Hi!

I just checked the source code of the ‘Mass Displacement’ calculation in the Module ‘MeasureObjectIntensity’.

I am not sure, but I think the formulas may not be correct (at least I do not understand their meaning ):

```
%%% Calculate the Mass displacment (taking the pixelsize into account), which is the distance between
%%% the center of gravity in the gray level image and the binary
%%% image.
PixelSize = str2double(handles.Settings.PixelSize);
BWx = sum((1:size(BWim,2)).*sum(BWim,1))/sum(1:size(BWim,2));
BWy = sum((1:size(BWim,1))'.*sum(BWim,2))/sum(1:size(BWim,1));
Greyx = sum((1:size(Greyim,2)).*sum(Greyim,1))/sum(1:size(Greyim,2));
Greyy = sum((1:size(Greyim,1))'.*sum(Greyim,2))/sum(1:size(Greyim,1));
Basic{Object,11} = sqrt((BWx-Greyx)^2+(BWy-Greyy)^2)*PixelSize;
```

I think it should read:

```
BWx = sum((1:size(BWim,2)).*sum(BWim,1)) / sum(sum(BWim));
BWy = sum((1:size(BWim,1))'.*sum(BWim,2)) / sum(sum(BWim));
Greyx = sum((1:size(Greyim,2)).*sum(Greyim,1)) / sum(sum(Greyim));
Greyy = sum((1:size(Greyim,1))'.*sum(Greyim,2)) / sum(sum(Greyim));
```

which would correspond to the following definition:

rCG = Sum[r*m®] / Sum[m®]

where the Sum goes over all vectors r, so basically, one computes a weighted average of all vectors, where the weight is the mass (=intensity).

does this make sense?!

another thing that I do not understand in this module is the following:

Greyim is obtained as follows:

Greyim = OrigImage(rmin:rmax,cmin:cmax);

I don’t see how you restrict the Center of Gravity computation to the pixels that belong to the corresponding object.

Shouldn’t it rather read:

Greyim = OrigImage(rmin:rmax,cmin:cmax) .* (LabelMatrixImage(rmin:rmax,cmin:cmax)==Object);

such that only the pixels contribute that belong to the current object?! (if objects are close to each other it will not be sufficient just cut out a square…)

(in the lines above, which deal with Perimeter related computations, this is not necessary, because you only access pixels belonging to the object perimeter…

for the center of gravity computation, however, I feel one needs it…)

what do you think?

Best,

Christian.