Matlab AVI help

Replies

• 

  sauravgoswami

  why u aint using simulink???....i will suggest you to use some other format of pic
• 

  prestonee

  Well Im not using simulink because im not aware of how exactly to do individual pixel processing.
  
  That and once we get the matlab code finalized I will be implementing it into hardware.
  
  I think my limiter atm is the getframe() function, it only supports 8 bit, do you know of any equivalents that support 16 bit? I realize that for human eye its very difficult to tell but it would be good to at least get 10bit on screen.
• 

  xheavenlyx

  Some points are in order:
  
  1. Try this: #-Link-Snipped-#
  
  use "movie" to create a movie based on frames, keep adding each frame to the "movie" object. and then use "movie2avi". I have never tried this but just in case it works.Plus try deleting useless or redundant frames OR actually reducing the framerate.
  
  2. I cant understand the 16bit/8bit deal. I think (from my experiences) that those numbers refer to the "color: bit depth" otherwise, video quality depends on the resolution rite? As the pixel values contain only the color information.
  
  3. Can you share the code? I will run it and try to figure it out.
  
  I just wanna thank you for writing a wonderful post. Usually we get Questions without even explaining what the program does.
• 

  prestonee

  Thank you for the reply =)
  
  The bit thing:
  
  This is not a color image but grayscale so the array is only a 3 dim array of row,col,frame
  the value contained in the array represents intensity and is 16 bit
  The reason we are using 16 bit is because our images have a signal range as far as intensity from val = 0 to val ~= 35000
  The high end changes depending on the scene being captured but doesnt go beyond 16bits.
  
  The issue:
  
  The avi file that im currently generating is 8bit so the range is cut in half providing less shades between black and white. The pixel resolution doesnt change but the 'resolution of the intensity is decreased making pixels that were once slightly different in the image now look identical.
  
  Code:
  
  Here is the code that im using to do this part of the program: notice im only doing an avi of a partial of the original image. Also I am storing the images as .png to preserve the 16 bit values. I did an aviread() to verify that the avi file is 8bit, while a imread() of the stored image shows 16 bit.
  
  imwrite(temp(1:400,300:656,i),strcat('D:\Bar\300\matlab\images_temp\temp',num2str(i),'.png'),'png');
  mov = avifile('MOVIE.avi');
  count=0;
  for i=1:number_of_frames
  name1=strcat(name,num2str(i),filetype);
  a=imread(strcat('D:\BAR\300\matlab\images_temp\',name1));
  while count<2
  count=count+1;
  imshow(a);
  F=getframe(gca);
  mov=addframe(mov,F);
  end
  count=0;
  end
  close all
  mov=close(mov);
  
  I will be pursuing what you mentioned while you look into the code, again thank you
  
• 

  xheavenlyx

  I will get back to you soon. Its 2 Am here 😀 trying the code was fun but tiering! Sorry for later reply.
• 

  xheavenlyx

  Here is what I have discovered:
  
  Problem:
  
  

  The avi file that im currently generating is 8bit so the range is cut in half providing less shades between black and white. The pixel resolution doesnt change but the 'resolution of the intensity is decreased making pixels that were once slightly different in the image now look identical.

  
  
  Analysis:
  
  You are using two main functions in your program:
  
  "getframe()" and "addframe()", the later one is used to add a frame to your open AVI file.
  
  However, the "addframe()" function adds frame to your AVI file with 8-bit precision, even if you open a .png file of 16-bit precision.
  
  Here is an extract from "addframe()" help [#-Link-Snipped-#]:
  
  

  aviobj = addframe(aviobj, frame)...frame can be either an indexed image (m-by-n) or a truecolor image (m-by-n-by-3) of double or uint8 precision.

  Now, initially I too was confused with uint8/uint16/double, until I realized you must use "double" instead of "uint16".
  
  Here are some useful definitions:
  
  uint8: Is 8 bit, or one Byte. 0 to 255 (0 black, 255 white).
  
  uint16: Is 16 bits or 2 Bytes. 0 to 65535 or -32766 to 32766 something, not sure here.
  
  Single: (src. wiki) Single precision is a computer numbering format that occupies one storage location in computer memory at a given address. A single-precision number, sometimes simply a single, may be defined to be an integer, fixed point, or floating point.
  
  Double: (src. wiki) Double precision is a computer numbering format that occupies two adjacent storage locations in computer memory. A double precision number, sometimes simply called a double, may be defined to be an integer, fixed point, or floating point.
  
  The solution:
  
  I came to know that there are two ways to designate gray scale images. uint8 and double. The difference; double is more precise since it uses "fraction, or decimal point" to display white to black gradient (0 to 1) instead of the uint8 method of 0 to 255 levels. Plus, "double" uses 64-bit storage to represent the fraction, much more accurate than 32-bit storage of "single" precision.
  
  So now you know, use double instead of uint16. Where do you apply that?
  
  In the original post its stated that you are receiving your images from a video source. If it is a webcam I think the problem can be solved.:
  
  start(vid); %vid is the video object
  mov = avifile('MOVIE.avi','compression','None') %your movie file object, use whatever compression.
  while(vid.FramesAcquired<=100) % Loop to capture rectangular area and video from source and store frames in MOVIE.avi. Stop after 100 frames.
  imgrgb = getdata(vid,1,'double'); %!IMPORTANT! Get data from video source of "double" precision. Original image in Color(RGB).
  I =.2989*imgrgb😀,:,1)+.5870*imgrgb😀,:,2)+.1140*imgrgb😀,:,3); % Convert to grayscale, *SEE NOTE AT END!!
  
  %
  
  mov = addframe(mov,I_withRect);
  end
  
  %% Garbage clearance
  stop(vid);
  mov = close(mov);
  
  
  
  * NOTE: My algorithm is the same as "im2gray"[#-Link-Snipped-#] uses, The grayscale image will be of original "double" precision, which can be easily sent to "addframe()" function, as the help stated, it will accept "double" and "uint8"!
  
  
  Let me tell you, I could not write an AVI file with any program on my PC, which must be because of some problem with compression and not related to this.
  
  Hope I was of help.
• 

  prestonee

  Sorry I have not replied I have been busy with an end of project report as well demonstrating the matlab processing file to various people on my side. Currently the system is working at 100% except for this 16b to 8b part which is a fairly low priority since this is just a visual assurance that the processing is occuring. I will try to convert the image files to double on monday and get back to you. I wouldnt expect an increase in visibility since we cant take advantage of any information stored on the right side of the decimal. But will try it and reply
• 

  xheavenlyx

  Yea, thats fine, ive been off too.
  
  To analyze data "on the right side of the decimal" is not a problem in MATLAB. It does the calculations to many many many significant digit. Otherwise decimal would not have existed in MATLAB if it couldn't "take advantage of it".
  
  And, anyway, if you are storing the data as AVI, compression will of course reduce visibility. Plus, AVI is designed to work with 8bit and double ONLY, not 16 bit. And double is a standard for black and white images. (Read that somewhere on Image possessing article from Adobe.)
  
  I hope you have read the whole post, there are a lot of surprising new details that are new even to me.