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BenC

Cleaning up the sides of a green screen

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Hi

I cant seem to find a way to additionally cut out the sides of my screen screen stage. I have tried using the effects mask but this doesnt work. I read somewhere that NCH were adding a polygon mask feature in 2015 but it still doesnt seem to be implemented. Whats the ETA on this and can anyone advise me on how to do this?

FOhStqN.png

note that I wanted also to clean the bottom edge of the matt. Mainly because it seems the resolution of pixelation is quite noticeable. Can you increase the edge resolution of the green screen.

 

BTW I have used an actual green screen in this shoot.

 

Thanks

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Upload your elements to Dropbox, Google Drive, MS OneDrive or the like and post a public link here, so someone can experiment.

You tried SCALE and CROP?

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Hi

The green screen effect is good but will render everything in the clip image transparent only if the shade chosen is an exact match. Other shades in the clip will remain visible. You can colour pick the shade needed with the pipette cursor. When the Green Screen effects pane is selected left click the required shade in the clip preview image. The threshold and fading controls will allow some variation to the effect.

However, and depending on the image the following is probably easier. The  part of the image required to remain visible can be obtained with the Polygon Mask and the Transparency effect.

For the polygon mask, click the FX box on the clip and then the second button along at the top of the effects pane. This has a small green cross and a black dot. (Add effect mask). Initially the mask is a red dotted rectangle. You can now grab the dotted line at any point (including the original corners) and deform the mask by dragging the point chosen to another position. You can do this at multiple points to create any chosen shape. If you undock the preview window the enlarged image will make this procedure easier to see. Once you have outlined the area required you can feather the edge if needed

The next step is to render the clip transparent. But first you need to set the control "Mask inside".  Ticking this makes the area inside the mask the focus and the masked area would become transparent.  Unticking it  makes the area outside the mask masked area the focus and this would subsequently become transparent.

In your case  as you would have masked out your lady on the mat so untick the box. Now add your Transparency effect (Tick the green cross and select Transparency). and set the value to  0.00.  (0% Opacity = 100% transparent) Your lady on the mat will now be the only part of the clip visible. Obviously both effects can be controlled with keyframes if animation is needed. Also the clip should be placed on an overlay track.

d01689e5a0c7b3889245ef748c505017.png

The above is a rough example. The cartoon image on Track 2. The polygon mask is on the left drawn on the cartoon, box unticked and with 100% Transparency the background now transparent is against a black blank frame on track 1 but you can use any image/clip you wish for the background.  (Note: No green screen required) I am using VP v 5.20.

Hope this helps

Nat

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I did try scale and crop but I need to just cut out the areas that are not transparent. I cant scale, zoom or crop because I need the space left and right of the matt for arms and legs.

I guess I will have to make a separate image that corresponds to the areas I want to remove and use that as a mask. Not a very elegant workaround because there will be different framing for different episodes and Ill have to make an image for each and every one.

A polygon mask cutout would be ideal.

edit: Just reading Nationsolo's reply which came in as I posted

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Great thanks that did it. Rather than spending a lot of time closely cutting out the body/hair and mat I would prefer to use a green screen. So I just drew the trapesium shaped box shown above in my first image (where you see I was trying to get Effect Mask to work). That cleaned up the sides. Then I loaded a green screen effect to key out the rest. It was the FX order, the Mask Inside box (confusingly labeled) and the additional use of the transparency effect that I didnt get before.

2Oxu65M.png

The only thing I'm not happy with now is the pixelation of the green screen edge. Wish there was a radius or edge blur. I've been using Davinci Resolve free in my tests as well. I got to the stage I am now (with Videopad) in Resolve within 30min with better results on the keying out quality. I liked the draw in quantifier range/position feature. What I like about Videopad is its export/import formats and simplicity.

 

My vid was shot using a Logitech c920 on 1920x1080 @ 30fps xRGB H264 native using the Logitech capture utility which is pretty badly designed. I'm currently experimenting with NCH Debut Capture but was pretty disappointed with the 2hour demo limit. Really! I cant continue to test to see if I want to buy it or not.

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Hi

Yes..With green screen the edges don't always come clean and still show some background colour.......i.e. if you have an image on a pure red background for example and pick a pure red screen to mask it off, the edge of the image often has a thin halo of a pixel or two.  This is because  where there is a slight slope or curve in the edge of the subject that is not absolutely vertical or horizontal it results in a "step" effect in the edge of the transparency mask around the image where it doesn't quite match the subject edge.

Here is an example of a white pentagon on a red background Green Screened using pure red to remove the background. Placed on the timeline against a black blank frame on the timeline it is obvious there are some pixels of red where edges are almost but not quite vertical...

3d5c44767abc5325a5e22bfd9e60489c.jpg

I note that your girl on a mat has a slightly sloping edge to the mat and there is a resulting slight halo of green pixels along this which is similar to my example above...You used green to remove your green background....My example used red. Hence your pixels are green and mine are red.

These pixels can be removed by increasing the  Threshold level  control from the default value of 9 to a value of 99... Monitor the effect in the preview screen.

81585bf66d6a0533c29f7d66c938d0c3.jpg

This is the result when the Threshold level is increased to 99....... The red has gone. (in your case the green would go. :)

2565c184456c78c76843da1cfe9ac2f3.jpg

 

Hope this helps

Nat

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