PAR RGB white color correction

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zolwik73
Posts: 1
Joined: 26 Jan 2020, 21:45

PAR RGB white color correction

Postby zolwik73 » 26 Jan 2020, 22:02

I am a new user of the program "titan go" and I wonder if there is white
color calibration in the PAR RGB reflectors.
It is known from physics that the white components of RGB include the
following proportions: 0.3R + 0.59G + 0.11B
(https://www.scantips.com/lumin.html).
If the reflector manufacturer has set the RGB proportions well in the
equipment, then giving RGB=255,255,255 we will get white, and each
other combination values will give the same color on the spotlight as the one selected
in the program.
However, spotlights usually have 0.33R + 0.33G + 0.33B equal
proportions, because identical LEDs are mounted for individual colors.
After converting the correct proportions into DMX values for white, we
get: RGB=130,255,48 instead of 255,255,255.
Can we calibrate ranges for RGB components in the program?
For testing, I modified the R and B ranges in the .d4 file and obtained
a good color reproduction according to the settings in the program, but
in the 'visualizer' window
the colors are badly mated, because 'visualizer' operates on absolute DMX values
and assumes a good calibration of the device manufacturer.
To sum up, I have good colors in 'visualizer' and bad on devices or good
on physical devices (after changing the .d4 file) and bad in 'visualizer'.
Has anyone had a smillar problem?
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phb
Posts: 100
Joined: 09 Apr 2019, 14:02
Location: Avolites, Park Royal, London
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Re: PAR RGB white color correction

Postby phb » 27 Jan 2020, 08:22

Hello,

The mapping of a given chromaticity ("white") to an RGB triple is a slightly complex process, and is dependent on a number of factors such as the RGB colour space used and the white point selected.

The article that you've quoted gives the formula for determining Luminance from Linear RGB values in the Y'UV colour space (see https://en.wikipedia.org/wiki/YUV). Luminance is a property of a given colour, useful when transmitting or processing colours, but doesn't actually specify how to mix any given colour, including white.

That is to say, it's not quite as simple as plugging the values into that formula; for example, different fixture manufacturers could (and do!) put different wavelengths of blue LED in different fixtures, which would immediately change the proportions of R,G,B required to create a given colour.

That said, if there's a fixture which doesn't seem to render its colours accurately in the visualiser, please do let us know and we can investigate the cause of this with Capture.
Pete Bridgman :: Avolites
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sideshowbond
Posts: 179
Joined: 18 Nov 2016, 20:58

Re: PAR RGB white color correction

Postby sideshowbond » 02 Feb 2020, 22:34

little side note to this:

Hog used to calibrate fixtures for the use of HSI. They did this predominantly High End fixtures. With the ever increasing amount of LED fixtures they have - to my knowledge - decided not to pursue this any further as it simply draws manpower from doing more important things.

Not to forget that even the same LED fixture can have different white points depending on what batch they are from.

I'd set my palettes right for real life and deal with it in Capture...

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