Find pixel coordinates value of a centroid ?

[EDIT: Fri May 13 20:58:34 UTC 2011 - Reformat - MKF]

I want to find the x n y coordinates and pixel value of the centroid. Here is the code I have:

I = imread('mobil.png');
%I2 = imtophat(I,strel('disk',15));
level = graythresh(I);
bw = im2bw(I,level);
I2 = 1 - bw;
I2 = bwareaopen(I2, 200);
I3 = imfill(I2, 'holes');
s  = regionprops(I3, 'centroid');
centroids = cat(1, s.Centroid);
imshow(I3)
hold on
plot(centroids(:,1), centroids(:,2), 'b*')
hold off
impixelinfo

The car is :

Image

[Doug Hull]

please clarify your question.

[Image Analyst]

Not sure how I messed this question (a year and a half ago), but I have a tutorial in my File Exchange where I find centroids: BlobsDemo

Answer 1

[Sean de Wolski]

centroids = round(centroids);
cent_vals = Inotbw(sub2ind(size(Inotbw),centroids(:,2),centroids(:,1)))

[Walter Roberson]

In this context I think Sean means

cent_vals = I3(sub2ind(size(I3),centroids(:,2),centroids(:,2)))

[Sean de Wolski]

I was assuming I3 was a label||binary image. Thus he'd have to use the original non-modified image to get the pixel value. It's hard to tell though...

[Walter Roberson]

Good point. Though if he wants the RGB values then the mechanism would need to be modified some in order to get all three planes.

[danny agus]

i have try the code

but i still don't know how to use it..

i don't get any pixel value ?

[Sean de Wolski]

Yes, something like this.

idxr = sub2ind(size(I3),centroids(:,2),centroids(:,1));

pixPerPlane = size(I3,1)*size(I3,2);

idxg = idxr+pixPerPlane;

idxb = idxg+pixPerPlane;

rgbCents = reshape(I3([idxr;idxg;idxb]),[],3);

[Sean de Wolski]

What doesn't work for you Danny? Does it error out? Does it return incorrect numbers? Is there an m-lint error because of a parenthesis?

[danny agus]

not return incorrect numbers..

but no numbers are shown

i'm using 2 version of matlab

to crosscheck the codes

but still no numbers are shown

[Sean de Wolski]

Edit your question to contain EVERYTHING in your script. We can't diagnose it without seeing it...

[danny agus]

146

181

96

170

162

144

the value above are the number that shown

but why the pixel value didn't match ?

here is the pixel value that i check with impixelinfo

(135,85)

(133,311)

(341,214)

(341,298)

(593,68)

(528,289)

[Walter Roberson]

Those look like pixel coordinates, not pixel values. What value is shown after the ")" when you position to those positions ?

[danny agus]

i have revise the question

i mean the pixel coordinates

sorry for the missunderstanding..

[Walter Roberson]

Then that should just be

round(centroids)

to within the nearest pixel.

[danny agus]

thx for the help

Answer 2

[Walter Roberson]

Is there a reason you are using the Pixel List instead of doing as Sean suggested to you before:

round the coordinates returned from regionprops and use those as indices to get the centroid.

[danny agus]

because i can't get the coordinates ..

so i think i can get the coordinates use the pixelinfo

Answer 3

[Sean de Wolski]

It works perfectly for me; I only had to modify the extraction to I instead of I3, as Walter and I had hypothesized about.

I = imread('ans513.png'); %your image
level = graythresh(I);
bw = im2bw(I,level);
I2 = 1 - bw;
I2 = bwareaopen(I2, 200);
I3 = imfill(I2, 'holes');
s  = regionprops(I3, 'centroid');
   centroids = cat(1, s.Centroid);
   imshow(I3)
   hold on
   plot(centroids(:,1), centroids(:,2), 'b*')
   hold off
centroids = round(centroids);
idxr = sub2ind(size(I3),centroids(:,2),centroids(:,1));
pixPerPlane = size(I3,1)*size(I3,2);
idxg = idxr+pixPerPlane;
idxb = idxg+pixPerPlane;
rgbCents = reshape(I([idxr;idxg;idxb]),[],3);

%{
rgbCents =
147  146  144
145  145  143
 66   62   63
 11   79  102  %%%This is the value of the pixel at the center of your car
 86   77   72
 83   70   64
%}

[danny agus]

sean

11 79 102

is that come from the original image ?

if i point my mouse to the centroid of my car ( after segmentation )

in impixelinfo show (344,214) 1

which the 1 is represent the pixel

and 344,214 represent X and Y

can i get those x n y value

[Sean de Wolski]

well it's a BINARY IMAGE!!!!!!!! That means only 1s and 0s and since your car is white it's a 1.

11 79 102 are the rgb intensity components of the original image.

imtool(I)

%hold your mouse near the centroid...

%or

imshow(I)

hold on

plot(centroids(:,1), centroids(:,2), 'b*')

hold off

Have a great weekend!

(hopefully away from the computer screen)

[danny agus]

i'm sorry for the wrong question

what i search is the

pixel coordinates from my centroid

sorry for the wrong question

[Walter Roberson]

Danny, what is

round(centroids)

showing for you?

[Raka Mukherjee]

Hi,

The x and y values that the centroid property of regionprops is returning, is it the centroid of the connected components? For eg., I have a binary image and I have detected the connected pixels and found out the centroid of those connected pixels with regionprops. now i want to convert those centroid values into geographic coordinates (latitudes and longitudes). If I use the following will it give what I need?

u=r2.Centroid;

x= u(:,1); % the x centroid value

y= u(:,2); % the y centroid value

[lat1, lon1]=pix2latlong(Ref,x,y);

[Lat, Lon] = projinv(info, lon1, lat1);

Please guide me in this as I am not being able to figure out what is the mistake since the coordinates are not matching with the original image.

[Areeba Naseer]

hey,

@Raka Mukherjee did you get any solution regarding this?....i intent to perform the same task...please help me with this.