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Updated: 12/13/2012

Digital Compression In More Detail

All commonly used digital video formats use some level of compression. Top-of-the-line digital camcorders use a "no compromise" digital 4:2:2 format, which has minimal compression, with the luma and chrominance recorded separately. This format also has a much higher digital sampling rate and requires considerable bandwidth to record.

Other camcorders use a 4:1:1 format, which depends on a greater level of compression, resulting in some minimal compromises in video quality.

Although an initial side-by-side comparison of the 4:2:2 and 4:1:1 may reveal little or no difference, the quality advantage of 4:2:2 becomes apparent when editing, copying, and complex visual effects are required.

The chart below may help in visualizing the different sampling formats. The B&W (black and white) designation shows the luma samples per given interval; the Color (chroma) designation represents the number of times the chrominance is sampled during that interval.  

4:4:4 Format

B&W/Color

B&W/Color

B&W/Color

B&W/Color

B&W/Color

B&W/Color

B&W/Color

B&W/Color

B&W/Color

B&W/Color

B&W/Color

B&W/Color

B&W/Color

B&W/Color

B&W/Color

B&W/Color

4:2:2 Format

B&W/Color

B&W

B&W/Color

B&W

B&W/Color

B&W

B&W/Color

B&W

B&W/Color

B&W

B&W/Color

B&W

B&W/Color

B&W

B&W/Color

B&W

4:2:0 Format

B&W/Color

B&W

B&W/Color

B&W

B&W

B&W

B&W

B&W

B&W/Color

B&W

B&W/Color

B&W

B&W

B&W

B&W

B&W

4:1:1 Format

B&W/Color

B&W

B&W

B&W

B&W/Color

B&W

B&W

B&W

B&W/Color

B&W

B&W

B&W

B&W/Color

B&W

B&W

B&W


The more times the color is sampled the better the picture quality; but, also, the more bandwidth involved and the more demanding the digital recording process becomes.

The 4:4:4 sampling process is associated with some of the high-end, professional equipment which is covered in Module 49. Quality compromises are made in anything less than 4:4:4, although it may not always be readily noticeable.

MPEG and JPEG Compression

The 4:2:2 format associated with a widely-used compression method (known as MPEG.  This is one of the most popular compression formats and it represents a practical middle ground between optimized quality and technical practicability.

To reduce editing problems, jpeg compression is used instead of MPEG compression in some cases. This is discussed here.

Like MPEG compression, JPEG compression is not without resulting artifacts. The two photos below show different levels of JPEG compression. The first photo has minimal compression; the second is compressed to such a degree that important detail is lost. You might also notice little "globs" or "blocks" of data, especially in the bottom right-hand area of the overly compressed photo.

Additional pictures showing the effects of video compression can also be found in this module.


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