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I've seen Drizzle mentioned in a few post. Can anyone point me in the direction of where to find it/what is please?

I thought it was a Meade software for de-rotating images taken using an alt/az mound?

Thanks,

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I used a 2xDrizzle in Deep Sky Stacker when stacking subs for M51, I read somewhere that it was good for bringing out more detail in smaller objects, I've also heard someone mention that its good for reducing noise. I know this all sounds a bit vague, I would also like to understand it a bit more as well, on a basic level I guess its just an algorithm for image processing?

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I only know of it from Deep Sky Stacker also, and, have no idea what it does. From experience, all the happens is the resulting image is much bigger than if x2 or x3 Drizzle hadn't been used. I am sure there is a reason it was coded, wouldn't have been done otherwise, I have not seen any benefit from using it.

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I'm not quite sure how it works and why it is better than simply resizing in Photoshop, but basically, it is a method for increasing the size of your image. Not normally used with the full image on a DSLR, but if you just select a small bit, a box around say M51, then check the box for 2x Drizzle, you will get a stacked image of the area inside the box scaled up 2x larger than original but somehow 'better' than if you stacked normally and doubled the size in Photoshop and then cropped the bit you want.

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It works like this, in my understanding; between exposures you move the camera very slightly each time. Now imagine you are photographing a perfect circle drawn on a page. In a single exposure, when you zoom in to pixels scale, you will see a staricase-like line rather than a circle because the pixels are square or oblong. They cannot produce a true curve. They have no information about what trajectory the curve really takes between steps. However, if you move the next exposure a tiny bit (by less than one full step of the staircase) the next image will still be staricase-like but the steps will be made by a slightly different part of the circle. In principle you now have two bits of information about the true curve and you could in principle make a picture of the circle in which the artificial steps were now half as big as in a single image. The more slightly shifted images you stack the more information you have about the true curve and the smaller the articial steps become. This process of telescope shifting between subs is called dithered guiding.

Now for drizzle; you take all your dithered images and combine their information so that you know a lot about the true circle on a sub-staircase level. Ah, but there's a problem; you don't have any more pixels on your screen than you have on your chip, so how can you present this extra information? You resize the image upwards (four times by area) and you can now present an image in which the dithered information can be applied and seen on the screen. Your steps will be smaller, your circle will be more circular, and you have pulled off the miracle of acheiving sub pixel resolution! Free lunch! Cigar! (In normal resizing you have no new information so you just double the size of your starcase steps, which is pointless.)

Planetary imaging is at such long focal lengths and has so much atmospheric dithereing that the dither is generated naturally. DS imaging uses guiding which should be well below pixel scale so the dither has to be engineered by the guiding software between exposures. You can still expect to get some due to imperfect PA, though.

I hope none of this is too far off beam but if it is I apologize!

Olly

Edited by ollypenrice
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Thank you Olly. That is a very clear allusion. I get a much better understanding I think.

So, if I am imaging, say, Jupiter with a f5 Newt and a webcam, it would be worth drizzling due to the natural dithering to get a much.'smoother' edge to the plant and thus, a more pleasing result?

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Thank you Olly. That is a very clear allusion. I get a much better understanding I think.

So, if I am imaging, say, Jupiter with a f5 Newt and a webcam, it would be worth drizzling due to the natural dithering to get a much.'smoother' edge to the plant and thus, a more pleasing result?

Sent from my GT-I9001 using Tapatalk 2

You'll get more than a smoother edge. The circle example I gave was the simplest way of explaining sub pixel resolution but the extra resolution will apply to all the details you capture and you'll have a larger image in which to enjoy them. We don't do much fast frame camera stuff but we sometimes shoot the Sun and the boost from simply checking the Drizzle box in Registax is phenomenal. Try it, you'll be amazed.

Olly

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As olly has said:

dither - moving the image betwen subs so that the image doesn't sit on the same pixels.

drizzle - upscaling each sub-image and then aligning and stacking. This recovers the small differences between the images - enhancing the final upscaled image.

I do a manual modified drizzle here: http://stargazerslou...on-enhancement/ with a 45 degree rotate to reduce the blockiness. Here on the bear galaxy:

Grr.. can't re-attach an image..

index.php?app=core&module=attach&section=attach&attach_rel_module=post&attach_id=70384%20

Edited by NickK
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