May
Continuing with the previous article on LEGAL or FULL export from DaVinci, we said that when exporting a Quicktime H264 file neither of these options gave us a correct file. This happens not only in DaVinci but in many other programs.
Testing with uncorrected SMPTE bars on a correct export the waveform drawing should look like the one in Figure 1.
However, if we export in FULL we can clearly see how the signal is excessively contrasted (figure 2).
And if we export in LEGAL, although at first sight of the PLUGE it seems that the export is correct if we observe the middle part of the bars (green and cyan for example) we can notice how the gamma has varied in the export (fig 3).
So how can we export to Quicktime H264 without changing the gamma (problem called quicktime gamma shift)? This problem is not only in DaVinci, from many other applications (like Avid) we have the same situation… I have not found the way to do it in a single step but I have found the way to solve it.
Export from DaVinci (or whatever application) a Quicktime with a correct gamma and bit rate equal or higher than our codec of work in DaVinci (if we have worked in DaVinci in Prores 422 we would export a Prores 422 or higher LEGAL) Here we must say that there may be a slight change in gamma resulting from the encoding process, it is minimal but we will have it in 80% of the cases with Prores or other codecs.
Once exported this Prores we do the compression to H264 from Quicktime Pro, yes, it seems that it is not yet time to get rid of this program and move to QT X as Apple wants…
If you do this and put the Quicktime back into DaVinci you will see that the final H264 has almost no contrast change from the original (fig 4).
I leave you some test files so that you can see it with media as well. You can download them here: Gamma Shift QT H264
And if you want to know more about all these calibration issues, we talk about them in our HD color correction course.
Do you know any other way to solve quicktime gamma shift? with more codecs? using other programs? If so, comments on this post are more than welcome!
