I've gone through all the posts and phone conversations between us and some of the things I've read on your LS website at different locations and came up with the following list of things in one location you've said to consider for a quality LUT calibration. This is very raw. Pls provide feedback.
Kind Regards, JJ:
Light Space: Determining the LUT Calibration Quality … Raw Quality Related Statements
1. A good calibration system will provide both ways to overcome display and probe problems and the system understands what can, and what can't be calibrated, and does the best it can to calibrate what can, and doesn't allow what can't be calibrated to adversely affect the final result.
2. The aim of any calibration is to maximise the accuracy of the display within the limits of the display's capabilities, with a focus on the central core of colours within the display's required colour space. Light Space does this. Understanding this is very important, as many calibration systems focus on the extreme colour space colours (the primary colours) only. In the real world we see very few 'primary' colours, and focusing on them for calibration can often lead to very inaccurate final results, especially as many displays struggle with accurate primaries.
3. Additionally, calibrating at low-light levels can be very difficult with the more cost-effective probes available, with the probes introducing errors into the profile that do not accurately represent the display. Combine this with cheap displays that have a colour cast within their back-light, that shows in low-light conditions, but is overcome by the display as brightness is increased. Light Space understands the Display’s limitations and knows what can and cannot be calibrated. Such back-light cast colours cannot be 'colour corrected' out, although the profile data may cause other colour calibration systems to attempt to do so, causing inaccurate calibration results.
4. Use 1D-LUT Viewer to verify no 'kinks' in the shadow area that may introduce unwanted colour artifacts into the final calibration that’s introduced into the calibration by the probe's inability to accurately measure low-light levels.
4.1.1. If they exist, use the LUT Manipulation tools with LightSpace CMS as it is very easy to remove these errors, while keeping the underlying profile data.
220.127.116.11. For example, the LUT Manipulation 'Axis Blend' and 'Smooth' tools can be used to reduce the error.
5. The only way to check a LUT is to re-profile through it.
6. A correct profiling system, such as LightSpace CMS, will generate an accurate profile of any display, and from that show what is or is not possible. The only way to do this is with a set of very standard profiling data/image. From this all displays can be compared. It is key that any calibration system understands what can, and what can't be calibrated, and does the best it can to calibrate what can, and doesn't allow what can't be calibrated to adversely affect the final result.
7. Quick Profiling can be perfect for displays with good RGB Separation. 3D Cube profiling, Display Characterization, is for displays with poor RGB Separation. With Display Characterization, you'll need a minimum of a 10 or 11 point cube (11x11x11) for any level of accuracy ... but 17pt is the best!. Many people just think the calibration LUT size, but the profile LUT size can be as important. However, for many displays the approach taken by the Quick Profile version of LightSpace is perfect. Calibration has to be a single approach, and the profiling specifically needs to be a single contained operation. For example, LightSpace does not need to know any of the display target parameters before profiling. That is key to a good calibration system - and yet few understand the importance of that simple fact. After generating a profile from a display anything is possible as far as calibration goes. Making sure the profile is good is critical, and that is what LightSpace focuses on.
8. PCs and Macs use ICC profiles for display calibration. But they are 1D LUTs only. To do real calibration you need a 3D LUT box, such as Pluto or Davio, or HDlink Pro (when BMD fix the problem with that box). See the Light Illusion website for more info on ICC profiles (SpaceMan), and the Forums for info on the HDlink problem.
9. The best way to calibrate is not with reference material, but with the workflow and images outlined on the Light Illusion website. Images are just used to set brightness and contrast limits, while the actual calibration should be done with automated patches that cover the required gamma and gamut. That's it - nothing else required
10. A .bcs file is the profile data, not a LUT. You can only see that via the 'display' function (CIE and Gamma charts). You need to then use 'Convert Colour Space' to 'show' the profile data as a LUT relative to any given colour space.
11. If there are cross-colour issues they will show within the RGB Separation Graph when doing the first profile. From this you should see all you need to understand the initial profile, and then the capabilities of the final result.
12. Make sure there are no ICC profiles active within the LightSpace PC as part of your Pre-Calibration setup. Use SpaceMatch DCM to verify no active ICC profiles are present. The HDMI out from the PC must be clean, with no ICC profiles.
13. Color Separation, LCD Displays: First, most LCD screens with no attempt at calibration have good RGB separation. We hardly find any that don't have good Separation. Plasmas can be a problem - but even then it's not bad at all. ICC profiles are used within PC and Mac systems to try to calibrate their displays, so when using the HDMI out of a PC to do patches for calibration you must make sure there are no ICC profiles active - this can be a problem as they can be very, very invasive, especially if you have ever used a ICC calibration program. The attached can be used to check the output for active ICC profiles. Any ICC will be reactivated when the PC is rebooted, so be aware. The comment on reducing brightness is only needed if you are changing the colour temp (white point) there is NO other reason to do that, and it really should not be left to the LUT to do that, as that will change the overall contrast/gamma of the display, which is bad! Always best the get the white point set as accurately as possible using the available controls first.
14. Check for no ICC profiles active. You then need to set all display controls to default, and do a Quick Profile to see what you have. You are looking to have an even cube display when you make a Rec709 LUT from the profile. Not a perfect cube, but one that is even in shape, with no kinks. Like the 'before' cube (the middle one) here for example: *** Spam Blocker deleted link *** (Scroll down the page a bit to the 3 cubes). Ideally, the LUT should not touch the sides of the Cube - showing you have enough gamut for calibration. The Gamut profile (after the 3 cubes) shows what that should be like, again with a bit wider gamut ideally. And the Gamma as close as it can be to the target ideally. And the RGB Separation should look close - maybe a bit of variation in the shadows, but that's all. Basically a single line. When you have this with the display it can then be calibrated. Keep the LightSpace PC directly connect to the display - no Lumagen. To check how well it can be calibrated make the LUT from the final profile, after you have the above set correctly. Then load the LUT into the Active LUT menu and re-profile. The result should look like Cube 3 in the above images. The RGB Separation may change as the calibration may have to distort that to get the correct colours. But is should be obvious that the calibration is working.
15. It's probably worth saying something further about RGB Separation... After calibration the RGB Separation will nearly always be worse as the calibration corrects the underlying colours, which can distort the RGB Separation if the gamut is under range in any area - if the gamut is larger than the target, across the whole range, the RGB Separation will remain good, or at least not get any worse. But, a raw (uncorrected) display should have near perfect RGB Separation - not having that is a good way to know that the display's internal image processing is not ideal (actually, it means it's bad!). To check this try profiling a good PC display - a Dell or HP screen for example. As they have little internal image processing they show what a raw LCD display should really be like. This is quite an eye opener!
16. The point pattern in a LUT is the 'inverse' of the display properties. So, if a point has move further into the cube (move further 'inside' the cube) it is showing the measured point on the display had too much 'colour' (gamut/saturation), and the LUT is reducing it. If a point has moved towards the outside of the cube is showing the measured point had too little colour... Points squashed at the edge of the cube show where the display is under gamut overall (same as the points in the CIE diagram being 'within' the target gamut). I'll work on a crib-sheet page for the website! But, a way to see what different point movement means is to make a 'New' LUT (File/New) and then use the 'LUT Manipulation' tools to see what effect changing Saturation, etc, has on the cube. For full Display Characterisation there really isn't a way to know what size cube profile is needed - a rule of thumb is the worse the display the larger the point size required...
17. From phone discussion with Steve: Use “Out of Gamut” color conversion feature to create a LUT cube image to visually see what colors the Display cannot produce, because they are Out of Gamut.
18. From phone discussion with Steve: Use Bars and Black Reference Image viewed through your Verification LUT (VLUT, rec709) to check for clipping and scaling issues. Check for any consistency with issues found in Out of Gamut LUT Image.