Control/Dimming Converting RGB to RGBAW and RWAGCBI

[John Roper]

Hi,

I have this formula to convert RGB to RGBAW but I was wondering if anyone could help me with formulas to convert to other common fixture color formats such as RGBI or RWAGCBI.

Formula for RGB to RGBAW:

w = min(ri, gi, bi)
a = ri-w
if (a>(gi-w)*2) a = (gi-w)*2
r = ri-w-a
g = gi-w-a/2
b = bi-w

 

[Colin]

Golly, I just use my eyes.

 

[Jay Ashworth]

You're making lots of assumptions in those formulas about the spectral properties of the various sources that I'm not sure actually hold...

 

[DrewE]

Wouldn't the most direct conversion be to set R=R, G=G, and B=B, and keep the other additional color sources at zero? It seems to me that would most closely mimic the RGB original, as well, since the advantage of the additional color emitters is generating light with spectral qualities that plain RGB cannot properly cover.

That, and as Jay says, there are a lot of assumptions about spectral properties (and relative intensities of color components) that very well might not hold in practice. I rather doubt that all RGB fixtures, and particularly inexpensive ones, give the same ugly sort-of-whitish-but-not-really light for r=g=b=max, for an obvious example.

 

[Jay Ashworth]

And, ironically, Drew, even that's not enough: R doesn't always equal R.

This is why things like the ION have profiles even for non-mover LED fixtures; they have *done* the colorimetry work on that, to get to CIE primary illuminants (I think that's the proper term).

 

[robmerow]

This works mathematically. But as others have said has no practical use or ability to be successful in real life.
It does not account for the CCT of the white chip or the relative brightness of any of the 4 or 5 chips.
Without calibrated, measured data for the exact fixture type being used (and even then you're at the mercy of the manufacturer's color consistency and binning), ANY equation will not work in practice.
ETC does this better than anyone IMO, and even then, using data from their measured profiles, I find better results tweaking it by eye to match two different fixture types.

 

[macsound]

Inaccurate led colors is always most obvious to me on digital billboards that have random chunks replaced.
Then an ad rolls by with a solid color background and the sign literally looks like a checkerboard and the ad is totally indistinguishable.