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Keying problem with sky replacement using Linear color key

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Claude Rozsa
Keying problem with sky replacement using Linear color key
on Aug 14, 2014 at 8:50:19 pm

Good evening or good morning.

I have a problem trying to replace the sky of the footage shown in the following screen capture:



As can be seen the sky is practically white with clouds. I can't remember why the video having been shot 7 or ten years ago. Anyway I now it was fair weather and I want to replace the sky will a full blue one.

I used to do this Linear color key. This is the result:



What bothers me is the presence of blue spots in the middle of the cliff where the rising sun gave a bright whitish color to the rocks; it is worse at the top of the cliff where the rocks are more yellow and gold than white when I correct the brightness and contrast of the footage to get an even color during the pan.

I tried different solutions seen on youtube's tutorial without results,it seemed that the methods could not replace the original sky transparent to enable to new one to be seen.

I use After Effects CS5.5 on windows 7 Pro 64bits. Please not that I'm not a professional, edit my videos of my hikes in Grand Canyon for my sole pleasure and rather new to the software. So be patient and give me precise instructions although they might be obvious for a professional user.

Thanks in advance
Claude
Paris-France


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Chris Wright
Re: Keying problem with sky replacement using Linear color key
on Aug 14, 2014 at 11:01:34 pm
Last Edited By Chris Wright on Aug 14, 2014 at 11:02:05 pm

see if this helps, its a procedural keyer i made that uses 3 instances in diff chroma modes layered on each other to key everything but white then reverse matte it. you can play with the matte choker or turn it off.

http://f1.creativecow.net/7029/ae-cs55-sky


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Claude Rozsa
Re: Keying problem with sky replacement using Linear color key
on Aug 15, 2014 at 6:44:49 am

Good Morning Chris;
Thanks for the help and the file; Lathough it may seem stupid I'm not sure where to introduce my 2 files in your project.
One is my video (AVI format at 25fps see full infos hereunder), the other the image of the sky (jpeg format).



I was wondering by the way if the video format I used to extract the clip with scene-analyser was not responsible for my problem.



I told you I'm not yet familiar with the subtleties of AE..."un bleu" as we say in French!lol!and a very old one (73!!!)

Claude


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Chris Wright
Re: Keying problem with sky replacement using Linear color key
on Aug 15, 2014 at 10:38:59 am

the sky.png is the video
the solid Blue SOlid 1 is the sky in comp final blur
-right click replace footage for both

-the mask comp has the 3 linear color keyes, just play with them and the matte choker
the mask in final blur has a levels and channel blur that softens the edges

you would also have to change the composition size and framerate.

hope you have luck!

if you're really lost, you can also try this free video tutorial which might help. I haven't used it myself.
http://www.videocopilot.net/tutorial/advanced_sky_replacement/


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Claude Rozsa
Re: Keying problem with sky replacement using Linear color key
on Aug 15, 2014 at 11:14:11 am

Thanks Chris, yes i tried the videocopilot video without success although Kramer is as usual a remarkable teacher which is not always the case with videos (too much talk besides the point, speaking too quickly not to mention sometimes difficult accents to get into!)

Yes I did change the composition settings for the fps and aspect ratio and preset. I tried to use rotobrush but I have problems because of the pan I must try it again after reviewing my knowledge about the tool...Well I'm stubborn and will succeed in the end! I can't stand that horrible washed sky knowing what it was like on the site!
I'm addicted to Grand Canyon and hiked down there some 1000 miles in the past 24 years. I'm lucky to be a close friend of the Grand Canyon Field Institute director, Mike Buchheit (check his photos which are great, he has a website)so he helps me with permits and advices for my hikes. I'm putting on my blog a book I wrote on my hikes and some advice for French hikers as there is nothing written in French on the matter and they do take inconsiderate risks like I did with my first hike. The videos are part of the book. And I completely re-edit all of them with my new softwares and the pc I built which is more powerful and gives better rendering even for my old analog videos.


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