How to convert RGB to CIE Lab color space?

How to convert RGB to CIE Lab color space?

Answer 1

[Image Analyst]

Convert the image to L*a*b* color space using makecform and applycform.

colorTransform = makecform('srgb2lab');
lab = applycform(rgbImage, colorTransform);

Here's a full demo here: http://www.mathworks.com/products/demos/image/color_seg_k/ipexhistology.html

[Sabarinathan Vadivelu]

How to seperate L, a and b?

[Image Analyst]

L_Image = lab(:, :, 1);  % Extract the L image.
A_Image = lab(:, :, 2);  % Extract the A image.
B_Image = lab(:, :, 3);  % Extract the B image.

[Deepak Panda]

I want to first quantize the RGB color space to 16 levels then I want to convert it to Lab color space. How can this be done.

This works well when, RGB color space have values between [0-255]

colorTransform = makecform('srgb2lab');

lab = applycform(rgbImage, colorTransform);

[Image Analyst]

Divide by 16, then make sure it's an integer (uint8). Then convert to lab. Or multiply by 16 and convert to lab, depending on what you want to do.

[zee falcon]

I want to convert rgb images to lab. But above code is not working.It not shows any output after the conversion.Help me out

[Adam]

doc rgb2lab

if you have >= R2014b and Image Processing Toolbox which you need for the above anyway (the toolbox)

[Image Analyst]

zee, you can also use rgb2lab(). But, what output are you expecting? You get an image. And to see that image you can use imshow(), or you can just look at its values in the variable editor in the workspace. But no output will get "shown" unless you do one of those two things. Otherwise all you get is a new variable.

If you want to see the 3-D color gamut, you can use colorcloud() (R2016b and later).

Answer 2

[Deepak Panda]

How can I transfer rgb to Lab color space with luminance [0 100], a [-86.18 98.23] and b [-107.86 94.47]

[Image Analyst]

Try this:

rgb2lab([1 1 1])
rgb2lab(uint8([255, 255, 255]))
rgb2lab(uint8([255, 0, 0]))
rgb2lab(uint8([0, 255, 0]))
rgb2lab(uint8([0, 0, 255]))

ans =          100     0.017536   -0.0061222
ans =          100     0.017536   -0.0061222
ans =       53.233       80.119       67.221
ans =       87.737      -86.176       83.183
ans =       32.303       79.204      -107.86

So a seems to go from about -86 to +80 and b seems to go from about -107 to +83. Why do you want something different? How will it help you?

[Deepak Panda]

I am following this paper.

Onur Kucuktunc, Ugur Gudukbay, and Ozgur Ulusoy. Fuzzy Color Histogram-based Video Segmentation. Computer Vision and Image Understanding, 114(1):125–134, 2010.

The authors have used L [0 100], a [-86.18 98.23] and b [-107.86 94.47].

[Deepak Panda]

Is there any difference between these two procedures of rgb to lab conversion

1. colorTransform = makecform('srgb2lab');

lab = applycform(rgbImage, colorTransform);

2. rgb2lab

[Image Analyst]

I wouldn't think so. Try it and see.

[Kondal Rao J]

If you have higher version than 2014....just rgb2lab is sufficient to convert the image to lab color space

Answer 3

[Yoon ThiriZaw]

Can we calculate rgb to lab without matlab code using hand calculation?

[Adam]

Of course. There are formulae. I don't know where, offhand, but it's just maths and I'm sure you are as able as me at doing an internet search to find it.

[Image Analyst]

Try here: easyrgb.com

First go from RGB to XYZ, then XYZ to LAB.

Or you could try Bruce Lindbloom's site

The above are just images so you can't click on them. But click on the link and go to the site and click on the formula you want and it will be there.

Just be aware that your LAB values will NOT be the same as what you get from a spectrophotometer, unless you do a calibration.

[Yoon ThiriZaw]

Thanks all!!!

Answer 4

[kasthuri c]

how to find the values of L paramete a parameter b parameter in Lab conversion method.

[Image Analyst]

labImage = rgb2lab(rgbImage);
LImage = labImage(:, :, 1);
aImage = labImage(:, :, 2);
bImage = labImage(:, :, 3);