off by 1 error?
tjreedy at udel.edu
Sat Apr 10 01:41:22 CEST 2010
On 4/9/2010 4:10 PM, david jensen wrote:
> Hi all,
> I'm trying to assign a color to various values between some arbitrary
> maximum and minimum, and i'd like to go from red to blue to green .
> Currently, I have the following, where i'm passing the minimum and
> maximum as a 2-tuple:
> def getcolor( minmax, curr ):
One would need more info re minmax and curr and their relationship to
definitively answer your question.
> rangesize = (minmax - minmax) - 1
I would expect that either +0 or +1 woult be correct
> currsize = float( curr - minmax )
> currpos = currsize / rangesize
> colornum = int( currpos*511 + 0.5 )
The .5 may be the reason for the '1/2' question.
> r = max( 255 - colornum, 0 )
> g = max( -256 + colornum, 0 )
r,g are both 0 for both 255 and 256. I suspect this is reason for the
> b = 255 - ( r+g )
> return r,g,b
> 1) is there a better way to do this?
> 2) at the extreme points, this doesn't work: the number of (255, 0,
> 0)s and (0, 255, 0)s are 1/2 what they should be, and (0, 0, 255) is
> double what it should be.
> the above algorithm at least doesn't give me things like (0, -1, 256),
> which i struggled with for a while, but where is/are my off-by-one(s)?
Again, start with a complete definition of the params.
Terry Jan Reedy
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