What is the difference between fac output and Color output in BLender? My understanding about fac is, it is grayscale information(devoid of any color). In which case it confuses me when people take a fac input and use a color output from nodes like Color ramp.

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    $\begingroup$ Fac is a single value (ie. Fac=0.75), Color is a RGB value (ie. (0.5, 0.7, 1.0)) $\endgroup$ – lemon Aug 16 '16 at 17:38
  • $\begingroup$ @lemon What does this single value represent, the brightness of the pixel? $\endgroup$ – ChrisOdney Aug 16 '16 at 17:51
  • $\begingroup$ This can be used as gray scale, but is often used to connect to 'fac' input in nodes such as "mix rgb" or "mix shader" (or as you said in a color ramp). Many possibilities... just think about it as a factor giving a 'shape' for the next node $\endgroup$ – lemon Aug 16 '16 at 17:54
  • $\begingroup$ As far as I know Fac is never an output but an input. Output would be value. $\endgroup$ – user1853 Aug 16 '16 at 18:34
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    $\begingroup$ I think I read somewhere that RGB to BW conversion in Blender is done using the Intensity channel in the HSI colour space, though I can't provide a source. From what it looks like to me, the Fac output of procedural textures, gives the same value as passing the Color output through an RGB to BW node, so I believe that the Fac output is basically the Intensity channel of the Color output. However, this is a guess based on my perception, and therefore I'm not prepared to give this as an answer. $\endgroup$ – user27640 Aug 16 '16 at 21:50

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