Brigthness center in image using a brightness threshold using image masking

brightnessCenter.m

% example determining brightness center from a given image A
% Args to provide: mask, image, threshold (perhaps).
% given a selection mask and image A like the following:

mask =

   1   0   0   0
   1   1   0   0
   1   1   0   0
   0   1   1   1
   
A =

    43.851   118.591   246.394    89.275
   143.459   165.610   236.542    17.549
   235.809   255.000   255.000   236.195
   108.995   255.000   255.000   225.598

[xMax, yMax] = size(A)

% assumption color values in [0,255] 
% thus values above 250 can be supposed as being bright color spots.
brightness_threshold = 250

% instead using conditional statements prepare another mask
belowBriThrMask = (A-(brightness_threshold+1)) >= 0.0

% normalizationF is used in order to determine relative position.
maskedA = A.*(mask.*belowBriThrMask)
normalizationF = sum(maskedA(:))

% (x,y) indices in image:
% all possible index pairs (x,y), i.e. pixel-coordinates
% are formed by collecting element-wise - in both matrices - their elements.
xIdx = repmat(1:xMax, yMax,1)
yIdx = repmat(1:yMax, xMax,1)'

maskedXIdx = maskedA.*xIdx
maskedYIdx = maskedA.*yIdx

birghtnessCenter = [sum(maskedXIdx(:)),sum(maskedYIdx(:))] / normalizationF