I have imported an image in matlab and before I display it how would I make the background of the image transparent? For example I have a red ball on a white background, how would i make the white pixels of the image tranparent so that only the red ball is visible and the white pixels are transparent?
You need to make sure the image is saved in the 'png' format. Then you can use the 'Alpha' parameter of a png file, which is a matrix that specifies the transparency of each pixel individually. It is essentially a boolean matrix that is 1 if the pixel is transparent, and 0 if not. This can be done easily with a for loop as long as the color that you want to be transparent is always the same value (i.e. 255 for uint8). If it is not always the same value then you could define a threshold, or range of values, where that pixel would be transparent.
Update :
First generate the alpha matrix by iterating through the image and (assuming you set white to be transparent) whenever the pixel is white, set the alpha matrix at that pixel as 1.
# X is your image
[M,N] = size(X);
# Assign A as zero
A = zeros(M,N);
# Iterate through X, to assign A
for i=1:M
for j=1:N
if(X(i,j) == 255) # Assuming uint8, 255 would be white
A(i,j) = 1; # Assign 1 to transparent color(white)
end
end
end
Then use this newly created alpha matrix (A) to save the image as a ".png"
imwrite(X,'your_image.png','Alpha',A);
Note for loops in MATLAB should be avoided at all costs because they are slow. Rewriting code to remove the loops is commonly referred to as "vectorizing" code. In the case of ademing2's answer, it could be done as follows:
A = zeros(size(X));
A(X == 255) = 1;
Related
Hello i need to make background color black and foreground color white. As u can see i did this with transfering image to 2 dimension. I want to make this color changes in 3 dimension, so we are nor allowed to transfer it bw. Is there any way to do this ?
logo=imread('logo.png');
subplot(2,2,1);
imshow(logo);
b=rgb2gray(logo);
subplot(2,2,2);
imshow(b);
c=im2bw(b,0.92)
subplot(2,2,3);
imshow(c);
c = 1-c;
subplot(2,2,4);
imshow(c);
Preface:
To set the pixel to white or black each layer of the pixel needs to be set to an intensity value of 0 (black) or 255 (white).
White Pixel → rgb(255,255,255)
Black Pixel → rgb(0,0,0)
The colon can be used to obtain all the indices in the 3rd dimension (grab all the layers). To grab one RGB-pixel in the top-left corner of the image:
RGB_Pixel = Image(1,1,:);
Method 1:
If you wish to retain the three colour channels you can use matrix indexing to change the white background to black. Matrix indexing can also be used to change anywhere that isn't white to white. This method may, unfortunately, break down if you have a coloured component with a 255 intensity component. This doesn't seem to be the case for your image though. You can use method 2 for a more safe approach.
logo = imread('logo.png');
[Image_Height,Image_Width,Depth]= size(logo);
new_logo = zeros(Image_Height,Image_Width,Depth);
new_logo(logo == 255) = 0;
new_logo(logo ~= 255) = 255;
imshow(new_logo);
Method 2:
Checks each pixel (RGB-triplet) using a set of for-loops that scan through the entire image. If the RGB-intensities of the pixel are rgb(255,255,255) then the pixels are set to 0 (black). If the RGB-intensities of the pixel are anything else the pixels are set to 255 (white). The ~ismember() function is used to check if the RGB-pixel has an intensity that is not 255 (not-white).
logo = imread('logo.png');
%Grabbing the size of the image%
[Image_Height,Image_Width,~]= size(logo);
for Row = 1: Image_Height
for Column = 1: Image_Width
%Grabbing RGB pixel%
RGB_Pixel = logo(Row,Column,:);
if(~ismember(255,RGB_Pixel))
%RGB pixel is white change
logo(Row,Column,:) = 255;
else
%RGB pixel is coloured change to black%
logo(Row,Column,:) = 0;
end
end
end
imshow(logo);
Using the repmat() function is also a great solution that the above comment suggested. Which possibly may be the quickest method since you already have the code that generates one layer from the greyscale image.
Ran using MATLAB R2019b
Trying to paint a river from black to yellow and I'm having a "small" issue.
The image that given on this problem is a simple grayscale image of a map where there's a river on it (original image).
The task is to "paint" this river from black (0,0,0) to yellow (255,255,0).
As far as I know, we can't actually paint grayscale images without "converting" it to RGB so what I did:
Got the image,
"Read" the image with imread(),
Used the function cat to concatenate my image (and apparently "turn" into a RGB image?),
Looped through each part of my image and checked which ones had values between 0 and 48 (according to what I read there are different shades of black and apparently it goes from 8 to 8 like (0,0,0), (8,8,8) and so on)
If there was a value within that range, I'dd color it yellow (255,255,0)
The problem is that not only the river was painted yellow but a relatively large yellow square has been added to the right side of the image. I'll post the image right after the code.
originalIM_River = imread('fig_lista4_2.bmp');
figure,title('Original image'),imshow(originalIM_River)
imRGB_River = cat(3, originalIM_River, originalIM_River, originalIM_River);
[nLine, nColumn] = size(imRGB_River);
for i = 1 : nLine
for j = 1 : nColumn
if imRGB_River(i,j) >= 0 && imRGB_River(i,j) <= 48
imRGB_River(i,j,:) = [255,255,0]; % (255,255,0) is yellow
end
end
end
figure, title('New imagem - River painted with yellow'),imshow(imRGB_River)
River painted with yellow
I've tried to separate each channel from the image (red , green, blue), find which pixels were within the range of 0 to 48 and paint it yellow to later concatenate them but that didn't work either.
The error lies with this line:
[nLine, nColumn] = size(imRGB_River);
Here imRGB_River is a 3-dimensional matrix, with 3 as the size of the third dimension. Since you only request 2 dimensions from the size function it will return the product of all non-singleton trailing dimensions in the last output, so nColumn will be returned as N*3, or three times bigger than you were expecting. To fix it, you could either use your original image matrix (before replicating the third dimension):
[nLine, nColumn] = size(originalIM_River);
Or call size as follows to ignore additional output dimensions:
[nLine, nColumn, ~] = size(imRGB_River);
How should I change the background image color to black or change the RGB values become black color background. I want to take the original leaf image only.
Leaf image
In order to change the background color to black you'll need the following:
calculate the background mask by using a threshold
The threshold can be either find automatically, by using the function graythresh, or manually, by looking at the image histogram.
perform thresholding by using the value from stage 1 in order to find the foreground mask. Also, pick the largest connected component and perform noise cleaning (imclose operation).
calculate the BG from the FG, and zero out the corresponding locations in the original input image.
Code example:
I = imread('YaEwk.jpg');
%converts to hsv colorspace, and takes the 3rd dimension. normlizes it.
im = rgb2hsv(I);
im = mat2gray(im(:,:,3));
%determines a threshold to distinguish between the leaf and its surroundings.
T = graythresh(im);
%defines FG as all the values below the threshold
%Also, keeps just the biggest connected component and perform noise
%reduction.
FG = im < T;
FG = bwareafilt(FG,1);
FG = imclose(FG,strel('disk',2));
%defines the background as the opposite of the foreground
BG = ~FG;
I(repmat(BG,1,1,3)) = 0;
%smooth the output
I(:,:,1) = medfilt2(I(:,:,1));
I(:,:,2) = medfilt2(I(:,:,2));
I(:,:,3) = medfilt2(I(:,:,3));
Result:
I have 2 images. One is background image and other image has same background but with some foreground object. I want to extract foreground object from background. Simple subtraction operation in matlab will not suffice as it subtracts RGB value of background image from that of foreground image (as in below code).
im1 = imread('output/frame-1.jpg')
im2 = imread('output/frame-7.jpg')
%# subtract
deltaImage = im1 - im2;
imshow(deltaImage)
So if background color is white and foreground object is blue, then output (i.e. deltaImage) comes foreground object with orange color with black background. However the output I want is foreground object with blue color (i.e. original color) with black background. How can I get this ? I tried to do it using below code, but output image is incorrect.
im1 = imread('foreground.jpg')
im2 = imread('background.jpg')
[m n k]=size(im2);
deltaImage = zeros(m,n,3);
fprintf('%d %d %d.\n',m,n,k);
for l=1:k
for i=1:m-1
for j=1:n-1
if im1(i:j:l)~=im2(i:j:l)
deltaImage(i,j,l) = im1(i,j,l);
end
end
end
end
imshow(deltaImage)
Background IMAGE
Foreground Image
Output Image (Here I want color of man to be blue)
You can use deltaImage to create a mask (zeros and ones image) that multiplies the foreground. However, note that you will have artifacts associated with lossy image compression (.jpeg). These can be reduced, to some extent, if you use a threshold, like the average difference or a specific value you want. Try this:
im1 = double(imread('~/Downloads/foreground.jpg'));
im2 = double(imread('~/Downloads/background.jpg'));
compute the difference of the averages of the 3 channels
deltaImage = mean(im2,3) - mean(im1,3);
then use the product of the mean by a standard deviation (~3), or uncomment the line below to use a specific threshold, like 128
mask = deltaImage>3*mean(deltaImage(:));
% mask = deltaImage>128;
then assuming all original images are in 8-bit format produce a result also in 8-bit format:
result = uint8(cat(3, im1(:,:,1).*mask, im1(:,:,2).*mask, im1(:,:,3).*mask));
imshow(result)
And this is the result you should get:
Again the weird looking pixels around the main object are artifacts of lossy image compression (.jpeg), you should try working with lossless like .png formats.
I am doing a research for my higher studies in automation. I have done the automation part of the microscope but I need help in MATLAB. An example of what I would like to segment is shown here:
I need to extract the dark purple pixels from this image and only display that in a figure. It is almost like colour based segmentation but I just want to only take the dark purple pixel from the whole image.
What would I do in this case?
Here's something to get you started. Let's go with the theme of colour segmentation where you only want to extract pixels that are of a deep purple. I would like to point you to the HSV colour space before we get started. The HSV colour space is ideal for representing colours in a way that is most intuitive to humans. We tend to describe colours by their dominant colour, followed by attributes such as how washed out or how pure the colour is, and how bright or dark the colour is. The dominant colour is represented by the Hue, the appearance of how washed out or how pure the colour is is represented by the Saturation and the intensity of the colour is represented by the Value, and hence Hue-Saturation-Value, or the HSV colour space.
We can transform a RGB image so that it becomes HSV by rgb2hsv. This will return a 3D matrix that has the hue, saturation and value as 2D slices in a 3D matrix, much like a RGB image where each slices represents the red, green and blue channels. Let's see what each component looks like once we transform the image into HSV:
im = imread('https://www.cdc.gov/dpdx/images/malaria/ovale/Po_gametocyte_thickB.jpg');
hsv = rgb2hsv(im2double(im));
figure;
for idx = 1 : 3
subplot(1,3,idx);
imshow(hsv(:,:,idx));
end
The first line of code reads in an image from a URL. I'm going to use the one that Hoki referred you to, as it's the most simplest one to deal with. For self-containment, this is what the original image looks like:
Once we do this, we convert the image into the HSV colour space. It is important that you convert the image to double precision and you normalize each component to [0,1], and that is performed by im2double. Next, we spawn a new figure, and place each component in a single row over three columns. The first column represents the hue, next column the saturation and finally the last column being the value. This is the figure that we see:
With the first figure, it looks like the dominant colour is purple, whether it's a light shade or a dark shade of the colour, so the hue won't help us here. If you look at a HSV colour wheel:
(source: hobbitsandhobos.com)
Normalize the wheel so that it falls between [0,1] instead of 0 to 360 degrees. The hue is actually represented as degrees due to the nature of the colour space, but MATLAB normalizes this to [0,1]. You can see that purple falls within a hue of [0.6,0.8], which corresponds to the first figure I showed you that displays the hue for our image. If you examine the pixels around the image, they fluctuate between this range. Therefore, the hue won't help us much here.
What will certainly help us are the saturation and value components. If you take a look, the deep purple pixels have a higher saturation than the rest of the background, which makes sense because the deep purple has a much more pure version of purple than the rest of the background. For the value, you can see that the brightness of the dark purple is darker than the background.
We can use these two points as an exploit to segment out the purple colour in the image. The easiest thing to do would be to threshold the saturation and value planes so that any values that are within a certain range you keep while those that are outside you throw away. Therefore, you can do something like this:
sThresh = hsv(:,:,2) > 0.6 & hsv(:,:,2) < 0.9;
vThresh = hsv(:,:,3) > 0.4 & hsv(:,:,3) < 0.65;
I used impixelinfo and I hovered my mouse over the saturation and value components to examine what the values were for the deep purple regions. It looks like those pixels that are deep purple have a saturation value between 0.6 and 0.9, while the value component has values between 0.4 and 0.65. The above code will create two binary masks where true means that the pixel satisfies our criteria while false means it doesn't. Because I want to combine both things together and not leave any stone unturned, let's logical OR the masks together for the final result:
figure;
result = sThresh | vThresh;
imshow(result);
We will also show the result too. This is what we get:
As you can see, this does a pretty good job, but we have remnants of the red arrow that we don't want in the final result. To do a bit of cleanup, we can use morphology - specifically an opening filter of a small window so that we don't affect the pixels that we want as much. We can use imopen to perform our opening operation for us. A morphological opening removes isolated pixels that appear around your image. You use what is called a structuring element that is used to look at local neighbourhoods of your image. For the basics, any pixel regions that are as small as the shape that is contained within the structuring element get removed. Because we want to preserve the shape of the other objects, we can try using a 5 x 5 disk structuring element to clean these pixels up:
figure;
se = strel('disk', 2, 0);
final = imopen(result, se);
imshow(final);
This is what we get:
Not bad! There are some holes that we need to patch up, so let's fill in those holes with imfill:
figure;
final_noholes = imfill(final, 'holes');
imshow(final_noholes);
This is what we get:
OK! So we have our mask. The last thing we need to do is present the image so that you only show the deep purple colours from the original image, and nothing else. That can easily be achieved with bsxfun:
figure;
out = bsxfun(#times, im, uint8(final_noholes));
imshow(out);
The above operation takes your mask, and multiplies every pixel in your image by this mask. One small thing I'd like to point out is that the mask we found in the previous step needs to be cast to uint8, because bsxfun requires that the multiplication (or whatever operation you perform) need to be the same type. We replicate this mask in 3D so that you mask out the unwanted RGB pixels and only keep the ones you are looking for.
This is what we finally get:
As you can see, it isn't perfect, but it's certainly enough to get you started. Those thresholds are what are important, but with some very simple thresholding, I extracted most of the purple pixels out.
To make it easier for you, here's the code that I wrote above that can easily be copied and pasted into MATLAB for you to run:
clear all; close all; clc;
im = imread('https://www.cdc.gov/dpdx/images/malaria/ovale/Po_gametocyte_thickB.jpg');
hsv = rgb2hsv(im2double(im));
figure;
for idx = 1 : 3
subplot(1,3,idx);
imshow(hsv(:,:,idx));
end
sThresh = hsv(:,:,2) > 0.6 & hsv(:,:,2) < 0.9;
vThresh = hsv(:,:,3) > 0.4 & hsv(:,:,3) < 0.65;
figure;
result = sThresh | vThresh;
imshow(result);
figure;
se = strel('disk', 2, 0);
final = imopen(result, se);
imshow(final);
figure;
final_noholes = imfill(final, 'holes');
imshow(final_noholes);
figure;
out = bsxfun(#times, im, uint8(final_noholes));
imshow(out);
Good luck!
Try this:
function main
clc,clear
A = imread('https://www.cdc.gov/dpdx/images/malaria/ovale/Po_gametocyte_thickB.jpg');
subplot(1,2,1)
imshow(A)
RGB = [230 210 200]; % color you want
e = 40; % color shift
B = pix_in(A,RGB,e);
B = B + 255.*uint8(~B); % choosing white background
subplot(1,2,2)
imshow(B)
end
function B = pix_in(A,RGB,e)
% select specific pixels in image
% A - color image (3D matrix uint8)
% RGB - [R G B] - color to select
% e - color shift/deviation
A = double(A); % for same class operations (RGB - double)
[m, n, ~] = size(A);
RGB = reshape(RGB,1,1,3);
RGB = repmat(RGB,m,n,1); % creating 3D matrix
b = abs(A-RGB) < e; % logical 3D
b = sum(b,3) == 3; % if [R,G,B] of a pixel in range
B = A.*repmat(b,1,1,3); % selecting pixels those in range
B = uint8(B);
end