To Drizzle Or Not to Drizzle
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- เผยแพร่เมื่อ 1 พ.ค. 2024
- They say drizzling decreases your SNR and is best done if you are undersampled. But if we process the same image with and without drizzling, we discover that theory often doesn't hold up to practical tests.
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I have the same experince. Always drizzle :)
This is new for me ... Thanks again ❤....
You're giving away all of our secrets! Just kidding 😀 Glad you made this as I have been telling people this all the time but your video drives it home 🙂 One thing you forgot to mention is that double stars also start to appear with the recover resolution. There was a double star on at the 6:47 part of the video. Also dither often if you drizzle. I dither every frame because I drizzle everytime! Clear Skies!
Yes, drizzling really brings out detail that could otherwise be missed. Another reason it's always worth the effort.
I had just been debating drizzling more often. Very timely video. Thanks!
I'm the same in Bortle 4. Drizzle always gives better results.
On a side note, my guiding improved a bit by adding a counterweight and moving them up the counterweight shaft, might be worth looking in to.
Thanks for the tip. Due to the small size of the observatory, I always push the counterweight bar in as much as possible. I never thought before that it might help guiding.
@SKYST0RY it helps by reducing the size of the moment arm, effectively reducing the work the mount has to do to lift the weight.
@@Reverend-JT Makes sense. Like a ballerina pulling in her arms.
Since I began drizzling a year ago my images have been consistently better than previously, regardless which camera or scope/lens I use, so I will continue to use it on every image, even if it doesn't do anything more than boost my confidence.
I really enjoy your videos. I learn a lot, especially when it comes to image processing techniques. You have a unique way to explain this subject. Thanks for sharing and please keep the videos coming!
My experience aligns with yours. I drizzle regardless if I'm under sampled or over sampled. I've never understood the "saying" that drizzling reduces SNR. I don't see that on my monitor nor using the SNR script in PI. I consistently get better SNR with a 2x drizzle vs no drizzle of about 1.5 - 2 dB SNR improvement. I pixel peep and on under sampled images it gives me a better SNR and takes care of the pixelated stars. On over sampled images I will after 2x drizzle apply 50% resample and I get another 2 - 3 dB SNR improvement so with my over sampled images after 2x drizzle and 50% resample I've gained 3 - 5 dB improvement. Plus with the resample, now the file is back to the size of the non-drizzled image which helps in processing speed. Now if the image started with 40 dB SNR, the improvement on the monitor is not easily seen, but being in Bortle 7/8 a lot of my images start around 30 dB and the noise improvement is easily seen on the monitor. Another important aspect is to sufficiently dither. In my testing, if I dither every 5 - 10 minutes I will see these improvements. I've dithered every frame, but did not seem to add much benefit and takes up imaging time waiting for tracking to pick back up. So I've found my dither frequency to be sufficient and a good balance. Always dither and always drizzle is my motto.
Great observations! I have found dithering becomes less important the shorter the subs. On the refractor, which only has an FL of 447 mm, I shoot 300s subs and dither every three frames for 33%. On the SCT, I shoot 60s subs and dither every 5 frames for 20% dither.
Fantastic, I thought it was just me. I have always drizzled in DSS and thought I was doing something wrong given the false myths. Call me the Drizzler.
Astrophotography is full of good tech and postulates. Test everything lol
Interesting.
Very interesting. I was noticing some subtle, but significant, differences along the way which you didn't comment on. For instance, at around 6:40 in the video, there is a bright star near the top that seems to have 2 very nearby dimmer stars in the drizzled image, which are not in the non-drizzled. Any thoughts what's going on there?
BlurXterminator often helps to resolve double and triple stars. However, sometimes it makes mistakes. A double star below it had the dimmer star vanish.
Very nice seeing the results of drizzled and non-drizzled data. Anyway I would love to use drizzled data but when I integrate with drizzeling once I unscreen the stars using StarXTerminator I have strange artefacts in my exosure. SXT moved certain information from nebulae or galaxies to the newly created stars image. This makes processing a pain as the areas that have those artefacts can not be processed in the way I would like to do. Once I add the stars back using pixel math the artefacts are gone again. But the photo stays with some areas that look different because the processing steps affected the artefact drifferent than normal nebula/ galaxy data.
So I have to wait for a SXT update or stay away from drizzling.
Interesting. That could be a result of using an older sensor, I guess. But I think it probably relates more to the order of processing. You mentioned "unscreening" the stars, so I am assuming you are removing the stars after a histogram stretch? If processing mono, try this order. After stacking is finished, open all channels. Do not follow standard recommended procedure; it's often based on truisms and not the best way to do things. Instead, on each individual channel, run BXT in correction mode only. Then run BXT in default mode. Then Star Align. Do not run Linear Fit (The standard instructions for how to use it are garbage, and it is very destructive to your data. I'll create a video on how to use it better soon.) Instead, combine your RGB channels. Now run SXT on the RGB. Then you can use the ScreenTransferFunction and Histogram tool to hold the stretch of your RGB star plate.
On the L channel, run BXT in correct then default mode. Now run SXT on the L channel and use the ScreenTransferFunction and Histogram tool to hold the stretch on the L star plate.
Use the LRGBCombination tool to combine the star plates and add back after finishing development of your image. Should work better then.
Be aware that SXT often removes important information form dense, bright region which can create artifacts, so sometimes you have to work around that.
Always drizzle: x2 drop 0.9 from 533 and x1 drop 1.0 from 571 (APS-C). More detail + better colors from SPCC (this is actually advise from PixInsight authors). Good video, love the examples!!!
Also, apologies but need to ask (as a pixelpeeper) - are you going to do something about those flares on the bright stars? It was killing me with my 8" ACF reduced to F/5.85. And so much that I moved to 10" Newt. Later on I read it may be caused by flexible dew shield I have for my SCT... but frankly I love my newts so much I rarely use SCT these days.
I kind of like the flares. I see them as part of the "SCT" look, but it seems to result from the heater ring on the front of the telescope. At the time I shot the image, my variable voltage power supply that I had on th eheater had been cooked so I had a fixed voltage power supply connected to the heat ring, giving it power at half voltage. I have a new variable voltage power supply on the heat ring and typically keep the voltage down around 10-15% which by and large gets rid of the flaring.
Hi and thanks. Always learning. Good information. Clear Skies in your bortle1! We’re in LA, bortle10
Bortle 10!!! Thank goodness for narrow band, eh?
I know it is recommended to drizzle OSC data even if only x1.
Interesting. However i suspect this only affects those who wish to observe for hours. I typically observe an object for no more than 30-45mins and the hassle of drizzling would not i suspect yield any real benefits in terms of time needed to undertake each drizzle. I did notice your brighter stars are flaring and the sharpening seems to enhance this in the drizzled version?
If extremely under sampled, drizzling probably will not help you much. Stars are flaring more in the non-drizzled information, however, the flaring around the edge of the image has more to do with the overheated dew ring than the drizzling process. My rheostat controller for the dew ring was broken and the ring was getting too much wattage which causes a little bit of warping on the optical window. The rheostat has since been replaced and the errors on the outer part of the image are much reduced now.
Do you dither in every light? How many pixels?
I always dither unless shooting lucky imaging. The amount to dither varies depending on your camera, telescope, imaging camera and guide scope. I have a guide for how to calculate dithering here: th-cam.com/video/fkPH3YiYg_I/w-d-xo.html
Each of my subs are over 300megs, so drizzling hurts :) a lot.
That is a massive sensor. I bet you'd still benefit from drizzling but it would take some serious processing power.
Awesome video - very informative without getting into the weeds with details. I redid a shot of NGC4565 that I took a couple weeks ago and used your method.... AMAZING difference.
I'd always been a bit confused with drizzling and what under/over sampling meant and this put it all together for me. Thank you very much! *subscribed* :)
I had to stop your video half way. Not sure why your comparison images are imaged at different scales. PixInsight allows you to drizzle at 1 to 1 scale. I do drizzle, but this comparison seems to me to be questionable.
What I'd like to see is your dithering routine, since the newer astro cameras produce impeccable dark frames. Dithering is said to not be needed here.
Thanks for your productions in AP.
Dan
I have a video on calculating dithering. This image was shot with 60s subs at 130 gain on the Player One Ares-M, dithered every 5 frames. However, I have cameras with new sensors with plenty of walking noise from not dithering. New or old sensors, my advice is unless you are lucky imaging, always dither.