MATLAB: How to know the size of pixel in mm/cm/m if i create randomly distributed circles or rectangulars

area of pixelmrandom number generator

I created my own black filled cirlces and rectangles in white pixel area (say 100×100) … can i determine the area of circle and image in other units like meter or cm or mm ?

Best Answer

As mentioned above, you need a reference for your pixels. This could be for example PPI (pixels per inch) for your monitor, or pixels per cm.

I would personally start with an image instead of using scatter(). You can generate a plain black 1000 x 1000 grayscale image with the following code

A=zeros(1000);
imshow(A);         % note that depending on your monitor size imshow() may also scale your image.

The insertShape() function can then be used to insert circles with specified x,y coordinates and radii. See documentation on insertShape() for squares and polygons.

X = 1000.*rand(30,1);
Y = 1000.*rand(30,1);
radii=20.*(ones(length(Y),1));
A=insertShape(A,'FilledCircle',[X Y radii],'Color','white','Opacity',1);
imshow(A)

Now, you could work out the percent area with respect to the total image if you wanted

percent_area=nnz(rgb2gray(A))/1000^2

Note that this does not double the area of overlapping pixels (i.e. where the shapes overlap, the overlapping region is only counted once). Although I suspect the above percent_area might be what you are looking for...?

Again, if you want mm^2, you need to provide a reference of some sort.

Related Solutions

MATLAB: AREA IN SQ.CM

Hi,

First, you must know about actual size of your picture in cm.

For example your picture has 1000 pixel of height x 600 pixel of width. You should measure 1000 pixel = ? cm and 600 pixel = ? cm

See this example

MATLAB: How to randomly generate multiple random shapes within a given area WITHOUT overlapping

One very general way is to just keep generating shapes randomly but throw away any newly-generated random shapes that overlap with ones you have previously generated. The algorithm might look something like this:

PixelUsed = false(n,n);  % the full area in which shapes are to be generated.  no pixels used yet.
while WantMoreShapes
    newShape = myRandomShapeGenerator;
    thisShapePixel = PixelMarker(newShape);  % PixelMarker returns (n,n) array indicating whether newShape uses each pixel.
    if ~AnyOverlap(thisShapePixel,PixelUsed)   % Check whether any pixel is true for both n,n arrays.
       % this newShape does not overlap with any used before
       iShape = iShape + 1;
       myStoreShape(iShape) = newShape;
       PixelUsed = PixelUsed | thisShapePixel;  % mark the pixels used by this shape
       WantMoreShapes = ???;
    end
end

Watch out---this process could easily get into an infinite loop, so you should add code to exit after a number of unsuccessful newShape's.

Also, the shapes generated later will tend to be smaller (since larger ones are more likely to overlap with something). If that is a problem for you, then this method probably won't work.

Best Answer

Related Solutions

MATLAB: AREA IN SQ.CM

MATLAB: How to randomly generate multiple random shapes within a given area WITHOUT overlapping

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