Tuesday, April 13, 2010

Green Screen for Still Photography

Courtney - Green Screen Background

Anybody who is interested in chroma key photography may find this interesting. If you're not familiar with the term chroma key, it is basically the process of compositing multiple images using green screen or blue screen technology. It may sound complex, and it can be very complex depending on the project you are working on, but for this post I am only sharing some samples of my experience creating still-photo portraits using the process.

We've all seen films like The Matrix, Avatar and Spider-man. Today's cinema blockbusters are using this technology to catapult films into huge money making film attractions. But it's not just big budget studios using the technology. Low budget independent films and even online video-bloggers have easy access to the technology, and many are using it effectively. While I have played around with it in some test videos, it is still-photos that I am playing around with right now.

The small image of Sacramento model Courtney Riggs (above) is a raw photo straight out of my Nikon DSLR. As you can see, Courtney is posing in front of a green background. A very bright green background. The photo below is the end result using the chroma key process. As you can obviously see, there is a dramatic difference to the image, yet still very much the same image.

Courtney - Green Screen

If you have ever extracted the background, or foreground, of an image to combine different images into one, or create effects, odds are you have used the marquee tool in Photoshop or another photo editing application at some point throughout the process. Chroma Keying let's you eliminate that time intensive technique by eliminating the green or blue hue with one click of your paint bucket or one short pass with your background eraser tool. Of course this is all assuming you are extracting on a budget.

Naomi - Green Screen B&W

There are plugins for Photoshop and stand-alone applications that will allow you to eliminate the green or blue hues from your images with precision accuracy. But they're not free. Digital Anarchy has a plugin for Photoshop that has a pretty good reputation. It is called Primatte Chromakey. There is also a stand-alone application called PhotoKey 3, and it is available for both Mac and Windows environments. Prices for both range from $150-$300, so you can start creating your own masterpieces within a relatively reasonable budget.

Sonar - Princess of Good

Of course you can always do it the hard way, like I did, without the aid of specialized software. But keep in mind, chroma key software was developed to easily correct all the mistakes one can make from doing it themselves using only a Photoshop extraction technique. One of those corrections is the correction of color cast or spill.

Color spill (or cast) is the result of color cast onto your subject via a reflective colored surface. When you use a blue or green screen as a backdrop, you are going to deal with the color of that backdrop effecting the visual area of your subject. Even after it appears that you have eliminated all the color to be extracted in your image. The closer your model is to the backdrop, the more spill you are going to deal with in the post processing stage. The farther away from the backdrop your model is, the lower the reflective area of color hitting your subject you will have to deal with.

So if you opt to do it yourself, prepare for a little trial and error. There are plenty of instructional books out there as well as tutorials online that will help guide you along the way.

One other benefit from using green screen as your backdrop, is that you can save a bundle of money on buying actual backdrops for portrait sittings. You have all the control in the world over color and patterns to place behind your subject instead of dishing out over $150 for a Muslin backdrop that is going to be tired looking after three portrait sessions. Of course you may run into problems with that philosophy if your subjects insist on wearing a lot of green (or blue in front of blue screen). So having a couple of options is always best.

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You can also find me at Sacramento Photography on ThinkTunk.com