target value. For displays within an ideal viewing environment, one that is close to that encountered within a grading environment, and with Rec709 (or BT1886) as the Colour Space target that would be 80 Nits to 120 Nits. For displays within a less than perfect viewing environment some compromises will have to be made - and that is a 'personal' issue, based on what 'feels' and 'looks' perceptually right...

  • Display a 100% white patch in the display, from any source - via the LightSpace CMS patch window, Ted's Disc, or any other method.
  • Place the probe on the patch (or aim at the patch if in non-contact mode), and from the LightSpace CMS 'Calibration Interface' window select Measure/Measure, and continuous measurement readings will be displayed within the 'Active Measurement' area of the LightSpace window.
    (A measurement 'cross' will also be displayed on the CIE diagrams, but is not used for peak white value setting.)
  • While taking the continuous measurements adjust the 'Backlight' control on the display to get the target Nits reading.
    (As before, you can set the 'Target' Luminance values with the Min & Max Luminance option under 'Setups/Options', but all that matters is the 'Actual' reading is correct.)
  • If the display has no 'Backlight' control, the 'Contrast' control will need to be used to set Peak White. Obviously, this could cause 'clipping' if the Contrast value is set higher than set previously with the ContrastCal image, so this defines the maximum Peak White the display can be set to.
  • Regardless, after setting the Peak White value is is imperative that the Black and White levels are re-checked, and on many displays (especially home TVs) it is very likely they will have changed, and clipping/crushing will now be happening.
    (And after the Black/White levels have been re-checked, the Peak White value will need re-checking...)

Select The Best Picture Mode

With The Black & White levels set, as well as the Peak White Luminance value, the next step is to select the best 'Picture Mode' to obtain the best initial start point for final calibration.

Note, that after the best Picture Mode has been defined and selected, the Black & White levels, and the Peak White Luminance value will need to be re-set.

  • Using the above defined 'Quick Profile' process, select each available Picture Mode in turn, and run a Primary & Secondary profile, as well as Gamut Sweeps, and Memory Colours, and compare each of the measured results.
  • The aim is to find the mode that best matches the desired target colour space - Rec709 for example.
  • 'Best Match' will vary depending on the specific display being calibrated, and may just be Gamut and Gamma, or may include Grey Scale colour temperature (RGB Balance). With the closest Picture Mode defined and selected the displays further controls can be used to maximise display calibration accuracy.
  • Remember to turn off all the unnecessary additional 'Modes' that will prevent accurate calibration, and which will again require running a Quick Profile after each change in 'Mode' to assess the benefits for turning each mode on/off.

The following Quick Profile results compare two different Picture Modes from the same home TV. Direct comparison of the results shows that 'Movie Mode' is the more accurate.

Picture Mode 'Standard'

Picture Mode 'Movie'

After selecting the best Picture Mode remember to go back and re-check the Black & White levels as well as the Peak White luminance value, as it is likely these will have changed.


Set Gamma

With the best Picture Mode selected, and all unnecessary modes turned off, the next stage of calibration is to verify the display Gamma and set it as accurately as possible to the desired colour space standard.

For most home TVs the target colour space will be Rec709, with a gamma within the range 2.2 to 2.4, or possibly BT1886, with a variable shadow range EOTF (Electro Optical Transfer Function). The best target will depend on the Gamma controls available. With many display that will be just different pre-sets, or a slider to set different power-law values.

  • From within LightSpace CMS select 'Calibration Interface', and from the 'Colour Standard Target' drop-down menu select the desired colour space.
    (As standard within LightSpace CMS, Rec709 has Gamma 2.4, but any Gamma value can be used by making a new Colour Space, with the desired Gamma value.)
  • To make a new Colour Space with a different Gamma value open 'Convert Colour Space', and in either Source or Destination select one of the pre-set standards (Rec709 for example), modify the Gamma to the desired value, and re-save a new Colour Space with a unique name.
  • For example, for home cinema applications, where viewing conditions are often less than ideal, a gamma of 2.2 can often be more desirable.

New Gamma Value

  • With the new Colour Space saved, it can now be selected from the Colour Space Target drop-down menu within any of the associated menus.
    (If using the Free LightSpace DPS version remember all user based colour space info will lost when LightSpace is closed.)
  • If the display just has a selection of Gamma pre-sets, select each in turn, and run a 'Grey Scale Only' Quick Profile, and compare the profile results with the desired Gamma target. Use the pre-set that provides the best Gamma match.

Grey Only

If the display has multi-point Gamma capability each point can be set using the continuous Measure mode within LightSpace, matching the 'Actual' probe measured Nits values to the 'Target' value, as defined by the Min & Max Luminance settings via 'Setups/Options'.

  • Within the Calibration Interface set the Min & Max Luminance targets using the 'Setups/Options' menu, with the Patch Colour set to 100% white (255, 255, 255), and the desired Colour Space Target select from the drop-down list.
    (The Patch Colour needs to be set to 100% white as the 'target' Nits value shows the target for the selected patch Colour.)
  • With all three Patch Sliders 'linked' using the Tick Boxes, the Sliders can be set to any specific Grey Scale patch value, or with the % box ticked, set to any percentage value.
    (The 'Step' function can be used to 'step' through specific patches, based on the step value, making it quick to step through a range of specific patches.)
  • Setting the patch sliders to each grey scale patch in-turn, matching the multi-point Gamma settings within the display enables every Gamma point to be accurately set.
    (Start at 100% white and work down towards black, matching the multi-point Gamma steps of the display.)
  • In the image below the Target for 50% is 21.99 Nits, and the display is presently showing 22.82 Nits, so needs to be raised.
    (The xy colour information and Zoom Widgets are not really used for Gamma setting.)
  • After all Gamma points have been adjusted correctly, run 'Grey Scale Only' Quick Profile to verify the results. If the Gamma is not correct at any point, re-adjust using the above procedure for the points in the specific location that is incorrect.
Calibrated Gamma

Gamma

Calibrated Differential Gamma

Gamma


Set Grey Scale Balance

With the Gamma set correctly, the same basic approach is used to set Grey Scale Balance, this time focusing on the colour component, rather than the Luminance values.

Depending on the display, Grey Scale Balance may be called White Balance, or RGB Gain, Bias, Offset, Cuts, Drive, or similar for 2-point control, and may also offer multi-point control, from 10-point, or more.

LightSpace CMS Flexibility

The way the same basic procedure and tools are used within LightSpace CMS for Gamma and Grey Scale calibration shows the very open and 'free-flow- approach LightSpace CMS uses, without the need to adhere to rigid pre-set structures or workflows, with the inherent limitations such rigid approaches suffer.

As already stated, for most home TVs the target colour space will be Rec709, or possibly BT1886, which sets the expected Grey Scale Balance at D65, which is x:0.3127, y:0.3290. In very simple terms the target for Grey Scale Balance is to set the entire grey scale range to these exact coordinates, using the probe readings as displayed in the Zoom Widget, and Active Measurement 'Actual' values.

  • From within LightSpace CMS select 'Calibration Interface', and from the 'Colour Standard Target' drop-down menu select the desired colour space.
  • From the 'Setups/Options' menu make sure the correct Min & Max Luminance values are correctly set for the display.

If the display has just 2-point Grey Scale Balance controls use approximately 20% and 80% grey to set the two points, starting with 80%, and cycle between the two checking and re-checking the resulting accuracy.

  • Set the Patch Colour Sliders to 204, 204, 204 (80%), and with the Free Floating Patch Window active on the display to be calibrated, and the probe positioned to read the patch, use Measure/Measure to start continuous measurement readings.
  • Adjust the display RGB 'High' balance controls to hit the required xy values, which places the 'cross' directly in the centre of the Zoom Widget, and balance the RGB and Delta-E Bars.

The RGB bars within the Bars Widget show both Colour Balance and Luminance Offset. If the RGB bars are equal height, but above or below the centre line it shows the Colour is correct, but the Luminance is incorrect (high or low). If all three bars are at 'zero' it shows both Colour and Luminance are correct.

The White Bar shows Delta-E, so when all bars are at zero the calibration for the colour being measured is accurate.

Initial Grey Measurement

Initial Grey

In this example the initial grey measurement is too Green (low Red), as is shown by the fact the cross is offset towards the Green/Blue edge colours surrounding the white central part of the Zoom Widget, and as defined by the RGB bars. The White Zoom Widget bar shows the Delta-E error.

Corrected Grey Measurement

Corrected Grey

Here the Grey has been corrected by using the display's RGB High controls to increase Red and reduce Green, pulling the cross back to the centre of the Zoom Widget and balancing the RGB bars, so reducing the Delta-E error, making the the 'Actual' measured xy values as close as possible to the Target values.

When adjusting RGB High values it is a common rule of thumb to leave Green alone, and just adjust Red and Blue. While this is a good basic rule, there is a potential problem if raising Red or Blue causes the colour channels to 'clip' at 100% white, making the white balance at 100% incorrect, even though 80% is correct. So, 100% white needs to be checked after 80% Grey has been corrected, including using the ContrastCal image to check for possible clipping.

There is a second rule of thumb for RGB High adjustments that says RGB values should be reduced, never increased, to prevent potential clipping issues at 100%. This may, or may not, be a better approach than simply leaving Green alone... in reality a combination of both approaches is usually better. But always double and triple check with the ContrastCal image to check for possible clipping after any RGB High adjustments.

  • Change the Patch Colour Sliders to 51, 51, 51 (20%), and repeat the measure and adjust procedure as above. using the RGB Low controls to again hit the required xy values, and place the 'cross' directly in the centre of the Zoom Widget, and null-out the bars.

There is a real potential issue on some displays with using 20% Grey for RGB Low balance, as the backlight on many displays - White LED illuminated LCD displays specifically - can be overly 'Blue', and the backlight 'colour' can't be corrected for through calibration (it can only be 'changed' by using a different backlight with a less blue spectral response, such as changing to a display with a full array RGB LED backligh). With LCD displays the backlight has an ever increasing influence on the display colourimetry as the brightness of the display gets lower. If a problem is encountered with 20%, move up to 30%, and don't worry about 20% and below.

Initial Grey Scale Balance

Initial Grey Scale Balance

The initial RGB (Grey Scale) Balance, with obvious blue bias from the display's backlight from around 20% and below.

Corrected Grey Measurement

Corrected Grey Scale Balance

The final calibrated RGB Balance, showing that the backlight bias is still prevalent in the shadows, but with some improvement.

When adjusting RGB Low values the rule of thumb is to only raise the necessary RGB values to attain Grey Scale Balance, and not reduce values. This is to prevent 0% blacks crushing. As with the RGB High rules of thumb, this is not always the best approach as lifting values may cause black to lift too much... Just always double and triple check with the BrightnessCal image to check for possible crushing after any RGB High adjustments.

  • Swap between the 80% and 20% patches and double and triple check the results, as altering 80% will effect 20%, and vice versa.
  • If the display has multi-point Grey Scale Balance as well as 2-point, use the same procedure as outlined above for each selectable point, after first using the 2-point setup.
  • Run another 'Grey Scale Only' Quick Profile, and verify the results. If any areas show results that are inaccurate, go back and use the multi-point Grey Scale Balance to focus on those areas.
  • If the grey scale points are reviewed via either of the two CIE diagrams, through the Manage Colour Spaces library 'Display' option, any point can be double clicked to see additional data, including Delta-E.
  • After Grey Scale Balance has been set, go back and re-verify Gamma as it is likely it will have changed. This is because if all three RGB channels are raised or lowered in relative unison, the 'brightness' at that point in the grey scale will be altered, as for a Gamma correction.

Set Gamut & Colour

Gamut calibration sets the display to correctly map given peak primary input colour values such that the on-screen colour (chromaticity) for 100% Red, 100% Green, and 100% Blue is correct for the expected colour space standard of the source images. For example, High Definition TV images 'expect' to be viewed within a Rec709 or BT1886 colour space, which as part of their specifications set the Gamut (the Gamut for both is identical).

Peak Colour x Chromaticity y Chromaticity Y Luminance
Red - 255, 0, 0 0.06400 0.3300 0.2126
Green - 0, 255, 0 0.3000 0.6000 0.7152
Blue - 0, 0, 255 0.1500 0.0600 0.0722
White - 255, 255, 255 0.3172 0.3290 1.0000

Luminance (Y) is specified as a percentage, as there is actually no set value for Y within any colour space standard. As mentioned previously, Rec709 for example specifies peak white for a grade-1 display as being between 80 Nits and 120 Nits. And for home TVs the 'ideal' peak white may need to be a lot higher to overcome environmental considerations.

Additionally, Secondary colour chromaticity is also not specified with any given colour space standard, as they are a direct calculation from the primary colours, and should fall into place when Primary colours are set accurately. However, due to the usually poor colour management processing within home TV displays, CMY Secondary colour control is often (incorrectly) provided, so know the target values can help.

Peak Colour x Chromaticity y Chromaticity Y Luminance
Cyan - 0, 255, 255 0.2250 0.3290 0.7874
Magenta - 255, 0, 255 0.3210 0.1540 0.2848
Yellow - 255, 255, 0 0.4190 0.5050 0.9278

Colour calibration means that the volumetric colours within the specific Gamut are also correct. As with Secondary colours, all the values for volumetric colours are a direct calculation from the RGB primary colours, and each colour target is calculated within LightSpace CMS on the fly, as each colour patch is generated - seen here for a 'Yellow/Orange' colour.

  • From within the Calibration Interface select the desired Colour Standard Target, usually Rec709
  • If the display only has limited colour controls - usually just Colour and Tint/Hue - the best approach to calibration is to run a Volumetric Quick Profile, such as 'Gamut Sweep With Secondaries', or 'Memory Colour With Secondaries', makes changes to the Colour and Tint/Hue controls and re-run the Volumetric Quick Profile, making adjustments until the best result is attained.
    (Such simple colour controls have little, if any, effect on gamut, having a greater effect on the volumetric colours with the pre-defined Gamut, with Colour altering volumetric Saturation, and Tint/Hue altering the relative colour alignment.)
  • To assist in the calibration process using the Colour control, put up 75% Red (255, 64, 64), 75% Green (64, 255, 64), and 75% Blue (64, 64, 255) patches in turn, while performing a continuous Measure, and adjust 'Colour' to get the best overall result,
  • For Tint, as it usually alters the balance between Red and Green, and for Hue, as it alters all colours simultaneously, put up 75% Yellow, and adjust Tint/Hue for the most accurate result.

After calibration has been set as above, run Quick Profiles for 'Gamut Sweep' and 'Memory Colours', and verify volumetric colour alignment, with the targets being the small circles, and the crosses the actual colour measurements, with the centre crosses being the grey scale.

Rec709 Gamut Sweep

Rec709 Gamut Sweep

Gamut Sweeps maintain the same 'colour' level (100%, or 75%), and change the saturation level in progressive steps.

Rec709 Memory Colours

Rec709 Memory Colours

Memory Colours are a selection of colours that are common in every day life, and which the human eye is accustomed to seeing, so quickly spots unexpected variations in such colours.

Displays with Advanced colour calibration capabilities offer a greater level of colour control. including Gamut (within the physical constraints of the display), and can be calibrated to a greater level of colour accuracy. This is usually defined as 'Colour Space', and provides a 'User' option for advanced adjustment of each colour in turn - Red, Green, and Blue primary colours, and often Cyan, Magenta, and Yellow secondary (although as stated previously, such secondary adjustments should not be required in a well designed display!).

  • If not already done, from within the Calibration Interface select the desired Colour Standard Target, usually Rec709.
  • As with the previous 'Colour' control, select Red, Green, Blue, and also Cyan, Magenta, and Yellow in turn, and adjust the associated display controls to correct the probe measurement reading to match the Target chromaticity (xy) values.
  • Again, better results may be attained using 75% saturation colour patches, rather than 100%.
  • As with other calibration controls, the various adjustments may 'interact', so it will be necessary to re-visit most entries for a second, or even third time, verifying the final results.

Different displays have different controls for colour adjustment - RGB, HSL, xyY, but the use of them is the same regardless. The aim is to always make the 'Actual' measured readings match the 'Target' values, as accurately as possible, using the two CIE diagrams and Yxy or Luv values, depending on the chart chosen.


Sharpness

Sharpness can be set just about any time during Calibration, and the goal is to use the SharpnessCal image and set the display to have no 'Ringing' or 'Edge Artefacts' around the single pixel lines on the image.

Sharpness Ringing Sharpness Ringing
Correct Sharpness Sharpness

For most displays the best setting for 'Sharpness' id 'Off', or '0', although that is not always the case, so it is bets to verify with the SharpnessCal image.


Calibration Report

After calibration has been completed run a full set of Quick Profiles and verify the results are as accurate as possible. To export a PDF of the profile data enter 'Manage Colour Spaces', select the desired profile, and 'Display' it. The 'Export to PDF' button can be found at the bottom of the 'Display' window.

Post Calibration Report

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