In a perfect world, video and still images would perfectly represent the original source image and have no visual artifacts at all. In real life artifacts can and do appear in almost all visual systems. Some artifacts are expected due to data compression or frame rates, others are unexpected and are a result of faulty hardware or network implementation. This article will help to educate you on what may be causing a visual artifact you've encountered.
The physical path
Video transport via TesiraLUX requires a few discrete physical steps.
- Source > HDMI/DP Link > TesiraLUX IDH-1 input > AVB network > TesiraLUX OH-1 output > HDMI Link > Display.
- The video source (either capture of new content by a live camera or playback of pre-made content) is connected via HDMI or DisplayPort cable to TesiraLUX IDH-1 input device. The source can provide video content resolution up to 4096x2160 at up to 60 frames per second.
- The TesiraLUX IDH-1 input device is connected via copper or fiber to an AVB-capable network switch. The network switch may be connected to other AVB-capable switches. A TesiraLUX OH-1 output device is connected via copper or fiber to the same AVB network.
- The TesiraLUX OH-1 output is connected via HDMI or DisplayPort cable to a video display.
The quality of the original content is typically the largest determinant of the image quality in Tesira Lux. If visual artifacts are present in the original signal, the display must show those artifacts on playback. If low quality footage is used in the original signal, it will remain low quality through the playback chain. It is critical that the original content being used for quality assessment does not contain artifacts which may be interpreted as transport faults by a viewer watching the video display endpoint.
The next area of concern are the links between TesiraLUX and the source and sink (display) hardware. Both HDMI and DisplayPort cables have constraints on their maximum lengths. They may experience signal degradation if the cable is simply too long, if the cable is bent or otherwise compromised structurally, or has a manufacturing defects. Voltage drop imposes limitations on the amount (bandwidth) of data which can be delivered reliably across the cable due to long cable lengths. Artifacts or faults that may be expected due to cable issues include “sparkles” or “snow”, loss of audio, loss of picture, or both.
HDMI and DisplayPort cables
Active or powered HDMI or DisplayPort cables are available and may offer a means to extend the cable length without losing image quality. These active cables are typically unidirectional since a signal booster (amplifier) is embedded in the cable connector.
Standard HDMI cables are rated up to 2.25Gbps for video up to 720p. High Speed HDMI cables are rated for up to 10.2Gbps for 1080p signals and beyond, including 4K. Premium HDMI is rated for 4K and other advanced features. All DisplayPort cables support up to 4K.
TesiraLUX hardware and the AVB network
In video systems artifacts can be introduced by encoder and decoder devices, for this reason Tesira LUX uses extremely high-quality components to ensure that the original content is reproduced as perfectly as possible.
Tesira LUX uses a lossless digital transfer transport over AVB. In a properly planned system there will be no artifacts or degradation of image quality introduced by the AVB network. If a source device pushes content to many receivers the data stream is duplicated in the switch network for transmission to each receiver, all receivers get a perfect duplicate of the original transmission – there is no loss of signal strength or quality over the AVB network. The AVB switch network is a key component of the audio-video system.
TesiraLUX allows the source material to be transmitted with or without data compression. Without compression, the signal is passed over the network without modification and is presented to the display as a bit-perfect copy of the original signal (1:1 transfer, or compression "Off"). Since uncompressed video signals can consume very large amounts of bandwidth, users will often need to reduce the bandwidth of the signal to fit the bandwidth constraints of the network. By selecting different maximum values for resolution or frame rates or by choosing to compress the video stream, users can constrain the maximum bandwidth usage for endpoints.
The Tesira Lux IDH-1 can apply extremely high-quality compression on a per frame basis (intraframe or I-frame compression). The real-time compression codecs used for TesiraLUX video are different from those used to optimize a video file for storage and playback (interframe compression). Therefore, many visual artifact types which users may be familiar with from video content streaming services or from storage sources such as DVD video will not be introduced by the Tesira Lux IDH-1 encoder and OH-1 decoder.
Artifacts which occur in Tesira Lux encoding and decoding will not persist across frames, as the interframe compression is done on a frame-by-frame basis and is not propagated across a long series of frames. This means that some artifacts such as color banding (which are a result of long term frame averaging and data storage optimization) will not be introduced by Tesira Lux compression.
Using compression on TesiraLUX video signals is very common, because the compression that TesiraLUX uses results in very few artifacts. In fact, under most circumstances, the signal can be compressed by a ratio of up to 4:1, and still be indistinguishable from an uncompressed video signal. This is often referred to as "visually lossless" compression, since even though the compression does result in the loss of some data, the losses are not significant enough to be perceived by the eye.
If an artifact is part of the original source material, it will of course be reproduced and seen at the output side.
Common digital video artifacts fall into a few categories, and may be caused by a variety of issues. Below are the common artifacts that might be experienced, along with troubleshooting suggestions.
- Lost frames or dropouts
- Compression artifacts
- Blocking / Color banding
- Ringing or haloing
- Jagged edges
- Motion blur
- Sparkles or snow
AVB Network artifacts
- Dropped frames – AVB clock sync issues.
- Dropped signal - audio, video, or both.
Verify the network integrity. If the listener's OSD does not appear check HDMI and DisplayPort cables at the listener location. Does the OSD of the listener indicate the talker is present? If yes, then check HDMI and DisplayPort cables at the talker location. If no, then troubleshoot the AVB network.
Verify the configuration settings on all connected AVB switches. Ensure that the switches in use are powerful enough for the application.
The video and audio being transmitted from end to end are digital signals, meaning they are a series of 1's and 0's. If they are corrupted or too weak at the receiving end due to excessive cable length you will typically lose the audio and/or video signal altogether. If the video and audio arrive they will be reproduced at the same quality as they were encoded - the signal will not degrade over the digital path.
TesiraLUX compression artifacts
In TesiraLUX, most compression artifacts can be resolved by choosing a lower maximum display resolution, a lower compression ratio, by changing to a lower minimum refresh rate, or a combination of these settings.
- Ray banding / compression banding / slice
TesiraLUX compression artifacts may be encountered when applying high compression rates on visually complex scenes. Compression is done (in part) by splitting the image into horizontal bands and compressing each band independently. If the IDH-1 cannot encode data within a particular slice fast enough, then artifacts are introduced and may be seen as blockiness or pixel flickering. They typically present as part of a thin horizontal band across the screen.
Sharp transitions from dark to light may exhibit "halo" or "ringing" effects.
Endpoint cable artifacts – HDMI and DisplayPort issues
- "Sparkle" or "snow" onscreen.
The result of random pixels not receiving their image data and displaying full on. This can range from mild "sparkle" to severe "snow". This typically indicates a faulty cable.
- Audio drop outs
- Video drop outs
- Tesira Lux on-screen display (OSD) pops up with connected device crossed out due to HDMI or DisplayPort cable sync issues.
Verify that the cables used are not physically compromised - bent, crushed or pinched, or otherwise damaged. Check that the molded connection ends are intact and fully seated in the connection. Ensure that the cables are not too long, if longer runs are required an active or powered cable may be needed - or you may want to relocate the Lux endpoint to a closer position.
Device interoperability artifacts
- Stretched or “wavy” output: Scaling artifacts if an endpoint mis-reports its capabilities (eg – a device reports it is 16:9 output but actually outputs 4:3)
- Green tinted video: An endpoint reports itself as an RGB device but delivers YUV content
Verification may require the use of 3rd party test equipment to validate the enumeration of the source or display.