Sharpcap saving multiple images while dithering?

[longinthetooth]

Sharpcap v4.1.12893
PHD2 v2.6.13
ZWO ASI1600mc Pro
Just started with guiding and dithering. No more walking noise! I am, however, perplexed by the following.
I took 90 x 3 minute subs of M31 but ended up with 420 images.
I had set dithering to take place after every 4 frames.
Looking at the text file for each image - frames 1 to 4 are all different but are then followed by 8 frames which appear to be identical to frame 4. This pattern repeats after every 4 frames although the number of duplicates is not always the same. I'm assuming this is a dithering issue since I haven't encountered it before.
I examined the subs using Pixinsight Blink and all look pretty similar - there are none which look like short exposures.
How can I prevent the duplication of images?
Stacklog attached
Thanks in anticipation.
JB

[admin]

Hi,

I think all you need to do is to change the option of which frames Live Stacking should save - there is a drop down to control the saving of raw frames and the four options are

Save None
Save Stacked
Save except when Paused/Dithering
Save All

I suspect you have 'Save All' selected, which is doing what it is supposed to do - if you are using dithering then either of the middle two are the options to use.

cheers,

Robin

[longinthetooth]

Thank you! That makes sense.
JB

[Alan_]

I discovered the same problem but I found that copies of the last frame were being saved. So if 5 frames of 60s are taken, during the following dither and settle about 5 additional copies of the last 60s frame are saved. During dither short subs are taken, for each short sub a copy of the last long sub is saved. This means that the extra frames can only be spotted by the identical noise or the short time gap between frame copies.

I think it would be better to save the short subs rather than a copy of a previous frame if the option to save all frames is switched on. This would allow subframes to be sorted based on exposure length.

I am running SharpCap 4.1.131520 - 24/02/2025

Alan

[admin]

Hi Alan,

thanks for reporting that issue - I hadn't noticed it, but I think I know where it comes from... The stacking keeps track of the last raw frame so that the 'unstack' button can work, and during dither or recenter, not updating that raw frame with the sort ones from the camera makes sense as it allows 'unstack' to continue to work correctly during the dither procedure. However, I think it is also meaning that the frame from before the dither is being saved multiple times.

I will have to have a think to work out if there is a good fix for this - I guess I could keep two different 'last raw' frames in this case, but that means more memory usage, which I don't think is justified... Maybe saving the raw frames during dithering will just have to be removed as 'unstack' is more useful.

cheers,

Robin