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Sunday, October 20, 2013

••◊ Problems with Premier Pro scopes

I recently had to master a few DVDs and Blu-ray disks for a film festival and, of course, I wanted to make sure that the final masters were done correctly.  The bottom line is that the scopes in Adobe Premier Pro don't work correctly. 

After doing some research I found that Blu-ray disks also have to be authored with levels between 16-235.  Why...after all this time and digital interfaces?  Beats me.  Computer screens are the same LCD panels as home TVs and yet we still have to deal with black at 7.5 IRE and white at 100 IRE.  Why not the same 0 IRE (=digital 0) and 109 IRE (=digital 255) that we play over the Internet all the time?

Another issue is that I used the "Dip to Black" transition in quite a few places in my film and didn't realize that this transition gets applied *after* all effects on the clip.  So even if you correct the levels to 16-235 using the "Levels" effect in a new master sequence, the "Dip to Black" transition brings the video levels down to the undesirable absolute black 0 IRE.  To work around this I rendered out the entire film to Quicktime uncompressed 10-bit YUV, then re-imported the uncompressed video and applied the "Level" effect to set the levels between the desired 16-235.

OK, so the levels should -in theory- be set correctly.  That should be easy to verify, right?  Maybe not.  Let's start with a simplified example of a black and white patch.  As anyone familiar with video engineering knows the levels should be at 0 IRE and 109 IRE for absolute black and absolute white respectively.  If you open the second picture you'll see that the luma waveforms show 0 IRE (correct) and 100 IRE (not correct), yet their y-axis goes up to 120 IRE!  Keep in mind that I'm using an "ancient" CS5 version of Premier Pro.  Maybe Adobe has fixed this by now(?)

 

Now let's apply a "Levels" effect to the both the black and white patch.  This will convert the black patch from 0 to 16 (7.5 IRE) and should in theory change the white patch from 255 to 235 (100 IRE).  The black patch looks almost correct by coming up just shy of the 7.5 IRE dotted line.  The white patch goes down to about 92 IRE...fail!


I don't know what to say here.  It seems like such a simple thing to make scopes work correctly.  Heck, I could write this code!  ...and don't get me started on their vectorscope that doesn't work properly for HD video.

This is something to watch out for when mastering any video for broadcast or silver disk distribution.  You just need to be aware that the Premier Pro scopes don't work properly.

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