I'm trying to plot small images on a larger plot... Actually its isomap algorithm, I got many points, now each point correspond to some image, I know which image is it... The porblem is how to load that image and plot on the graph?
One more thing I have to plot both image and the points, so, basically the images will overlap the points.
Certainly, the type of image given here
Something like this should get you started. You can use the low-level version of the image function to draw onto a set of axes.
% Define some random data
N = 5;
x = rand(N, 1);
y = rand(N, 1);
% Load an image
rgb = imread('ngc6543a.jpg');
% Draw a scatter plot
scatter(x, y);
axis([0 1 0 1]);
% Offsets of image from associated point
dx = 0.02;
dy = 0.02;
width = 0.1;
height = size(rgb, 1) / size(rgb, 2) * width;
for i = 1:N
image('CData', rgb,...
'XData', [x(i)-dx x(i)-(dx+width)],...
'YData', [y(i)-dy y(i)-(dy+height)]);
end
Related
I am trying to rotate an image in Matlab about an arbitrary set of points.
So far, I have used imrotate, but it looks like imrotate only rotates about the center.
Is there a nice way of doing this without first padding the image and then using imrotate?
Thank you
The "nice way" is using imwarp
Building the transformation matrix is a little tricky.
I figured out how to build it from a the following question: Matlab image rotation
The transformation supports rotation, translation and zoom.
Parameters:
(x0, y0) is the center point that you rotate around it.
phi is rotation angle.
sx, sy are horizontal and vertical zoom (set to value to 1).
W and H are width and height of input (and output) images.
Building 3x3 transformation matrix:
T = [sx*cos(phi), -sx*sin(phi), 0
sy*sin(phi), sy*cos(phi), 0
(W+1)/2-((sx*x0*cos(phi))+(sy*y0*sin(phi))), (H+1)/2+((sx*x0*sin(phi))-(sy*y0*cos(phi))), 1];
Using imwarp:
tform = affine2d(T);
J = imwarp(I, tform, 'OutputView', imref2d([H, W]), 'Interp', 'cubic');
Here is a complete executable code sample:
I = imresize(imread('peppers.png'), 0.5); %I is the input image
[H, W, ~] = size(I); %Height and Width of I
phi = 120*pi/180; %Rotate 120 degrees
%Zoom coefficients
sx = 1;
sy = 1;
%Center point (the point that the image is rotated around it).
x0 = (W+1)/2 + 50;
y0 = (H+1)/2 + 20;
%Draw white cross at the center of the point of the input image.
I(y0-0.5:y0+0.5, x0-19.5:x0+19.5, :) = 255;
I(y0-19.5:y0+19.5, x0-0.5:x0+0.5, :) = 255;
%Build transformation matrix.
T = [sx*cos(phi), -sx*sin(phi), 0
sy*sin(phi), sy*cos(phi), 0
(W+1)/2-((sx*x0*cos(phi))+(sy*y0*sin(phi))), (H+1)/2+((sx*x0*sin(phi))-(sy*y0*cos(phi))), 1];
tform = affine2d(T);
J = imwarp(I, tform, 'OutputView', imref2d([H, W]), 'Interp', 'cubic');
%Draw black cross at the center of the output image:
J(end/2:end/2+1, end/2-15:end/2+15, :) = 0;
J(end/2-15:end/2+15, end/2:end/2+1, :) = 0;
%Shows that the center of the output image is the point that the image was rotated around it.
figure;imshow(J)
Input image:
Output image:
Note:
Important advantage over other methods (like imrotate after padding), is that the center coordinates don't have to be integer values.
You can rotate around (100.4, 80.7) for example.
I'm using processing, and I'm trying to create a circle from the pixels i have on my display.
I managed to pull the pixels on screen and create a growing circle from them.
However i'm looking for something much more sophisticated, I want to make it seem as if the pixels on the display are moving from their current location and forming a turning circle or something like this.
This is what i have for now:
int c = 0;
int radius = 30;
allPixels = removeBlackP();
void draw {
loadPixels();
for (int alpha = 0; alpha < 360; alpha++)
{
float xf = 350 + radius*cos(alpha);
float yf = 350 + radius*sin(alpha);
int x = (int) xf;
int y = (int) yf;
if (radius > 200) {radius =30;break;}
if (c> allPixels.length) {c= 0;}
pixels[y*700 +x] = allPixels[c];
updatePixels();
}
radius++;
c++;
}
the function removeBlackP return an array with all the pixels except for the black ones.
This code works for me. There is an issue that the circle only has the numbers as int so it seems like some pixels inside the circle won't fill, i can live with that. I'm looking for something a bit more complex like I explained.
Thanks!
Fill all pixels of scanlines belonging to the circle. Using this approach, you will paint all places inside the circle. For every line calculate start coordinate (end one is symmetric). Pseudocode:
for y = center_y - radius; y <= center_y + radius; y++
dx = Sqrt(radius * radius - y * y)
for x = center_x - dx; x <= center_x + dx; x++
fill a[y, x]
When you find places for all pixels, you can make correlation between initial pixels places and calculated ones and move them step-by-step.
For example, if initial coordinates relative to center point for k-th pixel are (x0, y0) and final coordinates are (x1,y1), and you want to make M steps, moving pixel by spiral, calculate intermediate coordinates:
calc values once:
r0 = Sqrt(x0*x0 + y0*y0) //Math.Hypot if available
r1 = Sqrt(x1*x1 + y1*y1)
fi0 = Math.Atan2(y0, x0)
fi1 = Math.Atan2(y1, x1)
if fi1 < fi0 then
fi1 = fi1 + 2 * Pi;
for i = 1; i <=M ; i++
x = (r0 + i / M * (r1 - r0)) * Cos(fi0 + i / M * (fi1 - fi0))
y = (r0 + i / M * (r1 - r0)) * Sin(fi0 + i / M * (fi1 - fi0))
shift by center coordinates
The way you go about drawing circles in Processing looks a little convoluted.
The simplest way is to use the ellipse() function, no pixels involved though:
If you do need to draw an ellipse and use pixels, you can make use of PGraphics which is similar to using a separate buffer/"layer" to draw into using Processing drawing commands but it also has pixels[] you can access.
Let's say you want to draw a low-res pixel circle circle, you can create a small PGraphics, disable smoothing, draw the circle, then render the circle at a higher resolution. The only catch is these drawing commands must be placed within beginDraw()/endDraw() calls:
PGraphics buffer;
void setup(){
//disable sketch's aliasing
noSmooth();
buffer = createGraphics(25,25);
buffer.beginDraw();
//disable buffer's aliasing
buffer.noSmooth();
buffer.noFill();
buffer.stroke(255);
buffer.endDraw();
}
void draw(){
background(255);
//draw small circle
float circleSize = map(sin(frameCount * .01),-1.0,1.0,0.0,20.0);
buffer.beginDraw();
buffer.background(0);
buffer.ellipse(buffer.width / 2,buffer.height / 2, circleSize,circleSize);
buffer.endDraw();
//render small circle at higher resolution (blocky - no aliasing)
image(buffer,0,0,width,height);
}
If you want to manually draw a circle using pixels[] you are on the right using the polar to cartesian conversion formula (x = cos(angle) * radius, y = sin(angle) * radius).Even though it's focusing on drawing a radial gradient, you can find an example of drawing a circle(a lot actually) using pixels in this answer
I'd like to plot a graph over an image. I followed this tutorial to Plot over an image background in MATLAB and it works fine:
% replace with an image of your choice
img = imread('myimage.png');
% set the range of the axes
% The image will be stretched to this.
min_x = 0;
max_x = 8;
min_y = 0;
max_y = 6;
% make data to plot - just a line.
x = min_x:max_x;
y = (6/8)*x;
imagesc([min_x max_x], [min_y max_y], img);
hold on;
plot(x,y,'b-*','linewidth',1.5);
But when I apply the procedure to my study case, it doesn't work. I'd like to do something like:
I = imread('img_png.png'); % here I load the image
DEM = GRIDobj('srtm_bigtujunga30m_utm11.tif');
FD = FLOWobj(DEM,'preprocess','c');
S = STREAMobj(FD,flowacc(FD)>1000);
% with the last 3 lines I calculated the stream network on a geographic area using the TopoToolBox
imagesc(I);
hold on
plot(S)
The aim is to plot the stream network over the satellite image of the same area.
The only difference between the two examples that doesn't let the code working is in the plot line, in the first case "plot(x,y)" works, in the other one "plot(S)" doesn't.
Thanks guys.
This is the satellite image, imagesc(I)
It is possible that the plot method of the STREAMobj performs it's own custom plotting including creating new figures, axes, toggling hold states, etc. Because you can't easily control what their plot routine does, it's likely easier to flip the order of your plotting so that you plot your stuff after the toolbox plots the STREAMobj. This way you have completely control over how your image is added.
% Plot the STREAMobj
hlines = plot(S);
% Make sure we plot on the same axes
hax = ancestor(hlines, 'axes');
% Make sure that we can add more plot objects
hold(hax, 'on')
% Plot your image data on the same axes
imagesc(I, 'Parent', hax)
Maybe I am preaching to the choir or overlooking something here but the example you used actually mapped the image to the data range of the plot, hence the lines:
% set the range of the axes
% The image will be stretched to this.
min_x = 0;
max_x = 8;
min_y = 0;
max_y = 6;
imagesc([min_x max_x], [min_y max_y], img);
where you directly plot your image
imagesc(I);
If now your data coordinates and your image coordinates are vastly different you either see one or the other.
Thanks guys, I solved in this way:
I = imread('orto.png'); % satellite image loading
DEM = GRIDobj('demF1.tif');
FD = FLOWobj(DEM,'preprocess','c');
S = STREAMobj(FD,flowacc(FD)>1000); % Stream network extraction
x = S.x; % [node attribute] x-coordinate vector
y = S.y; % [node attribute] y-coordinate vector
min_x = min(x);
max_x = max(x);
min_y = min(y);
max_y = max(y);
imagesc([min_x max_x], [min_y max_y], I);
hold on
plot(S);
Here's the resulting image: stream network over the satellite image
Actually the stream network doesn't match the satellite image just because I'm temporarily using different images and DEM.
I'm trying to convert an image with many circles with the same center, from Cartesian to Polar (so that the new image will be the circles but lines instead of the circles, see the image below), and that's working out just fine using the following code:
[r, c] = size(img);
r=floor(r/2);
c=floor(c/2);
[X, Y] = meshgrid(-c:c-1,-r:r-1);
[theta, rho] = cart2pol(X, Y);
subplot(221), imshow(img), axis on;
hold on;
subplot(221), plot(xCenter,yCenter, 'r+');
subplot(222), warp(theta, rho, zeros(size(theta)), img);
view(2), axis square;
The problem is, I don't understand why does it even work? (obviously it's not my code), I mean, when I use the function cart2pol I don't even use the image, it's just some vectors x and y generated from the meshgrid function..
and another problem is, I want somehow to have a new image (not just to be able to draw it with the wrap function) which is the original image but by the theta and rho coordinates (meaning the same pixels but rearranged)... I'm not even sure how to ask this, in the end I want to have an image which is a matrix so that I can sum each row and turn the matrix into a column vector...
You can think of your image as being a 2D matrix, where each pixel has an X and Y coordinate
[(1,1) (1,2) (1,3) .... (1,c)]
[(2,1) (2,2) (2,3) .... (2,c)]
[(3,1) (3,2) (3,3) .... (3,c)]
[.... .... .... .... .... ]
[(r,1) (r,2) (r,3) .... (r,c)]
In the code that you posted, it maps each of these (X,Y) coordinates to it's equivalent polar coordinate (R, theta) using the center of the image floor(c/2) and floor(r/2) as the reference point.
% Map pixel value at (1,1) to it's polar equivalent
[r,theta] = cart2pol(1 - floor(r/2),1 - floor(c/2));
So whatever pixel value was used for (1,1) should now appear in your new polar coordinate space at (r,theta). It is important to note that to do this conversion, no information about the actual pixel values in the image matters, rather we just want to perform this transformation for each pixel within the image.
So first we figure out where the center of the image is:
[r, c] = size(img);
r = floor(r / 2);
c = floor(c / 2);
Then we figure out the (X,Y) coordinates for every point in the image (after the center has already been subtracted out
[X, Y] = meshgrid(-c:c-1,-r:r-1);
Now convert all of these cartesian points to polar coordinates
[theta, rho] = cart2pol(X, Y);
All that warp now does, is say "display the value of img at (X,Y) at it's corresponding location in (theta, rho)"
warp(theta, rho, zeros(size(theta)), img);
Now it seems that you want a new 2D image where the dimensions are [nTheta, nRho]. To do this, you could use griddata to interpolate your scattered (theta, rho) image (which is displayed by warp above) to a regular grid.
% These is the spacing of your radius axis (columns)
rhoRange = linspace(0, max(rho(:)), 100);
% This is the spacing of your theta axis (rows)
thetaRange = linspace(-pi, pi, 100);
% Generate a grid of all (theta, rho) coordinates in your destination image
[T,R] = meshgrid(thetaRange, rhoRange);
% Now map the values in img to your new image domain
theta_rho_image = griddata(theta, rho, double(img), T, R);
Take a look at all the interpolation methods for griddata to figure out which is most appropriate for your scenario.
There were a couple other issues (like the rounding of the center) which caused the result to be slightly incorrect. A fully working example is provided below
% Create an image of circles
radii = linspace(0, 40, 10);
rows = 100;
cols = 100;
img = zeros(rows, cols);
for k = 1:numel(radii)
t = linspace(0, 2*pi, 1000);
xx = round((cos(t) * radii(k)) + (cols / 2));
yy = round((sin(t) * radii(k)) + (rows / 2));
toremove = xx > cols | xx < 1 | yy > rows | yy < 1;
inds = sub2ind(size(img), xx(~toremove), yy(~toremove));
img(inds) = 1;
end
[r,c] = size(img);
center_row = r / 2;
center_col = c / 2;
[X,Y] = meshgrid((1:c) - center_col, (1:r) - center_row);
[theta, rho] = cart2pol(X, Y);
rhoRange = linspace(0, max(rho(:)), 1000);
thetaRange = linspace(-pi, pi, 1000);
[T, R] = meshgrid(thetaRange, rhoRange);
theta_rho_image = griddata(theta, rho, double(img), T, R);
figure
subplot(1,2,1);
imshow(img);
title('Original Image')
subplot(1,2,2);
imshow(theta_rho_image);
title('Polar Image')
And the result
What I would like to do is plot an image of a graph (from say a pdf file or a scanned image). Next, I would like to overlay an axis on the graph in the image, and then plot data on that axis (over the image).
Using imtool, I know the coordinates of the graph in the image (x range = ~52-355 pixels, and y range = 23(top) - 262(bottom) pixels in this case).
This is what I have tried:
I = imread('C:\MATLAB\R2014a\help\images\ref\ftrans2_fig.png');
I = squeeze(uint8(mean(I,3)));
figure, imshow(I)
[rows, cols] = size(I);
x_data = (-1 : .01 : +1)';
y_data = 1 - x_data.^2;
h1 = axes('Position',([52, 23, 355-52, 262-23] ./ [cols, rows, cols, rows] ));
set(h1, 'Color', 'none')
hold on
plot(x_data, y_data, '-rx')
Question: Knowing the pixel coordinates of the graph in the image, how do I determine the proper position of the axis in the figure, (my code fails to account for the actual size of the figure box, the gray border around the image). I have to do this for several images and sets of data, so I would like an automated method, assuming I find the coordinates of the graphs in the image ahead of time.
Thanks for your reply! (1st time posting, please be kind)
You may be able to solve your problem by forcing the image onto the same axis as the plot. Try this:
I = imread('C:\MATLAB\R2014a\help\images\ref\ftrans2_fig.png');
I = squeeze(uint8(mean(I,3)));
[rows, cols] = size(I);
x_data = (-1 : .01 : +1)';
y_data = 1 - x_data.^2;
h1 = axes('Position',([52, 23, 355-52, 262-23] ./ [cols, rows, cols, rows] ));
set(h1, 'Color', 'none')
hold on
image(I, 'Parent', h1);
plot(h1, x_data, y_data, '-rx')
That should at ensure that the plot axis and the image axis have the same origin, as they will be one and the same. You may need to adjust your sizing code. Let me know if that doesn't do it for you.
Good Luck!
I think I have it figured out.
It would have been easier if I could use:
figure, h1=imshow(I)
get(h1,'Position')
but that results in "The name 'Position' is not an accessible property for an instance of class 'image'."
Instead, this appears to work:
I = imread('C:\MATLAB\R2014a\help\images\ref\ftrans2_fig.png');
I = squeeze(uint8(mean(I,3)));
in_mag = 300;
figure, imshow(I, 'Border', 'tight', 'InitialMagnification', in_mag)
[rows, cols] = size(I);
x_data = (-1 : .01 : +1)';
y_data = 1 - x_data.^2;
% Coord of graph in image pixels
x_0 = 50; x_max = 354; y_0 = 262; y_max = 23;
h1 = axes('Position',([x_0, rows-y_0, x_max-x_0, y_0-y_max] ...
./ [cols, rows, cols, rows] ));
set(h1,'Color','none')
hold on
plot(x_data, y_data, '-rx')
ylim([0,1.4])
set(gca,'YColor', [0 0 1], 'XColor', [0 0 1])
However, if anybody has a better idea, I would be very happy to explore it!
Thanks