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Converting RGB image to Binary Image without using im2bw function

         In the first example, image is filled with primary colors (RGB). So I am finding the sum of the values in the pixel position. If the sum is greater than zero then the value will be 1(white) otherwise zero (black).

       In the second example, the following steps are needed to convert a RGB image to binary image.

  1. Convert the RGB image into grayscale image.
  2. Find the threshold value. If the value at the pixel position is greater than the threshold value then the value will be 1(white) else zero (black).

    function mybinary
    global GIm T1;
    A=imread('shapes.bmp');
    figure,imshow(A);
    title('Original image');
    B=zeros(size(A,1),size(A,2));
    for l=1:size(A,1)
        for m=1:size(A,2)
            if(sum(A(l,m,:))>0)
                B(l,m)=1;
            end
        end
    end
    B=logical(B);
    figure,imshow(B);



    Im=imread('gantrycrane.png');
    figure,imshow(Im);
    title('Original Image');
    %0.2989 * R + 0.5870 * G + 0.1140 * B
    GIm=uint8(zeros(size(Im,1),size(Im,2)));
    for m=1:size(Im,1)
        for n=1:size(Im,2)
            GIm(m,n)=0.2989*Im(m,n,1)+0.5870*Im(m,n,2)+0.1140*Im(m,n,3);
        end
    end
    we can perform the grayscale conversion without using the for loop:

    %GIm=0.2989*Im(:,:,1)+0.5870*Im(:,:,2)+0.1140*Im(:,:,3);



    
    
    ssz = get(0,'ScreenSize');
    T.fg=figure('Visible','on','Name','IMAGE THRESHOLDING','NumberTitle','off','Position', ssz);
    T.holder=axes('units','pixels','Position',[ssz(3)/35 ssz(4)/4 ssz(3)-(ssz(3)/3) ssz(4)-(ssz(4)/3)]);
    imshow(GIm);
    set(T.holder,'xtick',[],'ytick',[])
    T.slid=uicontrol('Style','Slider','Visible','on','Value',1,'Max',255,'Min',0,'Sliderstep',[1 1],'Position',[ssz(3)/35 ssz(4)/5 ssz(3)-(ssz(3)/3) 20],'Callback', @tresher);
    T.ent=uicontrol('Style','pushbutton','Visible','on','String','THRESHOLD VALUE','Position',[ssz(3)-(ssz(3)/4) ssz(4)-(ssz(4)/8) 105 30]);
    T.ed=uicontrol('Style','edit','Visible','on','String','0','Value',1,'Position',[ssz(3)-(ssz(3)/4) ssz(4)-(ssz(4)/6) 90 20]);
          function tresher(object,~)
            val=get(object,'value');
            in=GIm;
            T1=Imthreshold1(in,val);
            T.view1=imshow(T1);
            set(T.holder,'xtick',[],'ytick',[])
           
            set(T.ed,'String',val);
          end
                                                                                 
                                                                                 
                                                                                 
                                                                                 
                                                                                 
                                                                                 
      function Im=Imthreshold1(Image,Tvalue)
    sz=size(Image);
    mybin=zeros(size(Image));
    for i=1:sz(1)
        for j=1:sz(2)
            if(Image(i,j)>Tvalue)
                mybin(i,j)=1;
               
            end
        end
    end


    Instead of this for loop, the equivalent one line code is:

    %mybin(find(Image>Tvalue))=1;

    Explanation:
    The output of find(Image>Tvalue) will be the values that are greater than Tvalue.



    For instance,
    consider a matrix,

    >> A=[1,2,3,4;2,4,6,8;3,6,9,12];
    >> A

    A =

         1     2     3     4
         2     4     6     8
         3     6     9    12

    >> find(mod(A,2)==0)

    ans =

         2
         4
         5
         6
         8
        10
        11
        12




    
    
    Im=logical(mybin);
    end
    end



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YIQ Image to RGB Image

MATLAB code:
%YIQ to RGB

%R=Y+0.956*I+0.621*Q
%G=Y-0.272*I-0.647*Q
%B=Y-1.106*I+1.703*Q
RGB=uint8(zeros(size(YIQ)));
for i=1:size(YIQ,1)
    for j=1:size(YIQ,2)
          RGB(i,j,1)=YIQ(i,j,1)+0.956*YIQ(i,j,2)+0.621*YIQ(i,j,3);
          RGB(i,j,2)=YIQ(i,j,1)-0.272*YIQ(i,j,2)-0.647*YIQ(i,j,3);
          RGB(i,j,3)=YIQ(i,j,1)-1.106*YIQ(i,j,2)+1.703*YIQ(i,j,3);
    end
end

figure,imshow(RGB);
title('RGB Image');

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RGB Image to YIQ Image

YIQ  builds the basis for the NTSC (National Television System Commitee) format.
The Component division of YIQ :
Y=0.30R+0.59G+0.11B
I=0.60R-0.28G-0.32B
Q=0.21R-0.52G+0.31B


MATLAB code:
Im=imread('peppers.png');


figure,imshow(Im);
title('Original Image')

%y=0.2989 * R + 0.5870 * G + 0.1140 * B 

%I=0.60*R - 0.28*G-0.32*B
%Q=0.21*R -0.52*G+0.31*B
YIQ=uint8(zeros(size(Im)));
for i=1:size(Im,1)
    for j=1:size(Im,2)
        YIQ(i,j,1)=0.2989*Im(i,j,1)+0.5870*Im(i,j,2)+0.1140*Im(i,j,3);
        YIQ(i,j,2)=0.596*Im(i,j,1)-0.274*Im(i,j,2)-0.322*Im(i,j,3);
        YIQ(i,j,3)=0.211*Im(i,j,1)-0.523*Im(i,j,2)+0.312*Im(i,j,3);
    end
end
figure,imshow(YIQ);
title('YIQ Image');

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RGB Image to Grayscale Image without using rgb2gray function

A gray-scale image is composed of different shades of grey color.
A true color image can be converted to a gray scale image by preserving the luminance(brightness) of the image.

Here the RGB image is a combination of RED, BLUE AND GREEN colors.
The RGB image is 3 dimensional. In an image ,
at a particular position say  ( i,j)
Image(i,j,1) gives the value of RED pixel.
Image(i,j,2) gives the value of BLUE pixel.
Image(i,j,3) gives the value of GREEN pixel.
The combination of these primary colors are normalized with R+G+B=1;
This gives the neutral white color.

The grayscale image is obtained from the RGB image by combining 30% of RED , 60% of GREEN and 11% of BLUE.
This gives the brightness information of the image. The resulting image will be two dimensional. The value 0 represents black and the value 255 represents white. The range will be between black and white values.


MATLAB CODE:

Im=imread('peppers.png');

figure,imshow(Im);
title('Original Image');

%0.2989 * R + 0.5870 * G + 0.1140 * B
GIm=uint8(zeros(size(Im,1),size(Im,2)));
for i=1:size(Im,1)
      for j=1:size(Im,2)
          GIm(i,j)=0.2989*Im(i,j,1)+0.5870*Im(i,j,2)+0.1140*Im(i,j,3);
      end
end

%Without using for loop:
%GIm=0.2989*Im(:,:,1)+0.5870*Im(:,:,2)+0.1140*Im(:,:,3);


figure,imshow(GIm);
title('Grayscale Image');











Check out : Partially colored gray scale image - MATLAB CODE
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