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• How to join pieces of images into one with using FFmpeg API ?

  23 juin 2016, par Arya GM

  I have parts of one image like

  • 0x0_img1.jpg
  • 100x200_img1.jpg
  • 300x0_img1.jpg
  • 360x420_img1.jpg
  • 1080x720_img1.jpg

  I just want to know how to merge these into a single image.

  Image name has quadrants details (0x0 , 100x200... etc,.), which are the start position of the parts to the orginal image

  Now how do I merge these parts of images using the FFMPEG c lib

• FFMPEG not extracting yuv colorspace images

  18 mars 2016, par DragonDance27

  I am using FFMPEG to extract images from MXF videos. I am interested in extracting tiff format images with the YUV (preferably 422) color space. The MXF videos are of the YUV color space. Hence why I want to continue to work in that color space. I have tried :

  ffmpeg -i video.mxf -pix_fmt yuv422p f%10d.tiff

  However the output images appear to be of the RGB color space. I use ImageMagick and the command line :

  identify -verbose output.tiff

  Which informs me that the image files are of the RGB color space. I have googled and tried variations to my FFMPEG command line but to no avail. What am I doing wrong ?

  ffmpeg console output as requested :
  First part of output
  Second part of output

  imagemajick identify (partial) result :
  (I’m not allowed to post more than two links*)

• Different filesizes for images generated using octave and python

  22 février 2017, par Lakshay Garg

  I am using python (scikit-image) and octave to generate 200 images as follows

  Python3

  import numpy as np
  
  from skimage.io import imsave
  
  
  
  images = [255*np.ones((100,100), dtype=np.uint8),  # white
  
               np.zeros((100,100), dtype=np.uint8)]  # black
  
  
  
  for i in range(200): # save alternating black and white images
  
      imsave('%04d.png'%(i+1), images[i%2])

  Octave

  pkg load image;
  
  
  
  im1 = 255*ones(100,100); # white
  
  im2 = zeros(100,100);    # black
  
  for i=1:200
  
      name = sprintf('%04d.png', i);
  
      if mod(i,2) == 0
  
          imwrite(im1, name);
  
      else
  
          imwrite(im2, name);
  
      end
  
  end

  Next, I use ffmpeg to generate two videos (alternating white and black frames) from these two sets of images using the following command

  ffmpeg -r 10 -loglevel quiet \
  
         -i ./%04d.png -c:v libx264 \
  
         -preset ultrafast -crf 0 ./out.mkv

  1. Sizes of image files generated by both these codes are different.

     • Octave white : 192 bytes, black : 98 bytes
     • Python white : 120 bytes, black : 90 bytes

  2. Sizes of video files generated from these octave and python images are significantly different from each other.

     • Octave filesize : 60 kilobytes
     • Python filesize : 116 kilobytes

  Why do we have this apparently very strange behavior ?

  EDIT

  Since it was suggested that the behavior might be dues to octave and python using different bit-depths to store the images, I changes the octave code to use 8 bit numbers

  im1 = uint8(255*ones(100,100)); # white
  
  im2 = uint8(zeros(100,100));    # black

  and now the image file sizes are nearly the same

  • Octave white : 118 bytes, black : 90 bytes
  • Python white : 120 bytes, black : 90 bytes

  but the problem is still the same for video files, octave : 60K, python : 116K