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LightSpace CMS and Lumagen Radiance

 
Author Harry
ZRO
#1 | Posted: 27 Jan 2013 15:05 
Does it make sense to perform a full 17x17x17 display characterization, even if the Radiance mini/XD/XS only supports a 5x5x5 LUT?

In other words: While the upload is running - does LightSpace any special downconverting to the generated colour space (making a 5x5x5 3D-LUT for the Radiance), so 17x17x17 profiling is always better than profiling with only 5x5x5?

Author Steve

INF
Male
#2 | Posted: 28 Jan 2013 16:04 
Hi Harry,

Yep, as is explained here: http://www.lightillusion.com/home_cinema_calibration.html

Having more information before makes the fianl LUT more accurate.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author waltervolpatto
ZRO
#3 | Posted: 30 Jan 2013 15:41 
Hi Harry,
in a theoretic world, if the density of a cube does not match the density of the measurement, other factor will came in play to see if make a denser cube will make sense in order to have the maximum precision allowed by your device display.

If you like a bit of technicality behind it...

One of the way to look at it, is the interpolation error of the LUT itself when applied to another image or LUT transformations: if the point you want to transform is indeed coincident with one of the original lattice you have a 100% precision, if you are in the middle of the lattice cube you have the minimum precision and the order of the error can be visible: this depend upon few factors: the lut distorsion, the precision in measurements, the clamping, the way a LUT is applied to a picture (usually a theathedrical, pyramidal or a trilinear math): the statistical delta from the book (colors appearance models) of a 17x17x17 equally spaced respect the real value can be in the order of 5% in the worst case scenario.

To give you an example, imagine in the diagonal of LightSpace CMS cube where it lies the greyscale representation: 17 diagonals point will represent it.
Regardless in how much precision in the measurement you place there, only 17 points will be your reference. In your case, only 5 point will be. pretty much all the LUT interpolations make linear math, so if you look at your 5x5x5 is a 4 segment line. How a SCurve is represented then? poorly.

So, a LUT helps, a lot, but it is not a 100% precise model. the bigger is the density of the lattice the better accuracy you get. up o the point that some fo the samples (in the blacks) can be smaller that the tool you use to measure the sample itself making the process even more silly....

A 5x5x5 cube will have only a certain precision in display a transformation but the measurement that we do with LightSpace CMS has more than enough for most of the representation as Steve showed in the above link.

you can have two way to approach a 5x5x5 matrices: either you measure only that, or you measure a denser cube and scale that down to 5x5x5. As long as the point that you try to measure is NOT an inbetween of the measured lattice you are OK.
luckily, a 17x17x17 (vertices) cube, represent a 16 single side cubes lattice and a 5x5x5 (vertices) cube represent a 4 single side cubes: the point of the 5x5x5 are indeed exactly represented in the model.

A 10x10x10 (vertices) represent a 9x9x9 single cubes per side and that will NOT be coincident to your 5x5x5 models, so you will have a faster measurement but on top of the imprecision of a lesser dense cube you will find an interpolation error in order to make your cube: the worst case shows up in a odd-by-one scenario: devices that support 16x16x16 will have only two point perfectly represented in the original lattice and all the other are inbetween with the bulk of the interpolated ones smack right in the middle of the color space you want to represent.

I will check with Steve if we can make a case where only a 5x5x5 can be measured to speed up the process.

-Walter

Author Harry
ZRO
#4 | Posted: 31 Jan 2013 19:38 
Thank you very much, Walter, great posting.

Only one question to be sure: If I perform a 17x17x17 measurement, then - regarding the 5x5x5 limitation of the Radiance - I must not do any manual downsampling - this will be done by the "upload" function - is that ok?

Author waltervolpatto
ZRO
#5 | Posted: 1 Feb 2013 15:07 
Yes, at the moment this is held true.

I will check with the software engi if we can implement a different structure in order to measure only the point that you really need in order to save time in cases like yours...

Author Steve

INF
Male
#6 | Posted: 1 Feb 2013 15:41 
The new 'Hybrid' profile mode is probably what you need
Steve Shaw
Mob Boss at Light Illusion

Author Harry
ZRO
#7 | Posted: 10 Feb 2013 11:41 
Hi Steve

just to be sure:
My Radiance HDMI input and output is set to video level range (16 ... 235) to be conform with DVD / Blu-Ray specification.

Now let's say, I've done a display characterization of any display/PJ.
With this profile data I generate a target LUT (Rec709).
If I'm right, this LUT basically does not know anything about a video level range (16 ... 235).

Before I upload the LUT into the Radiance I have to convert the "full range" LUT into this video level range, using the prepend function 1023 -> 64-940 - should be correct, or?

Author Steve

INF
Male
#8 | Posted: 10 Feb 2013 12:03 
No, the LUT should just be uploaded as is - no alteration. The ONLY LUT box that many need a re-scale is the eeColor when used for video level signals, and that is a specific 'problem' with the eeColor.

We have a beta version of LightSpace that can use the Lumagen as a pattern generator - send me a private e-mail if you would like to 'test' it...
Steve Shaw
Mob Boss at Light Illusion

Author Harry
ZRO
#9 | Posted: 10 Feb 2013 12:15 
Thanks Steve!
Good to know that, I would've done it wrong.

And yes, I would like to "test" it; you got mail.

Author colorado
ZRO
#10 | Posted: 27 Feb 2013 20:18 
i have problems getting LS to connect to the Radiance.
using a Mac running VMWare i had no issues updating the firmware of the Radiance but LS just won´t let me connect
and upload LUTs.

has anyone here successfully achieved this?

Author Steve

INF
Male
#11 | Posted: 28 Feb 2013 08:35 
I would check the USB to Serial converter - some can be temperamental depending on the load they are put under.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author Harry
ZRO
#12 | Posted: 28 Feb 2013 11:47 
@colorado

maybe this link can help you ... I was also run into some Radiance USB connection trouble with my first LightSpace testings:
http://www.lightillusion.com/forums/index.php?action=vthread&forum=8&topic=72&page=7# msg607

Author colorado
ZRO
#13 | Posted: 28 Feb 2013 16:22 
i have now tested three different adapters and had luck with a CH340 USB Serial Adapter!

thanks for the tips though! i saved some money not buying the quite expensive Keyspan USA19HS USB-RS232 ; )

cheerz
mark

Author Steve

INF
Male
#14 | Posted: 28 Feb 2013 16:24 
Great news! USB to Serial converters can be a real hit/miss affair!

Steve Shaw
Mob Boss at Light Illusion

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