I want to display an image with axes that has a different vertical and horizontal scale.
The following code gives me an image that is very long and thin. If I multiply the scale of the y-axis by 250 (commented line) I get the aspect ratio of the image I want but now the scale on the y-axis is wrong.
A = rand(100,400);
A_image = mat2gray(A);
A_image = imresize(A_image,2);
RI = imref2d(size(A_image),[0 800],[-1 1]);
%RI = imref2d(size(A_image),[0 800],250*[-1 1]);
figure(1);
imshow(256*A_image,RI,jet)
xlabel('$t$ (s)');
ylabel('$z$ (m)');
Changing the world reference changes the axis labels to match that world reference, but you can always change the labels back.
xlabels=get(gca,'XTickLabels'); % //this will get your current labels;
nlabels=length(xlabels); % //Get how many we need
new_xlabels=linspace(-1,1,nlabels); % //Create a linear space at each label point
set(gca,'XTickLabels',new_xlabels); % //apply the new labels
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 am using this code simulate real camera to capture 3D object:
patch(ax, Object3D, 'FaceColor', 'flat');
camva(ax, rad2deg(VerticalAOV)); % Set the camera field of view
camup(ax, [0 -1 0]);
campos(ax, [CameraPosition.X CameraPosition.Y CameraPosition.Z]); % Put the camera at the origin
camtarget(ax, [CameraPosition.X CameraPosition.Y CameraPosition.Z] + [0 0 1]); % The camera looks along the +Z axis
camproj(ax,'perspective');
axis image;
axis off;
WidthResolution = SensorWidthResolution/(ax.Position(3));
Image = export_fig('temp.jpg',ax, sprintf('-r%f', WidthResolution),'-nocrop');
[ImageHeight, ImageWidth, Channels] = size(Image);
Image = imcrop(Image,[(ImageWidth-Width)/2, (ImageHeight-Height)/2, Width-1, Height-1]);
The problems are:
I used VerticalAOV as input for camva. I chose VerticalAOV based on this image. However, this is illogical. To get real view, one should provide both Horizontal and Vertical Angle.
[ImageHeight, ImageWidth, Channels] = size(Image); returns wrong
values. ImageWidth and ImageHeight does not provide the correct
values. It is clear that one of the dimessions would wrong since only
one dimension of the AOV was provided. However, why both of them are
not correct?
The crop I made is to correct the dimensions of the image. However,
it seems to be not useful step (I checked the result using ground
truth data I have and they did not match).
P.S. export_fig can be found here: https://github.com/altmany/export_fig
How to know the exact size and position of the axis box (without axis labels and numbers)? For example, if I use
figure
contourf(x,y,u,100,'linestyle','none')
axis equal
set(gca,'position',[0.1,0.1,0.7,0.8]) %normalized units
The size of the axis frame/box is varyed in the case of the figure window resizing (or using axis equal), but the value of get(gca,'position') remains unchanged. For example:
figure
Z = peaks(20);
contourf(Z,10)
set(gca,'Units','pixels')
get(gca,'position')
axis equal
get(gca,'position')
ans =
0.1300 0.1100 0.7750 0.8150
after axis equal, the axis box is changed, but get(gca,'position') gives the same coordinates:
ans =
0.1300 0.1100 0.7750 0.8150
I need these to align the colorbar to the axis box (with fixed gap between them) in the case of axis equal.
When you call axis equal, the axis box aspect ratio is fixed and the Position property is treated as a maximum size. When you resize the figure window, the axis box will remain centered in the Position rectangle, but in order to maintain the same aspect ratio as before, it may not take up the entire Position rectangle.
If you want it to take up the entire Position rectangle, you can call axis equal again. (this may depend on your MATLAB version; it worked for me in R2015b).
This is also discussed in a bit more detail on MATLAB Central.
To answer your original question, it's a bit complicated. You'd have to get the plot box aspect ratio (using pbaspect() or the axes PlotBoxAspectRatio property) and figure it out:
ah = gca();
% Get the axes Position rectangle in units of pixels
old_units = get(ah,'Units');
set(ah,'Units','pixels');
pos = get(ah,'Position');
set(ah,'Units',old_units);
% Figure the PlotBox and axes Position aspect ratios
pos_aspectRatio = pos(3) / pos(4);
box_aspect = pbaspect(ah);
box_aspectRatio = box_aspect(1) / box_aspect(2);
if (box_aspectRatio > pos_aspectRatio)
% PlotBox is wider than the Position rectangle
box_height = pos(3) / box_aspectRatio;
box_dy = (pos(4)-box_height) / 2;
box_position = [pos(1), pos(2)+box_dy, pos(3), box_height];
else
% PlotBox is taller than the Position rectangle
box_width = pos(4) * box_aspectRatio;
box_dx = (pos(3)-box_width) / 2;
box_position = [pos(1)+box_dx, pos(2), box_width, pos(4)];
end
Note that this will give you the box position in pixels; if you want it in the normalized units that are the axes default, you'll need to normalize it:
fig_pos = get(get(ah,'Parent'),'Position');
box_position = box_position ./ fig_pos([3 4 3 4]);
I made a plot and wanted to add a second y-axis with different units of measurement.
Here is what I did:
...
...
plot(x,y,x,y1,x,y2)
ax1=gca;
set(gca,'YTickLabel',num2str(get(gca,'YTick').'))
legend('0.5 atm','1 atm','2 atm','Location','best')
title('H_2S equilibrium partial pressure for different total pressures')
xlabel('Temperature (K)')
ylabel('Partial pressure (Pa)')
hold on
ax2 = axes('Position',ax1.Position,...
'YAxisLocation','right',...
'Color','none');
ax2.YLim = [0 0.25];
ax2.XTick = [];
ylabel(ax2,'Partial pressure (atm)') % label right y-axis
Here is the result:
How do I get the right label to have the same padding between itself and the edge of the figure as the left label and border?
(view the picture on a dark background to see what I mean)
I've just discovered export_fig.
It automatically crops extra space from plots and also adds nifty features, such as anti-aliasing!
I am using WindowAPI (http://www.mathworks.com/matlabcentral/fileexchange/31437) to show a black full screen in matlab.
When drawing on screen, turns out drawing using line() and rectangle() functions is extremely slow.
How can I set values of pixels without going through matlab's mechanism? Getting the window's canvas for example would be great.
One way to imitate a "canvas" is by using a MATLAB image. The idea is to manually change its pixels and update the 'CData' of the plotted image.
Note that you can use an image with the same dimensions as your screen size (image pixels will correspond to screen pixels one-to-one), but updating it would be slower. The trick is to keep it small and let MATLAB map it to the entire fullscreen. That way the image can be thought of as having "fat" pixels. Of course the resolution of the image is going to affect the size of the marker you draw.
To illustrate, consider the following implementation:
function draw_buffer()
%# paramters (image width/height and the indexed colormap)
IMG_W = 50; %# preferably same aspect ratio as your screen resolution
IMG_H = 32;
CMAP = [0 0 0 ; lines(7)]; %# first color is black background
%# create buffer (image of super-pixels)
%# bigger matrix gives better resolution, but slower to update
%# indexed image is faster to update than truecolor
img = ones(IMG_H,IMG_W);
%# create fullscreen figure
hFig = figure('Menu','none', 'Pointer','crosshair', 'DoubleBuffer','on');
WindowAPI(hFig, 'Position','full');
%# setup axis, and set the colormap
hAx = axes('Color','k', 'XLim',[0 IMG_W]+0.5, 'YLim',[0 IMG_H]+0.5, ...
'Units','normalized', 'Position',[0 0 1 1]);
colormap(hAx, CMAP)
%# display image (pixels are centered around xdata/ydata)
hImg = image('XData',1:IMG_W, 'YData',1:IMG_H, ...
'CData',img, 'CDataMapping','direct');
%# hook-up mouse button-down event
set(hFig, 'WindowButtonDownFcn',#mouseDown)
function mouseDown(o,e)
%# convert point from axes coordinates to image pixel coordinates
p = get(hAx,'CurrentPoint');
x = round(p(1,1)); y = round(p(1,2));
%# random index in colormap
clr = randi([2 size(CMAP,1)]); %# skip first color (black)
%# mark point inside buffer with specified color
img(y,x) = clr;
%# update image
set(hImg, 'CData',img)
drawnow
end
end