I am doing a road sign recognition program in Matlab and I want to recognize circular roadsigns. Therefore I use the matlab function imfindcircles. I would like to crop only the circular roadsigns and to put them in an isolate figure. However, we have other roadsigns on each figure (triangles or squares) but I don't want them. I have no idea how to do this. Here my code :
[im_bw,map] = imread('roadsign.JPG'); %image black and white
S = regionprops(im_bw,'Extrema','Centroid','BoundingBox');
[centers, radii] = imfindcircles(im_bw,[12 40]);
for k = 1:length(S)
im_cercle = imcrop(im_bw, S(k).BoundingBox);
im_cercle = padarray(im_cercle, [20 20]); % put each roadsigns in a small figure
if radii(k) ~= 0 % Error
figure,imshow(im_cercle); title 'Circle spotted'; % Show every circular roadsigns in a figure
else
figure('visible','off'),imshow(im_cercle); title 'wrong raodsign';
end
end
I tried some other conditions with centres and radii but when I execute the code, i get dimension errors or sometimes it shows me a shape which is not a circle. I also tried to do a variable that only sets when he finds a circle, but without results. Can you help me please ?
Thanks in advance.
What you do you expect the output of regionprops to be? It isn't picking out the circles - it's picking out all the "areas" (anything that is a connected area in im_bw). In addition while imfindcircles can find circles that overlap with other things, regionprops will detect overlapping areas as a single object.
On the other hand, you call imfindcircles and then do nothing with the output.
Rather than doing anything with regionprops, just use the values of centers, radii to define a bounding box around each detected circle (optionally with some additional padding), crop that area out of the image and save/display it.
Related
If I have an arbitrary shape (attached is a really simple mock up), how would I estimate the area of the enclosed surface in Matlab. To get some random points along the curve, I used the ginput command to get a rough estimate of the curve, with unequal spacing between the points. I want to get an estimate of the area, but I believe the trapz command would overestimate the area due to the overlap (Please correct me if I am wrong here). Is there a more accurate way to obtain the area?
Thanks!
Well, you didn't really give enough info to solve the problem entirely, but here's one approach you can take to find the boundary automatically in order to calculate the area:
% Get image and convert to logical mask
img = ~im2bw(imread('polyarea.jpg'));
% Fill the hole
img = imfill(img,'holes');
% Get boundary
b = bwboundaries(img);
% Approximate area of boundary
area = polyarea(b{1}(:,1), b{1}(:,2));
% Print area
disp(['Area: ' num2str(area)]);
imshow(img);
hold on;
plot(b{1}(:,2),b{1}(:,1),'go');
The idea is you have an input, you form a logical mask, get the boundary of the mask, and then you can approximate the area enclosed by the boundary by using polyarea.
The output is:
Area: 228003
Additionally, you could also use regionprops(img,'Area') which outputs:
ans =
Area: 229154
How do I separate the two connected circles in the image below, using MATLAB? I have tried using imerode, but this does not give good results. Eroding does not work, because in order to erode enough to separate the circles, the lines disappear or become mangled. In other starting pictures, a circle and a line overlap, so isolating the overlapping objects won't work either.
The image shows objects identified by bwboundaries, each object painted a different color. As you can see, the two light blue circles are joined, and I want to disjoin them, producing two separate circles. Thanks
I would recommend you use the Circular Hough Transform through imfindcircles. However, you need version 8 of the Image Processing Toolbox, which was available from version R2012a and onwards. If you don't have this, then unfortunately this won't work :(... but let's go with the assumption that you do have it. However, if you are using something older than R2012a, Dev-iL in his/her comment above linked to some code on MATLAB's File Exchange on an implementation of this, most likely created before the Circular Hough Transform was available: http://www.mathworks.com/matlabcentral/fileexchange/9168-detect-circles-with-various-radii-in-grayscale-image-via-hough-transform/
This is a special case of the Hough Transform where you are trying to find circles in your image rather than lines. The beauty with this is that you are able to find circles even when the circle is partially completed or overlapping.
I'm going to take the image that you provided above and do some post-processing on it. I'm going to convert the image to binary, and remove the border, which is white and contains the title. I'm also going to fill in any holes that result so that all of the objects are filled in with solid white. There is also some residual quantization noise after I do this step, so I'm going to a small opening with a 3 x 3 square element. After, I'm going to close the shapes with a 3 x 3 square element, as I see that there are noticeable gaps in the shapes. Therefore:
Therefore, directly reading in your image from where you've posted it:
im = imread('http://s29.postimg.org/spkab8oef/image.jpg'); %// Read in the image
im_gray = im2double(rgb2gray(im)); %// Convert to grayscale, then [0,1]
out = imclearborder(im_gray > 0.6); %// Threshold using 0.6, then clear the border
out = imfill(out, 'holes'); %// Fill in the holes
out = imopen(out, strel('square', 3));
out = imclose(out, strel('square', 3));
This is the image I get:
Now, apply the Circular Hough Transform. The general syntax for this is:
[centres, radii, metric] = imfindcircles(img, [start_radius, end_radius]);
img would be the binary image that contains your shapes, start_radius and end_radius would be the smallest and largest radius of the circles you want to find. The Circular Hough Transform is performed such that it will find any circles that are within this range (in pixels). The outputs are:
centres: Which returns the (x,y) positions of the centres of each circle detected
radii: The radius of each circle
metric: A measure of purity of the circle. Higher values mean that the shape is more probable to be a circle and vice-versa.
I searched for circles having a radius between 30 and 60 pixels. Therefore:
[centres, radii, metric] = imfindcircles(out, [30, 60]);
We can then demonstrate the detected circles, as well as the radii by a combination of plot and viscircles. Therefore:
imshow(out);
hold on;
plot(centres(:,1), centres(:,2), 'r*'); %// Plot centres
viscircles(centres, radii, 'EdgeColor', 'b'); %// Plot circles - Make edge blue
Here's the result:
As you can see, even with the overlapping circles towards the top, the Circular Hough Transform was able to detect two distinct circles in that shape.
Edit - November 16th, 2014
You wish to ensure that the objects are separated before you do bwboundaries. This is a bit tricky to do. The only way I can see you do this is if you don't even use bwboundaries at all and do this yourself. I'm assuming you'll want to analyze each shape's properties by themselves after all of this, so what I suggest you do is iterate through every circle you have, then place each circle on a new blank image, do a regionprops call on that shape, then append it to a separate array. You can also keep track of all of the circles by having a separate array that adds the circles one at a time to this array.
Once you've finished with all of the circles, you'll have a structure array that contains all of the measured properties for all of the measured circles you have found. You would use the array that contains only the circles from above, then use these and remove them from the original image so you get just the lines. You'd then call one more regionprops on this image to get the information for the lines and append this to your final structure array.
Here's the first part of the procedure I outlined above:
num_circles = numel(radii); %// Get number of circles
struct_reg = []; %// Save the shape analysis per circle / line here
%// For creating our circle in the temporary image
[X,Y] = meshgrid(1:size(out,2), 1:size(out,1));
%// Storing all of our circles in this image
circles_img = false(size(out));
for idx = 1 : num_circles %// For each circle we have...
%// Place our circle inside a temporary image
r = radii(idx);
cx = centres(idx,1); cy = centres(idx,2);
tmp = (X - cx).^2 + (Y - cy).^2 <= r^2;
% // Save in master circle image
circles_img(tmp) = true;
%// Do regionprops on this image and save
struct_reg = [struct_reg; regionprops(tmp)];
end
The above code may be a bit hard to swallow, but let's go through it slowly. I first figure out how many circles we have, which is simply looking at how many radii we have detected. I keep a separate array called struct_reg that will append a regionprops struct for each circle and line we have in our image. I use meshgrid to determine the (X,Y) co-ordinates with respect to the image containing our shapes so that I can draw one circle onto a blank image at each iteration. To do this, you simply need to find the Euclidean distance with respect to the centre of each circle, and set the pixels to true only if that location has its distance less than r. After doing this operation, you will have created only one circle and filtered all of them out. You would then use regionprops on this circle, add it to our circles_img array, which will only contain the circles, then continue with the rest of the circles.
At this point, we will have saved all of our circles. This is what circles_img looks like so far:
You'll notice that the circles drawn are clean, but the actual circles in the original image are a bit jagged. If we tried to remove the circles with this clean image, you will get some residual pixels along the border and you won't completely remove the circles themselves. To illustrate what I mean, this is what your image looks like if I tried to remove the circles with circles_img by itself:
... not good, right?
If you want to completely remove the circles, then do a morphological reconstruction through imreconstruct where you can use this image as the seed image, and specify the original image to be what we're working on. The job of morphological reconstruction is essentially a flood fill. You specify seed pixels, and an image you want to work on, and the job of imreconstruct is from these seeds, flood fill with white until we reach the boundaries of the objects that the seed pixels resided in. Therefore:
out_circles = imreconstruct(circles_img, out);
Therefore, we get this for our final reconstructed circles image:
Great! Now, use this and remove the circles from the original image. Once you do this, run regionprops again on this final image and append to your struct_reg variable. Obviously, save a copy of the original image before doing this:
out_copy = out;
out_copy(out_circles) = false;
struct_reg = [struct_reg; regionprops(out_copy)];
Just for sake of argument, this is what the image looks like with the circles removed:
Now, we have analyzed all of our shapes. Bear in mind I did the full regionprops call because I don't know exactly what you want in your analysis... so I just decided to give you everything.
Hope this helps!
erosion is the way to go. You should probably use a larger structuring element.
How about
1 erode
2 detect your objects
3 dilate each object for itself using the same structuring element
I would like to recognize one white pixel of the carplate on a image. I do not know how to recignize it because the color of the car is somewhere more "whiter" than the carplate's white color. I wrote a runable code but I have to select one of the car plate points with mouse, and then I found the carplate and I could draw a rectangle around it.
Do you have any idea how to automatize finding one white pixel of the carplate?
Here is the code:
clear all;
close all;
I= imread('volvo_frame_0001.bmp');
figure, imshow(I)
level=0.5;
BW=im2bw(I,level);
figure, imshow(BW);
BW2 = bwselect(BW,4);
figure, imshow(BW2);
hold on;
C = corner(BW2);
min_x = min(C(:,1));
max_x = max(C(:,1));
min_y = min(C(:,2));
max_y = max(C(:,2));
figure, imshow(I);
hold on;
BoxPolygon = [min_x, max_y; max_x, max_y; max_x, min_y; min_x, min_y; min_x, max_y;];
line(BoxPolygon(:, 1), BoxPolygon(:, 2), 'Color', 'g');
Actually the answer of your question is an application field called Licence Plate Recognition (LPR) in which you can find hundreds, if we don't say thousands, of programs either in Matlab or any other language, such as a this free Matlab code.
Anyway, if you insist on writing the code from the scratch, I suggest you not to look for white pixels! because you can't tell a pixel is white or not since the pixels values are in wide range (0 - 256^3) and the "color label" is a term which you cannot simply assign to a pixel (see this as an illustration to the fact). Instead you better use other "features" of plates. Such as the fact that a plate is a "rectangle" and is the one with identical "ratio" of sides. Thereafter you can use "canny" to find edges (dramatic changes of light or color in an image) by which shape characteristics can be more easily judged. which means you can more easily find rectangles within this kind of image.
When you found rectangles, you can check some other "features" within those rectangles to ensure whether the rectangle is a plate or some other form of object which is close to a plate in shape, not in content. For example the histogram or any other method.
Hope this helps
Cheers
As a preface: this is my first question - I've tried my best to make it as clear as possible, but I apologise if it doesn't meet the required standards.
As part of a summer project, I am taking time-lapse images of an internal melt figure growing inside a crystal of ice. For each of these images I would like to measure the perimeter of, and area enclosed by the figure formed. Linked below is an example of one of my images:
The method that I'm trying to use is the following:
Load image, crop, and convert to grayscale
Process to reduce noise
Find edge/perimeter
Attempt to join edges
Fill perimeter with white
Measure Area and Perimeter using regionprops
This is the code that I am using:
clear; close all;
% load image and convert to grayscale
tyrgb = imread('TyndallTest.jpg');
ty = rgb2gray(tyrgb);
figure; imshow(ty)
% apply a weiner filter to remove noise.
% N is a measure of the window size for detecting coherent features
N=20;
tywf = wiener2(ty,[N,N]);
tywf = tywf(N:end-N,N:end-N);
% rescale the image adaptively to enhance contrast without enhancing noise
tywfb = adapthisteq(tywf);
% apply a canny edge detection
tyedb = edge(tywfb,'canny');
%join edges
diskEnt1 = strel('disk',8); % radius of 4
tyjoin1 = imclose(tyedb,diskEnt1);
figure; imshow(tyjoin1)
It is at this stage that I am struggling. The edges do not quite join, no matter how much I play around with the morphological structuring element. Perhaps there is a better way to complete the edges? Linked is an example of the figure this code outputs:
The reason that I am trying to join the edges is so that I can fill the perimeter with white pixels and then use regionprops to output the area. I have tried using the imfill command, but cannot seem to fill the outline as there are a large number of dark regions to be filled within the perimeter.
Is there a better way to get the area of one of these melt figures that is more appropriate in this case?
As background research: I can make this method work for a simple image consisting of a black circle on a white background using the below code. However I don't know how edit it to handle more complex images with edges that are less well defined.
clear all
close all
clc
%% Read in RGB image from directory
RGB1 = imread('1.jpg') ;
%% Convert RPG image to grayscale image
I1 = rgb2gray(RGB1) ;
%% Transform Image
%CROP
IC1 = imcrop(I1,[74 43 278 285]);
%BINARY IMAGE
BW1 = im2bw(IC1); %Convert to binary image so the boundary can be traced
%FIND PERIMETER
BWP1 = bwperim(BW1);
%Traces perimeters of objects & colours them white (1).
%Sets all other pixels to black (0)
%Doing the same job as an edge detection algorithm?
%FILL PERIMETER WITH WHITE IN ORDER TO MEASURE AREA AND PERIMETER
BWF1 = imfill(BWP1); %This opens figure and allows you to select the areas to fill with white.
%MEASURE PERIMETER
D1 = regionprops(BWF1, 'area', 'perimeter');
%Returns an array containing the properties area and perimeter.
%D1(1) returns the perimeter of the box and an area value identical to that
%perimeter? The box must be bounded by a perimeter.
%D1(2) returns the perimeter and area of the section filled in BWF1
%% Display Area and Perimeter data
D1(2)
I think you might have room to improve the effect of edge detection in addition to the morphological transformations, for instance the following resulted in what appeared to me a relatively satisfactory perimeter.
tyedb = edge(tywfb,'sobel',0.012);
%join edges
diskEnt1 = strel('disk',7); % radius of 4
tyjoin1 = imclose(tyedb,diskEnt1);
In addition I used bwfill interactively to fill in most of the interior. It should be possible to fill the interior programatically but I did not pursue this.
% interactively fill internal regions
[ny nx] = size(tyjoin1);
figure; imshow(tyjoin1)
tyjoin2=tyjoin1;
titl = sprintf('click on a region to fill\nclick outside window to stop...')
while 1
pts=ginput(1)
tyjoin2 = bwfill(tyjoin2,pts(1,1),pts(1,2),8);
imshow(tyjoin2)
title(titl)
if (pts(1,1)<1 | pts(1,1)>nx | pts(1,2)<1 | pts(1,2)>ny), break, end
end
This was the result I obtained
The "fractal" properties of the perimeter may be of importance to you however. Perhaps you want to retain the folds in your shape.
You might want to consider Active Contours. This will give you a continous boundary of the object rather than patchy edges.
Below are links to
A book:
http://www.amazon.co.uk/Active-Contours-Application-Techniques-Statistics/dp/1447115570/ref=sr_1_fkmr2_1?ie=UTF8&qid=1377248739&sr=8-1-fkmr2&keywords=Active+shape+models+Andrew+Blake%2C+Michael+Isard
A demo:
http://users.ecs.soton.ac.uk/msn/book/new_demo/Snakes/
and some Matlab code on the File Exchange:
http://www.mathworks.co.uk/matlabcentral/fileexchange/28149-snake-active-contour
and a link to a description on how to implement it: http://www.cb.uu.se/~cris/blog/index.php/archives/217
Using the implementation on the File Exchange, you can get something like this:
%% Load the image
% You could use the segmented image obtained previously
% and then apply the snake on that (although I use the original image).
% This will probably make the snake work better and the edges
% in your image is not that well defined.
% Make sure the original and the segmented image
% have the same size. They don't at the moment
I = imread('33kew0g.jpg');
% Convert the image to double data type
I = im2double(I);
% Show the image and select some points with the mouse (at least 4)
% figure, imshow(I); [y,x] = getpts;
% I have pre-selected the coordinates already
x = [ 525.8445 473.3837 413.4284 318.9989 212.5783 140.6320 62.6902 32.7125 55.1957 98.6633 164.6141 217.0749 317.5000 428.4172 494.3680 527.3434 561.8177 545.3300];
y = [ 435.9251 510.8691 570.8244 561.8311 570.8244 554.3367 476.3949 390.9586 311.5179 190.1085 113.6655 91.1823 98.6767 106.1711 142.1443 218.5872 296.5291 375.9698];
% Make an array with the selected coordinates
P=[x(:) y(:)];
%% Start Snake Process
% You probably have to fiddle with the parameters
% a bit more that I have
Options=struct;
Options.Verbose=true;
Options.Iterations=1000;
Options.Delta = 0.02;
Options.Alpha = 0.5;
Options.Beta = 0.2;
figure(1);
[O,J]=Snake2D(I,P,Options);
If the end result is an area/diameter estimate, then why not try to find maximal and minimal shapes that fit in the outline and then use the shapes' area to estimate the total area. For instance, compute a minimal circle around the edge set then a maximal circle inside the edges. Then you could use these to estimate diameter and area of the actual shape.
The advantage is that your bounding shapes can be fit in a way that minimizes error (unbounded edges) while optimizing size either up or down for the inner and outer shape, respectively.
I have an image and I want to crop the circular region of interest around a point. I did following in MATLAB:
vessel=imread('vessel.jpg');
imshow( vessel)
t = 0:pi/20:2*pi;
xc=230; % point around which I want to extract/crop image
yc=79;
r=20; %Radium of circular region of interest
xcc = r*cos(t)+xc;
ycc = r*sin(t)+yc;
roimaskcc = poly2mask(double(xcc),double(ycc), size(vessel,1),size(vessel,2));
pr_gccc = find(roimaskcc);
roimean_cc= mean(vessel(pr_gccc));
figure, imshow(roimaskcc)
roimaskcc is correct but when I do the following it gives in nX1 matrix but not the region of interest under mask:
vessel_undermask=vessel(roimaskcc==1);
Can anybody pls. help to extract the circular region of interest around point of interest (xc, yc).
Thanks
What you're doing is extract everything from vessel that's outside the mask. Since there's no such thing as circular matrices, Matlab's solution is to output a vector of all values inside the mask.
While that is technically correct, that vector can be pretty hard to work with. An alternative solution is to leave the data matrix square, and set everything outside the mask to NaN:
% make a copy
vessel_undermask = vessel;
% NaN everything outside the mask (in R, G and B layers)
vessel_undermask(repmat(~roimaskcc,[1,1,3])) = NaN;
imshow(vessel_undermask)
This should give you a matrix that's somewhat simpler to work with.
Note that
vessel_undermask(~isnan(vessel_undermask)) == vessel(roimaskcc)
Yes I got it. I did something like that:
vesseltry=vessel;
vesseltry(~roimaskcc)=0;
vesseltry is now my new image with circular region of interest...