How to write this equation in matlab??

Hello everyone.In the below equation can anyone suggest me how to write this eqn in matlab..

L_in (x,y)=0.299.I_in^R (x,y)+0.587I_in^G (x,y)+0.114I_in^B (x,y).

where I_in is input image.

Many thanks in advance..

Answer 1

[Image Analyst]

Images are not indexed (x,y), they (like all matrices) are indexed (y, x) which is (row, column).

So, L_in (x,y)=0.299.I_in^R (x,y)+0.587I_in^G (x,y)+0.114I_in^B (x,y) would be

L_in(y, x) = 0.299 * I_in(y, x) ^ R(y, x) + 0.587 * I_in(y, x) ^ G(y, x) + 0.114 * I_in(y, x) ^ B(y, x);

Looks like a very strange equation though. What are R, G, and B and why are you raising the gray level of the image to those powers? And is I_in a gray scale image (which I assumed above), or an RGB image. If it's an RGB image, you might possibly want (the still weird):

L_in(y, x) = 0.299 * I_in(y, x, 1) ^ R(y, x) + 0.587 * I_in(y, x, 2) ^ G(y, x) + 0.114 * I_in(y, x, 3) ^ B(y, x);

or maybe you want (if you're trying to convert an RGB image into a gray scale image one pixel at a time in a loop):

L_in(y, x) = 0.299 * I_in(y, x, 1) + 0.587 * I_in(y, x, 2) + 0.114 * I_in(y, x, 3);

or (NOT in a loop over x and y):

L_in = 0.299 * I_in(:, :, 1) + 0.587 * I_in(:, :, 2) + 0.114 * I_in(:, :, 3);

or even, more simply:

L_in = rgb2gray(I_in);

[Rocky]

In the above equation,I'm separating only luminance part from rgb.I'm not using (rgb2gray)..instead ycbcr is used.

[Image Analyst]

rgb2gray() gets the luminance part of a color image. It's basically the same as if

1. you used rgb2hsv() and took the V component, or
2. rgb2ycbcr() and took the Y component, or
3. rgb2lab() and took the L component.

They're all basically the monochrome brightness or intensity of the image.

Actually they're not, UNLESS you do a color calibration, which most people (NOT including me) do. But that's a whole other story. Just be aware that if you look at any of those components with a genuine spectrophotometer (the gold standard instrument for measuring color), your digital values will not match the actual real-world colors measured with that instrument. It's a complicated topic and may not be needed for some situations. See attached tutorial.

Whoever did that crazy equation you had in your original post didn't know what they were doing.

[Rocky]

Thank you for your guidance..I will go through the link..

Answer 2

[David Hill]

If I is X-Y-3 matrix, then:

L=0.299*I(:,:,1)+0.587*I(:,:,2)+0.114*I(:,:,3);

You should look at:

L = rgb2gray(I);%converts with built in matlab function

[Rocky]

Thank you for your response..but I need to use ycbcr instead of gray..I need to know how to use x,y part(L_in(x,y))