I am pretty new to MatLab. I simply want to display an image for viewing, the image is 1024 x 1024 array. I have been using imagesc to display the image with a line of code such as this:
imagesc(xRange, yRange, imageData, [Min Max]);
However my image dimensions are not equal. For example, my image width is 10mm but in height it is 300mm, so I want it to appear reflecting this, so in this case I would expect it to appear very narrow but tall because the height is so much greater than the width. Instead it displays as a square which does not reflect the true dimensions.
I have looked at some MatLab functions but have not been successful in finding the correct one to do this. Does anybody know how i can set it so each pixel, point in the image is displayed reflecting its true dimensions? Thanks!
Try using daspect
imagesc( imageData );
daspect([ 1 30 ] );
Set your x and y ranges in terms of the desired image dimensions, and set the axes to be equal:
imagesc(xRange, yRange, imageData, [Min Max]);
axis equal tight
Related
Is there any way of labeling plots with images. For example, when I use the following:
plot(Y(:,1),Y(:,2),'o','LineWidth',2);
gname(names)
I can label each dot in a plot with a name. Is there any way to insert images instead of names?
It is possible, but not as convenient as gname by far. You can use the low-level version of image to insert images in your plot at arbitrary positions. Here's a simple example which puts the "Mandrill" image that comes with Matlab with its upper left corner pixel at the position (pi/2, 0):
% example plot
x = linspace(0, 2*pi, 100);
plot(x, cos(x))
% insert image
load mandrill
colormap(map)
image('CData', X, 'XData', [pi/2, pi/2 + 0.5], 'YData', [0, -0.3])
The result looks like this:
Problems with this approach:
There is no interactive point-and-click facility, you have to explicitly insert and position the image labels programmatically, or program such a point-and-click facility yourself. ginput might help doing so.
A figure window can only have one associated color map. That means if you have different images, they either all have to use the same colormap or have to be truecolor images.
Not just the position, but also the display size of the image has to be specified in the call to image, and both are by default specified with respect to the plot's coordinate system. This makes it hard to achieve the correct aspect ratio. You can switch (temporarily) to absolute units using the axes property 'Units' , but then you have to figure out the correct position in e.g. absolute millimeters or inches. Moreover, images are usually indexed with vertical coordinates increasing from top to bottom, while plots usually have vertical coordinates increasing from bottom to top. This is the reason for the negative value -0.3 in the 'YData' property above.
Alternatively, you can insert images each in their own little axes sitting on top of the plot's axes, which makes it easy to get the right orientation and aspect ratio using axis image. You'll still have the problem though to figure out the correct position for the axes.
What happens with the code below is that image width is scaled to 100% as expected and the height also scales as expected keeping the aspect ratio correct. Issue is that there is a margin at the bottom and that seems to be the height of the original contentHeight of the image. How can I get rid of that?
I am using percentages so that it scales when device orientation changes.
backdrop.source = "http://cf2.imgobject.com/t/p/" + "w342" + data.backdrop;
backdrop.scaleMode = "letterbox";
backdrop.horizontalAlign = "left";
backdrop.verticalAlign = "top";
backdrop.smooth = true;
backdrop.percentWidth = 100;
The answer to your question is don't use the letterbox setting. That is going to preserve the aspect ratio and make the black area, hence the name letterbox :)
Try setting scaleMode to zoom instead. As the documentation states, zoom will result in one axis being clipped. This should scale the image, preserve the aspect ratio, but clip some edges of the image to avoid having the black area.
Other solutions to this problem are:
modify the original image outside of Flash
use a mask to achieve similar results that the zoom setting will provide. In this approach you make the image bigger, but then apply a square mask to the image. The mask reveals only the square portion ... clipping what is outside the mask.
(undesirable in most cases) use the scaleMode setting of strectch (and specify both width/height) so that the area is filled, this will not preserve the aspect ratio
PS: There is no way to avoid the black area if the image's aspect ratio is not square. Even with HTML/CSS. This is just math/geometry. The same thing happens in HTML -- the image is either stretched, clipped, or will not fill both dimensions.
[Edit]
PPS: One other idea, if you know the original aspect ratio of the image, is to calculate a new width that will be closest to the desired width, but naturally preserves the width to height aspect ratio.
For example, the width:height ratio is 4:3. Your desired width is 500 pixels. Using cross products you get this:
4 500
- = -
3 x
Using cross products you get the equation:
4x = 3*500
Now solve for x:
x = 3*500/4 = 375
Therefore, if the original aspect ratio is 4:3, you can set a width of 500 and a height of 375 to scale the image and not have any black areas. You can even write code that dynamically calculates the aspect ratio, and applies this logic to scale something nicely. The point is that you have to the respect aspect ratio when scaling the image to avoid the "black" areas.
Is it possible to display an image in multiple subplot axes, such that the image appears at the desired scale?
subplot(3,3,[1 4 7]);
%# image scaled down to fit 1 set of axes
imshow(img);
subplot(3,3,2);
plot(relevantData);
%# And so on with 5 other plots
I want to have the image scaled to either a fixed size or to fit the axes available to it, rather than to the size of a single axes.
My use case is to show a video alongside plots derived from the video, such that the plots are progressively drawn in step with the video. Once the display is correct I can save each image and combine them into a video.
Clarification
I am asking if it is possible to produce a figure as described without specifying the position of every element in absolute terms. Though one can make arbitrary figures that way (and in fact I have done so for this project), it is very tedious.
Edit:
For changing the size of the subplot:
In help subplot they mention that you can set parameters on the selected "axes" (that's what they call a plotting area in Matlab).
Using that, you can set the 'position', as seen in help axes. This property takes takes as argument:
[left, bottom, width, height]
As pointed out by #reve_etrange, one should use absolute positioning for axes 'Position'and 'OuterPosition' parameters. they can be in normalized coordinates, though.
For changing the size of the image in the subplot:
I think there are 2 useful things for you in the help imshow output:
'InitialMagnification': setting the magnification of the image.
'Parent': determines which parent imshow will use to put the image in (never tried using imshow with subplots).
I'm using matlab in order to perform modifications on an image.
I have loaded an image on Matlab. (the image may be in different resolutions)
Converted the image to gray scale then converted the image's matrix to double.
I have drawn grid lines on the image
(I have posted the code how to do that somewhere here on stack over flow).
My problem is that I may have upon the 1000 squares as a result from girding the image on the X axis and the Y axis.
I'd like to numbering the squares in that image.
Is there an option of drawing numbers on Matlab ?
I'd be glad to receive any information about that (except from being a clicking monkey and writing 0 till 1000 on paint haha... ).
Cheers
S
Here is a code example to put text labels on an image in the middle of grids:
x = imread('cameraman.tif');
image(x)
axis image
grid on
%# grid domains
xg = 0:50:200;
yg = 0:50:200;
%# label coordinates
[xlbl, ylbl] = meshgrid(xg+25, yg+25);
%# create cell arrays of number labels
lbl = strtrim(cellstr(num2str((1:numel(xlbl))')));
text(xlbl(:), ylbl(:), lbl(:),'color','w',...
'HorizontalAlignment','center','VerticalAlignment','middle');
Use text
text is the low-level function for creating text graphics objects. Use
text to place character strings at specified locations.
text(x,y,'string') adds the string in quotes to the location specified
by the point (x,y) x and y must be numbers of class double.
I want to crop an image from a specific row onwards. Please help me how can I do this. I am a beginner in Matlab.
This page has a lot of great info on dealing with images in matlab.
When you load an image in matlab, it is loaded as a MxNx3 matrix. The third dimension stores the RGB values of each pixel. So to crop an image you simply select just the range of rows and columns you want to keep:
cropped_image = image(RowStart:RowEnd,ColStart:ColEnd,:);
See this: http://www.mathworks.com/help/techdoc/creating_plots/f9-47085.html
There is a graph editor icon in the screen where you see your graph, it should look like this:
Press it, you will get a big graph editor, now try pressing on the graph or one of the functions, in the lower right part you can set ranges, this will crop the image.
You can use imcrop function in Matlab
CropIm = imcrop(I, rectangle);
rectangle is a four-element position vector [xmin ymin width height] which indicates the size and position of the crop rectangle.
Im = imread('test.tif');
Im2 = imcrop(Im,[75 68 130 112]);
imshow(Im), figure, imshow(Im2)