MATLAB: Remap values of 256×256 array based on ranges

arrayscode generationdigital image processingimageimage processing

done like this
if (n_rounded>=-90.0) && (n_rounded<-67.5)
n_rounded=-90;
elseif (n_rounded>=67.5) && (n_rounded<90.0)
n_rounded=-90;
elseif (n_rounded>=-67.5) && (n_rounded<-22.5) 
   n_rounded=-45;
elseif (n_rounded>=-22.5) && (n_rounded<22.5)
     n_rounded=0;
elseif (n_rounded>=22.5) && (n_rounded<67.5)
n_rounded=45;
end
getting error Operands to the and && operators must be convertible to logical scalar values.

Best Answer

The basic problem is that both logical short-circuiting operators || and && operate on scalar value only. Here is an example:
>> false || true % both operands are scalar -> okay!
ans =
     1
>> false || [true,false] % scalar and vector -> error!
Operands to the || and && operators must be convertible to logical scalar values.
So clearly your n_rounded is not a scalar, as the inputs to the || and && operators are non-scalar. You can remove this error this by using standard or | or and & operators. Then you will meet another behavior that confuses many beginners: all elements must be true for an if to run:
if [true,false]
   disp('this will never run')
end
if [true,true]
   disp('this code will run')
end
Alternative Solution
Simply vectorize whole thing and use histc:
>> n_rounded = 180*rand(5)-90
n_rounded =
  -14.8919   -1.9345   50.4454  -66.2448  -47.7396
  -81.0622  -29.2105  -19.8470   79.5691  -26.4315
   72.4889   72.0097  -46.4956   82.1042   57.8149
   80.0617  -23.5356  -17.2958   13.5375  -87.2274
   -1.6445  -69.9835  -72.6382  -79.2397  -82.2557
>> edg = [-90,-67.5,-22.5,22.5,67.5,90+eps];
>> rep = [-90,-45,0,45,90,NaN];
>> [~,idx] = histc(n_rounded,edg);
>> rep(idx)
ans =
     0     0    45   -45   -45
   -90   -45     0    90   -45
    90    90   -45    90    45
    90   -45     0     0   -90
     0   -90   -90   -90   -90
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