Hot Pixel detection doesn't seem to work

[udoo]

Hello

I followed the tutorial on https://affinity.serif.com/en-gb/tutorials/photo/desktop/video/504454921/ and fail with the automatic hot/cold pixel detection for some FITS file I took last night. There are definitely hot and cold pixels, but no matter what threshold I set for hot and cold pixels, no automatic detection takes place. "Detect hot pixels" and "Detect cold pixels" are both checked as well as "show bad pixels" and "mode" is set to "pixels". I can select bad pixels manually, but - as I said before - there is no automatic detection.

A few more points that might be important:

My system:

• Affinity Photo 1.10.4 trial version
• MacBook Pro (14", 2021) with Apple M1 Pro chip
• macos 12.2.1

The FITS files are pre-calibrated by the telescope/astrophotography software.

 

[stokerg]

Hi @udooand Welcome to the Forums,

Could you upload the images you are using to our Dropbox here and i can see if i can replicate the problem and get it logged with the Dev team  

[udoo]

Hi @stokerg,

Thanks for taking care of my problem! As you asked I have uploaded two samples files (one taken by a color ccd and the other one taken by a monochrome camera). Additionally, I uploaded a screenshot showing a spot in the upper left corner with a hotpixel in the rgb file.

Best regards

Udo

[stokerg]

Hi @udoo,

Can you upload all of the images (lights, darks ect...) you are using for your stack to the Dropbox link? As it's a combination of all of the images used in the stack which identifies the hot/cold pixels. 

[udoo]

Hi @stokerg,

 I took the images at itelescope.net and they are already pre-calibrated, so one doesn't have to deal with calibration images.

But shouldn't it just work with lights only?
Does Affinity need multiple images to detect hot pixels? I tried it with a stack of two calibrated "lights" images (I uploaded them to the link you sent me) but it didn't work either.

Best regards

Udo

 

[James Ritson]

Hi @udoo, a couple of things to note:

• For sigma clipping to be effective, you need to provide at least three images so that the pixel ranges can be evaluated, and outlier pixels can be rejected
• The default sigma clipping threshold of 3 is usually too conservative for most mono image data—try reducing it to 2 before stacking

Pre-calibrated data does not require additional calibration frames, but you will often find that the calibrated frames (e.g. from iTelescope, Telescope Live) still contain a myriad of hot pixels and inconsistent pixels. That's where sigma clipping comes in—as noted above, the default value of 3 will probably leave you with unwanted hot pixels, so try reducing the value and stacking again until you get a good result. When you repeat the stacking process, it will be significantly quicker since Photo has already registered and aligned the data for stacking.

You will really need more than three images for effective outlier pixel rejection—have you got a sufficient amount of captured data for this?

Hope that helps,
James

[udoo]

Hi @stokerg,

arg, you should not do this at the same time as your actual work

Sorry I may be confusing you, but now I've uploaded another stack of 4 calibrated images (monochrome with red filter):

• calibrated-T24-udoo-0019P-20220214-183235-Red-BIN1-W-120-001.fit
• calibrated-T24-udoo-0019P-20220214-184122-Red-BIN1-W-120-001.fit
• calibrated-T24-udoo-0019P-20220214-184952-Red-BIN1-W-120-001.fit
• calibrated-T24-udoo-0019P-20220214-185816-Red-BIN1-W-120-001.fit

regards,
Udo

[udoo]

Hi @stokerg,

would it be possible to send me a stack of files where it should work from your point of view, and I'll give it a try on my side?

 

Best regards

Udo

Edited February 16, 2022 by udoo

[stokerg]

@udoo,

Please see the reply from our resident expert on Astrophotography  

[udoo]

Hi @stokerg, @James Ritson,

your advice is very much appreciated! 🙂 Especially the hint on the sigma clipping threshold is very helpful.

As quoted above, I also tried with 4 images and I even have an example with 6 images per color channel (but they are not mine and I don't know if I am allowed to upload them). But no matter how hard I try, I can't get the hot pixel detection to work 😞

How do we get ahead here? Would it be possible for me to try an example from you guys?If it works, then the fault was mine, and if it does not work, then it is either a software bug or the combination of Affinity and my system.

Are there any log files from Affinity that could help?

I would like to buy Affinity if it works for me.

Best regards

Udo