HD Video Surveillance
in an end user making an investment in HD video surveillance, if the compression levels required to meet transmission and storage needs end up removing a high degree of detail.
Coding considerations
Once a cornerstone of digital recording, JPEG - later followed by M-JPEG - compression was originally developed with the goal of efficient storage of individual photographic frames. The JPEG compression standard has become more sophisticated and it’s hard to distinguish between compressed and uncompressed images when compressions factors are low. To cater for the video market, Motion JPEG
(or M-JPEG) was created to bring together a series for individual frames to create motion. As the standard was created for still images, it is based around keeping detail for that purpose. With so much detail being stored in the frames, storage levels and bandwidth usage are high. Each frame is just that, a complete frame. M-JPEG is still common because image quality can be very high. MPEG compression, developed by the Motion Picture Experts Group, serves the purpose of compressing video data as opposed to still images. Full frame images are captured as a reference point - the aforementioned I-Frames - and frames between these are created by referencing the I-Frame and only refreshing any changes. This makes the compression more efficient for storage and transmission purposes. When there is lots of motion, images suffer from artefacts and distortion in the areas and on edges where movement occurs. There have been a number of versions of the MPEG method, and until very recently, MPEG-4 was probably the most adopted form of video
compression for surveillance. MPEG-4 uses the same techniques as it predecessors, but is more geared towards low bandwidth applications. There is much hype surrounding the
introduction of H.264 in the security industry. For a couple of years now, manufacturers have touted H.264 as the next big thing in video compression. H.264 is actually another form of MPEG compression. It’s often referred to as MPEG-4 Part 10 or Advanced Video Codec and is an evolved version of MPEG-4 compression. H.264 is incredibly broad and you will often see it mentioned in the same breath as Blu Ray and HDTV. Cynics could argue that this helps manufacturers market the product. The confusion surrounding H.264 stems from its different profiles: Baseline, Main and Extended. The most common profile applicable to surveillance is the Baseline profile, which has been tailored for small bandwidth applications. It is claimed to require less processing power and deliver vastly improved storage efficiency. It uses block based encoding, as does
MPEG-4, but the block estimations are lot more sophisticated. H.264 has greater flexibility in the sizes of the blocks that estimate the scene change, and these change according to what is in the scene. Elements such as pieces of sky will use larger blocks, whereas parts of scenes that require more detail will use smaller blocks, which in theory provides better visual detail. Also helping improve detail compared to other methods is the fact that H.264 puts the blocks on a grid, as opposed to the arbitrary nature of other compression methods. This allows for better results, but quality does depend on how the estimation techniques are implemented by the codec developers. Just because one device uses H.264 doesn’t mean that its compression will be as good as another H.264 device. H.264 has almost become an ever-present
part of HD video surveillance. Its enhanced efficiency has certainly allowed HD video to become a credible solution for many applications.
In Summary
H.264 is often quoted as if it is some guarantee of image quality. It’s not! However, well-implemented H.264, applied correctly in a well-designed system, can ensure that HD video surveillance delivers the high quality real-time images that end users expect.
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