Take the 2-minute tour ×
Video Production Stack Exchange is a question and answer site for engineers, producers, editors, and enthusiasts spanning the fields of video, and media creation. It's 100% free, no registration required.

I have a video of smoke shot against a black background. I would like to make the background transparent so the smoke shows over the video in the background.

I originally tried Remove Matte but that didn't seem to have any effect on the smoke video. I then tried Color Key and I was left with what you see below. (Original smoke is on left, the "keyed" version is on the right.)

Screenshot of Smoke

I am using Adobe Premier Pro CC (v7.2.1). What is the best way to cleanly remove the black background while leaving the smoke. The goal is to have the smoke over the background video.

I am a novice at this so please use clear instructions. If an option is buried in a menu, please tell me which menu. What I have tried has come directly from the Premier's Effects Panel.

share|improve this question

3 Answers 3

While chroma-keying is a good technique for dealing with solids, it doesn't work so well when dealing with transparent or semi-transparent objects. Because the difference can be very subtle, you want to copy the difference instead or blend off luminance.

In Premiere, you can use the Set Matte effect to set a track as a luminance matte. In the case of the sample of smoke from mmphilips post, the luminance was a bit low so I put it in a separate sequence and used curves to boost the overall luminance. I then placed the matte on Video 3 and made it invisible. I then placed the Set Matte effect on Video 2, pointed it at Video 3 and specified that it should use Video 3 as the matte.

Premiere

The same thing can be accomplished in After Effects in a similar manner. Again two copies are placed on the composition and the top most is made invisible. The modes option toggles is clicked to bring up the proper controls and luminance is chosen for the second layer so that the third layer is used as a matte. As shown, I applied curves to the third layer directly to make it blend more naturally. Note that in this screen shot I actually inverted the matte layer and thus used inverted luminance, but those steps aren't necessary, I just made an error while getting it working and didn't bother to correct it.

After Effects

Note how this results in much smoother results than a luminance key or chroma key since a luma or chroma key makes a hard cut off and is not able to do alpha blending based on the intensity of the smoke. Smoke however is somewhat transparent and you want to be able to see through it where it is darker. That's why this blending technique works.

share|improve this answer
    
While this is a very good answer that will produce good results, the "proper" way would be to simply use the "screen" blend mode as mentioned by Justin Brunson in his answer. Its the standard way of dealing with any particle type stock footage on black background. That doesn't mean you shouldn't try the other ways mentioned here, not every footage is made for the screen blend mode. –  Professor Sparkles Apr 22 at 23:57
    
I'd disagree on this not being a proper way to do it. Screen blending is simpler and is also proper, but this gives greater control over the masking and way that it blends without impacting what you are actually blending. This is a more advanced technique, but perfectly valid. Without tweaking the mask, the result would actually be very close to screen as it is blending the smoke/particle layer on to the base via luminosity, which is the same result as a screen blend. –  AJ Henderson Apr 23 at 2:08
    
Thats why I put it in qoutation marks. Every way that gets you there is a proper way. The screen blend mode is just the most common way to do it. You also have control over the outcome by using a level and or curve adjustment. –  Professor Sparkles Apr 23 at 2:18

First off, you would normally use After Effects for special effects such as Chroma Keying. That being said, Premiere Pro is capable of chroma keying quite decently. Here's an example using free smoke effects by JohnnyFXEffects.

Set up your scene as you usually would, and then go to the 'Effects' tab. (1) From the 'Keying' folder, select the 'Chroma Key' option. (2) Simply drag and drop it onto your smoke video file. (3)

Next, select your smoke clip by clicking it, and go to the 'Effect Controls' tab in the upper left workspace. (1) Expand 'Chroma Key' (2) and click the eyedropper icon in the same column as "Color". (3) Next, select the color you want to chroma key away by clicking in an area of your video with that color. (4)

Keep fiddling with your Chroma Keying settings untill you get the desired result. I found that setting similarity to around 7,5% (1) and Cutoff to around 50,0% (2) gave me a decent result.

enter image description here

Optionally add a few more video effects untill you get the desired result.

share|improve this answer

The simplest way would be to set the blending mode of the smoke clip to "screen". You'll find this setting in the "Effect Controls" panel under Opacity.
Screen basically ignores black. A better description is found on Adobe's site: http://helpx.adobe.com/en/photoshop/using/blending-modes.html

share|improve this answer
    
+1 for being a simpler way than using an independent mask. –  AJ Henderson Apr 23 at 2:09

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.