Canon 1D X: What the compression?

Just the Cut

Hooray! Canon has dropped a next generation DSLR on us and we couldn’t be more disappointed? Wait a minute what? Ok, ok, so maybe it is not what any of us had expected but it does show where they’re thinking about what DSLRs mean to Canon.

The newly announced 1D X offers the next generation of EOS movie mode. This of course is expected. Although, many us us are scratching our head to what this all means. Here is quote from the Canon Professional Network Europe site:

The biggest change to the movie shooting is the ability to choose from two different compression methods — IPB or ALL-I — depending on your needs. The EOS-1D X still records movies using the H.264 codec but it is the compression type within this codec that has been changed.

When shooting movies, the frames that are captured are usually split into key frames or Intra-Frames and predicted frames. These Intra-frames are used as reference frames to help with compression.

The first type of compression available is IPB. The B in IPB stands for Bi-directional compression. With IPB differential compression is carried out by predicting the content of future frames, with reference to both previously captured frames and subsequent frames. Like the IPP compression method used in previous EOS DSLRs, some data is stored in a Group Of Pictures (GOP), meaning that frame-by-frame editing will result in lower image quality. When using IPB editing video in-camera to trim clips can only be done in one-second increments.

The second method of compression is designed for users working in high-end editing systems or those looking for the very highest quality. This compression is called ALL-I. ALL-I stands for ‘Intra-coded Frame’ and it differs from IPB and IPP because all frames captured are treated as Intra-frames or key frames. Although each frame is still compressed, there is no further compression as each frame is seen as an individual image.

When filming with ALL-I, file sizes will be around three times larger than with IPB, and it is easier to edit to an individual frame without degrading the image quality. Despite the extra file size, ALL-I compressed footage actually requires less computer processing power than IPB or IPP and consequently will playback more smoothly on lower specification computers. This is because there is no rendering needed to extrapolate data from the GOPs used in IPP and IPB.

Canon has given us the choice now to choose what type of in-camera compression is applied to the movie files. They still are wrapped in a H.264 Quicktime Movie wrapper. Most likely still in 4:2:0 8-bit. What type of compression that happens within that wrapper is determinate to the shooter. After a interesting look at the leaked Japanese press release I saw the words VBR thrown in there. This would hopefully mean that depending on the mode of shooting the bit rate would be adjusted accordingly. Whether in 1080p24,25,30 or 720p50,60. Again, they included the older EOS movie compression which compresses groups of pictures in an inter frame compression mode. Great for a small file size but does sacrifice image quality and of course compression artifacts. This is the cool part. Also included is a new intra frame compression mode. Instead of compressing groups of pictures it compresses each individual frame captured maintaining frame to frame picture information. Each frame now is compressed. The downside is a larger file size but a better looking, lesser compressed image. With the addition of the new DIGIC V processors and the 1D X’s new CMOS sensor this should make for a better EOS movie file than we’ve been used to seeing.

Now comes from the fun part. What does this mean for the November 3rd announcement? Will Canon implement this new EOS movie mode to a new Super 35/APS-C sensor? Will they take this new full frame sensor instead? What about the current XF codec in the camcorder line? Having 50Mbps 4:2:2 chroma sampling and 8-bit color depth in a MXF wrapper would sound nice behind that new sensor. Add a PL mount option and a 10-bit SDI out a la Sony F3 and we may have a giant bomb exploding soon. Maybe. Of course RED is chiming in too with Scarlet part deux(?)

Exciting times to be in for sure. All just fun speculation till the curtain is raised and we know for sure what’s up Canon’s sleeve.

Chris Marino
Chris Marino is a cinematographer based out of San Francisco. Being also an editor, he also writes about post production for the site. Most of his work has been on commercial spots and short narratives. Follow @chrisMmarino
  • http://twitter.com/Sebastian_TR Sebastian TR

    Looking forward to Nov 3rd! assuming Canon unveil 2 purely video based cams based on S35/APS-C sensor with improvements (PL / EF ?) that still leaves the 5dmk3 in mystery. Curious to see what RED are going to unveil as well to counter all this.

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