How to subtract image < double> from image<uint8>?

Hello, I have one CT image. and I have written code as-

I=imread('E:\ME IInd year\data base\ct data\download.jpg'); I1=imresize(o,[160 160]); a=rgb2gray(I); %original image

%find local max and min of image

p=imregionalmax(a); q=imregionalmin(a);

 %max-min average

M=(p+q)/2;

%subtract averaged image from original image

Max=uint8(M); %converted from double to uint8

Z = imsubtract(a,Max); %original CT - averaged CT

in this code imshow(M) shows averaged image but when I convert them to uint8 and write imshow(Max) then gives black screen. so, subtraction result is same as original image this is my problem. Why this is happening?

[Matt J]

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