www.photomacrography.net :: View topic - Zerene subframe scaling
www.photomacrography.net Forum Index
An online community dedicated to the practices of photomacrography, close-up and macro photography, and photomicrography.
Photomacrography Front Page Amateurmicrography Front Page
Old Forums/Galleries
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
Zerene subframe scaling

 
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Macro and Micro Technique and Technical Discussions
View previous topic :: View next topic  
Author Message
Beatsy



Joined: 05 Jul 2013
Posts: 1428
Location: Malvern, UK

PostPosted: Thu Jun 14, 2018 1:28 am    Post subject: Zerene subframe scaling Reply with quote

When scaling is enabled, will Zerene ever upscale individual images to align them, or is it always downscaling? Thanks.

Edit: supplementary question. If I stack highest-quality jpegs and save the result as a 16-bit TIFF, is it a true 16-bits. That is, are there (potentially) 65536 different intensity values for each colour, or are there only 256 quantised ones (i.e 0,1,2,3,4 in the jpg becomes 0,256,512,768,1024 in the TIFF)? If the former, what's the source of the extra "in-between" values? Perhaps from sub-pixel sampling when aligning and scaling? Thanks again.
Back to top
View user's profile Send private message
rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 19403
Location: Richland, Washington State, USA

PostPosted: Thu Jun 14, 2018 8:26 am    Post subject: Re: Zerene subframe scaling Reply with quote

Beatsy wrote:
When scaling is enabled, will Zerene ever upscale individual images to align them, or is it always downscaling?

Upscaling is the normal action. By default, Zerene Stacker starts at the "narrow" end of the stack, the end having the smaller field of view. To make other frames align with that, they get cropped to the same field of view and then expanded to the same pixel dimensions, so you get more pixels covering the same area.

But if you want it to go the other way, downscaling a smaller field of view to match a larger one, then you can force that by un-selecting Options > Preferences > Alignment > "Automatic order", and if necessary, manually putting the wide end first with File > "Re-order input frames" > "Reverse order" (formerly just File > "Reverse order").

Quote:
If I stack highest-quality jpegs and save the result as a 16-bit TIFF, is it a true 16-bits. That is, are there (potentially) 65536 different intensity values for each colour, or are there only 256 quantised ones (i.e 0,1,2,3,4 in the jpg becomes 0,256,512,768,1024 in the TIFF)? If the former, what's the source of the extra "in-between" values? Perhaps from sub-pixel sampling when aligning and scaling?

Yes, potentially all values. The in-between values can come from sub-pixel sampling, from brightness adjustment, from weighted averaging on frame transitions in DMap, and from pyramid recombining in PMax. In-between values are actually pretty hard to prevent. You have to turn off brightness correction, turn off scaling, avoid PMax, and be lucky enough to avoid weighted averaging in the DMap.

--Rik
Back to top
View user's profile Send private message Visit poster's website
Beatsy



Joined: 05 Jul 2013
Posts: 1428
Location: Malvern, UK

PostPosted: Thu Jun 14, 2018 9:04 am    Post subject: Reply with quote

Thanks Rik. I do find this hard to get my head round. Since the camera is moving, then every frame is essentially at the same scale (in my mind). This is why I asked.

I'm interested because I'm finally getting true pixel-level resolution at low mags and thought up-sampling might affect sharpness (not resolution) more than down sampling. But only when pixel-peeping and not likely of any real consequence anyway - except perhaps for 100% crops.

The "true 16-bit" is good news. I was doing several quick stacks with jpg instead of the usual RAW and convert to TIFF. My jpg tests are usually double spaced and downsampled 50% for speed. I forgot to change the step size for one (for the first time ever) and ended up doing a "proper" stack using jpg source files. The end result was indistinguishable from RAW and TIFF! Shocked

I'm sure RAW is still best where there's huge dynamic range and shadows need pushing to get detail out. But I'll be using jpg with "well lit" subjects from here on in. The quality is so much better than I assumed it would be. Enormously faster without the import, convert and export step too. I can just stack straight from the camera memory card instead. My recent Speedwell post was done that way.
Back to top
View user's profile Send private message
Beatsy



Joined: 05 Jul 2013
Posts: 1428
Location: Malvern, UK

PostPosted: Thu Jun 14, 2018 9:08 am    Post subject: Reply with quote

PS. I'm still confused. Should I start the stack from the furthest focus distance, or the nearest to get downsampling?
Back to top
View user's profile Send private message
rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 19403
Location: Richland, Washington State, USA

PostPosted: Thu Jun 14, 2018 10:10 am    Post subject: Reply with quote

Beatsy wrote:
PS. I'm still confused. Should I start the stack from the furthest focus distance, or the nearest to get downsampling?

That question is more subtle than you might guess. It depends on exactly what optics you're using and how you're doing the focus stepping.

In "Tutorial #2: Using a Macro Lens on a DSLR", it is discussed that the wide end is either the front or the back, depending on whether focus is stepped by ring or by rail.

With most optics -- the ones that have normal perspective -- if you're focusing by rail then the wide end will be the front because that's the end where the lens is farthest from the subject.

Quote:
I do find this hard to get my head round.

Yeah, me too, despite years of practice.

Quote:
Since the camera is moving, then every frame is essentially at the same scale (in my mind).

Every frame is the same scale in its own plane of focus. But in every frame, the scale changes from front to back due to perspective. So when you step focus by moving the camera, you're changing the scale of every part of the subject.

To make the details line up properly, source frames need to be resized so that each part of the subject has the same scale in all frames. If you don't do that, then subject details cannot be lined up properly and you'll get smearing.

To get a better feel about what's going on, I suggest to process a stack, then use press-and-drag in the list of input files to "play" the stack as if it were a filmstrip. Do this with and without "Show as adjusted" checked, and think about the difference.

--Rik
Back to top
View user's profile Send private message Visit poster's website
Beatsy



Joined: 05 Jul 2013
Posts: 1428
Location: Malvern, UK

PostPosted: Thu Jun 14, 2018 10:41 am    Post subject: Reply with quote

Thanks again, I'll try your suggestions. As I said before, it probably doesn't make a blind bit of difference in the output, but I want to reassure myself that's actually the case - and understand it...
Back to top
View user's profile Send private message
Lou Jost



Joined: 04 Sep 2015
Posts: 2881
Location: Ecuador

PostPosted: Thu Jun 14, 2018 10:50 am    Post subject: Reply with quote

These effects are why some people like telecentric lenses, whose FOV does not change as the lens moves up and down during stacking. It is actually very weird and unnatural to see it in action, but it eliminates the need for shrinking or stretching the frames of a stack, and so it could actually preserve pixel-level detail better.
_________________
Lou Jost
www.ecomingafoundation.wordpress.com
www.loujost.com
Back to top
View user's profile Send private message Visit poster's website
naturepics43



Joined: 11 May 2015
Posts: 72
Location: Hocking County, Ohio , USA

PostPosted: Thu Jun 14, 2018 12:22 pm    Post subject: Reply with quote

Beatsy wrote:
Thanks again, I'll try your suggestions. As I said before, it probably doesn't make a blind bit of difference in the output, but I want to reassure myself that's actually the case - and understand it...



In a lot of cases it DOES make a big difference. From my experiences (which are limited), I found that if the stack is run from the last frame taken to the first frame taken, the finished image will be very close to the actual magnifaction that you used. If the stack is run from the first frame taken to the last frame taken, ( You get "streakies" on the edges ), the magnifaction of the finished image will be smaller than what was used. VERY important if you want the scale bars to be accurate. It's very easy to verify. Run a stack in both directions and compare the finished image sizes. Maybe this will help you determine which way is downsampling. That part also confuses me. Hope this helps.
Back to top
View user's profile Send private message
rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 19403
Location: Richland, Washington State, USA

PostPosted: Thu Jun 14, 2018 12:44 pm    Post subject: Reply with quote

naturepics43 wrote:
VERY important if you want the scale bars to be accurate.

This may be phrasing it a bit harshly, but if processing front to back versus back to front has much effect on the accuracy of scale bars, then the scale bars are not to be trusted anyway.

That's because if the scales at front and back of the stack are different, to which depth does the indicated bar apply?

--Rik
Back to top
View user's profile Send private message Visit poster's website
Display posts from previous:   
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Macro and Micro Technique and Technical Discussions All times are GMT - 7 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group