On 2/22/06, Andrea Galligani <[EMAIL PROTECTED]> wrote:
> I calculated the delta E between this lab points:
> L = 54.44073903
> a = -34.82222743
> b = 0.18986800
>
> L = 54.92340686
> a = -33.45703125
> b = 0.00000000
>
> using several formulas obtaing this values:
>
> cmsDeltaE = 1.460
> cmsCIE94DeltaE = 0.719
> cmsCMCdeltaE = 0.769
> deltaCIE00( 1.0, 1.0, 1.0 ) = 52.908
>
> Is it right deltaCIE00 produces a so big value?
>
> If I modify the function in this way
> I obtain a value 0.72243850693447653.
>
> Is it correct?
Hi Andrea,
If I try this calculation in VIPS I also get 0.7224 for dE00, so I
think you are correct.
I do the quadrant test on a/b rather than on the result of atan(),
which seems safer to me. VIPS has:
/* Find h in degrees from a/b.
*/
double
im_col_ab2h( double a, double b )
{
double h;
/* We have to be careful we have the right quadrant!
*/
if( a == 0 ) {
if( b < 0.0 )
h = 270;
else if( b == 0.0 )
h = 0;
else
h = 90;
}
else {
double t = atan( b / a );
if( a > 0.0 )
if( b < 0.0 )
h = IM_DEG( t + M_PI * 2.0 );
else
h = IM_DEG( t );
else
h = IM_DEG( t + M_PI );
}
return( h );
}
John
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