How to add caption/subtitles to Video in MATLAB

                                    In my previous post, I discussed about how to create videofrom still images and now we can add subtitles to the video. I used the ‘text’ function to add the subtitles.

The procedure to add subtitles to the Video:

·         Read an video file

·         Read each video frame data

·         Add text to each frame using the syntax ‘text(x,y,string)’.

·         Use imshow to display the image.

·         Get the frame from the figure displayed.

MATLAB CODE:

%Input a Video file

obj=mmreader('Poem.avi');

A=read(obj);

j=1;

%Preallocate the frame structure

Frame=struct('cdata',1,'colormap',cell([1 100]));

                                 INPUT VIDEO

 

%Get the first frame as image

%Add text

%Use 'getframe' to grab the figure

Caption={'How to add Caption/Subtitles';'to video in MATLAB';'GET CODE AT http://angeljohnsy.blogspot.com/';};

I=A(:,:,:,1);

imshow(I),hold on

text(80,100,Caption{1},'Color','w','FontWeight','Bold','FontSize',30);

text(150,200,Caption{2},'Color','w','FontWeight','Bold','FontSize',30);

text(300,480,Caption{3},'Color','r','FontWeight','Bold','FontSize',15);

Frame(j:j+9)=getframe;

j=j+10;

%Get the Second frame as an image i.eA(:,:,:,2);

%Add the Poem title and the author name

Title_={'THE ROAD NOT TAKEN';'-ROBERT FROST'};

I=A(:,:,:,2);

imshow(I), hold on

text(40,100,Title_{1},'Color','k','FontWeight','Bold','FontSize',40);

text(350,550,Title_{2},'Color','k','FontWeight','Bold','FontSize',30);

Frame(j:j+9)=getframe;

j=j+10;

%Create a cell array with the Poem versus

Txt={'TWO roads diverged in a yellow wood,';

'And sorry I could not travel both';

'And be one traveler, long I stood';

'And looked down one as far as I could';   

'To where it bent in the undergrowth;';

'Then took the other, as just as fair,';   

'And having perhaps the better claim,';

'Because it was grassy and wanted wear;';  

'Though as for that the passing there';

'Had worn them really about the same,';

'And both that morning equally lay';   

'In leaves no step had trodden black.';

'Oh, I kept the first for another day!';   

'Yet knowing how way leads on to way,';

'I doubted if I should ever come back.';

'I shall be telling this with a sigh'; 

'Somewhere ages and ages hence:';  

'Two roads diverged in a wood, and I—';

'I took the one less traveled by,';

'And that has made all the difference.';};

%display the image

%Add the poem lines

%Grab the frame

%There are 20 lines totally

%Add 3 and 2 lines alternatively in each frame

    inc=0;

for i=3:size(A,4)

   

    n=mod(i,2);  

    I=A(:,:,:,i);

   

    imshow(I), hold on

for k=1:2+n

    text(80,440+(k*40),Txt{k+inc},'Color','w','FontWeight','Bold','FontSize',25);

   

end

    inc=inc+2+n;

    Frame(j:j+19)=getframe;

    j=j+20;

 end

Create a Video File:

obj=avifile('Road Not Taken.avi','FPS',3);

 obj=addframe(obj,Frame);

obj=close(obj);

                            VIDEO WITH  SUBTITLE

Explanation:

       text(40,100,Title_{1},'Color','k','FontWeight','Bold','FontSize',40);

                This code will add the text ‘THE ROAD NOT TAKEN’ with color font size 40, font weight bold and color black (k).

          

Extraction of Connected components without using BWLABEL function

             Many of the visitors to this blog mailed me to post a MATLAB code for extracting the connected components.  In MATLAB, a function called BWLABEL is available to label the connected components.  

Based on the following iterative expression, the connected components are extracted.

where k=1,2,3…

Using the above expression, connected components are extracted without using the function BWLABEL

LABELLING:

MATLAB CODE:

I=imread('label3.jpg');

I=im2bw(I);

%Structuring element
B=strel('square',3);
A=I;
%Find a non-zero element's position.
p=find(A==1);
p=p(1);
Label=zeros([size(A,1) size(A,2)]);
N=0;

while(~isempty(p))
    N=N+1;%Label for each component
    p=p(1);
X=false([size(A,1) size(A,2)]);
X(p)=1;

Y=A&imdilate(X,B);
while(~isequal(X,Y))
    X=Y;
    Y=A&imdilate(X,B);
end

Pos=find(Y==1);

A(Pos)=0;
%Label the components
Label(Pos)=N;

p=find(A==1);

end
imtool(Label);

EXPLANATION:

1. Read an image (A) and convert it into binary image.
2. Define a structuring element (B).
3. Initialize the Label matrix with zeros.
4. Find a non-zero element position in the input matrix A.
5. Initialize a matrix X with zeros and place 1 in the non-zero element position found in the previous step.
6. Perform dilation using the structuring element B on matrix X. i.e. imdilate(X,B);
7. Perform intersection with the matrix A. Y= A&imdilate(X, B).
8. Check whether Y==X. If no, then X=Y and perform steps 6 and 7 again else stop the iteration.
9. Find the non-zero elements position in the Y. In matrix Label place a number N in those positions. N is for labeling the connected components.
10. Similarly, place zero in those positions in the input matrix A.
11. Again find a non-zero element position in the matrix A. If found, goto step 5 else stop the iteration.
12. Using the labels the connected components can be extracted.

EXTRACTION:

MATLAB CODE:

%Extracting the components
Im=zeros([size(A,1) size(A,2)]);
ele=find(Label==1);
Im(ele)=1;
figure,imshow(Im);title('Label:1');

To obtain the first component, find the positions with value=1 in the Label Matrix. Similarly, other components can be extracted.

%Extracting the characters 'I M A G E'
ele=find(Label==2|Label==3|Label==6|Label==7|Label==9);
Im1=zeros([size(A,1) size(A,2)]);
Im1(ele)=1;
figure,imshow(Im1);title('Specific components');

From the Label matrix, I extracted the characters I, M, A, G and E alone by specifying the label numbers 2,3,6,7 and 9.

%Total number of Letters

Total=sprintf('Total Number of Letters:%d',N);
display(Total);

 The total number of components extracted in the above example Image:

Total =

Total Number of letters:14

%Differentiate each component with a specific color
RGBIm=zeros([size(Label,1) size(Label,2) 3]);
R=zeros([size(Label,1) size(Label,2)]);
G=zeros([size(Label,1) size(Label,2)]);
B=zeros([size(Label,1) size(Label,2)]);
U=64;
V=255;
W=128;
for i=1:N
    Pos=find(Label==i);
    R(Pos)=mod(i,2)*V;
    G(Pos)=mod(i,5)*U;
    B(Pos)=mod(i,3)*W;
   
   
 end
RGBIm(:,:,1)=R;
RGBIm(:,:,2)=G;
RGBIm(:,:,3)=B;
RGBIm=uint8(RGBIm);
figure,imshow(RGBIm);title('Labelled Components');

For each label, unique color is given.  Here is another example for labeling and extracting the components. Read the image, ‘coins.png’ , convert it into binary and fill the holes. Then perform labeling and extraction.

Total =

Total Number of coins: 10

How to get frames from a video

MATLAB CODE to get images from video:
To extract frames from a video.

              Frames can be obtained from a video and converted into images. To convert a video frame into an image, the MATLAB function ‘frame2im’ is used.  

                                      To read a video in avi format, the function ‘aviread’ is used.  The original format of the video that I am using as an example is .gif file format. I converted the .gif file format image into an avi format video. Learn how to convert a gif image into a video...

 For instance, in the ‘fun.avi’ video I am interested in the frame number 58. So I am converting the 58^th frame into an image.

MATLAB CODE:

%How to get frames from a video

mov=aviread('fun.avi');

Im=frame2im(mov(1,58));

figure,imshow(Im);

Frame 58

The above process can be done using 'mmreader' function also.

MATLAB CODE:

Vobj=mmreader('fun.avi');

Im=read(Vobj,58);
imshow(Im);

After playing the video, I thought of modifying some frames. So I converted the frames from 58 to 64 into images and added a smiley to the images by performing image arithmetic operations.

Then I converted those images into frames and saved as a video file in ‘smiley.avi’.

Lmov=aviread('smiley.avi');

MIm=frame2im(Lmov(1,1));

figure,imshow(MIm);

Modified Frame 58

%Preallocating the structure array

frame=struct('cdata',1,'colormap',cell([1 91]));

I added the modified frames to the original video.

%Modify the video in the middle

frame(1,1:57)=mov(1,1:57);

frame(1,58:87)=Lmov(1,1:30);

frame(1,88:91)=mov(1,64:67);

implay(frame,5);

  If we are interested in playing only some of the frames in the original video then, we can view those frames alone. Here I am interested in viewing the frames from 27 to 33.

%Part of the video

scz=figure;

set(scz, 'position', [300 100  size(Im,1)+130 size(Im,2)-100]);

FRange=[1 27:33];

%Here 1 is for the number of times the video has to be repeated

%27:33 indicates the frames from 27 to 33.

movie(scz,mov,FRange,5);

We can also save the desired frames into a file. An avifile object is created with the file name ‘VidPart.avi’. Then the desired frames from 27 to 33 are added by using the syntax ‘addframe’.

%To save the desired part alone

obj=avifile('VidPart.avi','FPS',5);

obj=addframe(obj,mov(27:33));

obj=close(obj);

More Examples at https://www.imageeprocessing.com/2016/06/read-process-and-save-video-in-matlab.html