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.

## 7 comments:

Thanks It is very useful and informative.

This code is not working

This code is not working.

It's working. Thanks alot

%Saturation

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

for this part I get this error.

"Subscript indices must either be real positive integers or logicals."

Hey will you please provide me code for RGB to HSL conversion ??? please any body help me for this topic

can you give me code in matlab to extract plate car's from image

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