The 'a' number represents the number of pixels in the top row that will be sampled for chroma. 'J' represents how many pixels wide the sampling pattern is. The common way of writing out the chroma subsampling ratio is J, a, b. The number of pixels that share the same data determines what the subsample rate is. Engineers developed a way for multiple pixels in an image to share the same chroma data, with acceptable loss in perceived quality. In order to try to save space when recording images. Viewers are much more sensitive to luminance accuracy than chroma accuracy. However, if you remove the luminance from your pixels, the picture is black. If you remove the chroma from your pixels, you end up with a greyscale image. The pixels that make up your footage have information about Luma, or brightness, and chroma, or color. If the subject is placed too close to the wall, or a rim light isn't used, it can create some difficult issues in post.Ĭhroma sub-sampling of your footage can also contribute to the issue. One reason this can occur is due to bad lighting.

After doing the initial work to pull a key, the subject is often left with a green outline, or jagged edges. When you see the sheer amount of work that goes into big-budget film green screen work, it's no wonder that sometimes our own results may not match up to our expectations.

Using chroma key in premiere pro, ultra key in premiere pro, and keylight in after effects, we'll fine tune those edges to get a great looking key. In this segment, we talk about fixing those rough and discolored edges that are often left after pulling an initial key. Green Screen work is complex, even under ideal circumstances, and working with footage that hasn't been shot properly can be pretty tough.

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