I'm looking for building a matrix of an image descriptron extracted from SIFT.
I got the descriptor's locations (X,Y), and I want to build the patch 15X15 pixels.
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(144,100)| | | |
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Is there any way to store the locations X and Y in one cell in a matrix. I dont know how to store the result.
Related
I have a square table similar to this:
| c | d |
| - | - |
a | 1 | 2 |
b | 3 | 4 |
I want to calculate matrix multiplication result where this table is multiplied by itself, i.e., this:
| c | d |
| -- | - |
a | 7 | 10 |
b | 15 | 22 |
While I understand that SQL should not be my language of choice for this task, I need to do this in that language. How do I do this?
It will make your life easier if you represent your matrix elements as (i,j,a[i,j]).
WITH matrix AS (SELECT * FROM
(VALUES ('a','a',1), ('a','b',1), ('b','a',2), ('b','b',3)) AS t(i,j,a))
SELECT m1.i as i, m2.j as j, sum(m1.a * m2.a) FROM matrix m1, matrix m2
GROUP BY m1.i, m2.j
ORDER BY i,j
This will handle sparse matrices nicely as well
Here a dbfiddle that you might be able to visualize.
I am trying to implement an algorithm that calculates the shortest path from the far left (A) to the far right node (B).
For example:
-----------------------------------------------
| |
| x |
| x |
| |
| x |
| A x |
| x |
| B |
| x |
-----------------------------------------------
So far I have an adjacency matrix. I have tried to implement this using Dijkstra's algorithm, but I only get the distance using this algorithm, I would also need the path information (which nodes are passed?).
How could I implement this?
I have a series of Images, stored into an array A. So every entry of A contains an Image (matrix). All matrices are equally sized.
Now I want to extract the value of a specific position (pixel), but my current approach seems to be slow and I think there may be a better way to do it.
% Create data that resembles my problem
N = 5
for i = 1:N
A{i} = rand(5,5);
end
% my current approach
I = size(A{1},1);
J = size(A{1},2);
val = zeros(N,1);
for i = 1:I
for j = 1:J
for k = 1:N
B(k) = A{k}(i,j);
end
% do further operations on B for current i,j, don't save B
end
end
I was thinking there should be some way along the lines of A{:}(i,j) or vertcat(A{:}(i,j)) but both lead to
??? Bad cell reference operation.
I'm using Matlab2008b.
For further information, I use fft on B afterwards.
Here are the results of the answer by Cris
| Code | # images | Extracting Values | FFT | Overall |
|--------------|----------|-------------------|----------|-----------|
| Original | 16 | 12.809 s | 19.728 s | 62.884 s |
| Original | 128 | 105.974 s | 23.242 s | 177.280 s |
| ------------ | -------- | ----------------- | ------- | --------- |
| Answer | 16 | 42.122 s | 27.382 s | 104.565 s |
| Answer | 128 | 36.807 s | 26.623 s | 102.601 s |
| ------------ | -------- | ----------------- | ------- | --------- |
| Answer (mod) | 16 | 14.772 s | 27.797 s | 77.784 s |
| Answer (mod) | 128 | 13.637 s | 28.095 s | 83.839 s |
The answer codes was modded to double(squeeze(A(i,j,:))); because without double the FFT took much longer.
Answer (mod) uses double(A(i,j,:));
So the improvement seems to really kick in for larger sets of images, however I currently plan with processing ~ 500 images per run.
Update
Measured with the profile function, the result of using/omitting squeeze
| Code | # Calls | Time |
|--------------------------------|---------|----------|
| B = double(squeeze(A(i,j,:))); | 1431040 | 36.325 s |
| B= double(A(i,j,:)); | 1431040 | 14.289 s |
A{:}(i,j) does not work because A{:} is a comma-separated list of elements, equivalent to A{1},A{2},A{3},...A{end}. It makes no sense to index into such an array.
To speed up your operation, I recommend that you create a 3D matrix out of your data, like this:
A3 = cat(3,A{:});
Of course, this will only work if all elements of A have the same size (as was originally specified in the question).
Now you can quickly access the data like so:
for i = 1:I
for j = 1:J
B = squeeze(A3(i,j,:));
% do further operations on B for current i,j, don't save B
end
end
Depending on the operations you apply to each B, you could vectorize those operations as well.
Edit: Since you apply fft to each B, you can obtain that also without looping:
B_fft = fft(A3,[],3); % 3 is the dimension along which to apply the FFT
I have the following table with names on column 1 and various questions that are answered 'Y' or 'N' and I want to create a graph as given in the link below. I want the Ys to show up in the graph
I tried IF-ELSE calculation but it gives me the the first condition that passes and ignores the rest and my viz now has just one mark per line item.
http://imgur.com/a/2G52b
*I've replaced the 'N' with blanks in this table here
+--------+----+----+----+----+----+----+
| Name | Q1 | Q2 | Q4 | Q5 | Q6 | Q7 |
+--------+----+----+----+----+----+----+
| Bhansa | | Y | | | | |
| Chaga | Y | Y | | | | Y |
| Chang | | | | Y | Y | |
| Cooke | | Y | | Y | | |
+--------+----+----+----+----+----+----+
As user Ben mentioned, the trick here is to do a pivot. You can do that by selecting the Question columns from the data source tab and right clicking at any of the header.
Once you have pivoted the data, you can create the chart as shown below. Please note that we are using a filter on 'Pivot Field Values' to filter out the 'N' values
I have a set of (x,y) points defined in the following way:
map=[0,0;66,0;66,44;44,44;44,66;110,66;110,110;0,110];
There is then a function that connects these points (which are vertices, i.e. corner points) together to form a closed shape. The example vertices I have given form a shape something like this:
________________________________________
| |
| |
| |
| ____________________|
| |
| |_______
| |
| |
| |
| |
|___________________________|
I would like to now automatically generate a second set of vertices that form a boundary inside the shape, offset by some amount. I.e. this:
inner_boundary=[5,5;61,5;61,39;39,39;39,71;105,71;105,105;5,105];
________________________________________
| ___________________________________ |
| | | |
| | _____________________| |
| | | ____________________|
| | | |
| | | |_______
| | |________ |
| | | |
| | | |
| |______________________| |
|___________________________|
Any ideas on how to do this? I've been racking my brains but can't think of a robust way to do this. I need it to automatically do this for any input set of vertices. Also, to clarify - I am just interested in how to specify the set of vertices, not the drawing part.
Many thanks!
Here is a solution based on Image Processing Toolbox functions. The basic idea is as follows:
Use "poly2mask" to create a BW (0-1) image from the polygon
coordinates
Use "imerode" to erode the mask by 1 pixel
Use "bwboundaries" to trace the new, eroded, boundary
Code example:
x = [4 10 10 4 4];
y = [4 4 10 10 4];
mask = poly2mask(x,y,12,12);
mask_eroded = imerode(mask, 1);
newBnds = bwboundaries(mask_eroded);
newBnds = newBnds{1};
Note that the newBnds will probably contain more points than you want because it traces every single pixel on the boundary. You can write a simple iterative routine to discard non-endpoints.