I am working on Image Inpaiting on video project and i am selecting the portion of the image on a screen(ROI) as a rectangle and i am inpaiting that portion of the image. Now i want to save five previous frame from live video(that i can do it) and save the pixels value of that ROI of five frame/image on five different array. I will use that array to generate the background and remove the foreground object.
Any one know how i can save pixel value in array for that selected area?
Thanks in advance.
C++ interface of opencv use cv::Mat for storing image pixel.
The following code shows you how to declare a matrix B "pointing" to a ROI of matrix A.
Matrices are images. ROI is a rectangle (x=0;t=0;width=0;height=100). Use opencv highgui function to save your image.
cv::Mat A(640,480,CV_8C3);
cv::Rect rect(0,0,100,100);
cv::Mat B = A(rect);
cv::imwrite("my_roi.pbg",B);
If you need to read frames from a video, use cv::VideoCapture cap and cap >> frame to grab and retrieve each images as cv::Mat. If you want to go to different position in your video file use cv::VideoCapture::set(..,CV_FRAME_MSEC) , read manual.
Related
I just imported an image taken from my iphone 7 onto matlab. It turns out that the image has 3d size instead of 2d.
boxImage1 = imread('IMG_5175.jpg');
boxImage1 480x640x3 921600 uint8
Can anyone explain why the size of image is in 3d instead of just two. I am trying to run object detection tools on a set of images to extract relevant objects.
Thanks,
As pointed out in the comments, the three dimensions corresponds with the R, G and B channels. Have a look into the matlab documentation:
If the file contains a truecolor image, then A is an m-by-n-by-3 array.
Converting it to grayscale, using rgb2gray, is often a good idea, but it may depend on your application:
I = rgb2gray(boxImage1); % 480x640 matrix
Let's say i have an image like that one:
After some quick messing around, i got a binary image of the axe, like that:
What is the easiest/fastest way to get the contour of that image using GNU/Octave?
In Octave you can use bwboundaries (but I will welcome patches that implement bwtraceboundaries)
octave:1> pkg load image;
octave:2> bw = logical (imread ("http://i.stack.imgur.com/BoQPe.jpg"));
octave:3> boundaries = bwboundaries (bw);
octave:4> boundaries = cell2mat (boundaries);
octave:5> imshow (bw);
octave:6> hold on
octave:7> plot (boundaries(:,2), boundaries(:,1), '.g');
There are a couple of differences here from #Benoit_11 answer:
here we get the boundaries for all the objects in the image. bwboundaries will also accept coordinates as input argument to pick only a single object but I believe that work should be done by further processing your mask (may be due to the jpeg artifacts)
because we get boundaries for all objects, so you get a cell array with the coordinates. This is why we are using dots to plot the boundaries (the default is lines and it will be all over the image as it jumps from one object to other). Also, it is not documented whether the coordinates given are for the continuous boundary, so you should not assume it (again, why we plot dots).
the image that is read seems to have some artifacts, I will guess that is from saving in jpeg.
You can use bwtraceboundary in the Image package. Here is the Matlab implementation but that should be pretty similar using Octave:
First estimate starting pixel to look for boundary and then plot (BW is the image). (Check here )
dim = size(BW);
col = round(dim(2)/2)-90;
row = min(find(BW(:,col)));
boundary = bwtraceboundary(BW,[row, col],'N');
imshow(BW)
hold on;
plot(boundary(:,2),boundary(:,1),'g','LineWidth',3);
Output:
I have two images and have to divide that image. Due to manual error the area in the image is not as same. How can i correct it automatically using matlab so as to perform divison pixel by pixel accurately?
Once you've read both image files into the variables, say A and B, assuming A contains the image of the size you actually want and B contains the image of the size you want to change, you could use:
[numrows numcols] = size(A);
A = imresize(A, [numrows numcols]);
If I have an image, how can I obtain the values of each pixel in that image using matlab
Thanks.
Images are matrices (2D if grayscale, 3D if colored) in MATLAB.
You can use x(i,j) to access a pixel at location (i,j) in a grayscale image.
If the image is colored, you can use x(i,j,:) to access the r, g, b values in a 3-vector, respectively. If you need individual channels, then, you can use x(i,j,1) for red for example.
You may read this page to learn more.
You can use reshape to extract all the pixel values of the image into a vector with pixel values:
frame = imread('picture.jpg');
frame_size = size(frame);
allpixels = reshape(frame, frame_size(1)*frame_size(2), frame_size(3))
This can be useful when you want to vectorize your Matlab code (to avoid a for loop that goes through every pixel). To get back the original image representation:
frame2 = reshape(allpixels, frame_size);
to get the values at pixel(1,1) we simply write image(1,1).
I'd like to show an image and plot something on it and then save it as an image with the same size as the original one. My MATLAB code is:
figH = figure('visible','off');
imshow(I);
hold on;
% plot something
saveas(figH,'1','jpg');
close(figH);
But the resulting image "1.jpg" has saved non-image areas in the plot as well as the image. How can I solve this problem?
The reason your new image is bigger than your original is because the SAVEAS function saves the entire figure window, not just the contents of the axes (which is where your image is displayed).
Your question is very similar to another SO question, so I'll first point out the two primary options encompassed by those answers:
Modify the raw image data: Your image data is stored in variable I, so you can directly modify the image pixel values in I then save the modified image data using IMWRITE. The ways you can do this are described in my answer and LiorH's answer. This option will work best for simple modifications of the image (like adding a rectangle, as that question was concerned with).
Modify how the figure is saved: You can also modify how you save the figure so that it better matches the dimensions of your original image. The ways you can do this (using the PRINT and GETFRAME functions instead of SAVEAS) are described in the answers from Azim, jacobko, and SCFrench. This option is what you would want to do if you were overlaying the image with text labels, arrows, or other more involved plot objects.
Using the second option by saving the entire figure can be tricky. Specifically, you can lose image resolution if you were plotting a big image (say 1024-by-1024 pixels) in a small window (say 700-by-700 pixels). You would have to set the figure and axes properties to accommodate. Here's an example solution:
I = imread('peppers.png'); %# Load a sample image
imshow(I); %# Display it
[r,c,d] = size(I); %# Get the image size
set(gca,'Units','normalized','Position',[0 0 1 1]); %# Modify axes size
set(gcf,'Units','pixels','Position',[200 200 c r]); %# Modify figure size
hold on;
plot(100,100,'r*'); %# Plot something over the image
f = getframe(gcf); %# Capture the current window
imwrite(f.cdata,'image2.jpg'); %# Save the frame data
The output image image2.jpg should have a red asterisk on it and should have the same dimensions as the input image.