Author Topic: Drizzle and images that are not undersampled  (Read 98 times)

Offline Geoff

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Drizzle and images that are not undersampled
« on: 2019 September 16 00:29:19 »
There seem to be some conflicting advice on drizzling.  Am I not understanding something?
In this post undersampling is stated to be necessary
If your images are not undersampled, the drizzle algorithm will not improve anything. At the contrary, since a drizzle integrated image always loses some signal (the amount of lost signal is directly proportional to the drizzle subsampling ratio), it will degrade the result in comparison with a regular integration.

While here we have a post that seems to contradict the one above

The *huge* benefit of drizzle integration is the total absence of pixel interpolation. This means absolutely no ringing and no aliasing artifacts, which is really great. In my opinion, DrizzleIntegration is the best option, in general, to achieve optimal results with any type of raw data in PixInsight. If using raw CFA data, enable CFA drizzle. If the images are undersampled and the amount of frames is reasonable, use drizzle x2. Otherwise, or if preserving the original scale is preferred, use drizzle x1.

I know that Drizzle has been updated between these posts--has that changed anything about undersampling?
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Offline aworonow

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Re: Drizzle and images that are not undersampled
« Reply #1 on: 2019 September 16 06:46:56 »
if your pixel size (arc-seconds) is less in size than the seeing allows, then you have all the resolution you can get. Drizzle will not improve anything. In fact, if your pixel size is not a few times larger than the seeing permits, than drizzle is not going to do anything noticeable, except make your images larger and able to consume more resources.

Offline Juan Conejero

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Re: Drizzle and images that are not undersampled
« Reply #2 on: 2019 September 16 09:04:39 »
Among many other things, I have changed (hopefully to improve ;) ).

Quote
If your images are not undersampled, the drizzle algorithm will not improve anything.

This is true for the original drizzle method, i.e. with a scaling factor > 1.

Quote
...a drizzle integrated image always loses some signal (the amount of lost signal is directly proportional to the drizzle subsampling ratio)

Again, true when the drizzle scaling factor (or subsampling ratio) is 2 or larger.

Quote
The *huge* benefit of drizzle integration is the total absence of pixel interpolation. This means absolutely no ringing and no aliasing artifacts, which is really great.

Always true.

Quote
If using raw CFA data, enable CFA drizzle. If the images are undersampled and the amount of frames is reasonable, use drizzle x2. Otherwise, or if preserving the original scale is preferred, use drizzle x1.

This is what I think currently. When applicable, drizzle always is, IMHO, the best way to integrate deep-sky data. Fortunately, drizzle is very well integrated with the entire preprocessing toolset in PixInsight, and even more in the next 1.8.7 version.
Juan Conejero
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