What is chroma bug?
The chroma bug is a visual distortion that is present in the output of some models of DVD players.
The flaw manifests itself as jagged lines or streaks of horizontal lines running through some parts of an image, usually on diagonal edges of high contrast colors, making that part look like it has some texture. The chroma bug effect can be clearly seen on large progressive displays, but could go unnoticed on smaller interlaced displays.
The chroma bug is technically known as a chroma upscaling error (CUE).
The chroma bug is a visual artifact that usually occurs in areas of deep red and blue, but can appear anywhere as long as there is high contrast between the areas. It wasn't a problem before large progressive displays became widespread.
MPEG decoders in DVD players must use a different upsampling algorithm for interlaced and progressive frames. The reality is that most of the decoders in early DVD players only use one algorithm for both types of frames, usually the one for interlaced frames, as most displays were interlaced before 2000 and only a very small proportion over 30 lay inches tall. As large progressive ads became popular, this inherent flaw became apparent.
The distortion in the video is due to the MPEG decoders in the DVD players, which do not convert 4: 2: 0 chromate information from the DVD to the correct 4: 4: 4 or 4: 2: 2 format that video encoders require. The MPEG specification states that the MPEG decoder should choose two different upsampling algorithms in order to convert 4: 2: 0 to 4: 2: 2 correctly. One algorithm should be used for 'interlaced' frames while the other should be used for 'progressive' frames. What happened is that most of the decoders in DVD players only use one algorithm for both (for interlaced frames) which causes the chroma bug to appear in progressive frames.