I`m working on script/function for school project which will generate all 24-bit RGB colors image in matlab.
I wrote something like this but it is slow (and matlab don`t like me and crashes a lot). Last time before crash it was working on for 5 days.
Here is the code:
a = 1;
for r = 0:255
for g = 0:255
for b = 0:255
colors(a,:) = [r g b];
a = a + 1;
end
end
end
colors = reshape(colors, [4096, 4096, 3]);
colors = uint8(colors);
imshow(colors);
imwrite(colors, 'generated.png');
Is there any faster approach to do this?
Build the three columns separately using repmat/repelem and then concatenate them.
colors = [repelem((0:255).',256^2),...
repmat([repelem((0:255).',256) repmat((0:255).',256,1)],256,1)];
It is generally a good idea to preallocate large matrices to speed up code. With your current implementation, the size of colors grows one row every iteration which requires a lot memory allocation resources. Try to define your matrix with
colors = zeros(2^24, 3);
at the beginning of your code. To save memory and time, you can even define the matrix as uint8 from the beginning instead of converting it afterwards
colors = zeros(2^24, 3, 'uint8');
Related
I am working on a signal processing related problem. I have a dataset of >2000 EEG signals. Each EEG Signal is represented by a 2D Numpy array (19 x 30000). Each row of the array is one of the channels of the signal. What I have to do is to find the spectrograms on these individual channels (rows) and concatenate them vertically. Here is the code I wrote so far.
raw = np.load('class_1_ar/'+filename)
images = []
for i in range(19):
print(i,end=" ")
spec,freq,t,im = plt.specgram(raw[i],Fs=100,NFFT=100,noverlap=50)
plt.axis('off')
figure = plt.gcf()
figure.set_size_inches(12, 1)
figure.canvas.draw()
img = np.array(figure.canvas.buffer_rgba())
img = cv2.cvtColor(img, cv2.COLOR_RGBA2BGRA)
b = figure.axes[0].get_window_extent()
img = np.array(figure.canvas.buffer_rgba())
img = img[int(b.y0):int(b.y1),int(b.x0):int(b.x1),:]
img = cv2.cvtColor(img, cv2.COLOR_RGBA2BGRA)
images.append(img)
base = cv2.vconcat(images)
cv2.imwrite('class_1_sp/'+filename[:-4]+'.png',base)
c -= 1
print(c)
And here is my output:
However, the process is taking too much time to process. It took almost 8 hours for the first 200 samples to process.
My question is, What can I do to make it faster?
Like others have said, the overhead of going through matplotlib is likely slowing things down. It would be better to just compute (and not plot) the spectrogram with scipy.signal.spectrogram. This function directly returns the spectrogram as a 2D numpy array, so that you don't have the roundabout step of getting it out of the canvas. Note, that does mean you'll have to map the spectrogram output yourself to pixel intensities. In doing that, beware scipy.signal.spectrogram returns the spectrogram as powers, not decibels, so you probably want to do 10*np.log10(Sxx) to the result (see also scipy.signal.spectrogram compared to matplotlib.pyplot.specgram).
Plotting aside, the bottleneck operation in computing a spectrogram are the FFTs. Instead of using a transform size of 100 samples, 128 or some other power of 2 is more efficient. With scipy.signal.spectrogram this is done by setting nfft=128. Note, you can set nperseg=100 and nfft=128 so that 100 samples are still used for each segment, but zero-padded to 128 before doing the FFT. One other thought: if raw is 64-bit float, it may help to cast it to 32-bit: raw = np.load(...).astype(np.float32).
I would like to resize a 512X512 image into 363X762 image which will be larger than the original image(of size 512X512). Those extra pixel values must be different values in the range of 0-255.
I tried the following code:
I=imread('photo.jpg'); %photo.jpg is a 512X512 image
B=zeros(363,726);
sizeOfMatrixB=size(B);
display(sizeOfMatrixB);
B(1:262144)=I(1:262144);
imshow(B);
B(262155:263538)=0;
But I think this is a lengthy one and the output is also not as desired. Could anyone suggest me with a better piece of code to perform this. Thank you in advance.
I think that the code you have is actually pretty close to ideal except that you have a lot of hard-coded values in there. Those should really be computed on the fly. We can do that using numel to count the number of elements in B.
B = zeros(363, 726);
%// Assign the first 262144 elements of B to the values in I
%// all of the rest will remain as 0
B(1:numel(I)) = I;
This flexibility is important and the importance is actually demonstrated via the typo in your last line:
B(262155:263538)=0;
%// Should be
B(262144:263538)=0;
Also, you don't need these extra assignments to zero at the end because you initialize the matrix to be all zeros in the first place.
A Side Note
It looks like you are spreading the original image data for each column across multiple columns. I'm guessing this isn't what you want. You probably only want to grab the first 363 rows of I to be placed into B. You can do that this way:
B = zeros(363, 726);
B(1:size(B, 1), 1:size(I, 2)) = I(1:size(B, 1), :);
Update
If you want the other values to be something other than zero, you can initialize your matrix to be that value instead.
value = 2;
B = zeros(363, 726) + value;
B(1:numel(I)) = I;
If you want them to be random integers between 0 and 255, use randi to initialize the matrix.
B = randi([0 255], 363, 726);
B(1:numel(I)) = I;
So some background. I was tasked to write a matlab program to count the number yeast cells inside visible-light microscopic images. To do that I think the first step will be cell segmentation. Before I got the real experiment image set, I developed an algorithm use a test image set utilizing watershed. Which looks like this:
The first step of watershed is generating a BW mask for the cells. Then I would generate a bwdist image with imposed local minimums generated from the BW mask. With that I can generate the watershed easily.
As you can see my algorithm rely on the successful generation of BW mask. Because I need to generate the bwdist image and markers from it. Originally, I generate the BW mask following the following steps:
generate the Local standard deviation of image sdImage = stdfilt(grayImage, ones(9))
Use BW thresholding to generate the initial BW mask binaryImage = sdImage < 8;
use imclearborder to clear the background. Use some other code to add the cells on the border back.
Background finished. Here is my problem
But today I received the new real data sets. The image resolution is much smaller and the light condition is different from the test image set. The color depth is also much smaller. These make my algorithm useless. Here is it:
Using stdfilt failed to generate a good clean images. Instead it generate stuff like this (Note: I have adjusted parameters for the stdfilt function and the BW threshold value, following is the best result I can get) :
As you can see there are light pixels in the center of the cells that not necessary darker than the membrane. Which lead the bw thresholding generate stuff like this:
The new bw image after bw thresholding have either incomplete membrane or segmented cell centers and make them unsuitable to the other steps.
I only start image processing recently and have no idea how should I proceed. If you have an idea please help me! Thanks!
For your convience, I have attached a link from dropbox for a subset of the images
I think there's a fundamental problem in your approach. Your algorithm uses stdfilt in order to binarize the image. But what that essentially means is you're assuming there is there is low "texture" in the background and within the cell. This works for your first image. However, in your second image there is a "texture" within the cell, so this assumption is broken.
I think a stronger assumption is that there is a "ring" around each cell (valid for both images you posted). So I took the approach of detecting this ring instead.
So my approach is essentially:
Detect these rings (I use a 'log' filter and then binarize based on positive values. However, this results in a lot of "chatter"
Try to remove some of the "chatter" initially by filtering out very small and very large regions
Now, fill in these rings. However, there is still some "chatter" and filled regions between cells left
Again, remove small and large regions, but since the cells are filled, increase the bounds for what is acceptable.
There are still some bad regions, most of the bad areas are going to be regions between cells. Regions between cells are detectable by observing the curvature around the boundary of the region. They "bend inwards" a lot, which is expressed mathematically as a large portion of the boundary having a negative curvature. Also, to remove the rest of the "chatter", these regions will have a large standard deviation in the curvature of their boundary, so remove boundaries with a large standard deviation as well.
Overall, the most difficult part will be removing regions between cells and the "chatter" without removing the actual cells.
Anyway, here's the code (note there are a lot of heuristics and also it's very rough and based on code from older projects, homeworks, and stackoverflow answers so it's definitely far from finished):
cell = im2double(imread('cell1.png'));
if (size(cell,3) == 3)
cell = rgb2gray(cell);
end
figure(1), subplot(3,2,1)
imshow(cell,[]);
% Detect edges
hw = 5;
cell_filt = imfilter(cell, fspecial('log',2*hw+1,1));
subplot(3,2,2)
imshow(cell_filt,[]);
% First remove hw and filter out noncell hws
mask = cell_filt > 0;
hw = 5;
mask = mask(hw:end-hw-1,hw:end-hw-1);
subplot(3,2,3)
imshow(mask,[]);
rp = regionprops(mask, 'PixelIdxList', 'Area');
rp = rp(vertcat(rp.Area) > 50 & vertcat(rp.Area) < 2000);
mask(:) = false;
mask(vertcat(rp.PixelIdxList)) = true;
subplot(3,2,4)
imshow(mask,[]);
% Now fill objects
mask1 = true(size(mask) + hw);
mask1(hw+1:end, hw+1:end) = mask;
mask1 = imfill(mask1,'holes');
mask1 = mask1(hw+1:end, hw+1:end);
mask2 = true(size(mask) + hw);
mask2(hw+1:end, 1:end-hw) = mask;
mask2 = imfill(mask2,'holes');
mask2 = mask2(hw+1:end, 1:end-hw);
mask3 = true(size(mask) + hw);
mask3(1:end-hw, 1:end-hw) = mask;
mask3 = imfill(mask3,'holes');
mask3 = mask3(1:end-hw, 1:end-hw);
mask4 = true(size(mask) + hw);
mask4(1:end-hw, hw+1:end) = mask;
mask4 = imfill(mask4,'holes');
mask4 = mask4(1:end-hw, hw+1:end);
mask = mask1 | mask2 | mask3 | mask4;
% Filter out large and small regions again
rp = regionprops(mask, 'PixelIdxList', 'Area');
rp = rp(vertcat(rp.Area) > 100 & vertcat(rp.Area) < 5000);
mask(:) = false;
mask(vertcat(rp.PixelIdxList)) = true;
subplot(3,2,5)
imshow(mask);
% Filter out regions with lots of positive concavity
% Get boundaries
[B,L] = bwboundaries(mask);
% Cycle over boundarys
for i = 1:length(B)
b = B{i};
% Filter boundary - use circular convolution
b(:,1) = cconv(b(:,1),fspecial('gaussian',[1 7],1)',size(b,1));
b(:,2) = cconv(b(:,2),fspecial('gaussian',[1 7],1)',size(b,1));
% Find curvature
curv_vec = zeros(size(b,1),1);
for j = 1:size(b,1)
p_b = b(mod(j-2,size(b,1))+1,:); % p_b = point before
p_m = b(mod(j,size(b,1))+1,:); % p_m = point middle
p_a = b(mod(j+2,size(b,1))+1,:); % p_a = point after
dx_ds = p_a(1)-p_m(1); % First derivative
dy_ds = p_a(2)-p_m(2); % First derivative
ddx_ds = p_a(1)-2*p_m(1)+p_b(1); % Second derivative
ddy_ds = p_a(2)-2*p_m(2)+p_b(2); % Second derivative
curv_vec(j+1) = dx_ds*ddy_ds-dy_ds*ddx_ds;
end
if (sum(curv_vec > 0)/length(curv_vec) > 0.4 || std(curv_vec) > 2.0)
L(L == i) = 0;
end
end
mask = L ~= 0;
subplot(3,2,6)
imshow(mask,[])
Output1:
Output2:
I've found some methods to enlarge an image but there is no solution to shrink an image. I'm currently using the nearest neighbor method. How could I do this with bilinear interpolation without using the imresize function in MATLAB?
In your comments, you mentioned you wanted to resize an image using bilinear interpolation. Bear in mind that the bilinear interpolation algorithm is size independent. You can very well use the same algorithm for enlarging an image as well as shrinking an image. The right scale factors to sample the pixel locations are dependent on the output dimensions you specify. This doesn't change the core algorithm by the way.
Before I start with any code, I'm going to refer you to Richard Alan Peters' II digital image processing slides on interpolation, specifically slide #59. It has a great illustration as well as pseudocode on how to do bilinear interpolation that is MATLAB friendly. To be self-contained, I'm going to include his slide here so we can follow along and code it:
Please be advised that this only resamples the image. If you actually want to match MATLAB's output, you need to disable anti-aliasing.
MATLAB by default will perform anti-aliasing on the images to ensure the output looks visually pleasing. If you'd like to compare apples with apples, make sure you disable anti-aliasing when comparing between this implementation and MATLAB's imresize function.
Let's write a function that will do this for us. This function will take in an image (that is read in through imread) which can be either colour or grayscale, as well as an array of two elements - The image you want to resize and the output dimensions in a two-element array of the final resized image you want. The first element of this array will be the rows and the second element of this array will be the columns. We will simply go through this algorithm and calculate the output pixel colours / grayscale values using this pseudocode:
function [out] = bilinearInterpolation(im, out_dims)
%// Get some necessary variables first
in_rows = size(im,1);
in_cols = size(im,2);
out_rows = out_dims(1);
out_cols = out_dims(2);
%// Let S_R = R / R'
S_R = in_rows / out_rows;
%// Let S_C = C / C'
S_C = in_cols / out_cols;
%// Define grid of co-ordinates in our image
%// Generate (x,y) pairs for each point in our image
[cf, rf] = meshgrid(1 : out_cols, 1 : out_rows);
%// Let r_f = r'*S_R for r = 1,...,R'
%// Let c_f = c'*S_C for c = 1,...,C'
rf = rf * S_R;
cf = cf * S_C;
%// Let r = floor(rf) and c = floor(cf)
r = floor(rf);
c = floor(cf);
%// Any values out of range, cap
r(r < 1) = 1;
c(c < 1) = 1;
r(r > in_rows - 1) = in_rows - 1;
c(c > in_cols - 1) = in_cols - 1;
%// Let delta_R = rf - r and delta_C = cf - c
delta_R = rf - r;
delta_C = cf - c;
%// Final line of algorithm
%// Get column major indices for each point we wish
%// to access
in1_ind = sub2ind([in_rows, in_cols], r, c);
in2_ind = sub2ind([in_rows, in_cols], r+1,c);
in3_ind = sub2ind([in_rows, in_cols], r, c+1);
in4_ind = sub2ind([in_rows, in_cols], r+1, c+1);
%// Now interpolate
%// Go through each channel for the case of colour
%// Create output image that is the same class as input
out = zeros(out_rows, out_cols, size(im, 3));
out = cast(out, class(im));
for idx = 1 : size(im, 3)
chan = double(im(:,:,idx)); %// Get i'th channel
%// Interpolate the channel
tmp = chan(in1_ind).*(1 - delta_R).*(1 - delta_C) + ...
chan(in2_ind).*(delta_R).*(1 - delta_C) + ...
chan(in3_ind).*(1 - delta_R).*(delta_C) + ...
chan(in4_ind).*(delta_R).*(delta_C);
out(:,:,idx) = cast(tmp, class(im));
end
Take the above code, copy and paste it into a file called bilinearInterpolation.m and save it. Make sure you change your working directory where you've saved this file.
Except for sub2ind and perhaps meshgrid, everything seems to be in accordance with the algorithm. meshgrid is very easy to explain. All you're doing is specifying a 2D grid of (x,y) co-ordinates, where each location in your image has a pair of (x,y) or column and row co-ordinates. Creating a grid through meshgrid avoids any for loops as we will have generated all of the right pixel locations from the algorithm that we need before we continue.
How sub2ind works is that it takes in a row and column location in a 2D matrix (well... it can really be any amount of dimensions you want), and it outputs a single linear index. If you're not aware of how MATLAB indexes into matrices, there are two ways you can access an element in a matrix. You can use the row and column to get what you want, or you can use a column-major index. Take a look at this matrix example I have below:
A =
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
If we want to access the number 9, we can do A(2,4) which is what most people tend to default to. There is another way to access the number 9 using a single number, which is A(11)... now how is that the case? MATLAB lays out the memory of its matrices in column-major format. This means that if you were to take this matrix and stack all of its columns together in a single array, it would look like this:
A =
1
6
11
2
7
12
3
8
13
4
9
14
5
10
15
Now, if you want to access element number 9, you would need to access the 11th element of this array. Going back to the interpolation bit, sub2ind is crucial if you want to vectorize accessing the elements in your image to do the interpolation without doing any for loops. As such, if you look at the last line of the pseudocode, we want to access elements at r, c, r+1 and c+1. Note that all of these are 2D arrays, where each element in each of the matching locations in all of these arrays tell us the four pixels we need to sample from in order to produce the final output pixel. The output of sub2ind will also be 2D arrays of the same size as the output image. The key here is that each element of the 2D arrays of r, c, r+1, and c+1 will give us the column-major indices into the image that we want to access, and by throwing this as input into the image for indexing, we will exactly get the pixel locations that we want.
There are some important subtleties I'd like to add when implementing the algorithm:
You need to make sure that any indices to access the image when interpolating outside of the image are either set to 1 or the number of rows or columns to ensure you don't go out of bounds. Actually, if you extend to the right or below the image, you need to set this to one below the maximum as the interpolation requires that you are accessing pixels to one over to the right or below. This will make sure that you're still within bounds.
You also need to make sure that the output image is cast to the same class as the input image.
I ran through a for loop to interpolate each channel on its own. You could do this intelligently using bsxfun, but I decided to use a for loop for simplicity, and so that you are able to follow along with the algorithm.
As an example to show this works, let's use the onion.png image that is part of MATLAB's system path. The original dimensions of this image are 135 x 198. Let's interpolate this image by making it larger, going to 270 x 396 which is twice the size of the original image:
im = imread('onion.png');
out = bilinearInterpolation(im, [270 396]);
figure;
imshow(im);
figure;
imshow(out);
The above code will interpolate the image by increasing each dimension by twice as much, then show a figure with the original image and another figure with the scaled up image. This is what I get for both:
Similarly, let's shrink the image down by half as much:
im = imread('onion.png');
out = bilinearInterpolation(im, [68 99]);
figure;
imshow(im);
figure;
imshow(out);
Note that half of 135 is 67.5 for the rows, but I rounded up to 68. This is what I get:
One thing I've noticed in practice is that upsampling with bilinear has decent performance in comparison to other schemes like bicubic... or even Lanczos. However, when you're shrinking an image, because you're removing detail, nearest neighbour is very much sufficient. I find bilinear or bicubic to be overkill. I'm not sure about what your application is, but play around with the different interpolation algorithms and see what you like out of the results. Bicubic is another story, and I'll leave that to you as an exercise. Those slides I referred you to does have material on bicubic interpolation if you're interested.
Good luck!
I am working on a project which is about pattern (male/female)classification with matlab.I have a problem, I need your help, please.
My program should find mean images of datasets. First dataset is women,second dataset is men. So first mean image has to look like a woman and second a man.I have different datasets which all have format of jpeg. I am trying different datasets for my program to check if it is working but when I use different datasets I can not see true mean images all the time, for ex:
They are mean images from a dataset:
But when I use another dataset my mean images are like this, they have no meanings, I mean they dont look like face:
What can be the reason for this? I should work with different datasets. Please help.
`
filenamesA = dir(fullfile(pathfora, '*.jpg'));
Train_NumberA = numel(filenamesA);
%%%%%%%%%%%%%%%%%%%% Finding Image Vectors for A
imagesA= [];
for k = 1 : Train_NumberA
str = int2str(k);
str= strcat(str);
str = strcat('\',str,'b','.jpg');
str = strcat(pathfora,str);
imgA = imread(str);
imgA = rgb2gray(imgA);
[irowA icolA] = size(imgA);
tempA = reshape(imgA',irowA*icolA,1); % Reshaping 2D images into 1D image vectors
imagesA = [imagesA tempA]; % 'imagesA' grows after each turn
imagesA=double(imagesA);
end`
`%%%%%%%%%%%%%%%%%%%%%%%% Calculate the MEAN IMAGE VECTOR for A
mean_vectorA= mean(imagesA,2); % Computing the average vector m = (1/P)*sum(Tj's) (j = 1 : P)
mean_imageA= reshape(mean_vectorA,irowA,icolA); % Average matrix of training set A
meanimgA=mat2gray(mean_imageA);
figure(1);
imshow(rot90(meanimgA,3));`
-------------------------------------And same for dataset B (male)
You could use a 3D matrix to store the images. I also cleaned up the code a bit. Not tested.
filenamesA = dir(fullfile(pathfora, '*.jpg'));
Train_NumberA = numel(filenamesA);
imagesA = [];
for k = 1:Train_NumberA
imgA = imread(strcat(pathfora, '\', int2str(k), 'b', '.jpg'));
imgA = rgb2gray(imgA);
imagesA = cat(3, imagesA, imgA);
end
double command moved out of loop.
imagesA = double(imagesA);
Calculate the mean over the 3rd dimension of the imagesA matrix to get the mean 2D image.
meanimage_A = mean(imagesA, 3);
Convert to grayscale image.
meanimgA = mat2gray(meanimage_A);
I think rot90 is not needed here...
figure(1);
imshow(meanimgA, 3);
Use a 3D array or cell array of images instead of reshaping 2D images into single rows of a matrix. The reshaping is unnecessary and can only add bugs.
If all your images are the same size, you can use a multidimensional array: Matlab documentation on multidimensional arrays
Otherwise, use a cell array: Matlab documentation on cell arrays