Fix Dlog-M Barrel Distortion in Camera

[Robert Granata]

Today I noticed that Litchi allows you to change the digital filter (Normal, Dlog-M, HLG) while recording video. If I start the video in Normal and then switch to Dlog-M there is no barrel distortion in the log footage. Conversely, if I start in Dlog-M and switch to Normal, the Normal footage has the distortion. I have attached a OneDrive link to the original footage straight from the M2P. They were shot in 3840 x 2160 FOV (to show more distortion). My question, to the many on this forum that are smarter than me, is what are the color depths? Is the non-distorted Dlog-M footage only 8 bit? And is the distorted Normal footage then 10 bit?

Microsoft OneDrive

1drv.ms

 

[kilomikebravo]

Rob: I sure hope someone smarter than I can explain what you found because it "just shouldn't be" ifyouknowwhatImeanVern.

 

[Robert Granata]

Rob: I sure hope someone smarter than I can explain what you found because it "just shouldn't be" ifyouknowwhatImeanVern.

That's what I thought, but, surprisingly, there seems to be little to no interest in it. After all the complaints about DJI needing to fix the distortion I figured there'd be some reaction, but nada.

 

[kawartha]

Interesting observation. I used MediaInfo on your files. Both are HEVC, so H.265. "Start in Dlog M.MP4" is 10-bit; "Start in Normal.MP4" is 8-bit. I do not know if bit depth changes when you change the color mode.

 

[Robert Granata]

Interesting observation. I used MediaInfo on your files. Both are HEVC, so H.265. "Start in Dlog M.MP4" is 10-bit; "Start in Normal.MP4" is 8-bit. I do not know if bit depth changes when you change the color mode.

Davinci Resolve gave me the same result and I'm having the same problem figuring out the depth after switching. Hoping someone here can analyze individual frames to find the answer.

 

[Robert Granata]

I started a file in Normal H.265 and just before the 5 minute file size limit I switched to Dlog-M to see if the new 5 minute file would have the barrel distortion. I hypothesized that the new file would have the distortion, but it didn't and the metadata in Davinci Resolve reports the second file as 8 bit also. I am thinking that what this turns out to be is a way to record Dlog-M in 8 bit with no barrel distortion and, alternatively, Normal in 10 bit with the distortion. Although I'm just basing this on the reported bit depths and my hypothesizes have just recently been proven wrong.

 

[kawartha]

You could try removing the first part of the file and see what bit depth the remainder shows. Sorry, I don't have any tools to do that or I would. I have a feeling bit-depth won't change. This is very interesting but I am hesitant to try this as DJI suffered quite a bit of PR and marketing flack because of the D-Log barrel distortion, and in the gazillion threads on the issue sensor overheating kept coming up as a possible cause. I would hate to do this and wreck my camera. What's especially neat about your finding is that the whole image appears, the distortion fix I do in Final Cut crops the image somewhat.

 

[kilomikebravo]

Rob: I just downloaded both files, (why can't Microsoft give OneDrive more bandwidth?!) and Properties for both files show HEVC 4:2:0 so they're both 10-bit. Sorta makes sense since for the first file where you started in DLog-M but why the distortion is missing in the second (Start in Normal) file when it switches to DLog is beyond me as is why starting in Normal is 4:2:0. Perhaps one of the camera-knowledgeable members will have an answer. Quite a find though, in any case...well done, Mavic scientist!

 

[zeeeegerman]

that sure is odd. I wonder if it's just some kind of glitch. I doubt that the non-barrel-distorted Log looking footage is truly DLOG-M. I bet you it's just normal 8bit with the colors of DLOG-M.

 

[kilomikebravo]

Zee: You may very well be correct, but Premiere did say it was HEVC 4:2:0.

 

[Robert Granata]

Zee: You may very well be correct, but Premiere did say it was HEVC 4:2:0.

Davinci Resolve metadata reports the Dlog-M footage (started in Normal) as 8 bit and the Normal footage (started in Dlog-M) as 10 bit. Even the second file, started after the 5:01 minute file size limit, reports these numbers.