Without a doubt, "Chroma keying" is one of the most exciting video editing tricks available today. If you've ever heard people mention the term "green screen" it's the same thing. What the chroma key technique allows editors to do is pick a single color from the spectrum and remove it completely from their screen. Green is often the color that editors choose to isolate and remove because the subjects of most chroma key video sequences are human, and green is not a color that naturally occurs in the human complexion.
Videographers will often film their subjects in front of a green backdrop with a plan to replace the green color with a different image of their choosing. The subject in the foreground remains the same, while what is seen behind them can change dramatically; often providing cool - seemingly impossible effects! Both blue and green backgrounds make it possible to work with this effect.
To help you create a chroma key effect with AlterCam, we've put together a brief how-to guide.
First, you'll need to decide what to use as your visual source during Live webcasting. A still frame image, prerecorded video, or your webcam feed are all possible with AlterCam; make sure that the background of your source media is either green or blue (more on that later). For demonstration purposes, let's use a still frame image featuring a subject that's sitting in front of a green backdrop.
Click Video Source to reveal a menu, and then click Choose Video File... This will open a view of your drive(s) where you can locate and select a source media file.
With a source file selected, you're ready to begin the process of replacing the green background with something new. This can be a color, an image or a pre-recorded video.
Click the Tricks tab and then click the Transparency By Color (Chromakey) button below it.
This will open the Transparent Video window. Click the green backdrop in the Original preview on the left: AlterCam picks that color and makes it transparent in the Processed preview on the right. Fine-tune the result with the Hue, Saturation and Brightness bars (see the guide below) and click OK.
Let's close this view for now and return to the Effects tabs. This time, let's click on Background. Here you will see options to add a solid color, broadcast what's showing on your screen (desktop) or add an image. For this example let's upload an image of a building.
In the Background options, make sure the Image box is checked and then pick one of the preloaded images, or click Add Image... to add your own (adding your own images requires the full version). Your new image will appear below the preloaded images.
TIP: if you know ahead of time that you want to use a custom background, you can load your image first thing to save time. We've done it in this order for demonstration purposes.
Let's see how it looks by returning to the Tricks tab and clicking the Transparency By Color (Chromakey) button once more.
TIP: for additional information on how to adjust and refine your chroma key effect refer to the Transparent Video Options Guide below.
Once you've successfully modified the background by replacing the green with a different media source, you're ready to broadcast. Click the Start AlterCam button in the main toolbar to apply your changes in real-time to your next webcast.
Transparent Video Options Guide
The Transparent Video window shows two previews: Original on the left and Processed on the right, where transparent areas are shown as a checkerboard. All the settings are below the previews.
Color is the backdrop color to remove. The easiest way to set it is to click the green (or blue) backdrop in the Original preview: while you move the mouse over the preview, AlterCam highlights the color under the cursor. You can also click the color box on the left and choose a color in the dialog. Green works best in most cases, but blue is a good choice if your subject wears green.
Hue, Saturation and Brightness bars set how wide a range of shades around the chosen color becomes transparent. If patches of the backdrop remain (usually in shadows and folds), drag the handles to widen the range. If parts of your subject start to disappear, narrow it. The gradual part of each range makes the edge soft, which looks more natural around hair and outlines. Double-click a bar to reset it.
Since version 6.8, AlterCam uses its own chroma key engine: it is about 20 times faster than before, so keying even Full HD and 4K video barely loads the CPU.
What's Next?
It's important to note that this is just one of many methods available to modify your Live webcast using the chroma key effect. We've used a still frame image for this guide because it's easier to illustrate.
Now that you have seen how to add media and modify the background using the chroma key effect, you're ready to experiment with other types of source files. Just make sure that when planning to replace your Live stream background using the chroma key effect that you take the "big three" factors into account. You want to make sure (whatever your background source) that it is (1) solid (2) well-lit and (3) with as few shadows as possible.
What if you have no green screen to replace your background? Nowadays, AI-based algorithms can replace the background with no special setup. In AlterCam we implemented the virtual background feature. Follow the link to learn the details.