[geometric vision] 4.2 piecewise linear transformation

Be confused ：
Gmax Fmax abcd Selected value // It's mentioned in the code

close all;clear all; clc;
R = imread('peppers.png'); %  Read in original image , Assign a value to R
J = rgb2gray(R);  %  Convert color image data R convert to J
[M,N]=size(J); %  Get the rows and columns of the gray image （M,N） For convenient use 
x =1; y =1;
%%  In order to highlight the objects of interest in the image , Carry out segmented transformation on the image 
%%
for x= 1:M
    for y = 1:N
        if(J(x,y)<= 35) % For grayscale image data J  To transform , The processed results are sent back to the matrix 
            H(x,y)=J(x,y)*10;  
        elseif (J(x,y)>35 && J(x,y))
            H(x,y)=(10/7)*[J(x,y)-5]+50;
        elseif(J(x,y)>75)
            H(x,y)=(105/180)* [J(x,y)-75]+150;
        end
    end
end
figure,
subplot(121),imshow(J);
subplot(122),imshow(H);
%%  The three-stage transformation method actually selects an interval  , Use this interval difference to multiply the addition operation 
%%  In this algorithm   The selection range is  a= 35  b= 75  And the gray value is  0 -255 Between ... 
%%  Take the final calculation as an example   c = 350  d = 360  Gmax = 465 Fmax = 255