Does Threefish encryption unresistant the differential attacks?

I applied Threefish encryption on grayscale image pixels (256*256). For analysis, I computed NPCR and UACI and found the following results:

NPCR = 0.0488 UACI = 0.0135 I use the following Matlab code for both NPCR and UACI:

D=(c1~=c2); % c1, c2 are cipher images with the same plain image but with 1 pixel difference

NPCR_m=sum(sum(D))/(256*256);

NPCR_m=NPCR_m*100

dif=(abs(double(c1)-double(c2)))/255;

UACI=sum(sum(dif))/(256*256);

UACI=UACI*100

Does Threefish encryption unresistant the differential attacks, or I made some mistakes in calculation?

[Walter Roberson]

Those formulas look plausible.

However for legal reasons we cannot discuss encryption here.

[Ansam Osamah]

Thank you very much