September 25

Blurry Backgrounds: A Neat Video Trick

This adorable picture of my precious baby daughter is a perfect example of the photographic concept of depth of field The concept of depth of field (DOF) explains why just the baby is in focus.  That didn’t happen by accident.

newborn baby

 

Once you learn the concept of depth of field, and study how to manipulate it, you’ll see that focus is quite controllable by using certain lenses and controlling the light.  Selective focus can be used in ways to enhance the artistry of your shot, or to impart storytelling information.

video iterview
Selective focus has the camera in sharp focus and the woman out of focus. If they had used a different lens and brighter light, they could have had both the camera and the woman in focus. Doing the shot this way emphasizes the camera, so would be good for an advertisement.

Selective focus makes the subject of your picture pop. In the baby picture, the background and foreground both are softly out of focus, so a viewer’s eyes instantly dart to the subject of the picture.   Brushing aside the obvious fact that my little girl is too cute, the depth of field in this image is one of the technical reasons why it is an outstanding picture.  The lighting was from windows off to the left I cropped out.

In professional videography, getting the background out of focus when taking pictures of people (or any subject matter) is highly desirable, so has developed into an art unto itself.  In fact, it is often faked.

Out of focus elements can look beautiful in an image, not just the background.   The term for out-of-focus elements used in a pleasing way in a photograph is called bokeh.  So background and foreground are commonly thrown out of focus, but sometimes, having the entire shot out of focus can look pretty, as in this shot of Christmas lights.  Out of focus lights give a dreamy feeling.

out of focus lights

A completely out of focus shot like this is commonly used as a background for a green screen headshot.  It will give you instant bokeh.  The TV station I used t o work for bought large, still pictures of the downtown Nashville area that were significantly out of focus.  If you didn’t know what they were for, a first glance might lead you to conclude they were an expensive mistake.   Far from it.

They used these behind the news anchors, like many TV news stations do, to provide instant bokeh and make the studio appear much larger than it was.  If your local newscast as the city skyline or other relevant landmarks behind the anchor people, look closely to see if you can tell whether is an out of focus shot for the purpose of bokeh.

If you ever shop for backgrounds made for professional photography, you will find many out of focus images for this reason.

There are a variety of ways you can achieve an out-of-focus background.  You can do it while you are shooting the video, (easier way) or you can fake it later in the edit room.

When I took a tour during a national network newscast a few years ago, I noticed they had an extremely out-of-focus still picture two inches behind a reporter’s head, because they do not have the room to do bokeh the “right” way.  🙂  

The easiest way and most natural way to get an out of focus background for your talking head shot is to set the camera up inside a room large enough to have the background fairly far away from the person on camera.  You also want plenty of room to back the camera up, so it can be at least several feet away from them.  Then, use a semi telephoto lens on their face.  (The longer your lens, the more shallow your DOF will be.  Length of the camera lens is one of the primary ways to alter DOF independent of all other conditions.)

If you would like to read in-depth explanations on the multiple factors affecting DOF, click here.

The rest of this post will describe how to achieve bokeh in post-production, which is an advanced video production technique.

BOKEH IN POST PRODUCTION

If you want to blur the background while EDITING, it takes a video program that has at least 2 lines of video in the timeline that will allow it.  This is considered an advanced editing technique, so a simpler program would not have the capacity.

video editing interface
The image shows the different sections within the video editing software, Windows Movie Maker. WMM was a simple program that would not be able to accomplish the editing technique I am describing to achieve bokeh.    

I have done it multiple times in FCP, but I never thought it looked very good because the video editing software had a difficult time cutting out someone’s head precisely, so you had to blur the dividing lines and it looked fake.

In a program like Photoshop, you can easily isolate any object, including someone’s head.  But in a program like FCP, you have to use a garbage matte, which is never going to be exact.  Maybe the programs will get better at it over time.

First, here is some quick background on video editing basics to make sure you understand what I am about to talk about.
When you are editing video, the process is to stack video and audio elements onto lines inside what is called a timeline.  The image below is a screenshot of a timeline from Final Cut Pro 10 with identifying text.  The horizontal lines of audio and video are arranged in the proper order on your timeline as you edit your movie.


Generally, the more complex the program, the more lines of video and audio you have available to you.  In a more complex program, you also have greater leeway with what you can put on any line.  I have seen simple programs that had two video lines, but the upper one would ONLY take text for a name super.

national head injury association

When you see multiple images on the video screen, like this interview with her name and professional affiliation used in a name super, the name graphics are video images stacked on top of the shot of the person speaking.  In your timeline, whatever video is on top is what will show.

If some of the shot in your top line is removed, then whatever video clip is on the line beneath it in your timeline will show.  So when you cut out the background from line 2 with a matte, the out of focus background from line 1 will show. 

It Takes Two

To blur the background behind people, takes two lines of video.  Here is why.  If a video editing program has the capacity to blur a shot, it will be an effect added to the ENTIRE shot.  This is true for all editing software, no matter how sophisticated.  (The blur feature on whatever program you use will probably be found under filters.) The trick is to use two lines of video in your timeline to make one part of the final image blurry and the other part not blurry.

Here is a step-by-step.

  • Take the shot of your person and duplicate it on top of itself.
  • Take the video on line 2 and cut out the person, probably using a matte filter.
  • Then, turn your attention to the video on line 1.  Add a filter to this bottom shot that takes it completely out of focus.
  • The video on line 2 is still in focus, and that is your person. 
  • Since you have cut away some of the shot on line 2 with a matte, whatever you cut away shows up only from the blurry video on line 1. 
  • To make this look natural, it takes some tweaking to soften the edges.  The better you cut out your people, the more natural it will look.

WHICH ONE IS FOR YOU?

Now you have all the information you need to compare the two techniques for yourself.  If you want the background out of focus in your shot, which way is more practical?  It’s up to you. Circumstances and room size often dictate which you chose.

THERE’S A THIRD WAY TOO

If you shoot your people in front of a green screen, you can cut them out precisely and put any background behind them that you want.  Green screen adds a whole new dimension to the process.  Read more on green screen at this post.

Thanks for reading Video Production Tips.

Lorraine Grula

FOOD FOR THOUGHT

  • Describe how selective focus can be used artistically and for storytelling.
  • Define bokeh.
  • Describe the process for creating bokeh in editing.

Tags

bokeh effect, depth of field, how to make video, video tips tricks and techniques, videotaping a talking head


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