How to calculate mid value of RGB image in matlab?

I did

RGB=cast(imread('Lenna.tiff'),'double'); 
c= mid(RGB(:));

And I got an error saying "Undefined function 'mid' for input arguments of type 'double'"

[Stephen23]

@Aarach Sap: I don't see any function listed in the documentation named mid:

https://www.mathworks.com/help/search.html?qdoc=mid

https://www.mathworks.com/help/search.html?qdoc=mid+type%3Afcn

Can you tell us exactly what you want MATLAB to do when you try to call a non-existent function?

[Aarach Sap]

I want to calculate max, min, and mid value of RGB image.

   M= max(RGB(:));
   m= min(RGB(:));
   c= mid(RGB(:));

But I got error on mid. How to calculate mid value ?

[Stephen23]

You possibly meant to call the median function, where the median is the standard mathematical term for the "mid value" of a set of values:

https://en.wikipedia.org/wiki/Median

Or perhaps the mean, where the mean is the standard mathematical term for the "average" of a set of values:

https://en.wikipedia.org/wiki/Mean

Answer 1

[Walter Roberson]

If you are referring back to that rgb2hsv and hsv2rgb C++ code you posted the link to, https://bitbucket.org/chernov/colormath/src/012a5ae28033dc8e91ec66ec349c95d81caddb71/colormath/hsv.cpp?at=default&fileviewer=file-view-default, then beware.

In the first of the routines there, rgb2hsv, mid is used as a variable that holds a copy of the value of one of the three color components. If you were to vectorize the code, then mid should be an array of values, not a function.

In the second of the routines there, hsv2rgb, mid is used as a pointer to one of the output values r, g, b, and after all the rest of the calculations, the value at that pointer is modified. If you were to vectorize the code, then you would need to make mid an array of indicators of which of the three values is to be modified for that location. The easiest way to do that would be to put your rgb together into a 3D array and then have mid be indices into the third dimension.