Avid DNxHD vs. Apple ProRes vs. GoPro Cineform: Recompression Generation Loss
Fallen Empire by Angelo Lorenzo
If you have a properly tuned post production workflow then the amount of times you’ll recompress an intermediate video is zero or once; the most common case is recompressing assets like intros, bumpers, motion graphics, and others once they make their way into a final program.
I wanted to do an informal test between Avid DNxHD, Apple ProRes HQ, and GoPro Cineform to see how they stacked up through 5 rounds of recompression. To illustrate the differences, I took my original test video into Adobe Photoshop, added the compressed video to the layer above, set the compressed video layer’s blend mode to difference, and applied an exposure adjustment layer with gamma correction set to 2.0 to more clearly see the differences. This comparison should casually highlight the generation loss inherent in each format.
The Original Video
Recorded by the Canon 5DmkIII, h.264 all-I 1080p29.97. This was recorded for NBC as part of a web clip around the time of the 2012 Olympics.
Avid DNxHD 175 8-bit
First up is Avid DNxHD 175 8-bit. These were encoded by Adobe Media Encoder to the MOV container using Avid’s official Quicktime codec. If you ever wondered what the number in each DNxHD preset means, it’s the bitrate in megabits per second. 175 was chosen because it is similar to ProRes HQ’s bitrate of ~180Mbps. Below is the normal screenshot followed by a difference comparison to the original frame. You’ll see, quite easily, substantial blocking artifacts in both screenshots. read more...
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