Better for screening: native t4i 1080p compression or ML raw 720p?
I have been doing quite a bit of research lately on Magic Lantern's raw possibilities, although there is one thing I can't seem to track down. The t4i's 24fps raw stream tops out at 720p due to the card bus speed limitation, so what I am wondering is this... for film screening purposes would it be better to stick with the camera's native 1080p capabilities and deal with the minor compression artifacts, or is 720p a high enough resolution for screening, getting the benefits of the raw footage?
Even if noone has firsthand experience with this specific workflow, perhaps someone with experience screening 720p footage could offer me an opinion as to how it compares to screening 1080p footage?
I've scaled the 720p RAW footage to 1080p and it looks about 1000x better than scaling compressed 720p to 1080p and at least 10x better than the cameras native 1080p in H264. The card bus speed limit is a huge bummer....my Extreme Pro's are writing at 60-105MB/s but the Rebels SD Card bus is limited to 30-40MB/s with 25MB/s~ usually being what I find tops out on my t2i. The chroma resolution on the H264 footage is literally 1/4th that of 4:4:4 video so jaggies around colors arent a problem with RAW video, the bit depth with RAW is 14-bit so a ton more room for color grading and no ringing around transitions in lighting or bright areas like a lamp or the sky. Its so much better...now the problems are no sound, lower resolution, etc. But to get around this one thing I like to do is shoot 2.35:1, you can squeeze out slightly more horizontal resolution with 2.35:1, I can get 1600~ lines across vs 1280 when shooting 2.35:1 which might seam small but it helps.
I think it would be good to mix RAW and H264 together depending on the needs even within a project, work really hard to get around the limits of H264 (just like many have both ameutur and professional to the highest level) and when something gets thrown at you use RAW...in the past if shooting 99% on DSLRs and something posed impossible for the in camera codec you had to find another camera, movies like Act of Valor had to use an Arri 435 for high speed scenes and certain scenes where 8-bit just didn't cut it.
For the H264 parts I would go ahead and set the bit rate on the in camera codec to 1.4x-2.0x via Magic Lantern, it won't do any miracles but it will give you less compression which is obviously important, it won't increase the bit rate all that much on still scenes but on motion ones it will allow it more head room....with my Sandisk Extreme Pro's I can shoot at 1.6x CBR and even 3x for short bursts and 120Mbps H264 vs 50mbps H264 in Canons flavor of the codec helps a ton in high motion scenes...of course this won't increase the bit depth limit or the chroma subsampling but its better than nothing. I would learn the RAW workflow for Canon RAW though, its not something I would like to jump into like other established RAW workflows like REDCODE. Find what works for you in tests...when I'm not shooting I'm testing! (which is allot these days!)
Thanks so much for the detailed reply, appreciate that. I'm all about doing extensive testing before the actual shoot, but in this case I don't really have the opportunity to actually 'screen' the footage to make a comparison. I agree with your thoughts on scaling up raw 720 from magic lantern as opposed to just going with the 1080 h264 as far as what I can see on the monitor etc., but without actually seeing it on an actual size screen its hard to say how the resolution would be affected. Would the absence of compression in the 720 magic lantern footage make up for the h264 artifacting in the full 1080 shots?
Actually, I've been thinking of just holding off for awhile until I can jump into the 5DmkIII and not even have to worry about using anything less than the full 1080 raw.
I find the 720p looks very much like 1080p, in fact there are a few workflows showing how the footage contains allot of potential for scaling. The 5D Mk.III can do 1080p native and obviously offers the prime solution for Magic Lantern Canon RAW video though, here's a video of the 5D Mk.II showing how scaling reveals a fair amount of more detail:
Personally I think it looks good, although there are a few artifacts I would consider a draw back but scaling to >3.5K might not be needed for your particular needs so the artifacts can be limited, also it could just be a mistake in the handling of that particular example I listed and generally speaking Canon RAW video from my t2i exhibits almost no artifacts, the grain structure looks very natural on the RAW, reminds me of some earlier digital cameras that shot uncompressed HD/RAW like the Viper Film stream to me. Very pleasant look, at higher ISO's its also easier to clean up noise in After Effects than H264. If you can do some tests even on a regular computer monitor no matter how small and limited I think you will be able to see the strengths and differences. Zooming in past 100% will always reveal color artifacts in chroma sub-sampled formats like 4:2:0 while RAW will exhibit less artifacting as its 4:4:4 (or non-chroma sampled).