[RealSense D435i] How to use emitter on/off mode in practice with Python

[zumpchke]

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Required Info
Camera Model	{ R200 / F200 / SR300 / ZR300 / D400 }
Firmware Version	(Open RealSense Viewer --> Click info)
Operating System & Version	{Win (8.1/10) / Linux (Ubuntu 14/16/17) / MacOS
Kernel Version (Linux Only)	(e.g. 4.14.13)
Platform	PC/Raspberry Pi/ NVIDIA Jetson / etc..
SDK Version	{ legacy / 2.. }
Language	{C/C#/labview/nodejs/opencv/pcl/python/unity }
Segment	{Robot/Smartphone/VR/AR/others }

Issue Description

Is the point of emitter on/off mode the ability to get a clean IR image but with accurate depth sensing?

And to do this does the user have to account for account for depth mismatching IR by 1 frame?

[MartyG-RealSense]

Hi @zumpchke Having the emitter on (which projects IR light onto surfaces and adds a semi-random invisible dot pattern to the scene) usually improves depth quality, whilst having the emitter off reduces depth quality unless the scene is strongly illuminated. The camera uses the dots cast onto the surfaces of objects in a scene as a 'texture source' that it can analyze for depth information, as low-texture or no-texture objects (such as doors, walls and tables) will be more difficult for the camera to depth-analyze.

However, for some users' projects it is important for them to have an IR image without a pattern, which is why they capture a frame with the emitter off as well as one with the emitter on.

An IR image will be pixel-perfect aligned, calibrated, and overlapped with the depth map, and also perfectly time-synchronized with it. It is the RGB sensor that is temporally offset from depth, bounded by a period of one frame with the lowest FPS.

If wait_for_frames() is used in a program script then the SDK tries to find the closest timestamp match between different stream types.

[zumpchke]

@MartyG-RealSense So is there a way to get simultaneous streams of depth and IR (with no dots)

[MartyG-RealSense]

You might be able to make a difference to the pattern without completely disabling the emitter if you configure the Advanced Mode's Color Correction Matrix values. The matrix is described at the link below.

https://dev.intelrealsense.com/docs/tuning-depth-cameras-for-best-performance#use-the-left-color-camera

There was also a Visual Preset camera configuration file for doing so called 'Left Imager Color w/o IR Pattern'.

https://dev.intelrealsense.com/docs/d400-series-visual-presets#preset-table

However, this was designed to be used with the D415 camera model rather than D435i. If you wanted to try to replicate this feature on D435i, it might be worth setting the Emitter Always On option to True so that the D435i's IR emitter behaves like the one on the D415 model. By default the D415's emitter is Always On, whilst the default state of the D435i's emitter unless Always On is true is to pulse in line with exposure.

Alternatively, if you wanted no dots then you could disable the emitter by setting the value of the Laser Power option to '0', but you would lose the advantage of the scene-illuminating IR light that the emitter projects.

[MartyG-RealSense]

Hi @zumpchke Do you require further assistance with this case, please? Thanks!