Terrence Meiczinger
Forum Replies Created
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OpenDCP deals with image frames, so there is no transcoding. You tell OpenDCP how to interpret those image frames. So, if you have a 20 second clip at 30fps, you’d have 600 frames. If you then tell OpenDCP it’s 24fps, you’ll end up with a 25 seconds picture track (600frames/24fps = 25s). It won’t magically rate convert your video. You can make a 30fps DCP (not 29.97) and most series 2 equipment will play it. However, some of the earlier digital systems may not. You’d have to check with the venue where your content would be playing. You could always make both.
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Flat 2K is 1998×1080, so 1920×1080 will result in 39 pixels of black pillar boxed on each side of the image. If you want to fill the entire 1998×1080, then you’d need to scale/crop your image. Depends on what you feel more comfortable with, but most people wouldn’t even notice the pillar boxing.
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If your material is 1920×1080, then you’d be all set. You just make the DCP and no further image scaling or adjustment is needed for 2K digital projection.
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The specs the festival is asking for seem a bit strange. It doesn’t really make sense to require 4K content, unless the point is to showcase 4K only source material. Scaling your content up to 4K could be worse than just creating a 2K DCP. The 4K digital projection systems are designed to handle 2K as well.
The other thing would be allowing Left, Center, Right channels. This is not a standard audio format. It should be Stereo, 5.1, 7.1. If you want Left/Center/Right you should make a 5.1 DCP with silence tracks for any missing channels.
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I’m not 100% sure, but I don’t think the JPEG2000 images created by Resolve are DCI compliant unless you export through the EasyDCP plugin. They don’t play in the standalone EasyDCP player because it does an actual check of the images.
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Sure, REC709 should have a decode gamma relative to the given scene, that’s one reason why color grading should be done prior to DCP creation. There are lots of variables and there is only so much that can be done downstream in the process.
OpenDCP’s main goal has always been to create a DCP from DCDM material for these reasons. However, since many people don’t have access or knowledge to do the XYZ conversion, one was implemented in OpenDCP for convenience. It’s going to be best effort since gamma, white points, etc can’t be determined from the image itself, so the conversion uses the most common values which will be good enough for the majority of cases.
You really can’t compare the results from a dedicated color grading application or workflow. My point is that OpenDCP’s conversion isn’t wrong, so much as there are more optimal workflows.
As for EasyDCP player, it does a decent job, but you can’t use it as an absolute reference. Their XYZ->RGB is going to be matched to their RGB->XYZ conversion, which may or may not be correct. I know that my tests on a reference digital projection system seem to indicate their conversion is overly dark.
In the end, free tools only take you so far. There is place for open source applications and for commercial ones. As always, your mileage may vary.
I’ll look into adding a gamma option in a future version of OpenDCP. Thanks for the feedback.
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I’m the sole developer of OpenDCP and what I said and have always said is that you should provide OpenDCP with DCDM (XYZ) graded material, if possible, as that is the proper workflow. You’ll also have more control over variables such as reference white points.
What other gamma’s would you want? There are generally only 3 sources sRGB, REC709, and P3 which have defined gamma values.
Aside from Adobe, do you have experience with applications you feel have a better conversion than OpenDCP?
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The XYZ conversion has been tested on a fully-calibrated projector system and measured with a Photo Research PR-655 SpectraScan Spectroradiometer (https://www.photoresearch.com/current/pr655.asp). All colors came out within specification.
Some people have said they have issues with elevated black levels and others have said it’s perfect. In the cases I have looked into issues were due to using 8-bit source images, not using full-range levels, selecting sRGB/REC709 incorrectly or they have been using EasyDCP player to view on an RGB monitor. I’m not saying there isn’t an issue, I’m not a color expert, but I have not had any issues with material I have personally converted.
Having said that, the proper digital cinema workflow is that the images should already be in the XYZ colorspace prior to DCP creation.
All the source for OpenDCP is available, if anybody can suggest an improvement or identify a problem, please feel to let me know. Any bug fixes, reports or suggestions are greatly appreciated.
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How are you viewing the results?
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There was a period where firmware versions were all over the place. Even several of the big commercial DCP encoders had serious compatibility problems with SMPTE. The push for DCI compliance this year has improved things a lot. I am surprised you had issues with the Dolby though, considering that is what I use and it was probably the most tested server, but again I always had updated firmware.
I totally understand your position. As with any open source software, mileage varies, especially software that is in development. Obviously, I have no financial gain if somebody uses OpenDCP or not, but I certainly want make it as solid as possible and any feedback helps.
I appreciate your responding back to my questions.