Photoshop image processing Algorithms-auto contrast and auto tone (auto levels)

1. Principle part

2. Program part (MATLAB)

Auto Tone

Clc;clear;close all;img=imread (' img_0950_cut.jpg '); Image=double (IMG)/255;figure (1); Imshow (Image); Percent  R=image (:,:, 1); G=image (:,:, 2); B=image (:,:, 3);p ercent=0.001;%% image_out (:,:, 1) =auto_tune (R, percent); Image_out (:,:, 2) =auto_tune (G, percent); I Mage_out (:,:, 3) =auto_tune (B, percent); figure (2); Imshow (image_out);

function I_out=auto_tune (I, percent)%%% the tonal range of the input image is 0-1. [Row, Col]=size (i);%%%sort the input Image valuei_sort=sort (I (:)); i_out=i;%%% based on the clipping percentage,%%% comput E the upper and lower boundaries if (percent==0)    i_min=min (i_sort)    I_max=max (i_sort) Else    I_min=i_sort ( Floor (row*col*percent))    I_max=i_sort (Floor (row*col* (1-percent))) ENDfor I=1:row for    j=1:col            if (I (I,J) <i_min)                i_out (i,j) =0;            ElseIf (I (i,j) >i_max)                i_out (i,j) =1;            else                i_out (i,j) = (I (i,j)-i_min)/(i_max-i_min);            End End End    

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Automatic contrast ratio

% Run File

Clc;clear;close all;img=imread (' lena.jpg '); Image=double (IMG)/255;figure (1); Imshow (Image); Percent  R=image (:,:, 1); G=image (:,:, 2); B=image (:,:, 3);p ercent=0.001;% to obtain the maximum minimum value for each channel [r_max,r_min] = Findmaxmin (r,percent); [G_max,g_min] = Findmaxmin (g,percent); [B_max,b_min] = Findmaxmin (b,percent);% to find a uniform maximum minimum value Max=max (max (R_max,g_max), B_max); Min=min (min (r_min,g_min), b_min); Image_out (:,:, 1) =auto_tune (r,max,min); Image_out (:,:, 2) =auto_tune (g,max,min) ; Image_out (::, 3) =auto_tune (b,max,min); figure (2); Imshow (image_out);

% to find the maximum minimum value of each channel cut by proportion

function [I_max,i_min] = Findmaxmin (i,percent)%%%sort the input image Valuei_sort=sort (I (:)); [ Row, Col]=size (I);%%% based on the clipping percentage,%%% compute the upper and lower boundaries if (percent==0)    i_m In=min (i_sort);    I_max=max (I_sort); else    i_min=i_sort (Floor (row*col*percent));    I_max=i_sort (Floor (row*col* (1-percent))); EndEnd

% is transformed according to the uniform Maximum minimum value

function I_out=auto_tune (i,max,min)%%% the tonal range of the input image is 0-1. [Row, Col]=size (i); i_out=i;for i=1:row for    j=1:col            if (i (I,J) <min)                i_out (i,j) =0;            ElseIf (I (i,j) >max)                i_out (i,j) =1;            else                i_out (i,j) = (I (i,j)-min)/(max-min);            End End End    

3. Operation Result

Figure 1 Original

Figure 2 Automatic contrast ratio

Figure 3 Auto Tone

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Photoshop image processing Algorithms-auto contrast and auto tone (auto levels)