8-bit Downstream Artifacts and What Shooters Can Do About Them

I will say it again and again until someone actually listens. This business of capturing high-quality video for broadcast should not be about capturing ever-higher resolution images. At NAB 2018, many of us will be looking at the latest and greatest 8K cameras, which almost assuredly will become (next year maybe?) the latest and greatest 12K and 16K cameras. So what exactly is the point, to capture images with ever more clarity and crispness that will then be subject to the bands, contours, and other artifacts in a still dominant 8-bit distribution system? Does this fixation with camera resolution really make sense when what’s important to viewers, and is readily apparent to everyone, is greater bit-depth? The truth is, for all the increases in resolution demanded of broadcasters in cameras over the last decade, the foibles of 8-bit video are still very much with us. Indeed, HDR makes ultimate sense to broadcasters and viewers because it delivers expanded dynamic range at 10 bits with smooth gradients, eliminating much of the 8-bit ugliness that have plagued SDR broadcasts for decades.

A few cameras, notably DSLRs like the Canon 5D Mk IV, still shoot 8-bit (long GOP) video when recording 4K internally. Such video is notoriously prone to banding and contours, and other defects associated with 8-bit capture.

A few cameras, notably DSLRs like the Canon 5D Mk IV, still shoot 8-bit (long GOP) video when recording 4K internally. Such video is notoriously prone to banding and contours, and other defects associated with 8-bit capture.

With standard definition NTSC and PAL disappearing from the broadcast landscape, one might assume a discussion of 8-bit video for shooters is no longer relevant. But given today’s higher resolution programming and the need to multiplex an ever-increasing number of program streams for distribution over satellite, cable, and the Web, the ever-more constrained bandwidth raises the likelihood that 8-bit downstream video will persist, despite its drawbacks, long into the future.

Just look at the less than stellar images many of us viewed from the Olympics at PyeongChang – many bright exterior scenes with large areas of snow and sky appeared blown out and devoid of detail, with banding, contours and other 8-bit defects readily apparent on my rather typical non-HDR home television.

We shooters can’t do much about the peril of compromised 8-bit video downstream, but we can do our part to minimize the risk of in-camera picture defects, which can be exacerbated and made much more apparent later when output from an 8-bit encoder for distribution.

Even as shooters have moved on to greater bit depths, the foibles of 8-bit video persist in the consumer market and in broadcast- in DVD, Blu-ray, satellite/cable, and the Web. HDR, delivering 10-bits to home receivers, helps suppress the ridges and contours in the sky as seen here, but downstream 8-bit artifacts remain a menace for millions of existing (non-HDR) viewers.

Even as shooters have moved on to greater bit depths, the foibles of 8-bit video persist in the consumer market and in broadcast- in DVD, Blu-ray, satellite/cable, and the Web. HDR, delivering 10-bits to home receivers, helps suppress the ridges and contours in the sky as seen here, but downstream 8-bit artifacts remain a menace for millions of existing (non-HDR) viewers.

Shoot Clean

Regardless of resolution, shooting clean images in the first place is the shooter’s best defense against defects ‘suddenly’ appearing downstream. Recording at a minimum of 10-bits reduces the risk of banding and contours from appearing in large, flat monochromatic areas of the frame, like the sky, or in walls and surfaces devoid of texture. Shooting in 10-bits also ensures more efficient post-production overall, allowing more precise keying and color correction, with less noise and concomitant opportunity for 8-bit encoding errors and snafus.

The choice of recording format and compression type can also contribute to the increased risk of picture defects. Long GOP formats, like Sony’s XAVC-L and Panasonic’s LongG, typically record only one complete I-frame out of every 15 frames; the increased processing load required to decode such streams increasing the risk of errors and objectionable artifacts appearing on screen in home receivers.

Reducing Master Detail (DTL) helps suppress artifacts during image capture.

Reducing Master Detail (DTL) helps suppress artifacts during image capture.

I-Frame

Selecting all I-frame (intraframe) compression at 10-bits or greater will also inhibit the manifestation of defects through post-production. While news operations may appreciate the reduced data loads of the long GOP formats, the increased risk of in-camera picture defects seem hardly worth it, even when one considers the cost saving from a reduced storage requirement.

Reducing the high frequency detail in-camera can also help minimize the risk of downstream 8-bit defects like banding and contours. Turning down (not off!) the Master Detail (DTL) is usually a good idea to minimize this threat. A weak diffusion filter like the Schneider DigiCon may be useful as well to tastefully attenuate the fine detail that can lead to problems in the output from the 8-bit encoder.

Use of a filter like the Schneider Digicon to attenuate fine detail that can cause problems later in the 8-bit environment.

Use of a filter like the Schneider Digicon to attenuate fine detail that can cause problems later in the 8-bit environment.

Good Lighting Craft

Finally, there is no substitute for good lighting craft to reduce the risk of encoding artifacts. Broadcast shooters should be careful to break up large flatly lit monochromatic surfaces like walls and ceilings that can wreak havoc in program streams disseminated over cable and the web. A simple pattern cut from a piece of Gam BlackWrap, or a commercially available gobo or ‘cookie’ can go a long way to adding texture and improve the compressability of a scene.

When lighting, be sure to break up large flat monochromatic surfaces like walls and sides of buildings. You can use a commercially available 'kook', or improvise one out of a scrap of Blackwrap. The downstream 8-bit encoder will thank you with a cleaner output!

When lighting, be sure to break up large flat monochromatic surfaces like walls and sides of buildings. You can use a commercially available 'kook', or improvise one out of a scrap of Blackwrap. The downstream 8-bit encoder will thank you with a cleaner output!

For those of us with a hand also in post-production, we must strive there as well for images free of artifacts to ensure the best results out of the 8-bit encoder. For footage already exhibiting common defects like ridges and contours in the sky, Digital Film Tools’ versatile DeBanding filter may prove useful.The filter works by separating an image into color and luminance, then applying a process in the luminance channel to isolate and eliminate the banding artifacts. Another technique I’ve used with more or less success when facing the banding issue is to introduce a small amount of noise or film grain. Not every project or producer of course will tolerate the additional noise, however, so as always let good taste and an understanding of the prevailing politics be your guide.

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