Drizzle

[Terry B]

Dear All
I have read about using drizzle to stack imsges that are a bit undersampled and have tried it using Iris.
An interesting article on it is on vol 2 no 2 on at this site (http://www.skyinsight.net/)
My question is that when I use it in Iris it averages the frames rather than stacking them. This still leaves me with very dim images all be it with better resolution. Can drizzle stack frames instead of averaging them?

[rogerg]

What you might want to do is first sum sets of images, and then average those with Drizzle.

For example if you have 10 frames total, create 5 frames which are each the sum of 2 frames. Then run the 5 frames through Drizzle.

That's the kind of thing I do sometimes, but not using Drizzle (which I've never quite mastered).

[adlsa5092]

You can use Drizzle (I assume you're talking about Meade Envisage) to stack frames, either on the go or after if you've selected to save individual frames. It's important to RENAME your images to get the correct stacking order because of the way images are numbered and then opened by Envisage. You rename by adding zeros.

The frames get numbered -1, -2, etc then -10, -11 and so on and then -100, -101 etc. So if you've taken 99 or less, you need only add one zero immediately BEFORE the 1, 2, etc up to 9 (01, 02 ... 09). If you've taken 100 or more, you need to add TWO zeros before numbers 1-9 (001, 002, ... 009) and then ONE zero before numbers 10-99 ( 010, 011, ..099). If you do not do this, the stack routine places images in the wrong order and can drop out espec if there is a significant positional difference between frames - this can also happen if you discard a few in a row during an after inspection.

To get it working, you need to select TWO stars (make sure these stars stay in the window by stepping through the frames beforehand, otherwise the stack will abort), as you do if you're using drizzle to stack images on the go. If it drops out on you because you might have discarded too many sequentials, stack up to where it drops out for #A, then from there on for #B and so on and then stack the resultants (you can see the frames being processed in the Envisage window to know where it drops out). If the positional differences are too great, you will have to stack them manually. Don't make your tracking squares too small, about 20mm sq.

You can then process the image in another prog.

[Terry B]

No, I don't use any meade imagers. What I am talking about is described here.
http://astrosurf.com/buil/us/spe9/lrgb22.htm
It is a dithering algorithm to stack frames.
Cheers