Why the Blink Tool in PixInsight is so Darn Handy

The Blink tool in PixInisght is a fantastic way to review your individual image frames on a target. This pre-processing tool allows you to isolate and dispose of poor image frames quickly.

Even if you do not use PixInsight for any other pre-processing steps (such as image stacking and calibration), the Blink tool is a useful tool to review your image data. I use this tool to filter out the bad sub-frames from my image set before stacking in DeepSkyStacker.

The Blink Tool in PixInsight let’s you watch an animation of your image frames.

Frames that include star trailing, clouds, satellites, poor focus, and more stick out like a sore thumb when you press the “play animation” button. Because this tool makes errors so obvious (when watching the animation) this tool may help you diagnose issues with your tracking telescope and/or polar alignment.

For a deep-sky astrophotography session, the Blink tool in PixInsight is the best way to review your image data at a glance. This tool works well for images taken with both a DSLR/mirrorless camera and a dedicated astronomy camera.

The process of removing the “bad frames” from your imaging session can be a humbling and possibly painful experience. Removing half of the precious exposure time you collected (or more) due to tracking errors or weather is not pleasant.

However, you certainly don’t want to include this data in your final image, as the added exposure time can not make up for the poor quality data. You are always better off with less overall integration time, using only your best frames. Remember that one.

How to Use the Blink Tool in PixInsight

To open a set of image frames in the Blink tool, navigate to Process > All Processes > Blink.

Once the Blink tool is open, click the little yellow folder icon at the bottom left of the dialog box to open up a set of image frames. By default, your image frames will have an Automatic Screen Transfer Function (AutoSTF) applied to them.

This is a handy feature, as you will be able to review the images in a much more practical way than you would by just reviewing the raw, linear (unstretched) image files. This is especially useful when reviewing the .FIT file type produced by a dedicated astronomy camera.

To open a set of image frames, click the yellow folder at the bottom left of the Blink tool dialog box.

STF

The “compute AutoSTF” button is applied to your image files by default.

I like to open up a large image window of my data and zoom in to about 100%. This way, I can see the detail of the stars, which is often a good indication of the image quality overall.

An image that may look “okay” from a glance, often does not live up to your standards when viewed up-close. It is important to remove these frames from your overall stack (integration) and not include them in your master image.

Video: Evaluate your Images using Blink

In the following video by Shawn Neilson, you’ll get a hands-on look at how the Blink tool works, and when you would want to use it in your astrophotography process:

Find Your Best Data

How you sort and organize the image frames is up to you. The idea is to pull the best data out of the folder to a new location, containing your absolute best data.

You have to option of copying the best image files to a new location or moving them. Although it uses more disk space, I tend to copy the files to a new location to maintain the original folder of all the frames captured.

I like to go through the image frames carefully and remove the worst frames by clicking the “close selected images” button. Then, I can select all of the files that are still open, and click the “copy selected files to a new location” button.

I almost always name this folder “good lights”. It doesn’t get more descriptive than that.

You may find it easiest to use to arrow keys of your keyboard to move between the images. This process moves at a much slower pace than playing the animation, but it is more precise.

If there is a batch of multiple image frames with issues (poor focus, passing clouds), you can select multiple frames at a time and remove them all at once.

Which Speed to Play the Animation?

I prefer to set the animation to 0.5 seconds and watch for passing clouds, and moments of poor tracking. This is especially useful when reviewing data captured on a star tracker without the use of autoguiding.

The inherent periodic error of the mount (without correction via autoguiding) will inevitably reveal itself over the course of an imaging session, especially when shooting at longer focal lengths. Even a precise polar alignment can’t get around this.

However, you should have a success rate of at least 75-80% (images with pinpoint stars) if your polar alignment and balance of the rig have been carefully tuned. But that’s just the tracking…

You may notice that your images have “fallen” out of focus over time as temperatures change, and your telescope points in a higher direction in the sky. Obviously, taking precautions to avoid this is preferred, but reviewing your image frames in Blink will tell the true story.

My image frames in the Andromeda Galaxy are out of focus!

PixInsight Blink Tool vs. DeepSkyStacker

Once you have successfully separated the best quality data from your image set, you are ready to stack the images in your preferred pre-processing tool. Currently, I prefer to stack and calibrate my datasets in DeepSkyStacker.

DeepSkyStacker has its own “scoring” tool to help your find and isolate your best image frames. It designates a score to each of your image frames based on a number of factors (numbers of stars, FWHM, sky background, etc.).

Using the scoring feature in DeepSkyStacker is useful but less visual.

Then, you can choose to only stack the image frames above a certain threshold (minimum score value) to only integrate your absolute best data. The problem with this system is that it is a lot less visual, and feels more like a guessing game.

The Blink tool animation makes subtle, brief dips in sky quality or tracking obvious, and it is the preferred method for most seasoned astrophotographers.

Additional Uses

The Image Blink tool is also a great way to look for things in space that do not appear all the time! This includes Supernova, Near Earth Objects, Comets, and more.

If you have image frames that include a comet in them at high magnification, you can play the blink animation to watch it move across the field. You can even export the animation video to share and save by recording your screen using an external tool such as IceCream Screen Recorder or a similar tool.

If you want to learn more about astrophotography image processing, check out my premium guide with over 100 pages of detailed instruction:

Helpful Resources:

Software for Astrophotography (AstroBackyard Resources Page)
Blink Tool Behaviour (Discussion in the PixInsight Forum)
Image Blinking (Tutorial Article by AstroGazer)