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• Seam carving

  9 juin 2010, par Mikko Koppanen — Imagick, PHP stuff

  Today I was reading trough the ImageMagick ChangeLog and noticed an interesting entry. “Add support for liquid rescaling”. I rushed to check the MagickWand API docs and there it was : MagickLiquidRescaleImage ! After about ten minutes of hacking the Imagick support was done. Needless to say ; I was excited

  For those who don’t know what seam carving is check the demo here. More detailed information about the algorithm can be found here : “Seam Carving for Content-Aware Image Resizing” by Shai Avidan and Ariel Shamir

  To use this functionality you need to install at least ImageMagick 6.3.8-2 and liblqr. Remember to pass –with-lqr to ImageMagick configuration line. You can get liblqr here : http://liblqr.wikidot.com/. The Imagick side of the functionality should appear in the CVS today if everything goes as planned.

  Here is a really simple example just to illustrate the results of the operation. The parameters might be far from optimal (didn’t do much testing yet). The original dimensions of image are 500×375 and the resulting size is 500×200.

  Update : the functionality is pending until license issues are solved.

  php

  < view plain text >

  1. < ?php
  2.  
  3. /* Create new object */
  4. $im = new Imagick( ’test.jpg’ ) ;
  5.  
  6. /* Scale down */
  7. $im->liquidRescaleImage( 500, 200, 3, 25 ) ;
  8.  
  9. /* Display */
  10. header( ’Content-Type : image/jpg’ ) ;
  11. echo $im ;
  12.  
  13.  ?>

  The original image by flickr/jennconspiracy

  

  And the result :

  

  Update. On kenrick’s request here is an image which is scaled down to 300×300

  

• FFmpeg option to convert to square pixels ?

  12 juin 2012, par John Smith

  I am looking for an FFmpeg option that will convert to square pixels.

  The only constant I want to provide is the output file's width.

  Right now I use -vf "scale=640:-1" which does this :

  • 1440x810 PAR 1:1 DAR 16:9 => 640x360 PAR 1:1 DAR 16:9
  • 1440x1080 PAR 1:1 DAR 4:3 => 640x480 PAR 1:1 DAR 4:3
  • 1440x1080 PAR 4:3 DAR 16:9 => 640x480 PAR 4:3 DAR 16:9

  But I would like that last test case to do this instead :

  • 1440x1080 PAR 4:3 DAR 16:9 => 640x360 PAR 1:1 DAR 16:9

  What option I can pass to do this ?

• ffpmeg vs ffprobe performance

  13 décembre 2016, par Thomas

  I wanted to try extracting frames at scene changes with ffmpeg, vs. getting the frame numbers with ffprobe and extracting them later.

  But I had a surprise : ffprobe seems to be much slower than ffmpeg, while ffmpeg is taking the frames, resizing and saving them as well.

  ffmpeg command line :

  ffmpeg -hide_banner -y -i d:/test/m/long.mkv -vf "select=gt(scene\,0.4), showinfo, scale=320:-1, tile=12x200" -vsync 0 thumbnails%03d.png

  this takes : 488 seconds

  ffprobe command line :

  ffprobe -show_frames -of compact=p=0 -f lavfi "movie=/test/m/long.mkv,select=gt(scene\,.4)"

  this takes : 899 seconds

  I am missing something ?