Stitcher element Additional Details

Image Stitching for NVIDIA®Jetson™
Before Starting
Image Stitching Basics
Stitching Projections
Overview
Stitcher Projector Typical Applications Limitations and known issues
Getting Started
Evaluating the Stitcher Getting the code Building Image Stitching
User Guide
Quick Start Guide Controlling the Stitcher Calibration GStreamer Additional details
Resources
3D bases Panoramic data 360 data
Examples
Basic pipelines Using Gstd Other pipelines
Spherical Video
About Equirectangular Projection Projector Building Projector Stitcher Calibration Tool
Performance
Orin Xavier Nano
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Additional Details

This wiki holds some additional notes and useful details to consider when using the stitcher element.

360 Video

In the case of 360 video stitching, the output video file can be displayed as a 360 degree video. The following command writes the spherical tag in the video file:

exiftool -XMP-GSpherical:Spherical="true" file.mp4

With the spherical tag video players like VLC will recognize and display the video as a 360 degree video.

Video Cropping

The stitcher element applies multiple transformations to the target sources in order to achieve a seamless match with the target. These transformations can in some cases distort the output resolution and provide an image that is a different size and shape than desired. The image below represents an example of this behavior:

before videocrop example

To crop the stitcher's output into the expected resolutions Gstreamer's videocrop element can be used. This element takes 4 main parameters (top, bottom, left, right) specifying the number of pixels to remove from each side respectively.

The basic idea for determining these parameters is to take the original (without cropping) output of the stitcher, and based on its dimensions, subtract from each side accordingly.

Using videocrop after the stitcher on your pipeline can reduce the output to only what is needed. The original image can then turn into:

after videocrop example

If you want to crop the output for the stitcher element you should add a videocrop element at the output and determine its parameters.

Obtain the following information:

• $width_{full}$: the full width of the image without cropping; same as the stitcher element.
• $height_{full}$: the full height of the image without cropping; same as the stitcher element.
• $width_{crop}$: the cropped width of the image, the same as the desired output.
• $height_{crop}$: the cropped height of the image, the same as the desired output.

From there the videocrop parameters can be determined:

• top: ${\frac {(height_{full}-height_{crop})}{2}}$

• bottom: ${\frac {(height_{full}-height_{crop})}{2}}$

• left: $(width_{full}-width_{crop})$.

• right: $(width_{full}-width_{crop})$.

The formulas for top and bottom parameters assume that the transformation produced deformation symmetrically in the vertical dimension; that is usually the case if cameras are parallel to one another; however, depending on your use case; you might need to adjust the proportion between the top and bottom accordingly.

That 50/50 assumption is usually a good place to start and adjust from there according to the output.