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IDProjectCategoryView StatusDate SubmittedLast Update
0002479KdenliveEffectspublic2012-01-14 13:462012-01-16 00:17 
Assigned Tottill 
Platform32 bit intel and alikeOSUbuntuOS Version10.04
Product Version0.8.2.1 
Target VersionFixed in Version 
Summary0002479: Greescreen filter takes away too much of blue
DescriptionAs you can see in the Screenshots at [^]

In the third picture of this collection there is a blue sign at the T-Shirt of the guy. The blue color can be seen in the vecotscope.

in the second picture with greenscreen filter switched on, with the selected colour key from the background and with a variance of 13, we get some keying, but not a good one.
We can see in the vectorscope that some of the green is keyed out, but not all.
I circled the keyed out green with a red circle. Teh blue t-shirt sign is still there.

In the first picture i increased the variance to 35. Now all green parts are
keyed, but also the blue sign on the t-shirt is keyed out.

It would be great if:

1) there would be a display in the Vectorscope which displays the chroma area which is cut out by the bluescreen filter.

2) the chroma region to define the bluescreen filter could be defined in the vectorscope by drawing an area into the vectorscope instead of defining just one key colour and a radius around this color point (= variance)

TagsNo tags attached.
Build/Install MethodDistribution package
Attached Filespng file icon Keying.png [^] (216,293 bytes) 2012-01-15 23:33

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-  Notes
ttill (developer)
2012-01-15 22:51

I will have a look at the filter in greater detail, the general problem however is that unlike the vectorscope it is based on the YUV color model, so you cannot directly compare these two. Therefore I don't think that it's a bug.

To fix your problem you might want to try out the "color selection" filter. Make sure you check "invert". "subspace shape" should probably be changed to "ellipsoid". Also experiment with the different "selection subspaces".
In case that also doesn't work out you can use the rotoscoping filter, set the operation to "add" and then draw a rough mask around the blue sign (just as you did in the screenshot). Since the blue area isn't that big compared to the t-shirt you should be able to handle movement with few not so accurate keyframes.
Btw. You can also use the rotoscoping filter to create a garbage mask removing the things in the corners...

I've be thinking about writing a slightly more powerful greenscreen filter to achieve better results at edges/hair by feathering, using spill removal and similar techniques for some days now. If I'll ever be able to realize this I'll also consider your ideas, although I don't see them matching very well with what I'm currently thinking of ;)
(0007787) (reporter)
2012-01-16 00:08

I dont know that much about chroma keying, but I found in the Video Editor EDIOS, that they can select a key as I described in my description.

I uploaded a screenshot with the key editor.

You can see its usage in the video [^]
which is in german.

But even EDIOS can not do what the programm Robuskey can do. [^]

You can also see the usage of Robuskey in the german video.

It can do transparent glass, hairs, motion blur, green spill and transparent garment.

Thank you for your response and considering to make a better chroma keying.


See some research done on keying [^]
(0007788) (reporter)
2012-01-16 00:17

Some nice greenscreen test video files can be downloaded for free at [^]

- Issue History
Date Modified Username Field Change
2012-01-14 13:46 New Issue
2012-01-15 22:51 ttill Note Added: 0007786
2012-01-15 22:51 ttill Assigned To => ttill
2012-01-15 22:51 ttill Status new => assigned
2012-01-15 23:33 File Added: Keying.png
2012-01-16 00:08 Note Added: 0007787
2012-01-16 00:17 Note Added: 0007788

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