what is the difference between rgb2gray and im2bw ?

I want to know the difference between the two functions ... arent both convert the rgb image to black and white image ?!

Answer 1

[Walter Roberson]

No, rgb2gray() converts to grayscale. For uint8 images, the output could have up to 256 unique values in the matrix. im2bw() converts to bi-level, and has only 2 unique values in its output matrix.

Effectively rgb2gray() converts RGB to "brightness", whereas im2bw() converts to two color ("logical" data type in fact.)

[Mahmoud Hassan]

its about that i face a problem in my code when i read image then try to binarize it using imb2w ... thats the error " Error using im2bw>parse_inputs (line 97)

IM2BW: Truecolor RGB image has to be an M-by-N-by-3 array."

so i thougt i have to use rgb2gray first then use imb2w ... am i right ?!

[Walter Roberson]

You can apply im2bw() to an RGB image or to a grayscale image.

But as discussed in my answer to your other question, https://www.mathworks.com/matlabcentral/answers/457695-how-to-know-if-image-is-rgb#answer_371591 there is a possibility that you are not using an RGB image. You might have RGBA or you might have a DICOM volume. Or maybe what you are passing is not a numeric array at all. Check with class() and size()