M13 RGB

[Rodd]

23 hours ago, vlaiv said:

This gives us nice chance to do comparison. In particular I want to focus on 3 prominent stars that are close together.

Vlaiv--Here is the result of what just modifying stretch can do for resolution.  While not as separated as I would have liked - I think this crop shows a noticeable improvement.  There is clear separation between all large stars of the triple system, and the small companion is definitely cleaner, though still attached.  I see the hint of separation though.  This is from the final image of the thread.

Edited May 18, 2021 by Rodd

[DaveS]

I've been following this discussion and it's inspired me to have a look at my recent imaging. My ODK 12 / G3 16200 has a native plate scale of 0.61"/px which is somewhat daft. Although the mount will certainly track well enough for that, and the optics will support it, my seeing is the limiting factor.

I took a set of raw stacks, binned them 2x2 in software and processed the result into a LRGB image. I then upscaled 2x to restore the raster size and compared with the native LRGB that I put into the imaging competition.

The binned and upscaled image is, if anything cleaner with the detail held with more solidity.

[DaveS]

Lets see

Native

Binned and upscaled

the other difference is that the native image had a denoise applied to the background while the binned and upscaled one didn't.

Edited May 18, 2021 by DaveS

[vlaiv]

@DaveS

Well, here is interesting thing - these images can be almost binned x4 without loss of detail.

Bottom is original version you posted and top one is that same version (as 8bit processed) reduced to only 25% size and then enlarged to 400% of that. Almost no detail is lost (tiny stars appear just a tad sharper in bottom image). Of course - noise grain is different (noise is high resolution - it is in fact equally present across frequencies - it changes grain when we discard high frequency components when we reduce sampling rate).

[Rodd]

19 minutes ago, DaveS said:

Binned and upscaled

The images are very close, but the binned one is obviously the better image due to greater dynamic range across the target--especially the dark lanes, which are more prominent--there are more details.  It almost looks like the softness of the native image is due to noise suppression--but you said it was only used on the background.  The other concern is processing differences.  Despite great efforts to perform the exact steps, no two images are exactly alike.  The question is, are the differences seen in the binned image the result of better processing.  I say this because we see here precisely the opposite of what one expects to se--we expect to see either the same details, or reduced details in the binned version--but we see more details-a sharper look.  

[DaveS]

My processing might have been a little lax as I wasn't thinking of posting at the time, it was a bit of an afterthought. I was just wanting to see if binning and then upscaling was a viable option. Looks like it might be. Possibly too my unsharp mask was applied slightly better.

This is with a masked denoise avoiding the "ball" of the galaxy

[vlaiv]

22 minutes ago, DaveS said:

I was just wanting to see if binning and then upscaling was a viable option

Now comes million dollar question.

Why do you feel you need to upscale it after binning? I mean - if detail is not there - what is the benefit of upscaling it?

[Rodd]

28 minutes ago, DaveS said:

Looks like it might be.

I'd say definitely....Its Better!  So at least as good with equivalent processing.  So equal with better SNR.  It all seems pretty close to me though--are teh differences either way all that much?  Its like driving 10 miles out of the way to save a nickle on gas

[DaveS]

6 minutes ago, vlaiv said:

Now comes million dollar question.

Why do you feel you need to upscale it after binning? I mean - if detail is not there - what is the benefit of upscaling it?

Because I want to print to a good size, even up to A3+ (Though I can't afford an A2 photo printer). Binning 2x2 only gets me 4 MP off the sensor, less after cropping of alignment edges etc.

[vlaiv]

1 minute ago, Rodd said:

I'd say definitely....Its Better!  So at least as good with equivalent processing.  So equal with better SNR.  It all seems pretty close to me though--are teh differences either way all that much?  Its like driving 10 miles out of the way to save a nickle on gas

I don't know about that.

If you bin x2 in linear stage - you recover x2 SNR. That is equivalent of imaging additional x3 as much as you already did (for total of x4 exposure length). If you bin x3 - that is as much as additional x8 time.

That sort of sounds to me like - go out of the way additional 50 yards (really - binning is couple of clicks) to save half a tank of gas.

[Rodd]

8 minutes ago, vlaiv said:

Now comes million dollar question.

Why do you feel you need to upscale it after binning? I mean - if detail is not there - what is the benefit of upscaling it?

Well--up to a point, it is easier to look at a 1 inch wide galaxy on the screen than a 1/4 inch galaxy.  The smaller an image gets, the less details can be really seen.  That's why a widefield high resolution image of a target is hard to appreciate from a resolution perspective.  The details are just to small to see.  Take the Hubble image of M16 and shrink it down to a postage stamp.  There is no way you can admire all the details that are there if they are only a few pixels wide (and teh screen size had been shrunk).  I agree upscaling to the size of the galaxies you posted is absurd--that's just too much.  But teh size he posted is a nice size--easy to look at without the need to zoom.

[vlaiv]

1 minute ago, DaveS said:

Because I want to print to a good size, even up to A3+ (Though I can't afford an A2 photo printer). Binning 2x2 only gets me 4 MP off the sensor, less after cropping of alignment edges etc.

Fair enough.

Don't know if there is much difference in print quality between you scaling the image and printer printing on lower DPI setting.

[Rodd]

2 minutes ago, vlaiv said:

I don't know about that.

If you bin x2 in linear stage - you recover x2 SNR. That is equivalent of imaging additional x3 as much as you already did (for total of x4 exposure length). If you bin x3 - that is as much as additional x8 time.

That sort of sounds to me like - go out of the way additional 50 yards (really - binning is couple of clicks) to save half a tank of gas.

What I meant was take a look at the completed images....the final images.  There won't be much of a difference at all.  the differences will be slight.  Half the time I reduce a stretch and do not make use of all the signal anyway because of noise and LP.  In the end, the theoretical benefits do not equate with a 1:1 image quality.

[vlaiv]

1 minute ago, Rodd said:

I agree upscaling to the size of the galaxies you posted is absurd--that's just too much. 

That is Dave's original image size when viewed 1:1 or 100%

[Rodd]

2 minutes ago, vlaiv said:

That is Dave's original image size when viewed 1:1 or 100%

Very few images can stand up to 1:1 viewing (if we are talking about the same 1:1).  1;1 is full resolution in astrobin or on SGL - only the very best can stand up to that without having been down sampled (reduces screen size).

[Rodd]

1 hour ago, vlaiv said:

Bottom is original version you posted and top one is that same version (as 8bit processed) reduced to only 25% size and then enlarged to 400% o

This is what I was talking about--increased 400%.  these are way to big for the resolution-  Maybe a Hubble image can be of this galaxy this size.

[vlaiv]

1 minute ago, Rodd said:

Very few images can stand up to 1:1 viewing (if we are talking about the same 1:1).  1;1 is full resolution in astrobin or on SGL - only the very best can stand up to that without having been down sampled (reduces screen size).

That is exactly what I'm talking about. Imaging so that your image looks too blurry when viewed 1:1 - just means that you are wasting SNR.

We might not agree on how much difference in depth there is between base image and image that has x2 higher SNR - but anyone of us can see that on real data. Just take the data you are working on - and stack only 1/4 of subs. Simple as that.

[Rodd]

10 minutes ago, vlaiv said:

Don't know if there is much difference in print quality between you scaling the image and printer printing on lower DPI setting.

But we are taking about screen viewing.  If I were to bin my M13 x4--the image would be little more than a postage stamp before resizing.  There comes a point where it would look like a crop.  

[vlaiv]

1 minute ago, Rodd said:

This is what I was talking about--increased 400%.  these are way to big for the resolution-  Maybe a Hubble image can be of this galaxy this size.

No - I did not increase to 400% - I first reduced size to 25% of original image. Then I took that small image and I increased it back to 400% of that small image - in effect, I was back to original size.

I reduced by 1/4 and then enlarged that by x4, 1/4 * 4 = 1. Both images are at 100% as recorded.

I wanted to demonstrate that data in the image can be recorded by 1/4 of resolution with almost no loss in detail - which means it is over sampled by factor of almost x4. If it were sampled properly for detail it contains - it would have had x4 SNR it has now (no idea if I managed to put everything in proper tense there ).

[vlaiv]

Just now, Rodd said:

But we are taking about screen viewing.  If I were to bin my M13 x4--the image would be little more than a postage stamp before resizing.  There comes a point where it would look like a crop.  

Not sure if your M13 needs to be binned by factor of x4. It contains quite a bit of detail.

[Rodd]

4 minutes ago, vlaiv said:

No - I did not increase to 400% - I first reduced size to 25% of original image. Then I took that small image and I increased it back to 400% of that small image - in effect, I was back to original size.

I reduced by 1/4 and then enlarged that by x4, 1/4 * 4 = 1. Both images are at 100% as recorded.

I wanted to demonstrate that data in the image can be recorded by 1/4 of resolution with almost no loss in detail - which means it is over sampled by factor of almost x4. If it were sampled properly for detail it contains - it would have had x4 SNR it has now (no idea if I managed to put everything in proper tense there ).

I see.  What I am saying is take a look at the lenticular (I think-maybe spiral on edge) galaxy to the left of Dave's.  It is small.  If you binned the main galaxy 4x, it would end up being about that size on the screen--maybe a bit bigger--but small.  It is a different viewing experience looking at something that small--even if highly detailed.  So upscaling it makes a lot of sense for screen viewing.

[vlaiv]

2 minutes ago, Rodd said:

I see.  What I am saying is take a look at the lenticular (I think-maybe spiral on edge) galaxy to the left of Dave's.  It is small.  If you binned the main galaxy 4x, it would end up being about that size on the screen--maybe a bit bigger--but small.  It is a different viewing experience looking at something that small--even if highly detailed.  So upscaling it makes a lot of sense for screen viewing.

I understand what you are saying. I guess that is personal preference, and this image was obviously taken in rather poor seeing conditions.

I rather like when image looks like this in detail it presents (that is equivalent of x4 bin for this particular image):

Now there is no trace of noise in the image and contrast is good and image looks sharp. I would be more than happy if image looked like that, at this resolution:

But it starts to go a little soft and a little noisy at this resolution (which is 50% of original - equivalent to bin x2). By the way - this is in ball park of what can be expected from amateur setups with larger apertures and good mounts - sampling rate of about 1"/px-1.2"/px. Anything below that is 99.99% unrealistic for amateurs in long exposure imaging.

[geoflewis]

Hi everyone,

I'm continuing to enjoy this discussion with the addition of @DaveS image and binning experiment, but it's taken me in to territory that I really don't understand, so I'm hoping that someone can clarify for me. The bottom line is that I don't fully understand the terminology, nor the real effects on an image of some of the operations being discussed. What do terms like downsample, upscale, binning actually mean in terms of image quality, resolution, or whatever is the correct term? I think I understand what hardware binning means, as that actually combines a grid of pixels (2x2, 3x3, 4x4, etc) on the sensor into an effective single pixel before downloading the data. Software binning is similar (?), but works differently (I think), but what about downsample, upscale, etc. Are these terms (especially downsample and binning) interchangeable, if not then what is the difference? If I bin 2x2 in sftware, then upscale x2, do I end up in 'exactly' the same place? What if I resize/upscale x2 then bin 2x2, is this also the same, i.e. what is actually happening with the image data as these operations are applied? Are resize x2 and upscale x2 even the same? What is downsampling? is it the opposite of upscaling? Sorry if I'm showing my ignorance too much, but I see these terms bandied about all over the place, but I can't find an authorative reference to distinguish between some of them. Anyone fancy taking a punt at this for me please?

Rodd, sorry for hijacking your thread, but it was following the discussion that started with your superb M13 that got me here.

[Rodd]

5 minutes ago, geoflewis said:

Rodd, sorry for hijacking your thread, but it was following the discussion that started with your superb M13 that got me here.

No problem.  Its all you Vlaiv! 

[DaveS]

I think I have to take some of the blame sorry. It was that image I chucked into the ring that did it .

 I'm still following it off and on, but it's getting a bit beyond me at the moment.