![]() ![]() If you are showing a full screen video or set a background color for your slide(s), then the key signal will actually be solid white because the entire fill area now has content covering the entire screen at 100% opacity.Īn NDI output is simply sent out over your Network and can be picked up by a suitable NDI program/application or a hardware unit. Any areas that are not solid white will show the content will some amount of opacity. Anywhere that is black will show whatever the other video source is that you are using under your key. You can see the difference in the lines outside of the box and with how the yellow lines interact with the green box. The even lines are blue and have 100% opacity. The green box with the text is set to 50% opacity. The odd number lines are yellow lines set to 25% opacity. You can see this best in the example in the upper right corner. ![]() The white areas are actually a grayscale from 0-100% representing the opacity of the pixel that exists at a given point in the signal. Any area that appears as black is actually representing no content, or a pixel with zero opacity. The key signal is actually more complex than that. ![]() The key signal appears as a black and white source and the fill signal looks like your content. You have to setup your switcher's keying settings to know which is the key and which is the fill signal, and then it handles processing the signal over your other sources.īefore we get into the setup of the alpha key, let's take a look at what's actually being sent for the key and fill signals. For SDI, you are sending two physical connections. For NDI, you are only making one connection and the receiving software processes the data and knows what to display. With an alpha key, you are providing a key and fill signal to your switcher. The difference with those types of keys and an alpha key is that they generally use a single video input and just remove a color. A true luminance key is usually only available on high-end switchers. You can do a chroma key with any solid color. Most switchers can also remove black and will call it a luminance (or luma) key, but it's actually just a chroma key, but using black instead of green. If you're familiar with seeing green screens get replaced with content, then you understand the concept of chroma keying. The other two methods are chroma keying and luminance keying.
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