What Is ProRes 4444 XQ? (updated)

Posted on by Larry

[ Updated with new information about the Rec. 2020 color space, and how ProRes 4444 XQ works. ]

Today, Apple released support for a new member of the ProRes family of codecs: ProRes 4444 XQ. This is a new, very high-quality codec, specifically designed for VFX work.

WHAT IS IT?

According to a white paper released this month from Apple:

Apple ProRes 4444 XQ: The highest-quality version of Apple ProRes for 4:4:4:4 image sources (including alpha channels), with a very high data rate to preserve the detail in high-dynamic-range imagery generated by today’s highest-quality digital image sensors. Apple ProRes 4444 XQ preserves dynamic ranges several times greater than the dynamic range of Rec. 709 imagery—even against the rigors of extreme visual effects processing, in which tone-scale blacks or highlights are stretched significantly.  Like standard Apple ProRes 4444, this codec supports up to 12 bits per image channel and up to 16 bits for the alpha channel. Apple ProRes 4444 XQ features a target data rate of approximately 500 Mbps for 4:4:4 sources at 1920 x 1080 and 29.97 fps.

Again, quoting from Apple’s white paper:

Traditionally, digital images have been limited to 8-bit samples. In recent years the number of professional devices and acquisition techniques supporting 10-bit and even 12-bit image samples has increased. 10-bit imagery is now often found in 4:2:2 video sources with professional digital (SDI, HD-SDI or even HDMI) outputs. 4:2:2 video sources rarely exceed 10 bits, but a growing number of 4:4:4 image sources claim 12-bit resolution, though with sensor-derived images the least significant one or two bits may have more noise than signal. 4:4:4 sources include high-end film scanners and film-like digital cameras and can include high-end computer graphics.

Apple ProRes 4444 XQ and Apple ProRes 4444 support image sources up to 12 bits and preserve alpha sample depths up to 16 bits. All Apple ProRes 422 codecs support up to 10-bit image sources, though the best 10-bit quality is obtained with the higher‑bit-rate family members—Apple ProRes 422 and Apple ProRes 422 HQ. (Note: Like Apple ProRes 4444 XQ and Apple ProRes 4444, all Apple ProRes 422 codecs can in fact accept image samples even greater than 10 bits, although such high bit depths are rarely found among 4:2:2 or 4:2:0 video sources.)

ALPHA CHANNELS

Alpha Channels store the transparency information in a clip. Unlike other members of the ProRes family, both Apple ProRes 4444 and ProRes 4444 XQ store alpha data. And, they store it in a mathematically lossless manner.

From Apple’s white paper:

Alpha values are essentially numeric data that specify how to blend, or composite, a foreground image into a background image. For this reason, Apple ProRes 4444 XQ and Apple ProRes 4444 encode alpha values exactly rather than approximately. This kind of exact encoding is called “lossless” (or sometimes “mathematically lossless”) compression. It uses different encoding techniques from those used by the Apple ProRes codec family for RGB or Y’CBCR pixel values, where approximate encoding is acceptable as long as differences from the original are not visible to the viewer and do not affect processing. The Apple ProRes 4444 XQ and Apple ProRes 4444 codecs losslessly encode alpha channel values of any bit depth up to and including 16 bits.

In summary, the Apple ProRes 4444 XQ and Apple ProRes 4444 codecs can be considered “visually lossless” for encoding the Y’CBCR or RGB pixel values intended for viewing, but “mathematically lossless” for encoding the alpha values that specify compositing. As a result, the degree of quality or fidelity is never a question for Apple ProRes 4444 alpha channels because the decoded data always matches the original perfectly.

DATA RATES

ProRes 4444 XQ is not a small file. It is designed for the highest possible quality, while still providing reduced file size when compared to an uncompressed source file.

According to Apple, both 1080i/30 and 720p/60 files require a data transfer rate of about 62 MB/sec, and use about 223 GB to store an hour of material. Other frame rates and images sizes will be somewhat different.

You can download the entire white paper from Apple here.

UPDATE: JULY 1, 2014

A reader asked about the relationship between ProRes 4444 XQ and Rec. 2020.

Rec. 2020 is a color space while ProRes is a codec. ProRes is capable of handling a Rec. 2020 signal, since ProRes can accommodate a wide range of color spaces.

Also, wide color gamut (like Rec. 2020) is different from high dynamic range, as Rec. 2020 is designed for reproducing a wider range of colors than Rec. 709.  For those people working with higher dynamic range footage, the increased data rate of ProRes 4444 XQ is beneficial for capturing the superior tonal range of HDR material like Log C. This is why ARRI is offering ProRes 4444 XQ recording in high-end configurations of the the ALEXA camera, which was announced yesterday.

UPDATE: JULY 15, 2014

Since I first wrote this article, I’ve learned more about ProRes 4444 XQ. It is principally designed for pro cameras that record High Dynamic Range (HDR) video, because the higher data rate of the format preserves the detail in these recordings. It is currently in use as a camera-codec, for example as part of the ARRI ALEXA. But it has benefits all the way through the video post production pipeline — especially for color grading and visual effects as I describe below.

ProRes 4444 XQ records color data — the red, green, and blue values in an image — with greater accuracy; that is, more decimal places. This precision is necessary when you are shooting a clip that you plan to alter with extreme color adjustments in post.

Here’s a simple analogy to illustrate the benefits of ProRes 4444 XQ. Let’s take a pixel recorded in AVCHD (an 8-bit codec) and compare it to a pixel recorded in ProRes 4444 XQ. Say the “true” source pixel value is 7.499, and you are going to apply an adjustment that effectively amplifies the value by 10x.

With lower bit-rate compression like AVCHD, the original 7.499 pixel value might be represented as 7. After the 10x effect is applied, the value becomes 70.

With high bit-rate compression like ProRes 4444 XQ, the original 7.499 pixel value might be 7.5. After the 10x effect is applied, the value becomes 75, which is much closer to the final value of 74.99 that represents perfect precision. Here is a summary:

AVCHD
ProRes 4444 XQ
Starting pixel value
7
7.50
Error
0.499
0.001
Effect
x 10
x 10
Final value
70
75
Error
4.99
0.01

With AVCHD, the difference in starting values between 7 and 7.499 might not be noticeable. But after the effect is applied, the difference between 70 and 74.99 may become significant. With ProRes 4444 XQ, the starting value is so accurate that even after the effect is applied, the error in the final value remains very small.

Because we started with more decimal places in ProRes 4444 XQ, we ended up with more accurate color at the end. This is the benefit that shooting ProRes 4444 XQ provides – more information is recorded at the beginning to allow more flexibility in editing at the end.

As always, let me know what you think.

Larry


16 Responses to What Is ProRes 4444 XQ? (updated)

  1. rd says:

    Yes but OS doesn’t support more than 8-bit color.
    How does FCPX render that?
    Apple doesn’t even sell monitor beyond 8-bit.

    H264 file format doesn’t support either.
    We have to wait for H265 for 10-bit and 12-bit.

    DisplayPort can’t even handle all this bandwidth either.
    not to talk about HDMI.

    Where can they show this in some fancy projection system.

    Besides higher bit rate require higher frame rates as well
    for all this HDR.

    • Larry says:

      RD:

      This isn’t totally true. H-264 is an 8-bit codec, as are many other web-based video formats. However, ProRes, DNxHD, and many RAW formats are 10-bit or greater. Bit-depth support is not OS-dependent, but codec-dependent. There are a number of 10-bit video monitors from companies like Sony, Flanders Scientific, Panasonic and many others that support full 10-bit images via a Thunderbolt or PCI connection.

      Also, bit-depth is not dependent upon frame rate. HDR, by definition, uses a higher bit-depth which is how it is able to achieve its “look.”

      Larry

  2. rd says:

    I am sorry sir,

    DisplayPort 1.2 has 17Gbps bandwidth limit
    HDMI 2.0 has limit of 14 Gbps
    HDMI barely support 4:4:4 16 bit at 4K @ 30 fps
    and only max 4K 4:4:4 8 bit @ 60 fps
    Display Port can do max 4K 4:4:4 10 bit @ 60 fps.

    Even Display Port 1.3 (Not out yet) will be 34 Gbps
    which means 4K 16bit @ 60 fps.

    That is why Thunderbolt 3 coming next year will have
    40 Gbps which is also needs newer version of DisplayPort 1.3.

    10 bit is no good until you can see it. color space (Rec.2020) which supports it.

    24 fps don’t make any sense if you are upgrading one part of the picture
    but not the other.
    3D needs 120 fps, so does VR. Sports needs 60 fps. Games need
    60 fps even CoreAnimation has 60 fps as ideal.
    So we are upgrading resolution and now color but fps don’t matter.
    I find that hard to believe.

    All the TVs are adding interpolated frames to 24 fps to match that TV running at 120 Hz.

    “Codec dependented” don’t make sense when it is the OS/AV Libraries/GPU that is unpacking all the information and sending to the monitor.
    Monitors have no knowledge of codecs.
    TVs only have H264/H265 decoders.

    If OS doesn’t support it. FCPX is not putting it on the screen.
    but is able to send to GPU/OpenGL and third party screen all the bits
    and that is how you are suppose to color grade it.

    • Larry says:

      RD:

      Again, I’m not sure I agree with you. However, I’m willing to do some homework and learn more. I’ve seen far too many demos of 10-bit and HDR media running off a Mac to dismiss 10-bit video as you are. Again, 3rd-party devices such as AJA and Blackmagic Design support capture and playback of higher bit-rate media. And not all files currently being played are 4K images. In fact, there are significant benefits to reducing the pixel count in favor of higher bit depth; as advocated by Dolby in their HDR tests.

      And, true, sports looks better at high frame rates, but in the US, CBS and NBC are both 30 fps networks broadcasting sports. If you are playing files directly from the computer, frame rates vary from 10 fps to 120 fps.

      Larry

    • Stu willis says:

      The mathematical usefulness of higher bit depth for image manipulation is not dependent on the quality of your display to show 10bit or 8bits.

      e.g. You will get different – and much better – results if the rendering engine in After Effects is working in 8bit or working in 32-bit linear.

      I am currently looking at using ProRes XQ to preserve image quality from OpenEXR half-float (16 bit).

      • Larry says:

        Stu:

        You are correct, in that the display does not affect video content. However, unless you can display higher bit depth video, you are not able to see what you are adjusting, which is essential in color grading.

        Larry

  3. Cem Yıldırım says:

    The release of ProRes 4444 XQ codec, implies that Apple is not leaving pro-video world anytime soon.

  4. DWalla says:

    I understand what rd is saying… but he’s missing the entire point of the new codec. It isn’t about displaying high-bit color. It’s about retaining high-bit color for the production world.

    Here’s a case in point. Our cameras all shoot RAW format at our studio. There isn’t a monitor on the planet that can show the full spectrum of what the RAW file is capturing. Even the Wide Gamut monitors cannot do such. HOWEVER, what it does give me is a huge amount of color and light data in which I can manipulate. This is the power of the new codec. So I can store massive amounts of color/detail/light data for post-work. Ultimately everything is output to an 8-bit format (H.264, AVCHD, and even H.265 will be nearly all 8-bit for deliver). Yes, these codecs have the ability store higher amounts of color, but not a single consumer product has even remotely close to the ability to display the additional color space. Compression size is more important for delivery/distribution than deep color space. The point isn’t to get 10-bit or 12-bit color to the consumer, it’s about giving pros the tools they need for content creation.

  5. HERBERT says:

    Muy interesante, hay que continuar investigando

    Very interesting, we further investigate!

  6. srinath says:

    what is dpx bit rate for per image channel and alpha channel

    • Larry says:

      Srinath:

      This is impossible to answer. DPX frame sizes will vary depending upon the frame size of your video, while the alpha channel can be anything from zero – where the entire frame is opaque – to really, really big – if you were rotoscoping a lot of fine detail in an image.

      A DPX frame has no internal limits on frame size, frame rate, or even bit-depth; for example, 16-bit video frames will be 256 times bigger than 8-bit video frames.

      All that being said, assume that a single DPX frame will be dozens of megabytes in size.

      Larry

  7. Larry knows his shit man. I own a Flanders 10bit monitor that runs HD-SDI
    BIT Depth is always going to be the determining factor due to the gradations of color going from 1 bit to the next. Images appear more flesh like. 6K, 4K, and 1080 differ but not that much depending upon your timeline resolution. But those monitors are used by colorist. Where moves are seen at their best quality.

  8. DWalla says:

    Just to be clear, 5K iMacs are actually running 16-bit wide gamut natively in the OS.

    And the wider gamut, with or without the monitor, benefits post work dramatically. For instance, there isn’t a monitor in existence that can display the full gamut capabilities of a DSLR RAW file…. yet you still get tremendous benefits when using that file.

    Even when displaying on an 8-bit monitor will see less banding when producing high-bit color.

  9. Fred Duffer says:

    My 2011 Macbook Pro {8,2} is having a hard time even importing this codec (4444XQ) guess its time to upgrade? Anyway, my head exploded about 5 replies in…

    • Larry says:

      Fred:

      ProRes 4444 XQ generates some seriously large files and there’s almost no reason to use it unless it is a format that your camera shoots natively. Otherwise, ProRes 422 is fine for most low-to-mid-range cameras. ProRes 4444 is best when the media originates on the computer; think Motion, After Effects or screen captures.

      I suspect the problem is with your storage, more than your computer, but, yup, I think you better start saving your pennies for some new gear.

      Larry

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