if i give a image sample RGB picture, what is the final number it gives to length?

Replies to This Discussion

Permalink Reply by David Rutten on June 26, 2012 at 1:15am

When you auto-convert a Colour to a Vector, it will remap the RGB channels onto XYZ coordinates. So first of all you lose the information in the Alpha channel, it's gone forever. The mapping of RGB (which are integers between 0 and 255 each) to XYZ which could be any floating point values, is as follows:

Dim factor As Double = 1.0 / 127.5
x = (colour.R * factor) - 1.0
y = (colour.G * factor) - 1.0
z = (colour.B * factor) - 1.0

So if a colour channel has the lowest value of 0, the corresponding coordinate will be -1.0. If the channel has the highest value of 255, the coordinate will be +1.0. In the case of [255,161,161] it does:

Dim factor As Double = 1.0 / 127.5
x = (255 * factor) - 1.0 which equals 1.0
y = (161 * factor) - 1.0 which equals 0.262745 (rounded to 6 decimal places)
z = (161 * factor) - 1.0 which equals 0.262745

 

So the length of the vector with these xyz coordinates is:

SquareRoot of (1.0² + 0.262745² + 0.262745²) which equals 1.066803 (rounded again)

 

It also follows the largest possible length of a vector created this way is the Square root of 3, which roughly equals 1.732050

 

This conversion works both ways incidentally, so as long as you convert unitized vectors into colours you'll always get a non-clipped result.

 

--

David Rutten

david@mcneel.com

Poprad, Slovakia

 

Permalink Reply by momafresh25 on June 26, 2012 at 3:10am

Thank you for so detailed tutorial! very clear, thank you