I have x and y coordinates of a contour. Now they cannot be used as pixel locations since they are not integers. I am unable to find a way to convert them into pixel locations. Floor and round functions do not help as they create blobs. I need a crisp contour similar as in a plot.
You can plot your (x,y) points, remove axis ticks, and grab the axes into image. Try this:
figure;
plot(rand(10,1),rand(10,1));
box on; set(gca,'XTick',[],'YTick',[])
F = getframe(gca);
Image = F.cdata;
figure; imshow( Image );
EDIT:
If you need to draw many lines on image you may consider Bresenham's line algorithm to draw lines on image. See, for exmple, question and suggestions there:
How to draw a line on an image in matlab?
MATLAB: Drawing a line over a black and white image
Related
If there is an easier way to do this in general any suggestions would be appreciated.
I have imported a .nc file into Matlab and currently have a surface plot created from the interpolated matrix of data which corresponds to longitudes and latitudes. An alpha scale has been applied to add opacity and now I would like to place a map of said longs and lats beneath it so that it acts as an overlay.
here is the code used to plot where xq,yq is the mesh longitude and latitude grid and newMatrix is the interpolated version of the original matrix. Attached is the top view surf plot which I would like a map of long lat restricted x,y axis beneath (line style or topographic)
f = figure;
ax = axes('Parent',f);
h = surf(xq,yq,newMatrix,'Parent',ax);
set(h, 'edgecolor','none');
view(ax,[0,90]);
alpha color
alpha scaled
grid off
colorbar;
I'm aware of geomap but I'm not sure how it can be used in this way without causing the axis to misalign or just not be applied correctly. Before I was using a contour plot but found it easier to interpolate and plot with surf as per this post: Matlab how to make smooth contour plot?
I have written a program to process and print a 81x81 2D surface plot, which needs to be used as an input. Saving the plot made by Matlab includes side axes as well as white margins on the sides.
How do I crop this image to get just the (81pixels)x(81pixels) output as an image?
Try placing this after your figure code, it will remove the margins around your figure.
set(gca,'units','pixels') % set the axes units to pixels
xx = get(gca,'position'); % get the position of the axes;
set(gcf,'units','pixels') % set the figure units to pixels
yy = get(gcf,'position'); % get the figure position;
set(gcf,'position',[yy(1) yy(2) xx(3) xx(4)]) % set the position of the figure to the length and width of the axes
set(gca,'units','normalized','position',[0 0 1 1]) % set the axes units to pixels
You can avoid using surf plot and just save your array as image. So, you have 81x81 array. I'll use this one for the example:
a = magic(81);
Now you need to normalize image in order to have values from 0 to 255:
a = (a - min(min(a)))/(max(max(a))-min(min(a)))*255;
Finally you use imwrite to save your array as image.
imwrite(a,jet(256),'SO_4.png')
The first argument is your 81x81 array. The second argument is colormap. You can specify any colormap you want, but I like the heatmap jet(256). You can skip this argument, in this case the image would be grayscale. From here you can find what colormaps are available and what they look like. The last argument is image name. The result is shown below:
Hope that helps, good luck.
I guess, I've got an colormap issue with Matlab2013. I plot a 3d surface plot with colormap hot and I would like to have in the same plot an bitmap (8bit colour image) on the x-y plane. Plotting both separately from each other works fine but as soon as I plot them in one figure the first surface plot is only black. I guess it is because the RGB image on the x-y plane uses a different colour map. Is there an option in Matlab to plot two different type of images in the same plot?
surf(X,Y,density,'FaceColor','texturemap','Edgecolor','none')
colormap hot
...
%// define the location of the bitmap
xImage = [miX maX; miX maX]; %// The y data for the image corners
yImage = [miY miY; maY maY]; %// The x data for the image corners
zImage = [zDist zDist; zDist zDist]; %// The z data for the image corners
surf(xImage,yImage,zImage,... %// Plot the surface
'CData',RGBImage,...
'FaceColor','texturemap');
Thanks!
Durin
I think this is an issue with the relative scaling of density and zImage. I can replicate this by doing the following:
1) Plot a surf where the third input is n x m which is scaled like some real data (-0.2 to +0.2, for example). This responds to changes in colormap as you'd expect.
2) After hold on, plot another surf where the third input is n x m x 3, like a RGB image, double values scaled between 0 and 1.
This causes the first image to go "dark" (or whatever the lowest color in that particular colormap is). The issue is that they share their CLim, being in the same axis, although the RGBImage doesn't, in fact, reference the colormap.
This is "fixable" by scaling/normalising the first plot (your density values) to be between 0 and 1 (in this case) - although this quick fix is going to give you issues if you then want to add a colorbar. Alternatively, first grab the "CLim" from your axis after plotting the first surf:
trueC = get(gca,'CLim');
Then set it back after you plot the image:
set(gca,'CLim',trueC)
I am running Isomap Dimensionality reduction in MATLAB on a series of images. I want to plot the image's thumbnail beside the point on the manifold corresponding to it.
I am currently using 2 differnt isomaps http://isomap.stanford.edu/ and http://robotics.cs.brown.edu/projects/stisomap/ .
The imagesc function can take arguments which dictate where the image is drawn, so I would use this. Here's an example of imagesc being drawn on top of a plot:
% Draw plot
vals=rand(2,100);
plot(vals(1,:),vals(2,:),'x');
hold on;
% Draw image
im=imread('moon.tif');
xs=linspace(0.1, 0.2, size(im, 2) );
ys=linspace(0.1, 0.2, size(im, 1) );
colormap gray;
imagesc(xs,ys,im)
Which looks like this:
Note the first two arguments to imagesc which define the range over which the image is drawn. Obviously you'll want to change the arguments to linspace, which will define the position and size of the image, and you'll need to take account for the aspect ratio if the image isn't square, but hopefully this will get you along the right lines.
I have a similar question than the one in this post.
I have a grayscale image and I plot points on it. Fro plotting the points I use colormap('jet') but as I want the image to be grayscale, after plotting the points I reset the colormap, colormap('gray').
But I want to show a colorbar! And the colorbar is plotted in grayscale, not 'jet'.
How can I do that?
EDIT:
I want a Colorbar showing the color of the points!
You should convert your image to RGB by putting the same data into R-, G-, and B-channels (this will be grayscale RGB image). Colormap in MatLab is not applied to RGB images, only to indexed ones. Then plot your points over the image with colormap you like.
As discussed here, there's a few ways:
If you have the image processing toolbox, use subimage to create an independent image with a separate colormap. Then plot the image, your points, and join them into one using linkaxes.
Use freezeColors from the file exchange (or multiple colormaps, which I haven't ever tested personally). This is a very easy way to create a larger colormap, and automatically selecting the right portion of the colormap for display of images and colorbars.
As answered by anandr, convert your greyscale image to RGB; Matlab doesn't use colormaps on RGB images, which leaves you freedom to plot your points and show their colorbar independent of the image.
Example code for (3):
I = imread('cameraman.tif');
imshow(cat(3,I,I,I))
hold on
x = #() round(size(I,1) * rand(50,1));
y = #() round(size(I,2) * rand(50,1));
plot(x(), y(), 'r.')
plot(x(), y(), 'g.')
plot(x(), y(), 'b.')
colormap('jet')
colorbar
result: