How to add certain elements of an array

I have two 200 x 200 arrays of pixel values.

They are all negative values representing -dB values

All of the signal pixel values are >= -20.

All other pixel values (no signal) have been forced to -60.

I want to add both arrays so that only the signal pixels are added to have a summated signal intensity.

This relates to TFM imaging in Ultrasonics.

[MaHa]

Convert your -60 values into NaNs :

noSignal = find(A == -60);
A(noSignal = NaN); 

Then do your addition

[Alan Keenan]

Thanks for your answer, however, there appears to be a problem with the syntax of A(noSignal = NaN);

I entered

noSignal = find(img_dbLL == -60);

img_dbLL(noSignal = NaN);

When trying to run, I get the following message:

Incorrect use of '=' operator. To assign a value to a variable, use '='. To compare values for equality, use

'=='.

Answer 1

[Matt J]

I'll call your two arrays A and B.

map=A<-20 | B<-20;
result=A+B;
result(map)=-60;

[Alan Keenan]

Thanks, this works, however, I had to do result=A-B as adding the 2 negative numbers gave a smaller summed signal intensity.

[Matt J]

You're welcome, but please Accept-click the asnwer if your issue is resolved.

[Alan Keenan]

Done, cheers.