Starguide - A Practical Guide to Astro-Photography

PixInsight - Comet Processing

 Option d) Creating a Comet Video Clip Using the Blink Process and ffmpeg

updated: 2024-03-09

Purpose

This PixInsight based procedure can be used to assemble a series of pictures into a one small video clip.

Basis for a successful video clip creation are:

• There should be no interruption or pause between the individual frames, or at least the pause between the individual images should always be of the same length
• avoid dithering and automatic autofocus corrections during the capture phase
• avoid Auto Meridian Flips (if possible) because this requires a couple of minutes for 180° equipment rotation and also new plate solving to center the frames to the same picture area as before
• Unfortunately I missed to deactivate dithering and additionally a Meridian Flip occurred after 26 exposures, but this was unavoidable.

The procedure is based on a set of exposures take on Feb. 8, 2023 of the C/2022 E3 comet. Of the original 100 frames captured, 2 frames (#79 and #80) had to be discarded due to a short guiding problem (reason was probably "a star lost" error due to variations of the sight conditions). The resulting video clip is available on  Starlust - Photos  

The post-processing was done in following steps:

• Use PixInsight - Blink Process to select the good frames
• Use Bulk Image Rotation to rotate wrong orientated frames (e.g. due to an meridian flip during the exposure phase)
• Use Debayer Function the pictures (if using an OSC or color CMOS camera)
• Use PixInsight - Blink Process to enhance the picture quality and to generate a video file using the external ffmpeg function
• and finally improving the video quality and reducing the file volume using an external tool like Movavi

Activation

see below

Input

Original light frames from subfolder "Light"

Output

An  AVI or MP4 video  file in subfolder with "Video/selected/rotated/debayer"

Previous Step

• Picture Shooting

Next Steps

• Learning, documentation and publishing 

Step

Description

Action

1

Pre-select good frames with Blink

• Process 🡺 All Processes 🡺 Blink
• see this description how to use Blink
• Move all good files to the subfolder ..Video/selected

2

Rotate wrong orientated frames with Fast Rotation (optional)

This step is required in case your equipment had to do a Meridian Flip during the capturing session.

• Process 🡺 Geometry 🡺 FastRotation
• follow the steps described in the chapter Bulk Image Rotation
• Set the output folder to the subfolder ..Video/selected/rotated

3

 Apply the Debayer function 

• Process 🡺 All Processes 🡺 Debayer
• Apply the debayer function to all rotated frames, see the Debayer Function descrpition.
• Output all debayered frames to the subfolder:  ..Video/selected/rotated/debayer

4

Open Blink again to generate the video file

• Process 🡺 All Processes 🡺 Blink

• activate Apply automatic histogram transformation for all frames.
• Do not activate Compute Auto STF if the quality of the images are too different (changing sky quality over time)
• Click on the film icon to open the video converter window:

4a

Blink Video Converter Settings

• Program: ffmpeg.exe (must be placed into the PixInsisght \bin folder to work)
• Argument examples:

• -y -r 25 -i Blink%05d.png Blink.avi for AVI files
• -y -r 25 -i Blink%05d.png Blink.mp4 for mp4 files
• Framerate: 25 fps, no downscaling applied, scale:  4144x2820 px
• Resulting video file has a size of 234 MBytes (using 98 frames of 4144x2820 px)
• -y -r 10 -i Blink%05d.png -vf scale=1280:800 Comet.mp4
• Framerate: 10 fps, Scale: 1280x800px
• Resulting video file has a size of 8.9 Mbytes.

• Frame file extension: .png (Blink will generate intermediate PNG files that will be used by ffmpeg for the video file generation)
• Some explanations about the ffmpeg parameters used in the example above:

• -y: Overwrite existing files without asking
• -r: frame rate specifier in frames per second
• -i (url) input: Input files, in this example (-i Blink%05d.png) will use file like Blink00001.png to Blink00099.png
• ( Blink.mp4): is the name of the output file generated by ffmpeg

• Some more Important ffmpeg parameters (see also: FFmpeg Commands: 31 Must-Haves for Beginners in 2023 - VideoProc) or ffmpeg Documentation

• Resize:  scale=1280:800 output.mp4
• Frames per second: ffmpeg -i input.mp4 -vf "fps=30" output.mp4
• Loop video:ffmpeg -stream_loop 2 -i input.mp4 -c copy output.mp4

4b

ffmpeg Conversion

When ffmpeg takes over to generate the video file, the processing screen looks like this:

5

More Post-processing

If more post processing is needed, e.g. to increase the contrast or saturation, you can use tools like Movavi. This video converter is easy to handle and provides options for many different target video file formats and devices in addition to water marks on videos and contrast and saturation enhancements..