Converting RGB Image to HSI

Converting RGB Image to HSI

H stands for Hue, S for Saturation and I for Intensity.

MATLAB CODE:

Read a RGB Image

A=imread('peppers.png');

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

%Represent the RGB image in [0 1] range

I=double(A)/255;

R=I(:,:,1);

G=I(:,:,2);

B=I(:,:,3);

%Hue

numi=1/2*((R-G)+(R-B));

denom=((R-G).^2+((R-B).*(G-B))).^0.5;

%To avoid divide by zero exception add a small number in the denominator

H=acosd(numi./(denom+0.000001));

%If B>G then H= 360-Theta

H(B>G)=360-H(B>G);

%Normalize to the range [0 1]

H=H/360;

%Saturation

S=1- (3./(sum(I,3)+0.000001)).*min(I,[],3);

%Intensity

I=sum(I,3)./3;

%HSI

HSI=zeros(size(A));

HSI(:,:,1)=H;

HSI(:,:,2)=S;

HSI(:,:,3)=I;

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

Explanation:

1.    Read a RGB image using ‘imread’ function.

2.    Each RGB component will be in the range of [0 255].  Represent the image in [0 1] range by dividing the image by 255.

3.    Find the theta value. If B<=G then H= theta. If B>G then H= 360-theta

4.    Use ‘acosd’ function to find inverse cosine and obtain the result in degrees.

5.    Divide the hue component by 360 to represent in the range [0 1]

6.    Similarly, find the saturation and the intensity components.

7.    Display the image.