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"replacing" an unwanted object in a video

Specific to Premiere Elements version 14

"replacing" an unwanted object in a video

Postby obbrock » Sat Nov 26, 2016 9:23 am

I am very new to PRE
I know the basics about how to set up a garbage matte and a track matte.
Here's how far I have gotten:

Video 1 track contains a video with an unwanted object--a light bulb shining brightly.
I do have a portion of the video where the light is turned off.
I've taken a freeze frame-export of this unilluminated portion and then brought it into Project assets and placed it on the Video 2 Track, stretching it out to cover the entire video 1.
I'd like to show the non illuminated version of the light bulb instead of the illuminated one.
Can you point me in the right direction? I'm confused about what matte to use, which video track to apply it to, transparency--things like that.
I've been trying various tutorials, but haven't gotten the hang of it yet. Can you point me in the right direction or give me a few steps to follow?

Thank you
Oscar
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Re: "replacing" an unwanted object in a video

Postby Bob » Sat Nov 26, 2016 7:59 pm

I'm confused about what matte to use, which video track to apply it to, transparency--things like that.
I've been trying various tutorials, but haven't gotten the hang of it yet. Can you point me in the right direction or give me a few steps to follow?


The Track Matte Key effect is used to composite, i.e. overlay, a foreground image over a background image. It does this by introducing transparency into the foreground image so that the background image can show through. The effect uses a third image, the matte, to define where transparency is to be introduced.

Transparency is a measure of how much an image on a lower track would show through. Opacity is the inverse of transparency. An image that is 100% opaque is 0% transparent. An image that is 0% opaque is 100% transparent. Transparency doesn't have to be all or nothing. Intermediate values of transparency will result in a blending of the two images.

When you use the Track Matte Key effect you will be using three tracks on the timeline. The background layer on track 1, the foreground layer on track 2, and the matte on track 3. The Track Matte Key effect is applied to the foreground layer on track 2. The Track Matte Key Effect has 3 properties that can be set in the Applied Effects Panel: "Matte", "Composite using", and "Reverse". The Matte property tells the effect which track contains the Matte. Set it to Video 3. The Composite Using property tells the effect how to interpret the Matte -- more on this in a minute. The Reverse property flips the areas of transparency and opacity. If you made the matte backwards so that the areas that should be transparent are instead opaque, check this box to reverse it.

The "Composite using" property has two values: "Matte Alpha" and "Matte Luma". The default is Matte Alpha. Matte Alpha tells the effect to use only the transparency values in the matte to create transparency in the foreground layer. For example, if you create a title with text, the text will be opaque and the rest of the title will be transparent. Matte Alpha will result in the text filled with the foreground image superimposed over the background. Matte Luma will do the same if transparency is present. But, in addition, the luminosity values of the matte will be used to determine transparency. The way it works is that areas of the matte that are pure black will be 100% transparent while areas that are pure white will be 100% opaque. Intermediate shades of gray will be partially transparent.

In your specific case, you placed your substitute fill layer on track 2. You want this layer to be opaque over the area of the light you want to cover. You will need to create a matte image that is white in that area and black where you want the original scene to show through. To avoid an abrupt change that will make the overlay obvious, you should blur the matte or use a black to white gradient to feather the transition and allow the images to blend across the junction.

Do you have a photo editor such as Photoshop Elements that you can use to make the matte image?

One problem you may run into is that the brightness and color of the room may change between when the light was on versus when the light was off. You may need to adjust your foreground layer to compensate.
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Re: "replacing" an unwanted object in a video

Postby obbrock » Thu Dec 01, 2016 8:44 am

What a wonderfully clear answer!
Thank you so much, Bob, for taking the time to write this.
have a great day.
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