I have pairs of concentric circles. I want to fill area btween these concentric circles in matlab. I am trying "fill" function...but it is filling the outre circle completely.
Here's a way using patch:
t = linspace(0,2*pi);
x0=1; y0=3; % circles center
rin = 0.4; rout = 0.6; % radii sizes
patch([x0+rout*cos(t),x0+rin*cos(t)],[y0+rout*sin(t),y0+rin*sin(t)],'r','linestyle','none');
Related
I have a grayscale image I want to extract the regions of interest using detectSURFFeatures(). Using this function I get a surfPoints object.
by displaying this object on the image I get circles as regions of interest.
For my case I want the rectangular areas encompassing these circles.
To be more clear i have a image 1:
I want to extract Region of Interest (ROI) using : detectSURFFeatures(), we obtain the image
if you can see we have circular region, and for my case i want the rectangular ROI that contains the circular region :
It looks like the radius is fully determined by the points.Scale parameter.
% Detection of the SURF features:
I = imread('cameraman.tif');
points = detectSURFFeatures(I);
imshow(I); hold on;
% Select and plot the 10 strongest features
p = points.selectStrongest(10)
plot(p);
% Here we add the bounding box around the circle.
c = 6; % Correction factor for the radius
for ii = 1:10
x = p.Location(ii,1); % x coordinate of the circle's center
y = p.Location(ii,2); % y coordinate of the circle's center
r = p.Scale(ii); % Scale parameter
rectangle('Position',[x-r*c y-r*c 2*r*c 2*r*c],'EdgeColor','r')
end
And we obtain the following result:
In this example the correction factor for the radius is 6. I guess that this value correspond to half of the default Scale propertie's value of a SURFPoints object (which is 12.0). But since there is no information about that in the documentation, I can be wrong. And be carreful, the scale parameter of each ROI is not the same thing as the scale propertie of a SURFPoints object.
I have detected a circle as shown below:
As later I want to detect what speed limit is in the detected sign, how do I crop it out so that I am left with an image like below?
When program finishes it, it shows me where the center is and the radii in terminal.
centers =
248.4873 170.4811
radii =
24.5024
I know how to use imcrop but how do I use the values that are returned instead of writing in them myself, as there might be more than 1 circle detected?
Code:
I = imread('p1.tif');
subplot(3,3,1); imshow(I); title('Original Image');
%sharpen edges
B = imsharpen(I);
subplot(3,3,2); imshow(B); title('sharpened edges');
%find circles
Img = im2bw(B(:,:,3));
minRad = 20;
maxRad = 90;
[centers, radii] = imfindcircles(Img, [minRad maxRad], ...
'ObjectPolarity','bright','sensitivity',0.87)
imagesc(Img);
viscircles(centers, radii,'Color','green');
Assuming you have one centre and one radius. This should do it
rect = [centers(1)-radii,centers(2)-radii,2*radii,2*radii]
I2 = imcrop(I,rect)
For multiple circles you can do this process for each of the circle returned in a loop.
In MATLAB, say I have the parameters for an ellipse:
(x,y) center
Minor axis radius
Major axis radius
Angle of rotation
Now, I want to generate random points that lie within that ellipse, approximated from a 2D gaussian.
My attempt thus far is this:
num_samps = 100;
data = [randn(num_samps, 1)+x_center randn(num_samps, 1)+y_center];
This gives me a cluster of data that's approximately centered at the center, however if I draw the ellipse over the top some of the points might still be outside.
How do I enforce the axis rules and the rotation?
Thanks.
my assumptions
x_center = h
y_center = k
Minor Axis Radius = b
Major Axis Raduis = a
rotation angle = alpha
h=0;
k=0;
b=5;
a=10;
alpha=30;
num_samps = 100;
data = [randn(num_samps, 1)+h randn(num_samps, 1)+k];
chk=(((((data(:,1)-h).*cos(alpha)+(data(:,2)-k).*sin(alpha))./a).^2) +...
(((data(:,1)-h).*sin(alpha)+(data(:,2)-k).*cos(alpha))./b).^2)<=1;
idx=find(chk==0);
if ~isempty(idx)
data(idx,:)=data(idx,:)-.5*ones(length(idx),2);
end
I have two matrices
timeline = [0.0008 0.0012 0.0016 0.0020 0.0024 0.0028];
Origdata =
79.8400 69.9390 50.0410 55.5082 34.5200 37.4486 31.4237 27.3532 23.2860 19.3039
79.7600 69.8193 49.8822 55.3115 34.2800 37.1730 31.1044 26.9942 22.8876 18.9061
79.6800 69.6996 49.7233 55.1148 34.0400 36.8975 30.7850 26.6352 22.4891 18.5084
79.6000 69.5799 49.5645 54.9181 33.8000 36.6221 30.4657 26.2762 22.0907 18.1108
79.5200 69.4602 49.4057 54.7215 33.5600 36.3467 30.1464 25.9173 21.6924 17.7133
79.4400 69.3405 49.2469 54.5249 33.3200 36.0714 29.8271 25.5584 21.2941 17.3159
When I plot them, I get a graph like below.
plot(timeline, Origdata, '.');
How can I draw a circle of radius 0.3524 value around each point? This radius should be relative to the y-axis only.
You can do this easily using viscircles (which requires the Image Processing Toolbox) however I don't think that the output is actually what you're expecting.
radius = 0.3524;
dots = plot(timeline, Origdata, '.');
hold on
for k = 1:numel(dots)
plotdata = get(dots(k));
centers = [plotdata.XData(:), plotdata.YData(:)];
% Ensure the the colors match the original plot
color = get(dots(k), 'Color');
viscircles(centers, radius * ones(size(centers(:,1))), 'Color', color);
end
The reason that it looks like this is because your X data is very close together relative to your y data and for circles to appear as circles, I have forced the x and y scaling of the axes to be equal (axis equal)
Edit
If you only want the radius to be relative to the y axis (distance) then we actually need to draw ellipses with an x and y radius. We want to scale the "x-radius" to make it appear as a circle regardless of your true axes aspect ratio, something like this can actually do that.
The trick to the code below is setting the data and plot aspect ratios (pbaspect and daspect) to manual. This ensures that the aspect ratio of the axes doesn't change during zoom, resizing, etc and makes sure that our "circles" remain circular-looking.
dots = plot(timeline, Origdata, '.');
drawnow
% Force the aspect ratio to not change (keep the circles, as circles)
pbaspect('manual')
daspect('manual')
hold on
aspectRatio = daspect;
t = linspace(0, 2*pi, 100);
t(end+1) = NaN;
radius = 4.3524;
% Scale the radii for each axis
yradius = radius;
xradius = radius * aspectRatio(1)/aspectRatio(2);
% Create a circle "template" with a trailing NaN to disconnect consecutive circles
t = linspace(0, 2*pi, 100);
t(end+1) = NaN;
circle = [xradius*cos(t(:)), yradius*sin(t(:))];
for k = 1:numel(dots)
x = get(dots(k), 'XData');
y = get(dots(k), 'YData');
color = get(dots(k), 'Color');
% Center circle template at all points
circles = arrayfun(#(x,y)bsxfun(#plus, [x,y], circle), x, y, 'uni', 0);
circles = cat(1, circles{:});
plot(circles(:,1), circles(:,2), 'Color', color)
end
Just to demonstrate, if we increase the circle radius to 4.3524 we can see the circles better.
And this works with all resizing etc.
To draw circles in MATLAB, you obviously have to use the rectangle function ;)
As mentioned in my comment, the size of 0.3524 does not match your axis, so I chose different sizes to have the circles actually visible, These are rx and ry
timeline = [0.0008 0.0012 0.0016 0.0020 0.0024 0.0028];
Orgidata =[79.8400 69.9390 50.0410 55.5082 34.5200 37.4486 31.4237 27.3532 23.2860 19.3039
79.7600 69.8193 49.8822 55.3115 34.2800 37.1730 31.1044 26.9942 22.8876 18.9061
79.6800 69.6996 49.7233 55.1148 34.0400 36.8975 30.7850 26.6352 22.4891 18.5084
79.6000 69.5799 49.5645 54.9181 33.8000 36.6221 30.4657 26.2762 22.0907 18.1108
79.5200 69.4602 49.4057 54.7215 33.5600 36.3467 30.1464 25.9173 21.6924 17.7133
79.4400 69.3405 49.2469 54.5249 33.3200 36.0714 29.8271 25.5584 21.2941 17.3159];
ry=1;
rx=0.0001;
dots=plot(timeline, Orgidata , '.');
hold on
for ix=1:size(Orgidata ,1)
for jx=1:size(Orgidata ,2)
rectangle('Position',[timeline(ix)-(rx/2),Orgidata(ix,jx)-(ry/2),rx,ry],'Curvature',[1,1],'EdgeColor',get(dots(jx), 'Color'));
end
end
I would like to enhance a portion of the image. I would like to enhance the regions within rectangular region esp on the green rectangle region
You can use imcrop.
[I2 rect] = imcrop(I)
This will ask you to draw a rectangle and rect will thus contain the coordinates of that rectangle. I2 contains the cropped image and you can then apply any function you would like on that matrix.
Using a function like ginput you can select a point on an image, and with having a width and height values of a rectangle, you can crop a rectangle from your image. Then you can use any function such as imadjust to enhance your cropped part.
a= 100; % height
b= 100; % width
I = imread('myimage.png'); % read the image file
figure;imagesc(I); % plot the image
[x,y] = ginput(1); % select a point
I2 = I(:,:,1); %
Ic = imcrop(I2,[x-a/2 y-b/2 a b]); % crop a rectangle around the selected point
J = imadjust(Ic); % adjust the contrast
If you want to be able to select a rectangle, you can use the following command:
imshow('myimage.png');
rect = getrect;