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What Affects Image Quality in Video Conferences?
Resolution, a key factor in image quality for displays and projection systems, is often mistaken as the key factor affecting image quality in video conferences. Videoconferencing call quality is affected by a number of factors and remarkably, increased resolution of a display can actually reduce image quality.
A vexing area of video communications relates to what is often referred to generally as "resolution". Resolution is generally accepted to define the clarity with which one sees a video image that is presented electronically on a monitor. In the realm of video communications, there are many factors that affect this and these factors interplay in such a way as to make improving video resolution or clarity a challenge.
There are three key areas to consider when tuning a video conference image:
- Motion handling
- Resolution Pixel, Spatial, Temporal
- Aspect Ratio
Motion Handling
Compression techniques for video communications include H.261, H.263 and H.264 among others. Generally H.264 is considered to be the most efficient compression technique of these and therefore video images are likely to show a greater level of clarity when transmitted and decoded using the H.264 algorithm.
Fixed and unchanging images such as those presented by a document camera may not require H.264 and these images may appear equally clear using other algorithms. Moving images, however, greatly benefit from the use of an efficient algorithm and the real time clarity of moving images is widely preferred using the H.264 codec.
Creating clarity of video images in a video conference requires assessment of the type of image that is going to be transmitted. For example, if moving pictures from a DVD player or an HD camera image of active group of people will be transmitted, selecting the codec properly is critical (in this case, we would recommend the efficient H.264 codec).
Codecs must be negotiated properly between video conferencing systems in order to function and so if H.264 is not available (which occurs with surprising frequency) then by increasing the bandwidth used in a video call, you can increase visual clarity of motion as well.
Resolution Pixel, Spatial, Temporal
Video conferencing systems can be configured to output varying Pixel Resolutions and this needs to be matched to the presentation setting on the monitor being used such as 1024x768. In addition to pixel resolution, the ability of a monitor to uniquely address each pixel (Spatial Resolution) will affect the clarity of the images presented. Spatial resolution can vary widely between monitors and this is something that can significantly affect image clarity. In addition to Pixel and Spatial resolution, Temporal resolution affects the clarity of moving images through frame and refresh rates of pixels.
Aspect Ratio
Video conference images can sometimes appear stretched or squashed depending on the aspect ratios of the video conferencing codec and the display to which it is connected. Aspect ratios of 16:9 are common for High Definition system and this selection should be made in the monitor or projector setting. When using Standard Definition video conferencing systems, images are best displayed in a 4:3 aspect ratio.
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