Sync can be adjusted by shifting Chroma, Luma or both. Color channels can be moved horizontally as well as vertically.

Y/C Correction

The Y/C Correction controls shift the Chroma or Luma components of a video image relative to one another. A common use of Y/C correction is to compensate for poor image alignment in analog dubs but it’s also quite useful for shifting DV chroma sampling against right-side color drift.

Original Image (200% enlargement)

This detail shows a slip in color of the pepper against the blue background resulting from NTSC DV’s 4:1:1 chroma sampling. All the color in the image is drifting to the right, resulting in a blue cast on the left edge of the pepper and a trailing reddish cast on the right edge. Additionally, the green stem has a yellowish left edge and a green shadow.

Horizontal offset: 2 px

Using the Y/C Correction controls, the color information can be shifted to the left, helping to better align the sampled color point against the Luma information. This still isn’t perfect, partly because of DV’s oversized and blocky Chroma sampling, but centering the color on the pepper helps to improve the quality of the image.

When viewed on a video monitor, this image showed a significant reduction in dot-crawl along the pepper’s horizontal edges .

Horizontal offset: 2 px Joe’s Channel Blur: Chroma only, 2px, aspect: 4

When combined with Joe’s Channel Blur to smoother out the Chroma, the resulting image appears smoother and less blocky. This process can be used to help improve the appearance and success of color keys pulled from DV material.

Adam Wilt’s DV Sampling page has much more information and examples about different methods of video color sampling.