Calibrate Tone Curve Only?

[Anonymous]

Is it possible to calibrate tone curve only? I don’t want a matrix or white point correction in the icc profile. I don’t trust any color measurements because the backlight type is PFS WLED but only has sRGB gamut coverage, so none of the supplied corrections are suitable (I don’t have a spectrometer either, only an i1display studio colorimeter). The display is “factory calibrated,” but only to sRGB (no alternative tone curves available) which limits its usefulness (I would like bt.1886 or 2.4 gamma, for example). Video tends to looks washed out with true sRGB gamma. Another solution would be to create a generic icc profile that converts sRGB->different tone curve without any measurement because the gamma tracking already has delta E <2, but I don’t know how to make an icc profile like that.

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[Vincent]

Is it possible to calibrate tone curve only? I don’t want a matrix or white point correction in the icc profile. I don’t trust any color measurements because the backlight type is PFS WLED but only has sRGB gamut coverage, so none of the supplied corrections are suitable (I don’t have a spectrometer either, only an i1display studio colorimeter).

Then it is not a WLED PFS and you are wrong. Or it is a WLED PFS and it is not sRGB only (on some OSD preset)…which means that you are wrong too. Those two statements cannot be true at the same time.

The display is “factory calibrated,” but only to sRGB (no alternative tone curves available) which limits its usefulness (I would like bt.1886 or 2.4 gamma, for example). Video tends to looks washed out with true sRGB gamma. Another solution would be to create a generic icc profile that converts sRGB->different tone curve without any measurement because the gamma tracking already has delta E <2, but I don’t know how to make an icc profile like that.

NO correction, Native/As measured whitepoint, choose desired gamma, calibrate & profile. In displaycal user data folder you’ll end with an ICM and a CAL file. Cal is 1D grey calibration. You can use commandline in ArgyllCMS to attach that .cal to whatever synthetic profile you want, like Rec709 with 2.4 gamma or 2.2.
Cal 1D calibration will be applied system wide, ICM gamut & TRC will be published to color managed apps.

This way you’ll get what you want.. BUT IT IS WRONG. Color managed apps will look bad if published gamut & TRC info are not accurate.
Even without CCSS correction reading native 255 RGB colors will give you a hint of actual native colorspace (if you measure it in soem native gamut OSD preset… otherwise it’s pointless).

[Anonymous]

Then it is not a WLED PFS and you are wrong. Or it is a WLED PFS and it is not sRGB only (on some OSD preset)…which means that you are wrong too. Those two statements cannot be true at the same time.

I did not believe it was PFS WLED at first, but it is. One of the material science engineers at GE who works on PFS phosphor (GE owns the patent for using PFS in LEDs) went to an electronics store and measured the SPD of multiple laptops that were on the show floor to see how much market penetration PFS has. One of them was my device (Surface Laptop 3). He also explicitly called out Microsoft as being a “long time partner” for PFS WLEDs in the video. The engineer doing the presentation said PFS has better efficiency than other red phosphors so perhaps Microsoft decided to use PFS to get a more efficient laptop display.  The video is called “Wide Color Gamut, Narrow Band Phosphors by GE” and is posted to the “GE Research” YouTube channel. I’ve attached a screenshot from the video that has a picture of my device (I’ve circled my device to make it easier to spot) and its SPD indicating it uses PFS. The Surface line of devices are infamous for having sRGB gamut coverage with no way to change it (except for the Surface Studio which does have P3 gamut support). One of the reviewers on anandtech does display analysis and uses an i1pro2 for color measurements. He has reviewed most Surface devices and always posts a calman gamut coverage chart.

NO correction, Native/As measured whitepoint, choose desired gamma, calibrate & profile. In displaycal user data folder you’ll end with an ICM and a CAL file. Cal is 1D grey calibration. You can use commandline in ArgyllCMS to attach that .cal to whatever synthetic profile you want, like Rec709 with 2.4 gamma or 2.2.
Cal 1D calibration will be applied system wide, ICM gamut & TRC will be published to color managed apps.

This way you’ll get what you want.. BUT IT IS WRONG. Color managed apps will look bad if published gamut & TRC info are not accurate.
Even without CCSS correction reading native 255 RGB colors will give you a hint of actual native colorspace (if you measure it in soem native gamut OSD preset… otherwise it’s pointless).

Thanks, I’ll try this. The display really only has sRGB coverage and there’s no OSD to change it. The device uses a custom driver to supply factory calibration because Windows is inadequate. The only controls available are to switch between a generic “sRGB” or “Enhanced” profile that don’t have calibration data in them, so the calibration data is interfaced by the driver only. Brett Howse on anandtech publishes gamut coverage charts from calman for his reviews and has reviewed my device. He uses an i1pro2 for gamut coverage and the gamut was only 98% sRGB.

[Vincent]

Then it is not WLED PFS or (exclusive) it is not sRGB only. Ther is no other way. Likely that “enhanced” is native gamut. A simple test in MS paint will reveal it.

[Vincent]

If enhanced is native gamut, you’ll have to use WLED PFS CCSS correction for colorimeter that best fit those native primaries (or  custom CCSS, made at native gamut) EVEN IF YOU USE sRGB MODE. All in gamut colors are a combination of native primaries.

[Anonymous]

Enhanced is not “native” gamut. It is sRGB. The reviewer from anandtech asked Microsoft what the enhanced profile is in a different surface pro review and the Microsoft rep said this:

“The Enhanced setting on the New Surface Pro is a profile within the sRGB space where through special hardware and proprietary color processing we take the mid-tones as close to P3-D65 color gamut as possible while leaving skin tones as is.  The overall color contrast is also enhanced.”

When looking at a red swatch in paint, red actually gets less saturated and appears pinker when the enhanced profile is enabled. The gamut is limited in firmware unable to be changed or by hardware with the color filters. The display is not wide gamut.

The display is clearly using PFS as you can see from the SPD given by the GE engineer. It has the characteristic red spike(s) of PFS and the engineer specifically called out Microsoft as being a long time partner for PFS. Another post on displaycal by Lukedriftwood about the Surface Book has a clearer SPD and it indicates PFS. The Surface Book only has sRGB gamut support and the “Enhanced” profile (no way to change to “native” gamut). Search “Surface book displaycal” into google and you’ll find the post:

The Panasonic IPS panels used in Surface Book and Surface Laptop employ a quite unique “white LED” phosphor blend, which may involve potassium fluorosilicate, creating a characteristic narrow red peak in the backlight spectrum. I don’t believe DisplayCal has a spectral offset for this specific backlight type when using a colorimeter.

So, with all that being said, how can I make a custom WLED PFS CCSS with sRGB primaries? Which green primary do you think would be best?

[Vincent]

For the last time: If a device has WLED PFS backlight it is not sRGB only. If it is sRGB only it is not WLED PFS.
You (or manufacturer) can run whatever lut-matrix or shader colorspace simulation on top of those widegamut RGB primaries to simulate sRGB, but it is not sRGB only. End of story.

Hence you must use native gamut CCSS correction (the one that best fit that backlight by looking at green main wvlength and the presence or not of hump in shorter wvlength in red channel)  for that backlight EVEN IF YOU USE sRGB MODE. All in gamut colors are a combination of (backlight) native primaries.

[Anonymous]

Okay.

[Author]

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