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x264_quality [2014/08/17 15:34]
beandog created
x264_quality [2014/08/17 15:46]
beandog [SSIM]
Line 6: Line 6:
  
 Use SSIM or PSNR to gauge differences between encoding settings. Use SSIM or PSNR to gauge differences between encoding settings.
 +
 +==== SSIM ====
  
 When comparing two values, here is the formula to discern what percentage amount something has improved. When comparing two values, here is the formula to discern what percentage amount something has improved.
Line 33: Line 35:
 <​code>​ <​code>​
 x264 [info]: SSIM Mean Y:0.9751283 (16.043db) x264 [info]: SSIM Mean Y:0.9751283 (16.043db)
 +</​code>​
 +
 +Here's the formula:
 +<​code>​
 +(((1 - old) / (1 - new)) - 1) * 100
 +</​code>​
 +
 +Here's a simpler visualization:​
 +
 +<​code>​
 +1 - 0.9613678 = 0.0386322
 +1 - 0.9751283 = 0.0248717
 +0.0386322 / 0.0248717 = 1.55325932686547361057
 +1.55325932686547361057 - 1 = 0.55325932686547361057
 +0.55325932686547361057 * 100 = 55.325932686547361057
 +</​code>​
 +
 +Rounding it out to an integer, would be 55, for a result of 55%.  So when encoding this particular video at double the bitrate, the SSIM increases by 55%.  Not bad!
 +
 +Here's a PHP function to do the same thing:
 +
 +<​code>​
 +function ssim_improvement($old_ssim,​ $new_ssim) {
 +
 +        $a = 1 - $old_ssim;
 +        $b = 1 - $new_ssim;
 +
 +        $c = $a / $b;
 +
 +        $d = $c - 1;
 +
 +        $e = $d * 100;
 +
 +        return $e;
 +
 +}
 </​code>​ </​code>​

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