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Auto levels? (colour correction)

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Auto levels? (colour correction)

Tue Feb 18, 2014 1:40 pm
i've got about 45 minutes of Protune footage (12GB) as source material, with a lot of lighting changes. there's a lot of dynamic range & headroom in the luma... a lot more than i need/want (kind of like the video version of cam-raw). normally i adjust the levels manually and get great results... but normally i just use short clips with little or no lighting changes.

is there an auto-levels tool? adjusting this manually would take ages, and it's not critical to get it perfect... just good.

here's a frame, with and without level adjustment, with histograms...

from the camera:
Image

with level adjustment:
Image

thanks!
User avatar TheDiveO
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Is this raw Protune footage or did you run it already through GoPro Studio to uncompress the tonal curves? If you developped the footage already in Studio, then you should use it also to control the levels. As far as I know there is no auto levels effect in Kdenlive (or MLT).

If it is raw Protune, then you need to use either a set of three Curve effects or a single Bézier Curve effect. The levels control will not be suitable in alone. You should notice that for the levels you set there are already artifical colors creeping into the picture which doesn't exactly look natural anymore, the sky seems to be affected. Details here: http://thediveo-e.blogspot.com/2013/10/ ... rline.html

You will also need to boost color saturation as well as do some careful sharpening when directly using Protune raw footage. Again, I give details for Kdenlive in the blog post I linked to above.


TheDiveO on YouTube: diving videos and aerial (quadcopter) videos, all made with Kdenlive.
TheDiveO Blog: know-how about Protune-grading in Kdenlive, GoPro HD Hero 3, DJI Phantom Quadcopter, full face mask diving, and some more...
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i'm dealing with files straight from the camera.

yeah... looks like i need auto-curves. too bad there's no such thing, yet, in FOSS :(
User avatar TheDiveO
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So you are using Protune raw material straight without tonal curve correction? Sorry, but then auto correction doesn't work either. The reason is that auto correction in all the cases I've encountered so far uses adaptive gamma correction in combination with black and white level shift. But Protune doesn't use gamma correction. It uses its own S-like tonal curves. In consequence, simply slapping gamma correction onProtune material more or less sucks, depending on the lighting conditions. Why are you using Protune after all if you insist on gamma correction?

Also, you need to increase saturation, as Protune tunes down the colors considerably. But I'm repeating myself here.

If you look at your own example you should notice that there is too much cyan in the sky. That's because you do simple gamma correction, which is incorrect for Protune footage. Also, you've lost all details from the cloud, but you won't be able to regain it using gamma correction. This is exactly a situation where you need to start with the S-like tonal curve, then adjust it in the lights and shadows to get the detail that Protune is designed for.


TheDiveO on YouTube: diving videos and aerial (quadcopter) videos, all made with Kdenlive.
TheDiveO Blog: know-how about Protune-grading in Kdenlive, GoPro HD Hero 3, DJI Phantom Quadcopter, full face mask diving, and some more...
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Re: Auto levels? (colour correction)

Thu Feb 27, 2014 10:26 pm
TheDiveO wrote:Why are you using Protune after all if you insist on gamma correction?

because... usually, i only want 1-2 minute clips for "final product", which makes all of the manual adjustments reasonable. in this case, i want 45 minutes of "door to door" footage, not just a minute or two cut out of it.

i've never played with gopro-studio software... does that have built-in smarts for doing this kind of correction on auto-pilot?
User avatar TheDiveO
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I still have the strong impression that you may have completely missed the crucial point in working with Protune footage in Kdenlive? I have to admit that I don't understand the answer you gave in response to my question of why you are shooting in Protune when you are not using proper tonal curve correction.

Using simple gamma correction is mostly pointless when working with and grading Protune material. There are cases where gamma correction can be used, but only in very specific lighting conditions. Otherwise gamma correction does no good to Protune footage. As you can see from the slight but yet clearly visible miscoloring in your stills. This isn't a problem of auto-correction, this is a problem of applying the gamma effect before applying the required tonal curve correction.

Is it clear to you what Protune causes to the raw video footage and what steps are necessary in post in order to deal with Protune? This is a central question, and it doesn't matter whether you are shooting ten seconds or ten minutes of footage. Incorrectly processed Protune footage lacks its brilliance.

And remember, you need also to increase saturation and apply some sharpening. Unless you do so, you won't use the potential of Protune even to the barest minimum. Believe me, it took me some time to figure out how to properly process Protune footage with Kdenlive.

I've never used GoPro Studio as it doesn't fit into the usual workflow of scene editing first, then grading. GoPro has managed to turn this well-proven workflow backwards for no other reason than to push its toy software. I'm afraid I can't help you with this software.


TheDiveO on YouTube: diving videos and aerial (quadcopter) videos, all made with Kdenlive.
TheDiveO Blog: know-how about Protune-grading in Kdenlive, GoPro HD Hero 3, DJI Phantom Quadcopter, full face mask diving, and some more...
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Re: Auto levels? (colour correction)

Mon Mar 03, 2014 11:45 pm
short answer - i was doing it wrong :<

just over the last few days i made some time to read through your posts on proper grading. AWESOME STUFF!

i'll give that a try and see how it goes. thanks!!!

 
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