Ring Nebula Drizzled

[Gerr]

What is drizzle (the usual weather outside)!!!???

I found this stacking technique very useful in processing M57 which I obtained with my Zwo ASI 294MC pro camera recently.

The target appeared small on the image sensor and I knew it would have to be cropped significantly to appreciate its colours and detail better.

I acquired 2hrs 20mins on this target (300sec lights) with the SW200P Reflector and just a UV filter on the colour camera.

Stacked in DSS and processed in photoshop CS2. The final version included more careful colour saturation and sharpening.

I have included the standard non-drizzle stacked image which was then cropped to better view M57.

The stack was then drizzled (x3) on a rectangular selected region of interest in DSS (about the same size as cropped version mentioned previously).

I think you will appreciate the difference in image quality this achieves.

CC's welcome.

M57 Original Image:

M57 Cropped Image (note blocky pixels when zoomed in on nebula edges):

M57 Drizzled x3 (much smoother - can be better processed):

 

 

 

[vlaiv]

19 minutes ago, Gerr said:

I think you will appreciate the difference in image quality this achieves.

I don't actually.

Here is your regular version x3 upscaled and a bit further processed:

To my eyes - it contains more detail than drizzled version. It goes deeper as well (look at Ha edge).

For reference here is Hubble version scaled and rotated similarly to above image:

Features present in regular version and brought forward with a bit more of processing are genuine as can be seen when comparing to reference version.

[Gerr]

Hi Vlaiv,

When I processed the Tiff files the difference was more obvious.  The final image used astro pro flat filter at end of process. I’ll have to look back and see if it clipped some edge detail off.

I liked the way that drizzle and region of interest box on DSS helped Ito upscale the DSO without losing the detail I perceived from  a cropped non- drizzled image of the same DSO.  The undersampling I noticed at the nebula edges became a lot less noticeable. I didn’t demonstrate that properly in these images. 

 

[Gerr]

9 hours ago, vlaiv said:

I don't actually.

Here is your regular version x3 upscaled and a bit further processed:

To my eyes - it contains more detail than drizzled version. It goes deeper as well (look at Ha edge).

For reference here is Hubble version scaled and rotated similarly to above image:

Features present in regular version and brought forward with a bit more of processing are genuine as can be seen when comparing to reference version.

Hi Vlaiv,

I went back to photoshop and loaded three images from DSS of the same M57 data but stacked normal, drizzled x2 and drizzled x3.

I framed them as a composite so they can be compared identically as they came out of DSS.

The images are Jpeg and Tiff and I'm sure you can now see the difference that drizzle makes in resolution that was my original point to this post. I have not upscaled or resampled any of the images - this may have its own benefits as you showed when you applied it to my one of my images earlier. Try zooming up on the nebula images now and you'll see what I mean.

It is a technique I haven't tried before and it has merit.

Happy for your input.

Ger.

 

M57 Composite.tif

[Gerr]

More on Drizzle!

So I had time after work to re-visit the M57 Ring Nebula and processed each one identically with curves, levels, saturation, contrast and high pass filter.

I then cropped each of them with a 5x4in crop set at 300ppi/inch resolution to make them all the same size.

Next I pasted them side by side onto a single image to better visualise any differences.

The result:

Yep;

Vlaiv was right - drizzle didn't improve my image after all. The detail looks better on the normal image on the left no matter what drizzle I applied to the stack in DSS.

The blocky pixels I was getting on the normal image on magnifying seemed to disappear after processing and saving it as a TIFF/JPEG image.

Drizzle makes the image larger and smoother perhaps but at a cost of detail which you can better realise once all images are cropped to the same size and compared.

Lesson learnt!!

 

 

[vlaiv]

23 minutes ago, Gerr said:

Drizzle makes the image larger and smoother perhaps but at a cost of detail which you can better realise once all images are cropped to the same size and compared.

Original drizzle algorithm was developed for HST and it works in very specific circumstances.

It requires under sampling to be present - that is not something that usually happens on amateur setups these days - pixels are getting smaller and seeing is the same as ever . It also requires pretty specific dithering - precise to a fraction of a pixel.

Possible in space but not possible on tracing mount (tracking mount error is often larger than dither needed - for example x3 drizzle requires pointing precision to 1/3 of a pixel - we often recommend rule of thumb that RMS guide error should be about 1/2 of imaging pixel size).

Only place where drizzling approach works in amateur setups is Bayer drizzle (to an extent - it works the best in planetary / lucky type imaging). It is used to recover resolution of OSC sensor defined by pixel size (otherwise OSC sensors sample at twice lower sampling rate - as if pixels are x2 as large).