4:2:0, 4:2:2, 4:4:4—we are all used to seeing these ratios, but there is often a lot of haze around chroma subsampling and how it works. Hopefully, this can clear up the basics. Compression First off, chroma subsampling is a type of compression. It is different from the spatial and temporal compression used by most video compression algorithms to detect areas of the image in a frame, or across a number of frames where there is redundant information that can be described using less data. Since human vision is much more sensitive to variations in brightness than color, we can split up image information into a luma component (Y’) and two chrominance components (Cb Cr) rather than the RGB primaries. This way we can reduce the resolution of the two chroma channels while keeping the luma channel at full resolution with very little loss in image quality. The 4:2:2 Y’CbCr scheme requires two-thirds the bandwidth of (4:4:4) R’G’B’ but at normal viewing distances, there is little perceptible loss by sampling the color detail at a lower rate. Luma Luma represents the brightness of an image. It’s just the gamma corrected luminance information without any color. Below you can see a full-color image at the top with it’s constituent luma and chroma components. Chrominance (Chroma) Chrominance (chroma or C for short) is only the color information of the picture, separately from the accompanying luma signal (or Y for short). Digitally, chrominance is represented as two color-difference components: Cb = B′ − Y′ (blue − luma) and Cr = R′ − Y′ (red − luma). Cr and Cb values can be positive or negative from -1 to 1. Sampling System and Ratios The subsampling scheme is expressed as a three part ratio J:a:b (e.g. 4:2:2), that describes the number of luminance and chrominance samples in a conceptual region that is J pixels wide, and 2 pixels high. J: horizontal sampling reference (width of the conceptual region). Usually, 4. a: number of chrominance samples (Cr, Cb) in the first row of J pixels. b: number of changes of chrominance samples (Cr, Cb) between the first and second row of J pixels. The mapping examples given are only theoretical and for illustration. The above is taken from Wikipedia. Considerations Subsampling can easily reduce the size of an uncompressed image by 50% with minimal loss of quality. However depending on what the post production demands may be, the full chroma information is not always redundant. For example, full chroma information is needed to pull high-quality chroma keys and will always be preferred for high-end color work. Some image compression algorithms also remove redundant chroma information. By applying chroma subsampling before compression, information is removed from the image that could be used by the compression algorithm to produce a higher quality result with no increase in size. In terms of what is good enough, many DSLR videographers are happily working with 4:2:0 media, and for some needs this is sufficient. For others, 4:2:2 hits a good compromise between having enough color information for manipulation in post production and smaller files than full 4:4:4 chroma. For the most demanding work, full resolution chroma is absolutely necessary. Keep in mind that you can’t convert upwards—if your media is originated and recorded at 4:2:0, converting to 4:2:2 cannot add back the missing chroma information that was never recorded. These are all things to keep in mind when you’re considering recording formats for your next camera purchase, or designing a post workflow with specific requirements in mind. It may seem like a lot of work to dig into the technicalities, but having a good understanding of these details really sets you free to make good choices that have a real impact on the images you create.Read more
External hard disk recorders like the new Atomos Ninja Star have been very popular. They offer an easy way to record to high quality easy to edit codecs on cameras that would only offer highly compressed quality. cinema5D reader Björn Kurtenbach shared a comparison he shot on a Canon C100 that shows off the difference between highly compressed internal AVCHD recording (which is a 4:2:0 signal) and external ProRes 422 and 422 HQ recording to an Atomos Ninja Star external recorder via the uncompressed HDMI output. Check out the great video comparison below. Which solution do you like better? Please let us know in the comments. Make sure you watch this in HD!!! What we see up here is surprising to say the least. In some moments it seems as though internal AVCHD recording is on par or actually better than ProRes. External on a Sony A7S? I just returned from a shoot with 3 Sony A7S cameras where I also tried to record the feed on an Atomos Ninja Star. Unfortunately at this time the ProRes signal on the Ninja cuts off some highlights and blacks on an A7S so it is not recommended. Sony needs to work on an update on numerous issues with the A7S firmware. Generally I would say the internal Sony A7S encoding is absolutely sufficient for most if not any application. The C100 codec is a lot weaker though.Read more
A few days ago Samsung announced their first video shooting large sensor camera. The Samsung NX1 can shoot 4K on an APS-C sized sensor. Furthermore the camera is the first to make use of the new H.265 codec. What’s remarkable about this camera is not just its price point ($1,499 at B&H) but Samsung’s decision to move with a 4K Super35 sensor (APS-C) into the HVEC H.265 codec space. The new codec succeeds the very common H.264 codec and is capable of providing ProRes quality at 1% of the file size (5Mbit bitrate for 500Mbit video quality). Samsung NX1 product manager Mr. Sung Lae Park also mentioned that the camera would have a clean 4:2:2 hdmi output for external recorders. The camera is avalable for pre-order here: LINKRead more
The firmware update for the Canon 5D Mark III scheduled for April 30 has just been leaked by an unknown source. It enables the camera to output clean HDMI, and according to Canon “HDMI Output makes possible the recording of high-definition uncompressed video data (YCbCr 4:2:2, 8 bit) from the EOS 5D Mark III to an external recorder via the camera’s HDMI terminal”.Read more
We thank our sponsor B&H who has made cinema5D’s news coverage of IBC 2012 possible. Get your gear through B&H to support this platform: www.bhphotovideo.com Jeromy Young and his disk recorders have been featured on cinema5D many times. That is not only because his products are targeted at people who want to get the best out of their cameras for the least amount of dinero, but also because Atomos has a vision and follows it obsessively. They keep close relations with all camera manufacturers and make sure their gear integrates with it in a simple yet effective way. In this interview Jeromy explains in detail why it’s nice to work with a disk recorder like the Ninja 2. It is confirmed that the C100 outputs a 4:2:2 signal through the hdmi port which the Ninja can record via a start-stop trigger signal and save to your editing ready ProRes 422 codec. If you go that route you basically end up with a file that has better compression than a Canon C300, if that is what’s important for you. The Ninja 2 is available for $995: The Canon EOS C100 has just been made available for pre-order. The pricetag says $6499:Read more
By: Sebastian Wöber In this 10 minute video David Shapton, President of Atomos EMEA, gives us an in depth look at the new Atomos Ninja hdmi to ProRes (HQ) recorder that will retail at $995. If you want one you should order now as this product will most likely sell like hot bread! As I told you in my post yesterday a new camera solution for the low budget filmmaker is imminent and will replace the current line of hdslrs in professional productions. We’re talking about a setup that will cost around $5000-$8000 and provide an alternative to cameras like the RED and give you much better results and workflow than a 1Dmk4 or 5D2 can. Yesterday we saw the Blackmagic Hyperdeck Shuttle, a portable device for just $345 that will record video uncompressed via hdmi or sdi onto a solid state drive. This is gamechanging! I will go more into detail in part 3 of this series of posts. Now I would like to present to you the Atomos Ninja which basically does the same as the Blackmagic Hyperdeck Shuttle but will save the recorded feed as ProRes 422 instead of uncompressed. This is good because it will save harddisk space, recompression time and the amount of harddisks you’ll have to use/buy. That means you’ll also save manpower and money over the Blackmagic. The harddisks you’ll be able to use with the Ninja are standard 2.5 inch notebook drives you can already buy for around 60 bucks. Let me break it down for you: Blackmagic: 15 minutes uncompressed (1.6 GB/s) = 180GB = 180GB ssd drive = $480 Atomos: 6 hours ProRes 422 (HQ) (220 MB/s) = 2.5″ 640GB drive = $50 www.atomos.com Thanks to Ralph Merzbach for holding the mic ;)Read more
By: Sebastian Wöber We didn’t think this would ever happen, but if you’re here at NAB 2011 and run around with open eyes and ears you’ll realize there’s a new low budget filmmaking tool right around the corner that will definitely kill the dominance of hdslr in the higher segment (speaking RED alternative) by summer this year. Here’s the first one of several pieces to the puzzle. The Blackmagic HyperDeck Shuttle. Make sure you check back here as I’ll continue this story further on. Let me just get some more interviews with Canon and Phantom here on the last day at NAB.Read more
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