Camera+

Introducing 10-bit… SDR‽‽


Karl Baron

Formerly-globetrotting developer, now settled down in Japan.

Way back in the turbulent days of 2020 Apple released the iPhone 12 series, and in response we released version 2.0 of our pro video recording app REC where we added support for Dolby Vision 10-bit HDR.

Now in REC 3.3, we’re adding a brand-new option ー recording in 10-bit SDR! Wait, what? When we already have 10-bit HDR, why would we add an SDR option?! HDR is better right? Why would you want to shoot in 10-bit SDR video?

Well, first of all let’s go back to the basics. What is 10-bit HDR video? Well, it’s a combination of two different features:

10-bit

This is what gives us more raw data than before out of the camera sensor.

This is what it looked like back when we first got 8 bits per channel color

Now we get 10 bits per color channel instead of the previous standard of 8 bits per channel (that Apple has been using since they introduced the Macintosh Display Card 8•24 over 30 years ago). This means we capture far more more nuanced gradiations in the colors that make up your recording!

How much more? I mean, just 2 bits can’t matter that much?

Well, using 8 bits per channel we just get a measly 256 possible values for each of red, green and blue, adding up to about 16.78 million. That sounds like a lot! But in the case of 10 bits, through the magic of exponents, we get 1024 possible values per channel, boosting the colors we can represent to over 1 billion different colors!

That’s a lot of colors!

Here’s a simulation of what banding looks like compared to a full-color image.

HDR

High Dynamic Range means we’re using a color space that can describe far richer colors.

The displays that were common when the old color standards were introduced were limited in what colors they could reproduce, but technology has moved on with time, and with HDR we get reds that are redder than SDR red and greens are greener than SDR green.

This produces impressive results for many types of footage, but it requires your display and all the steps in between – encoders, streaming services, boxes, and cables to be capable of compressing, transmitting and displaying those richer colors. This is true in the case of your iPhone screen, but many TVs and streaming services still use the older, more limited color palette, where you can’t enjoy this improved range.

And even if you have a modern TV capable of HDR color display, not all of them use the same color format! Apple has chosen the HLG format in combination with Dolby Vision, but many TVs support a competing format called HDR10. This is another format war (we thought the industry finally learned with HD-DVD vs Blu-ray), and the story is similar to earlier format wars where Dolby Vision is more capable, but HDR10 doesn’t require the same onerous licensing.

Here’s another simulation, this time showing the kind of effect you can get when moving from SDR to HDR

10-bit SDR?

So this new setting we’re introducing gives you only the first of these features. We take advantage of the increased sensitivity of the iPhone sensor, but with the same color encoding that is applied to SDR content.

The technical way to describe it would be to say that we are using 10-bit per channel, encoded according to the BT.709 color primaries.

But why?

Why would you want to use a color representation that’s inferior to the one applied in full HDR mode?

One possible reason is that you’re producing content that you know will be targeted to people watching on a service or display that will only display in SDR, such as when you’re targeting a wide range of varying spec smartphones. But the astute observer objects – in that case, you don’t even need 10-bit! YouTube doesn’t even support 10-bit! Almost nothing does!

Well that assumes you don’t plan on editing your video! Having those extra bits gives you far more leeway to tweak your brightness, contrast and colors in post-editing, such as applying those LUTs everyone is raging about. Without the extra color gradiations, you’re likely to exaggerate the color banding inherent in 8-bit video, especially in dark areas (leading to artifacts that will remind people of a certain Season 8 episode of Game of Thrones).

Another advantage is purely practical – that video stored in SDR color mode will require less storage space than the one recorded in wide color.

The status quo

The Camera app that comes with your iPhone records in either “SDR” mode (which means 8 bits and SDR color), or “HDR” (meaning 10 bits and HLG / Dolby Vision).

All Apple gives you is this on/off switch!

REC is able to provide you with more options to cater for a wider variety of situations. In addition, we also offer a wider variety of bit rates, so you can decide the storage vs quality compromise that is best suited for your project.

So what should I do?

As a general guideline, here are our suggestions for how to use the different settings:

  • Use 8-bit if your footage will be watched on SDR devices or color fidelity is not that important, and you’re not planning to any post-processing beyond basic video cuts. Also recommended if you want to optimize storage as much as possible.
  • Use 10-bit if your target is SDR displays or streaming services, or you’re concerned about maximum compatibility, but still want the flexibility to edit your videos with high-quality results.
  • Use 10-bit HDR for the best possible results, but keep in mind that storage will be larger and you may need to export your final project using different formats depending on your audience. Use our “Normal”, “High” or “Max” bit rates in REC to choose the balance between recorded quality and size that is right for your project.

Now have fun and go create some awesome content!

Find out more about REC – the app for cinematic film recording

Published by Karl Baron

Formerly-globetrotting developer, now settled down in Japan.