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How do I get exposure correct with X7 in EI Mode and D-Log?
1409 7 2018-6-1
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InterMurph
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A film production I am flying for next week wants EI Mode/D-Log footage.  I am unclear on how to get the exposure correct in this mode.

I found this YouTube video, which has a link to download the EI footage:    I downloaded it and loaded it up in Premiere Pro CC.  The image is flat as expected, and the waveform shows that the pixels are between 20% and 80% IRE.  I applied the DJI D-Log-to-Rec.709 LUT, and it expanded from 15% to 95%, and looks great.

But when I try to replicate this, I can't get the exposure correct.  I shot some footage in EI Mode in which the waveform in the DJI Go 4 app was between 25% and 75%, but when I load it into Premiere and apply the same LUT, it actually got brighter overall, but did not increase in contrast.  So that tells me that I need to under-expose it according to the Go waveform.

My searches indicate that the Go app used to have a button that produced a Rec.709 preview in the app display, but that button is now gone.  In the video settings where one enables EI Mode, there is an item called SD/Liveview Looks that has a Rec.709 option.  When I enable that, the preview image looks more normal, and the waveform is stretched up and down.  Is the waveform in this mode a reliable indicator of the exposure?

I am incredibly frustrated with the lack of documentation on EI Mode.  It is exactly what the production wants, and the fact that I own the X7 camera with this feature is the reason I got the job.  But I am very hesitant to shoot in this mode on the set without the ability to know that the exposure is correct.  How do you do this?
2018-6-1
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Barry Goyette
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Without seeing your actual footage, it's difficult to know what's happening with premiere. I'm unfortunately not much of an expert with premiere, but I have played with lumetri and it does allow for ISO adjustments along with LUT corrections, so this may be part of your problem. FWIW, I use EI mode extensively with Final Cut Pro, and rarely do I use a LUT to grade it. Generally adjusting the highlights, shadows and saturation is all that's needed....but the LUT DJI supplied works just fine in FCPX.

Not sure your experience with LUTs and log footage, but if it's limited, I can tell you that a LUT will work best, out of the box,  if the footage is shot to a monitor applying the same LUT, otherwise there will almost always be an exposure "error" that needs to be adjusted in post. Most LOG gammas (like EI mode D-log) perform best when shot "to the right"...meaning you want to increase exposure so that brightest meaningful highlights aren't clipped, but are shifted as close to the maximum encode value (clipping point) as possible. This will give you the least noise and maximum dynamic range. This approach, however, will almost always require some exposure adjustment in post. If you want a more "out of the box LUT experience" ...you might try turning off EI mode...adjusting your exposure in "normal" mode to taste, and then turn EI mode back on.  It's not how you'd optimally shoot EI mode, but in theory, it should allow you to apply DJI's LUT and get the expected result.
2018-6-6
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InterMurph
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I think I figured it out.   In my original post, I said:

"In the video settings where one enables EI Mode, there is an item called SD/Liveview Looks that has a Rec.709 option.  When I enable that, the preview image looks more normal, and the waveform is stretched up and down."

I verified this earlier in the week.  Setting the "SD/Liveview Look" to Rec.709 resulted in 1) EI/D-Log footage written to the SSD, and 2) corrected image being displayed on the RC screens.  I verified with the production company that the resulting footage was exposed correctly, and they are extremely happy with the quality of the footage we are getting.

My challenge to you, and to everybody else:  show me where this is documented by DJI!

Thanks.
2018-6-7
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rlkaerial
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Hey thanks for the post. I was also curious about how to optimize EI mode to ensure I have the correct exposure on Dlog. This was helpful, much appreciated.

2018-6-7
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guido's account
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Hi there, Im in the same situation, but using DaVinci. Can you let me know your experience with exposure? Thanks in advance.
2018-7-12
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InterMurph
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Please refer to the third post.  Once you set the SD/Liveview Looks option to Rec.709 , the screen display, histogram, and waveform display are all corrected, and can be use to determine proper exposure as usual.
2018-7-13
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fansdfc2d304
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InterMurph Posted at 2018-6-7 08:40
I think I figured it out.   In my original post, I said:

"In the video settings where one enables EI Mode, there is an item called SD/Liveview Looks that has a Rec.709 option.  When I enable that, the preview image looks more normal, and the waveform is stretched up and down."

Thanks for posting about this, I was wondering the same.

So you exposed for the waveform that was showing the Rec 709 and the results were good? I just want to make sure I understood this correctly, if that's the case, awesome!
3-9 14:32
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InterMurph
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fansdfc2d304 Posted at 3-9 14:32
Thanks for posting about this, I was wondering the same.

So you exposed for the waveform that was showing the Rec 709 and the results were good? I just want to make sure I understood this correctly, if that's the case, awesome!

Yes.

PS  This forum won't let me post a reply of fewer than 10 characters, so I'm typing this.
3-10 08:08
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