An Intro to Louper Color Accuracy

We've partnered with expert colorist José Maria Abreu Santos to help us run a series of end-to-end color pipeline tests to shed some light on the color accuracy of Louper. This is by no means a definitive a post, and due to the nature of viewing devices & environments, future product updates and more, we expect this information to change and evolve over time.

TLDR: With a correctly configured pipeline, Louper does not add any color shifts or processing to livestream signals. However, different client browsers and devices may render signals differently.

Target Codec & Format

Louper currently supports the streaming and viewing of H.264 8-bit 4:2:0 SDR streams in all major browsers. Color accuracy tests were performed and recommendations made based on this format.

In the future, codecs like AV1 will enable the ability to stream and view up to 12-bit 4:4:4 HDR streams directly in the browser - and you can be sure that Louper will support those workflows.

But for now, H.264 8-bit 4:2:0 SDR is what Louper supports. Many users report that this is sufficient for a variety of work, especially work that is destined for the web.

Hardware & Software

Grading & Testing System

• Davinci Resolve v18.0.3
• Blackmagic Decklink 4K Extreme 12G
• Blackmagic UltraStudio Recorder 3G
• LBS v1.3.1
• ColorSpace v1.0.0.1472
• LightSpace Connect v5.2 (566)
• xRite i1 Display Pro
• Windows 10

Since signals are being handled by Blackmagic hardware, there should be no difference in signal processing on the source side between macOS and Windows systems.

Pipeline Setup

There are a variety of ways to get a signal into LBS (from where it is streamed to a Louper room). We tested a number of them, including NDI, to determine which offer the best color accuracy.

We found that using a Blackmagic Ultrastudio or Decklink I/O card in conjunction with LBS offered the best color-accuracy. This option has the distinct advantage that many colorists already possess such I/O cards. The cheapest model, the UltraStudio Recorder 3G, can be had for around $150.

The two pipelines we settled on were:

1. Davinci Resolve -> Blackmagic Decklink 4K Extreme 12G (signal looped) -> LBS -> Viewing Device

2. Davinci Resolve -> Blackmagic Decklink 4K Extreme 12G -> UltraStudio Recorder 3G -> LBS -> Viewing Device

LBS Settings - Blackmagic Source

In LBS, we added a Blackmagic Device as a source in LBS and configured the following:

• Mode: Auto
• Color Space: BT.709
• Color Range: Partial (this can be set to Full if you are working with a Full range signal in Resolve)

Confirming Platform Color Accuracy

In order to establish that there is no color shift being applied to livestreams by the Louper platform, we measured a signal being sent from Davinci Resolve via over HDMI to an EIZO CG279X display and compared it to the measurement of the stream being viewed in the Louper player via Chrome on the same monitor.

Profiles

Blackmagic Decklink 4K Extreme -> HDMI -> EIZO CG279X

dE00 Coverage

<1: 520 (97.56%)
>1 <2.3: 13 (2.44%)
>2.3: 0 (0.00%)

dE00 Limits
Min: 0.1461
Max: 2.0936
Avg: 0.4850

Chrome Browser -> GPU -> HDMI -> EIZO CG279X

dE00 Coverage

<1: 514 (96.25%)
>1 <2.3: 20 (3.75%)
>2.3: 0 (0.00%)

dE00 Limits
Min: 0.0436
Max: 2.2543
Avg: 0.4635

What This Means

What this data allows us to verify is that there are no significant color shifts or image alterations added by the Louper platform when streaming.

By measuring the same display twice, through a “proper” signal image path and though the Louper player, we can establish that there are no significant differences between the two viewing pipelines. Although there are minor differences in the Delta E’s between the two profiles, those can be attributed to rounding errors or probe/display heating derived drift.

Viewing Devices and Trusting Your Colorist

With most clients, it's the wild west out there in terms of viewing devices, environments and software versions. We regularly hear from Louper users that their clients are viewing livestreams in offices with mixed lighting, sometimes on subpar internet connections using Macbook Pros or iPads or even iPhones. For many types of jobs, this is not a huge issue as often these are the devices on which the end product will be viewed.

In such circumstances, there is definitely a point at which the livestream signal needs to be "close enough" to the source and where super fine color adjustments should be left in the hands of the colorist, who has the correct hardware, reference displays and a properly calibrated environment.

There may also be differences in the ways that browsers on different devices interpret video color or gamma. For that reason, we highly recommend that colorists test their signal path and view their Louper livestreams on the same devices their clients use.

Wrapping Up

Ensuring that your signal path and client devices are configured correctly will result in a viewing experience that can be used to achieve sufficient accuracy for SDR 4:2:0 streams.

In the future, Louper will support 4:2:2 10-bit (and higher) streams, as well as HDR, with innovative ways to ensure color accuracy across browsers!