- UID
- 8612
- 阅读权限
- 60
- 居住地
- 北京市
- 公司
- AV IT 4 HD Co., Ltd.
- 注册时间
- 2011-1-20
认证会员
尊正专业视频技术监视器代理商
- 注册时间
- 2011-1-20
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原帖地址：http://www.lightillusion.com/idiots_guide.html
Idiot's Guide to Display Calibration IDIOT'S GUIDE (Step-By-Step Display Calibration)
The following is a step-by-step guide to using LightSpace CMS for display calibration. 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.
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Step-by-step Guide to Display Calibration
The first step for any display calibration is to set the underlying display Black, white and colour temp and gamma to be as accurate as possible, using a minimum of the display's in-built controls.
It is imperative for final accurate calibration that 'the minimum' of in-built controls is used during this stage of set-up, including not using, or setting to 'off' any in-built calibration capabilities such as 'THX/ISF' type set-ups and controls. The reason for this is that such controls can distort the underlying display's colour balance (RGB Separation for example), introducing distorted cross-colours, making later accurate calibration next to impossible.
For a step-by-step guide to this initial stage of display set-up see the Initial Display Calibration page.
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LightSpace CMS Hardware Configuration
The simplest way to use LightSpace CMS is to utilise the PC's HDMI output to directly drive the display to be profiled and calibrated in extended display mode.
Direct HDMI Calibration
Additionally, when using a PC for direct profiling make sure all power saving and screen saver modes are deactivated. Not just because the screens need to remain active for profiling, but because such modes kicking in and out can cause USB communication errors that will invalidate and profile being made!
Using HDMI works because the EDID (Extended Display Identification Data) provided from the display as part of the HDMI standard lets the PC know what it is expecting in the way of signal levels (and more). So, for TVs the PC HDMI out re-maps the 0-1023 (0-255) range to 64-940 (16-235), as is expected, and as is correct for calibration. If this wasn't done, the lower blacks from the PC would be incorrectly clipped on most TV display, but displayed correctly on normal PC monitors.
This is true when using a PC output to a TV for desktop and stills presentation, NOT video footage. When a software DVD player or similar is used on the PC the DVD window is treated differently by the HDMI signal chain - the same as with normal DVD players - setting black to be 64 (16).
If problems are encountered with levels not behaving correctly it is likely the PC or the display is not providing or understanding the EDID correctly. Placing a Lumagen, or similar, in the path, and setting the input/output manually - PC or Video - can overcome such problems.
As stated above, it is imperative all inbuilt display calibration and management is deactivated prior to accurate profiling and calibration being performed. As a guide, the following images show some of the problems if internal display calibration remains operational, specifically on home TV systems.
Default Sony Bravia Gamut
Default Sony Bravia Gamma
Default Sony Bravia RGB Separation
Sony Bravia Gamut - Internal Calibration Off
Sony Bravia Gamma - Internal Calibration Off 
Sony Bravia RGB Separation - Internal Calibration Off
After calibration the display can be made as accurate as possible, allowing for the display's underlying capabilities.
Final Sony Bravia Calibration
Displays and Underlying Ability
Unfortunately, the images processing electronics used in most home TV sets is of very poor quality, making the default colourimetry less than ideal. This can be seen in the graphs above, which even with all user colour controls set to 'off' still generates a RGB Separation that is less than perfect.
By comparison the following graphs are from a standard HP PC display, showing that LCD screen really should have near ideal underlying ability. These displays are slightly low on Gamut, but Gamma, and more importantly RGB Separation, are good 'out of the box'.
Underlying Display Profile Calibrated Display Profile
 
The original Gamma profile is further out, but after calibration is just about spot-on.
The RGB Separation is close initially, and a little further out after calibration due to the underlying low Gamut of the display.
Compare the above 'original profile' graphs (the ones on the left) with to the previous Sony Brava TV original profiles. There is no reason for the Bravia to show such poor RGB Separation. other than poor internal image processing.
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Calibration Interface - Probe Options
The first step in profiling and calibration is probe and LightSpace configuration for direct live feedback measurements.
Attach the probe, and run LightSpace CMS, and then open the 'Calibration Interface' menu, accessed via the circular 'Target' button from the main level function icons.
The likely probes to be used with LightSpace can be selected when LightSpace CMS is installed. While multiple probes can be selected some probes will fight for USB activation, so it is best to limit the selected probes to the ones needed. Specifically, only select one of the 'i1' range (which excludes the i1 Display Pro as that is active by default, along with the Hubble).
When the 'Calibration Interface' is run the 'Probe Options' menu can be accessed from the 'Setups' areas, and brings up the Probe Options menu. From here different parameters can be set for different connected probes, depending on the probe's capabilities. Review the options and set as needed.
The main likely option is 'Integration Time', which if available should be set to a longer time for accuracy, and shorter for speed. Short times can be used for quick checking of a display prior to final profiling with longer integration times. For example, with the i1 Display Pro use 0.25 secs for quick checking (with the understanding that accuracy is limited), while using 3.0 seconds for final accurate profiling.
Set the 'Luminance Units' to the desired measurement format - Nits for monitors, and Ftl for projectors.
Other options may include display type (LCD/Projector/CRT), and Calibration Settings for backlight type (CCFL/LED/etc...). For backlight type refer to the display manufacturer's information on the type in use.
For initial operation ignore the Active Probe/Display Data & Reference Prob/Display Preset, and Probe Offset settings. These advanced tools can be of great help for advanced calibration, but are not necessary or basic operation.
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Calibration Interface - Measurement
The first step in calibration is to measure the display's underlying capabilities, using direct feedback from the probe and the 'Measure' capabilities of LightSpace.
The 'Colour Standard Target' area of the Calibration Interface is where the colour space the display 'should match' can be selected from the drop-down menu - for example, if the display 'should' match Rec709, select Rec709... This is not a requirement for profiling as LightSpace CMS profiling is totally separate from the target colour space, but is does give a comparison for the measured values, so can be very helpful to set when live measuring and profiling. Use the Colour Standard target drop-down menu to select the display's expected colour space. When selected the CIE graph circles show the expected values, with the cross showing the probe's actual readings. As there are no standard Luminance levels for the various colour spaces the manual slider can be used to set the expected level as a visual reference. The large primary colour circles on the CIE and the bar width on the Luminance thermometer provide an acceptable tolerance measurement.
The 'Patch Colour' area of the Calibration Interface is where the colour being measured is set. Clicking on the small colour rectangle patch will open a pop-up 'Calibration Area' window, which can be resizes and repositioned as required for direct probe measurement. Using Extended Display mode within the LightSpace PC, and direct HDMI connection to the display to be measured, the Calibration Area window can be relocated to the extended display.
When 'Measure' is selected there are two or three options available, depending on the probe in use. The main function to use is 'Measure', which plots the measured Gamut directly onto the CIE diagram displaying the value as a cross, and the measured luminance on to the associated 'thermometer' bar graph as a red horizontal line. Actual numerical values are reported in the 'Active Measurement' area of the menu. Obviously this requires the probe to be placed on the Calibration Area patch.
Using the 'Patch Colour' drop-down menu the required primary and secondary colours can be selected in turn to compare to the given Colour Standard Target as displayed on the CIE and Luminance thermometer graphs. The drop-down menu also provides 21 step grey scale patches so the colour temperature can be set as accurately as possible, using the minimum of display controls, as stated previously! The RGB primaries should be checked to be wider than the target colour gamut to allow 'meat' for final calibration. If the RGB primaries are very close to, or smaller than the target gamut final calibration will be a compromise, but still as good as it can be for that specific display (see the Initial Display Calibration page for further information on this subject.
Note: Secondary CMY colours should always be a simple calculation from the RGB primaries, and not be independently controlled. If they are, this suggest the display has inherent problems with calibration, which allowing secondary colour control attempts to overcome, and it is likely true accurate calibration will be difficult to attain.
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Calibration Interface - Quick Profiling
With the above live feedback 'Measure' operation having been used to check the display is as accurately set-up as possible, using the minimum of manual controls provided on the display, a Quick Profile can be made to check the rest of the display's underlying capabilities, including Gamma and RGB Separation.
The Quick Profiling capability is accessed via the 'Profiling' menu button, and opens up a new window with options applicable for Quick Profiling.
Before going on, it is important to understand that Quick Profiling is not a 'low quality' profiling option, but is actually better than a lot of the far slower, and more complex profiling techniques provided by alternative calibration systems. This is because of the way LightSpace separates profiling from calibration and LUT Generation.
Within the Quick Profiling menu the 'Set Time Per Patch' options configure the way profiling will be performed. With direct HDMI connection to the display to be profiled 'Closed Loop' mode is the main operation to be used, as LightSpace is directly controlling the colour patches being displayed. This is the fasted profiling mode as the probe is allowed to tell LightSpace as soon as it has a stable reading, and LightSpace responds by moving on to the next patch. In Closed Loop mode the time per patch slider is deactivated.
The 'Use Primary Only' and 'Primary & Secondary' options set the number and colour of patches to be used for profiling. As stated above, the secondary colours should always be a direct calculation of the primary colours, and so selecting 'Primary & Secondary' is only of use for display checking. Should there be a significant difference in the secondary colour accuracy compared to the primary colours the display will also have a very poor RGB Separation, and will not be suitable for 'Quick Profile' calibration - full Display Characterisation with an 11 to 17 point cube profile will be required.
Quick Profiling is based on 21 steps per colour, including grey scale, giving 84 patches total - 21x4. However, as the first patch for each colour is black, this patch is only displayed once, making a total of 81 patches for 'Primary Only' Quick Profiling.
To perform a quick profile, place the probe in the screen, click the small 'Patch Colour' to launch the 'Calibration Area' window, and position the window under the probe. Click the 'Profile' button found under the 'Quick Profiling' heading, and set to 'Closed Loop', 'Use Primary Only', and make sure the 'Active LUT' box has no LUT selected. Then select 'Start', enter a distinctive name for the profile, and click 'OK'.
After the profile has been completed the 'Gamut', 'Gamma', and 'RGB separation' tabs can be used to show the various parameters of the display.
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Convert Colour Space - Using a Profile
When the profile has been completed the 'Convert Colour Space' menu can be used to generate a calibration 3D LUT, for use in any number of systems that are 3D LUT capable.
In the 'Source' Colour Space drop down menu select the desired colour space. In the 'destination' Colour Space drop down select the actual display profile just generated.
Selection of Peak Luma, or the alternative Peak Chroma, defines the parameters the LUT is generated with - Peak Luma maintains the overall Luminance of the display, while Peak Chroma will drop the Luminance if required to prevent colour distortion, or colour clipping, in peak whites.
Peak Luma & Peak Chroma
A simple way to understand the difference between Peak Luma and Peak Chroma is to think about colour temperature, and what that means for peak white when colour temperature is changed from the display's initial set-up to an alternative colour temperature.
For example, if the standard display colour temperature is too yellow and too green, correcting it will require blue to be raised, while green is lowered, assuming red is approximately correct. As a result, the blue channel will clip (blue has to be raised as yellow can't be reduced as all displays are RGB only).
Using Peak Chroma will prevent the blue channel from clipping, but will reduce the overall white point, and will simultaneously reduce contrast and the overall gamut.
This is why setting colour temp as close as possible, but with the minimum use of the display's manual controls, is a key initial set-up as explained in the Initial Display Calibration page.
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After a LUT has been generated the effect of the LUT can be checked within LightSpace by using the 'LUT Preview' function. Using this display function on the display being calibrated - using the PC's extended desktop - gives a direct view of the LUT's effect.
Using the Calibration Images to preview the LUT gives a good visual indication of the LUT's effect.
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Calibration Interface - LUT Verification
After the calibration LUT has been generated it can be verified by loading the LUT into the 'Active LUT' box within the Quick Profiling menu, and performing a second Quick Profile.
The 'Active LUT' is applied to the colour patches before they are presented to the display, applying the calibration correction and enabling the LUT and therefore the calibration to be verified.
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Export LUT
When happy with the LUT and calibration the LUT can be exported in any of the many LUT formats LightSpace is compatible with.
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发表于 2012-10-26 20:55
中枪............................倒了..................
