Q & A

What is the purpose of Sequator?

A simple, easy and friendly toolkit for star photography.

I don't like maze. I don't like too many confusing choices. I don't like boring trials. I don't like waiting. I only need a simple tool which can efficiently & effectively do my process. In addition, I need some functions helpful for stacking & pre-processing.

So I realized my thought with Sequator, and shared with people.

Why not add more functions into Sequator?

First of all, I hope Sequator can be kept simple. As there are already many post-processing programs, user does not need another Photoshop or PixInsight. Therefore I selected most valuable, unique features into Sequator. If some processing can be easily done with other existing programs, I won't implement it.

On the other hand, it will be limited by my resource. And I am allowed to develop Sequator only on free weekends or to sacrifice my sleep.

"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away."

- Antoine de Saint-Exupery, a French poet

Opposite to what Sequator does not have, any uniqueness does Sequator have?

If you are seeking a free image processing program, try GIMP.

Will Sequator be a replacement of DSS or existing stacking software?

No, it is not the purpose of Sequator.

I developed Sequator only because I can not stand for the complexity or ineffectiveness of existing software. This does not imply you must have the same thought. Sequator tries to suppress the learning curve to beginners. Sequator does effectively for most circumstances. The efficiency of Sequator saves your time, save the power, and then save polar bears finally. :)

Even I did my best, Sequator may be limited by my experience and resource. If existing software is suitable to you & works well, you don't have to abandon it. Select the most useful program according to your condition. Of course, if you encounter any problem or think Sequator can be better, welcome to give feedback and discuss with me.

Sequator does not work as my expectation, what's wrong?

Maybe you forgot to read the manual. Some common issues:

- Bad stacking quality: did not specify sky mask for freeze ground; did not fix exposure parameters(ISO, WB, ...)

- Unexpected contrast/color: too strong or improper light pollution filter setting

- False corner star trails: did not enable distortion correction

- Halo / middle circle: did not correct vignetting or improper vignetting images. Note vignetting images must be taken with exactly the same lens, aperture and focus length

- Too bright stars: improperly enhanced star light

- No noise reduction: stacked with the same frame

- Image downsized: because enabled merge pixels

- Failed to align: stars out of focus, under/over-exposed sky, significantly trailed stars, unsupported TIFF compressed data

- Unnatural sky glow above darker foreground: try intelligently-aggressive

- Vignetting images are rejected: image resolution does not match the input

- Missing DLLs: you didn't extract all files into a normal folder

Known Incompatible or Unsupported:

- TIFF exported by ON1

- ProPhoto RGB

Why is the color of result different from the RAW imported into PhotoShop?

Every program may have its own color preference or tuning. The raw decoding library used by Sequator(LibRaw), will try to recover the white balance recorded by the camera, from the raw file. If you hope the color is exactly the same as another program, you can export to 16-bit TIFF by the program first, then perform stacking.

Remind, do not change the linearity of data or apply any effect while exporting.

The jpeg or the thumbnail embedded in the raw is already processed by the camera. But stacking prefers original raw data for mathematical correctness.

Why no score system?

Hmm... not just because it is not another DSS. With some observations, I found a simple index is too rough. Consider:

- How if a thin cloud passed through the sky?

- How if an aircraft flied across?

- How if a bright star rise from the image corner?

- How if the star dense area goes from center to corner? or from corner to center?

- How if a firework suddenly lighten the background?

... etc

Simple index can not identify similar quality issues. Many and many cases, it will be wrong and easily lead to misunderstanding. I don't have good solution yet so I left the problem to manually review.

The "select best pixels" implements sigma-clipping method. It is a good mathematical rejection method and may mitigate the problem.

How to eliminate walking noises?

You have 3 options in Sequator:

1. Provide proper noise images

2. If you don't have noise image, turn on "remove dynamic pixels"

3. Try "select best pixels"

Why does Sequator not support median?

Sequator strictly picks best methods and discards others. As sigma-clipping average is much better than median in most cases, also more flexible, and the implementation is sufficiently fast, you won't need median anymore.

Why does Sequator not support bias frame?

1. Bias is included in dark frame. When subtract dark frame, the bias is also subtracted

2. Modern DSLRs are well-calibrated. Bias is relatively too tiny(almost 0) and unobservable in flat frame. If you insist bias to correct flats, why do you think dark of flat is unnecessary?

3. Difficult concept & often lead to mistakes. Unless every photographer really understands the system of his camera (Yes, the raw file of a modern camera is not as "raw" as you think)

Over-exposure/over-saturation on some objects?

You may try:

1. Disable "auto brightness" but only enable "HDR." The "auto brightness" allows slight over-exposure sometimes. HDR-only will carefully calculate to reserve values; however, the image may be darker.

2. If no improvement, change the color space to "linear." By following the standard of sRGB/AdobeRGB, Sequator has to adjust the tone curve before saving. The "linear" option can force Sequator to output linear data, but you have to adjust the tone curve by yourself on post-processing software.

Stitch first or stack first for panorama?

Stack first. Panorama program may destroy the linearity of data, and introduce inconsistent object movements or fusions.

Why does Sequator ignore light-painted shot while stacking?

Only one light-painted shot will be considered as noise. Sequator can not distinguish between intentionally illuminated foreground and merely brighter noise. If you really need a brighter foreground, you have to:

1. Identically illuminate all shots (trigger flash every time)

2. Adjust tone curve after stacking

3. Post composite but lose the benefit of stacking

Single light painting works on star trails mode.

Can Sequator provide a smaller brush for the mask? Why no zoom function?

The method used by Sequator is different from people's imagination. "Freeze ground" does not need a precise mask. The algorithm has the ability to detect moving pixels & select stable pixels, perform intelligent interpolation. So that it automatically works for complex foreground, near-horizon fog, and sky glow. You only have to specify the mask roughly, around the trees.

Can the "Freeze ground" support tracked images?

No, sorry. It was developed for stable shots on a tripod.

Will Sequator support other platform, such as Mac, iOS, or Android?

No plan yet. I don't have resource to develop on multiple platforms. On the other hand, I don't have sufficient time to migrate & maintain.

Is Sequator open source project?

No, sorry.