How to vectorize this code to eliminate nested For loops?

Question

Jae Min Lee 2018-9-6

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/417761-how-to-vectorize-this-code-to-eliminate-nested-for-loops

评论： Greg 2018-9-6

Would like to know how this code is vectorized:

for r=1:rows
  for c=1:cols
      if ((Lin <= Limg(r,c)) && (Limg(r,c) <= Hin))
          enhanceImg(r,c) = Lout + (Hout - Lout) * ((Limg(r,c) - Lin) / (Hin - Lin))^gamma;
      elseif (Limg(r,c) > Lin)
          enhanceImg(r,c) = Hout;
      else
          enhanceImg(r,c) = Lout;
      end        
  end
end

Lin, Hin, Lout, Hout, gamma are scalar values.

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Greg 2018-9-6

+1 for a very well formed question. Clear and concise, showed an attempt, and described relevant variable sizes.

That all makes it much easier to answer.

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Answer 1

Greg 2018-9-6

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/417761-how-to-vectorize-this-code-to-eliminate-nested-for-loops#answer_335649

编辑：Greg 2018-9-6

在 MATLAB Online 中打开

Most of that is straightforward, just a couple elementwise periods for safety. Then, the hardest part is getting the logic to put the right values into your output matrix.

%%%Pre-allocate to Lout saves one round of comparison + assignment
enhancedImg = Lout.*ones(rows,cols);
%%%Build a mask for your first if condition
blnOne = (Lin <= Limg) & (Limg <= Hin);
%%%Assign the arithmetic result to elements behind that mask
enhancedImg(blnOne) = Lout+(Hout-Lout).*((Limg(blnOne)-Lin)./(Hin-Lin)).^gamma;
%%%Another mask for the elseif condition
blnTwo = Limg > Lin;
%%%Assign Hout to those elements
enhancedImg(blnTwo) = Hout;
%%%As mentioned above, all remaining elements are already Lout, so no "else" condition is needed