<p>Those are probably just &quot;hot pixels&quot; that don't move on the sensor like the real stars do, so that the stacking spread them out in an arc.</p>
<p>I don't think the software processes and treats each star separately, they can't be &quot;skipped stars&quot; mingled with &quot;recognized stars&quot;. Notice that they are all 1 pixel wide, whereas stars are much wider.</p>

CC BY-SA 4.0
2021-05-06T13:11:17.820Z
Not thinking of a "deliberate" separate treatment but I was thinking of somehow different sets. But your idea of hot spots is quite sensible. As I understand the software could make arcs and not straight strikes because (relative to) of the arc motion that it fixes. Is this that you mean?
Alchimista
CC BY-SA 4.0
2021-05-06T14:06:45.367Z
@Alchimista yes that's just what I mean; the stars move in arcs that are all centered on the north or south celestial poles. Stacking rotates the images around a point to make them line up, and so the fixed hot pixels end up rotating instead. Most cell phone software masks out the hot pixels in the sensor when it makes JPEGs for us, but these are .dng (raw data) images so the hot pixel artifacts are clearly visible. If you look at a single .dng very closely and carefully you should be able to see them.
uhoh
CC BY-SA 4.0
2021-05-06T14:41:51.210Z
I must consider a most careful use of dark frames and base etc... I think yours is the explanation...  @uhoh
Alchimista
CC BY-SA 4.0
2021-05-06T14:45:08.390Z
@Alchimista I'll recommend somehow closing the cross-posted duplicate in Photography SE to avoid answer-fragmentation.
uhoh
CC BY-SA 4.0
2021-05-06T14:52:07.767Z
see my comment to fasterthanlight. I think I can manage this, at least for a while.
Alchimista
CC BY-SA 4.0
2021-05-07T08:15:50.660Z
I noticed that, giving that the camera was pointing about South and latitude was about 47 N, the arcs have the wrong curvature. This seems to me a proof that the points were indeed not moving and sequator did a good job. Does this simply geometrical reasoning proof or corroborate your answer? They should indeed acquire that curvature as opposed to that of the apparent motion of stars, when the latter is removed.
Alchimista
CC BY-SA 4.0
2021-05-07T12:59:18.153Z
hang on, I'm trying to use [Astronmetry.net](https://astronomy.stackexchange.com/q/33575/7982) to figure out where this is exacly...
uhoh
CC BY-SA 4.0
2021-05-07T13:29:22.720Z
aim was Berenice, which is indeed there in the right half of the photo middle height. Latitude perhaps 43 N not 47. But the geometrical reasoning seems linear (although I don't know the details of Sequator algorithm, it make sense that if it fixes something moving along a concave arc, it makes a convex arc of something immobile, or viceversa....). I am really convinced of your answer.
Alchimista
CC BY-SA 4.0
2021-05-07T14:40:34.540Z
@Alchimista I see, How much time is there between the first and last exposure?
uhoh
CC BY-SA 4.0
2021-05-07T15:26:55.073Z
100 frame 2 sec each separated by 1 sec. About 300 if the apps worked smoothly. But I think your answer is correct ( even if it would be another reason :)) because  it makes much sense.
Alchimista
CC BY-SA 4.0
2021-05-07T16:58:58.460Z
unrelated to the Q/A. I've tried astronometry but it failed telling me about objects in the south emisphere while it was a clear pic of Orion :))
Alchimista
CC BY-SA 4.0
2021-05-06T13:02:55.020Z
2021-05-06T13:02:55.020Z
uhoh
<p>Stacking by <a href="https://sites.google.com/view/sequator/" rel="nofollow noreferrer">Sequator</a> 100 <a href="https://en.wikipedia.org/wiki/Digital_Negative" rel="nofollow noreferrer">dng</a> photos of night sky taken with a smartphone resulted in a (beautiful, I would say) populated star field where undesired arc streaks are seen all over the field. It is like as the program treated the vast majority of stars as wanted, while (perhaps the less brighter) others are just rendered as they moved along the 100 frames period.</p>
<p>Align stars was chosen then accumulation.</p>
<p><strong>Question:</strong> Is this a common problem using Sequator, or at least happened to some of you? Is there any trivial setting or way to redo the stacking? Thanks.</p>
<p>Attached is a compressed copy of the final photo. </p>
<p><a href="https://i.sstatic.net/OfHVH.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/OfHVH.jpg" alt="enter image description here" /></a></p>
<p><strong>the above is cross posted</strong> in Photography SE</p>
<p><a href="https://photo.stackexchange.com/questions/124748/arcs-in-stacked-star-field">https://photo.stackexchange.com/questions/124748/arcs-in-stacked-star-field</a></p>

CC BY-SA 4.0
2021-05-06T12:40:40.447Z
Cross-posting is generally frowned upon, as you may receive answers on both sites and users may not be able to find other good answers related to it.
WarpPrime
CC BY-SA 4.0
2021-05-06T13:00:40.630Z
I wonder if those are just "hot pixels" that don't move on the sensor like the real stars do, so that the stacking spread them out in an arc. I don't think the software processes each star separately, they can't be "skipped stars" mingled with "recognized stars". Notice that they are all probably 1 pixel wide, whereas stars are much wider.
uhoh
CC BY-SA 4.0
2021-05-06T13:13:30.923Z
@fasterthanlight I am aware therefore I have signalled the occurrence. I am also thinking of joining the more relevant material by future editing.
Alchimista
<photography><image-processing><post-processing>
Streaks on a stacked star field
Alchimista
# Streaks on a stacked star field

(Asked by: username_0 on 2021-05-06)

Stacking by [Sequator](https://sites.google.com/view/sequator/) 100 [dng](https://en.wikipedia.org/wiki/Digital_Negative) photos of night sky taken with a smartphone resulted in a (beautiful, I would say) populated star field where undesired arc streaks are seen all over the field. It is like as the program treated the vast majority of stars as wanted, while (perhaps the less brighter) others are just rendered as they moved along the 100 frames period.

Align stars was chosen then accumulation.

**Question:** Is this a common problem using Sequator, or at least happened to some of you? Is there any trivial setting or way to redo the stacking? Thanks.

Attached is a compressed copy of the final photo.

[![enter image description here](https://i.sstatic.net/OfHVH.jpg)](https://i.sstatic.net/OfHVH.jpg)

**the above is cross posted** in Photography SE

<https://photo.stackexchange.com/questions/124748/arcs-in-stacked-star-field>

**Tags:** photography, image-processing, post-processing
> **Comments:**
> **username_1**: Cross-posting is generally frowned upon, as you may receive answers on both sites and users may not be able to find other good answers related to it.  
> **username_2**: I wonder if those are just "hot pixels" that don't move on the sensor like the real stars do, so that the stacking spread them out in an arc. I don't think the software processes each star separately, they can't be "skipped stars" mingled with "recognized stars". Notice that they are all probably 1 pixel wide, whereas stars are much wider.  
> **username_0**: @fasterthanlight I am aware therefore I have signalled the occurrence. I am also thinking of joining the more relevant material by future editing.  

---

## 1 answers

### Answer by username_2 on 2021-05-06. Score: 4 | Accepted answer

Those are probably just "hot pixels" that don't move on the sensor like the real stars do, so that the stacking spread them out in an arc.

I don't think the software processes and treats each star separately, they can't be "skipped stars" mingled with "recognized stars". Notice that they are all 1 pixel wide, whereas stars are much wider.

> **Comments:**
> **username_0**: Not thinking of a "deliberate" separate treatment but I was thinking of somehow different sets. But your idea of hot spots is quite sensible. As I understand the software could make arcs and not straight strikes because (relative to) of the arc motion that it fixes. Is this that you mean?  
> **username_2**: @Alchimista yes that's just what I mean; the stars move in arcs that are all centered on the north or south celestial poles. Stacking rotates the images around a point to make them line up, and so the fixed hot pixels end up rotating instead. Most cell phone software masks out the hot pixels in the sensor when it makes JPEGs for us, but these are .dng (raw data) images so the hot pixel artifacts are clearly visible. If you look at a single .dng very closely and carefully you should be able to see them.  
> **username_0**: I must consider a most careful use of dark frames and base etc... I think yours is the explanation...  @uhoh  
> **username_2**: @Alchimista I'll recommend somehow closing the cross-posted duplicate in Photography SE to avoid answer-fragmentation.  
> **username_0**: see my comment to fasterthanlight. I think I can manage this, at least for a while.  
> **username_0**: I noticed that, giving that the camera was pointing about South and latitude was about 47 N, the arcs have the wrong curvature. This seems to me a proof that the points were indeed not moving and sequator did a good job. Does this simply geometrical reasoning proof or corroborate your answer? They should indeed acquire that curvature as opposed to that of the apparent motion of stars, when the latter is removed.  
> **username_2**: hang on, I'm trying to use [Astronmetry.net](https://astronomy.stackexchange.com/q/33575/7982) to figure out where this is exacly...  
> **username_0**: aim was Berenice, which is indeed there in the right half of the photo middle height. Latitude perhaps 43 N not 47. But the geometrical reasoning seems linear (although I don't know the details of Sequator algorithm, it make sense that if it fixes something moving along a concave arc, it makes a convex arc of something immobile, or viceversa....). I am really convinced of your answer.  
> **username_2**: @Alchimista I see, How much time is there between the first and last exposure?  
> **username_0**: 100 frame 2 sec each separated by 1 sec. About 300 if the apps worked smoothly. But I think your answer is correct ( even if it would be another reason :)) because  it makes much sense.  
> **username_0**: unrelated to the Q/A. I've tried astronometry but it failed telling me about objects in the south emisphere while it was a clear pic of Orion :))  

---

