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Zerene: Difference between DMap & PMax with scaling OFF

 
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Lou Jost



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PostPosted: Fri Oct 06, 2017 8:57 am    Post subject: Zerene: Difference between DMap & PMax with scaling OFF Reply with quote

I was experimenting with telecentric Nikon MM 10x measuring objective pushed down to lower magnifications than its designed m. Stacking was in Zerene. I knew it would no longer be telecentric when pushed down to a wider FOV, but still I wanted to see what would happen if I turned off scaling in Zerene. Zerene's reported scaling factor near the end of these stacks was around 1.01 so definitely not telecentric. With scaling turned on, there was almost no difference between the resolutions of the images produced by the two stacking options, PMax and DMap, and both showed the fine ridges on the butterfly scales. When I turned scaling off, I still got quite good resolution of the ridges using PMax, but in DMap I lost most of them. This was a curious result which I do not understand.

You may wonder why anyone would turn off scaling when the lens is not telecentric. I would want to do this when I need to stitch several stacks together, to avoid artifacts. I am sure this produces its own artifacts, but these might be manageable.

Here are the two images with scaling turned off, blown up to 200%; on the left is PMax and on the right is DMap. Both are made from the same stack. Pardon the purple fringes, the MMs have a lot of that. You can see that the PMax image shows good ridges on the scales, but these are largely lost in the DMap image.


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rjlittlefield
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PostPosted: Fri Oct 06, 2017 2:19 pm    Post subject: Reply with quote

Quote:
This was a curious result which I do not understand.

Yeah, me either.

The characterization "difference...with scaling OFF" is one that I have not seen before. I strongly suspect that what you're seeing is due to some other cause that is just coincidentally correlated with scaling.

To briefly review, DMap works by selecting pixels from individual as-adjusted source frames, as indicated by the depth map, or forming weighted averages of two adjacent source frames where the depth map is transitioning between source frames.

When DMap misses detail that is present in some source image, it must be that the depth map did not select that image. Common causes include estimation radius and/or smoothing radius too big, and/or contrast selection slider too far to the right (too much "black in preview").

If this stack were sitting on my computer, the first thing I would do is to compare the as-adjusted source images against the DMap output to try identifying how the depth map had gone wrong.

It is best to do this in retouching mode. That's because when not retouching, the source image panel is likely to be showing a low quality "screen preview" image rather than the full quality source image. In retouching mode you also have the S key to flash between source and output to facilitate comparisons. To get faster transitions between source frames, it helps to select one of the advanced brushes such as Pixels.

From what I can see here, it looks like maybe the depth map is properly tracking the high contrast edges of the scales, but not the lower contrast bases and interior areas where the fine ridges are.

--Rik


Last edited by rjlittlefield on Fri Oct 06, 2017 2:19 pm; edited 1 time in total
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mawyatt



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PostPosted: Fri Oct 06, 2017 2:19 pm    Post subject: Reply with quote

Lou,

Very interesting, I would not have thought this would have so much effect on Dmap and not Pmap. Certainly a good reason to keep scaling ON in most cases!!

Best,

Mike
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Lou Jost



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PostPosted: Fri Oct 06, 2017 2:52 pm    Post subject: Reply with quote

Quote:
I strongly suspect that what you're seeing is due to some other cause that is just coincidentally correlated with scaling.


But with the very same source images, there is no difference between DMap and PMax when scaling is left on. I'm not sure what I should look for in the adjusted images....I'll re-run the stacks now.
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Lou Jost



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PostPosted: Fri Oct 06, 2017 3:08 pm    Post subject: Reply with quote

Aha, I see that I took four shots at each camera position, and I may have changed the "use every n-th shot" setting between stacks. Will run everything again. Maybe that's the explanation.
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Lou Jost



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PostPosted: Fri Oct 06, 2017 3:42 pm    Post subject: Reply with quote

OK I've redone the four stacks, using every fourth frame.

The result is just as I presented above. When Scaling is checked, there is no difference in resolution between DMap and PMAx outputs. When Scaling is unchecked, there's a huge difference in resolution between the two outputs.

Also, comparing PMax outputs alone between "checked" and "unchecked", there very little resolution difference.

All these are done on the exact same set of source images.
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rjlittlefield
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PostPosted: Fri Oct 06, 2017 3:45 pm    Post subject: Reply with quote

Are you able to upload the stacks so that I can take a look at them?

--Rik
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Lou Jost



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PostPosted: Fri Oct 06, 2017 4:06 pm    Post subject: Reply with quote

Rik, do you mean the final results, or the whole set of source images? I can send you the final stacked images but the bandwidth here is not great enough to send you the source images.
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rjlittlefield
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PostPosted: Fri Oct 06, 2017 5:21 pm    Post subject: Reply with quote

I was thinking of the whole set of sources. I don't know how to investigate the relationship between sources and outputs unless I can access the sources.

Can you isolate the problem to a smaller set of images, or cropped to a smaller ROI?

--Rik
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Lou Jost



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PostPosted: Fri Oct 06, 2017 5:24 pm    Post subject: Reply with quote

I can see if the set of images can be reduced to the few which contribute to the scales I am looking at. But this may have to wait, I am about to travel to the US and have not finished my "real" work...or maybe I can copy them and send them when I am in the US. Where to send them? It is about 3 Gb.
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rjlittlefield
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PostPosted: Fri Oct 06, 2017 5:35 pm    Post subject: Reply with quote

Most people would upload to DropBox or send via wesendit.com, but I'm pretty sure that 3 GB at one time would exceed their limits.

If you want to send DVD, the best place would be the address shown at https://zerenesystems.com/cms/about_us .

For reducing the frame count, try first just restricting the stack to be the images contributing sharpness to the crop that you've shown.

--Rik
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