Avid DNxHD encoding: mastering quality
The Avid DNxHD codec is specifically designed for nonlinear editing and multi-generation compositing, including collaborative postproduction and broadcast news environments. It has the ability to maintain image quality – which is essential to mastering for television broadcast – more effectively than other HD acquisition codecs. Avid DNxHD delivers more precise color correction, graphics, effects, and compositing over multiple generations of post production processing. The result is image quality that is virtually indistinguishable from the original image, regardless of source material.
The image below of a HDTV Multiburst signal indicates the frequency response characteristics of Avid DNxHD (upper) versus DVCPRO HD (lower) codecs. The test chart raster is 1280x720 pixels. The two resulting compressed images are combined in a split screen. Then a negative image of the original uncompressed test signal is 50% superimposed as a dashed strip across the center of the split screen. The highest multiburst frequencies are to the right. These areas clearly show the softening effects of the DVCPRO HD codec. Signal errors are very apparent in the DVCPRO HD image under the -50% mix of the original test signal.
Click on the image for a larger view
Unlike Avid DNxHD encoding, most camera acquisition formats compress the image through horizontal down-sampling – discarding pixel information and high-frequency color information in the process. This results in the image becoming softer during postproduction processing:
| FORMAT | Bit Depth | RESOLUTION / FRAME RATE | Y | CHROMA | Using Avid DNxHD
Restored Y* | |||
|---|---|---|---|---|---|---|---|---|
Bit Depth |
From |
To |
From |
To |
From |
To |
||
HDCAM |
8 |
1080i/60 |
1920 |
1440 |
960 |
480 |
1440 |
1920 |
HDCAM |
8 |
1080p/23.976 |
1920 |
1440 |
960 |
480 |
1440 |
1920 |
HDCAM |
8 |
1080p/24 |
1920 |
1440 |
960 |
480 |
1440 |
1920 |
HDCAM |
8 |
1080p/25 |
1920 |
1440 |
960 |
480 |
1440 |
1920 |
DVCPRO HD |
8 |
1080i/ 59.94 | 1920 |
1280 |
960 |
640 |
1280 |
1920 |
DVCPRO HD |
8 |
1080i/50 |
1920 |
1440 |
960 |
720 |
1440 |
1920 |
DVCPRO HD |
8 |
720p/ 59.94 | 1280 |
960 |
640 |
480 |
960 |
1280 |
| DVCPRO HD | 8 |
720p/50 |
1280 |
960 |
640 |
480 |
960 |
1280 |
DVCPRO HD |
8 |
720p/ 23.976 | 1280 |
960 |
640 |
480 |
960 |
1280 |
*C values are also restored
Avid DNxHD encoding prevents further image deterioration associated with multigenerational sub-sampling when editing native HDCAM or DVCPRO HD source material. Avid DNxHD offers significant advantages:
- Avid DNxHD encoding preserves the full raster of the original HD frame with no reduction in the horizontal luminance and chroma samples.
- Avid DNxHD also uses two-pass encoding, first analyzing every pixel of the full frame, and then adjusting the encoding settings to capture the optimum quality.
- Avid DNxHD encoded images are properly aligned so that downstream processes such as MPEG2 encoding can be better optimized resulting in a higher quality image for broadcast.
The images below are examples of how Avid DNxHD can be seen to preserve image quality in multigenerational postproduction processing.
| This example image represents what the camera lens actually sees in the 1920x1080 full high definition raster. |  |
| This is the same image after its raster has been horizontally sub-sampled down to 1440 pixels and recorded to videotape. |  |
| The same image returned to its normal raster. Sharpness deteriorates after multiple generations of sub-sampling in post production. |  |
| This is an A and -B mix of the original image and a negative of the subsampled image. The horizontal sub-sampling losses quickly become obvious. |  |
| This is an A and -B mix of the original image and a negative of the Avid DNxHD image. |  |
You can perform the A and -B mix test on any NLE or switcher to test for quality losses through any digital process. When you establish a 50/50 mix of any original digital signal with a negative image of the same signal after passing though a process to be tested the resulting visual differences are the errors generated by the process being tested. A blank image with no notable visual differences indicates a very high degree of quality and accuracy in the process.
Avid DNxHD Comparison Gallery
(DCI STEM sequence)
The still images here available for download were then exported out of a Media Composer Adrenaline system as uncompressed 16-bit TIFF files. We recommend ingest of these images into a timeline for playback to an NTSC monitor.
Click on the thumbnail to load the full resolution images (12,159 KB each)
or download all images in one file (98,366 KB).
 Avid DNxHD 145 |
 Avid DNxHD 145 |
 Avid DNxHD 145 |
 Avid DNxHD 220 |
 Avid DNxHD 220 |
 Avid DNxHD 220 |
 Avid DNxHD 220x |
 Avid DNxHD 220x |
 Avid DNxHD 220x |
 DVCPRO HD |
 DVCPRO HD |
 DVCPRO HD |
These images were originally 4K scanned 35mm film saved as 16-bit RGB TIFF files with a 2:40 aspect ratio. They were imported into an Avid DS Nitris system and a 16:9 extraction was created. The files you see here were exported out of the Avid DS Nitris system as uncompressed 16-bit TIFF files at HD resolution and imported at various resolutions into Media Composer Adrenaline.