I'm generating a rec 709 correction LUT for a Panasonic BT-LH1700WE broadcast monitor. Overall the initial profile looks pretty good, but at low levels it's showing a clear bias towards blue, which looks to be caused by the backlight.

In the Probes User Guide on this site (http://www.lightillusion.com/probe_use.html) it says that

"it is imperative for clean calibration that the calibration software 'works with' this bias, and doesn't attempt to 'calibrate it out' as this is both impossible, and will result in unacceptable distortions in the shadow areas of any displayed image."

I just wanted to check if there's anything I should be doing within Light Space to make sure it's not trying to counter the backlight bias?

Thanks in advance!

Please explain further how you are 'seeing' this blue bias.

Steve

All the low level results skew towards blue below 35 IRE, for both greyscale and primaries. It's best if I just show a screen grab:

Is that the original profile?

Steve

Yes, I just did a quick profile, and will run a full one tonight when I've finished cutting here.

Ok - then yes, the display has a severe blue back-light bias.
(Actually, a lot worse than I would expect on a professional display...)

But, LightSpace will simply deal with that - nothing 'special' you need to do.

Also, the gamut is already lower that Rec709, and no 'calibration' will fix that.
You cannot 'add' gamut to a display that is low in gamut.

Can the display be set to a 'raw' mode?

Steve

Thanks for your help, Steve.

I'll dig around the settings but haven't found any options to set it to 'wide gamut' or anything similar yet. I'm aware I can't get the LUT to add colours the display can't reproduce. I'm just trying to make the best of what I have to work with.

It's not looking good - a min Luma of 0.4 Nits is way over acceptable levels for a professional display.

Steve

The backlight was cranked all the way up, so taking that down brought the minimum Luma down with it. I've reprofiled it, as well as the Panasonic client monitor, a TX-L47FT60B, which shows less of a colour bias but a higher minimum Luma.

I appreciate I'm making compromises with either of these (and I promise I'm saving for my own reference grading monitor to save me from this in the future!), but which one would be the lesser of two evils to generate a correction LUT for?

Neither is good at all
Peak Luma really needs to be 100 Nits, and Min 0.05 Nits
And both show inaccurate Gamut.
I would actually send them back the the supplier as not being fit for purpose.

Steve

I'm stuck with them for now unfortunately (it's not my kit and I'm working on someone else's premises). I'll be keeping my eye out for that Flanders Scientific, then...

Again, thanks for all your help. I'm learning a lot here. Even if it is the hard way.