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• How to use ffmpeg's sws_scale from multiple threads ?

  25 avril 2013, par Asik

  I have a color space conversion function based on sws_scale. It will be called from multiple different threads during the lifetime of the application. I don't know, however, how thread-safe sws_scale is and I did not find it mentionned in its documentation.

  I would assume that each thread requires its own SwsContext as this parameter will be shared, but is this enough to guarantee there won't be any internal collisions ?

• Perspective transformations

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

  Finally (after a long break) I managed to force myself to update the PHP documentation and this time it was distortImage code example. Things have been hectic lately but that does not quite explain the 6 months(?) break between this and the previous post. As a matter of a fact there is no excuse for such a long silence so I will try to update this blog a bit more often from now on.

  Back in the day I used to blog the examples and update the documentation if I remembered but I am trying to fix this bad habit. Most of the latest examples have been updated in to the manual. In the case of the two last examples I updated the documentation first and then blogged on the subject.

  I took some time to actually understand the perspective transformations properly using the excellent ImageMagick examples (mainly created by Anthony Thyssen) as a reference. The basic idea of perspective distortion seems simple : to distort the control points to new locations. Grabbing the syntax for Imagick was easy, an array of control point pairs in the form of :

  php

  < view plain text >

  1. array(source_x, source_y, dest_x, dest_y ... )

  The following example uses the built-in checkerboard pattern to demonstrate perspective distortion :

  php

  < view plain text >

  1. < ?php
  2. /* Create new object */
  3. $im = new Imagick() ;
  4.  
  5. /* Create new checkerboard pattern */
  6. $im->newPseudoImage(100, 100, "pattern:checkerboard") ;
  7.  
  8. /* Set the image format to png */
  9. $im->setImageFormat(’png’) ;
  10.  
  11. /* Fill background area with transparent */
  12. $im->setImageVirtualPixelMethod(Imagick: :VIRTUALPIXELMETHOD_TRANSPARENT) ;
  13.  
  14. /* Activate matte */
  15. $im->setImageMatte(true) ;
  16.  
  17. /* Control points for the distortion */
  18. $controlPoints = array( 10, 10,
  19.             10, 5,
  20.  
  21.             10, $im->getImageHeight() - 20,
  22.             10, $im->getImageHeight() - 5,
  23.  
  24.             $im->getImageWidth() - 10, 10,
  25.             $im->getImageWidth() - 10, 20,
  26.  
  27.             $im->getImageWidth() - 10, $im->getImageHeight() - 10,
  28.             $im->getImageWidth() - 10, $im->getImageHeight() - 30) ;
  29.  
  30. /* Perform the distortion */ 
  31. $im->distortImage(Imagick: :DISTORTION_PERSPECTIVE, $controlPoints, true) ;
  32.  
  33. /* Ouput the image */ 
  34. header("Content-Type : image/png") ;
  35. echo $im ;
  36.  ?>

  Here is the source image :
  

  And the result :
  

• Fill patterns

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

  My work life has been quite busy lately and I haven’t had a chance to sit down and blog. I have been touring around London and some parts of the northern England consulting and organizing some training here and there. Luckily I have had the chance to do some work on Imagick and the 2.2.0 beta release is getting closer. The internal structure was completely restructured and broken down into several smaller files. During this time Imagick was adapted to follow the PHP Coding Standards more closely. Still a work in progress

  I committed slightly modified version of this example to PHP Manual http://uk.php.net/manual/en/imagick.examples.php page a few days ago. The example illustrates using an image as a part of a named fill pattern. The fill pattern is used to annotate text but the named pattern could also be used to fill any shapes that allow fill to be specified (include circles, ellipses, rectangles, polygons etc etc). The code itself is pretty straight forward : Read the image, create the pattern and use the pattern as a fill.

  The ice formations image is from http://www.photoeverywhere.co.uk/west/winterholiday/slides/iceformations5679.htm.

  php

  < view plain text >

  1. < ?php
  2.  
  3. /* Create a new imagick object */
  4. $im = new Imagick( ’iceformations5679.JPG’ ) ;
  5.  
  6. /* Create imagickdraw object */
  7. $draw = new ImagickDraw() ;
  8.  
  9. /* Start a new pattern called "ice" */
  10. $draw->pushPattern( ’ice’ , 0 , 0 , 50 , 50 ) ;
  11.  
  12. /* Composite the image on the pattern */
  13. $draw->composite( Imagick: :COMPOSITE_OVER, 0, 0, 50, 50, $im ) ;
  14.  
  15. /* Close the pattern */
  16. $draw->popPattern() ;
  17.  
  18. /* Use the pattern called "ice" as the fill */
  19. $draw->setFillPatternURL( ’#ice’ ) ;
  20.  
  21. /* Set font size to 52 */
  22. $draw->setFontSize( 52 ) ;
  23.  
  24. /* Annotate some text */
  25. $draw->annotation( 5, 50, "Hello World !" ) ;
  26.  
  27. /* Create a new canvas and white image */
  28. $canvas = new Imagick() ;
  29. $canvas->newImage( 310, 70, "white" ) ;
  30.  
  31. /* Add black border around the resulting image */
  32. $canvas->borderImage( ’black’, 1, 1 ) ;
  33.  
  34. /* Draw the ImagickDraw on to the canvas */
  35. $canvas->drawImage( $draw ) ;
  36.  
  37. /* Set the format to PNG */
  38. $canvas->setImageFormat( ’png’ ) ;
  39.  
  40. /* Output the image */
  41. header( "Content-Type : image/png" ) ;
  42. echo $canvas ;
  43.  ?>

  And the result is here :