Crosstalk

In general, crosstalk is when information leaks into an unintended channel. So, at its core, crosstalk is when information shows up where it shouldn't.

In the particular case of stereo 3D, here’s how it works:

1. A 3D display must show at least two slightly different images: one for your left eye, one for your right.
2. The brain merges them, creating the illusion of depth.
3. Crosstalk occurs when this separation isn't perfect - when each eye sees a little bit of the other image. It's like our whisper example, but with light instead of sound: some of the "left eye message" leaks into the right eye, and vice versa.

Why is crosstalk bad?

Crosstalk is bad because it completely can break the 3D effect. Look at the image below. On the left side of our muse Ada, you’ll see a faint ‘ghost’ of her, that’s crosstalk in action. This is why sometimes crosstalk is called ghosting or leakage.

While providinga quality number is diffcult, we can describe the impact of crosstalk quantitatively:

1. A little ghosting? The brain can usually ignore it and still fuse the 3D image. Not a great effect, but still fine for very short moments.
2. Too much ghosting? The brain can’t merge the images anymore so the 3D effect breaks. Worse, if ghosting gets very bad, it gives quite some discomfort.

Why Does Crosstalk Happen?

Crosstalk stems from hardware limitations and is often made worse due to content choices. Here are the most common culprits:

1. Poor Optical and Hardware Design Cheap or poorly designed displays often cut corners on optical quality. And while it is understandable that devices of different quality will exist, sometimes they hide fundamental errors on how light should separate between views. Also, both single viewer a multiple viewers displays combine different hardware components. Because the brain is very good getting 3D clues, all components must work together properly or any error or misalignment will be visible as crosstalk.

2. Extreme Contrast (Black & White) While high-contrast scenes look striking and elegant, they’re a nightmare for stereo 3D. And if the scene has strong depth, then the effect is even worse. This is an issue when designing content that I have seen countless times. Note that even displays with low crosstalk can struggle with pure blacks/whites, creating visible ghosting.

This doesn’t mean that you can’t create a 3D scene using blacks and whites, only that you have to carefully design it to create good 3D.

3. Pushing the Display’s Limits Every 3D display has a "sweet spot" and usually near and far limits are communicated by the manufacturer. In general this is the area where crosstalk is minimized. Ignoring this (e.g., placing viewers too close/far, or too far to the sides) forces the optics to work outside their ideal range, which results in visible crosstalk.

How to Reduce Crosstalk (Practical Tips)

While we can't eliminate crosstalk because it’s related to the optical stack, these strategies help minimize it:

1. Know Display's Limits Cheap 3D displays (like phone attachments) will always have noticeable crosstalk. On the other hand, high-end professional displays will have lower crosstalk and also handle it better with better correction and filters. So chose your target and then adjust your content accordingly.

2. Ditch Extreme Contrast Avoid pure black/white scenes with strong depth effects, they maximize ghosting. Use complementary colors instead, they work better with anti-crosstalk filters. But if you must use black/white, either try to find stereo 3D displays that use OLED panels that handle contrast better than LCD or restrict high contrast to low depth areas. For example, a black box with white text in the 2D UI.

3. Test Early, Test Often Always preview your content on the actual target display. Don't rely on monitors, VR headsets or even similar stereo 3D displays, because each device shows crosstalk differently. If you can’t test on every target display, at least try to find the edge cases to have a worse and best case scenarios.