How can I measure the centroid of the object of an image and how to measure the distance from the centroid?

I need to measure the centre point of a lip image and measure the distance from the centroid to some point (left side, right side, up and down) of the lip. Must I convert the image to gray image first or can I convert it into YCbCr colour space?

Answer 1

[Image Analyst]

Try the color thresholder on the apps tab of the tool ribbon to get a mask. Then call regionprops on the mask to get the centroid. Then use sqrt() to get distances from the centroid to other locations you're interested in.

[Evelynn Tan]

If i want to measure multiple images, is there anyway to write a code for that?

[Image Analyst]

See the FAQ: http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

Answer 2

[Evelynn Tan]

I could not get a nice mask when I was trying on a lip image that I've cropped from a real person's photo. Is mask like this acceptable? And I'm still can not managed to get the distance from the centroid.

[Image Analyst]

Only you can say whether the mask is acceptable to the remainder of your algorithm.

To find distance, use sqrt(). To find centroids, use regionprops(). To get rid of small blobs, use bwareafilt().