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Can Zerene Stacker "screw a lot the black value"?

 
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mjkzz



Joined: 01 Jul 2015
Posts: 945
Location: California/Shenzhen

PostPosted: Thu Sep 20, 2018 4:09 am    Post subject: Can Zerene Stacker "screw a lot the black value"? Reply with quote

Several people on Facebook claim that Zerene Stacker can, and I quote, "screw a lot the black value" and one showed an image of final stacked and one of the image in stack.

So, maybe Zerene does do something with color as we have seen before, but I personally have not experienced this in general stacking, only in odd situations. When I get hazy black background vs pure black, it is always my fault, not checking lighting setup during stack, particularly deep stack that can run 10mm where at beginning it might be OK, but at the end of stack, the lens changed position and light might enter lens, just one example of it.

I stacked this image from 141 images (dropbox, warning 929mb file : https://www.dropbox.com/s/093gvv1g0u98ipd/DSC00114.zip?dl=0) and this is straight out of Zerene (except resizing), I find it the opposite that Zerene actually made the bg darker.


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Last edited by mjkzz on Thu Sep 20, 2018 2:54 pm; edited 2 times in total
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rjlittlefield
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PostPosted: Thu Sep 20, 2018 8:37 am    Post subject: Re: Can Zerene Stacker "screw a lot the black value&quo Reply with quote

mjkzz wrote:
Several people on Facebook claim that Zerene Stacker can, and I quote, "screw a lot the black value" and one showed an image of final stacked and one of the image in stack.

There are several ways in which Zerene Stacker can change colors, all of them documented at https://zerenesystems.com/cms/stacker/docs/faqlist#my_colors_changed_a_little_why_is_that :
Quote:
My colors changed a little. Why is that?

There are three reasons that output images can have different colors from the input: 1) brightness adjustment, 2) PMax, and 3) “Retain extended dynamic range” when saving. “Brightness adjustment” refers to Zerene Stacker's attempt to correct for uneven exposure between various input images. That feature is turned on by default, but you can turn it off by un-checking Brightness at Options > Preferences > Alignment. “PMax” refers to the PMax stacking method, which often makes slight changes in brightness, contrast, and saturation as a side effect of doing its focus stacking. This behavior is an unavoidable side effect of PMax and should be considered as one of the tradeoffs of PMax versus DMap. “Retain extended dynamic range” when saving causes the range of internal pixel values to be compressed if necessary to fit within the 0-255 range of image files. Internally the range can exceed 0-255 as a result of PMax, brightness adjustment, or even just pixel interpolation during alignment.

Color/brightness/contrast changes can be completely avoided by using the DMap stacking method, with Brightness adjustment turned off at Options > Preferences > Alignment, and “Retain extended dynamic range” turned off at Options > Preferences > Image Saving or in the file save dialog.

The most common complaint is addressed by its own separate FAQ, https://zerenesystems.com/cms/stacker/docs/faqlist#why_do_my_saved_output_images_look_washed_out :
Quote:
Why do my saved output images look washed out?

Probably you accidentally put a checkmark on “Retain extended dynamic range” while saving the image. Remove that checkmark at Options > Preferences > Image Saving, or when you save your next image, and the problem will go away.

Brightness correction is enabled by default, and PMax is the first stacking method in the list, so those are very natural issues for people to run into.

"Retain extended dynamic range" is not set by default, but I guess its brief description is very tempting to people who have not read the tooltip: "If checked, reduces contrast and changes brightness if necessary to prevent clipping at black and white levels."

--Rik
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mjkzz



Joined: 01 Jul 2015
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Location: California/Shenzhen

PostPosted: Thu Sep 20, 2018 8:58 am    Post subject: Reply with quote

Sorry Rik, forgot to include the screen capture of the FB page, but here it is. I do not have original files, but can color change that much -- from almost black to hazy black. I really doubt it, but if that is the case, maybe the option to make it happen should be defaulted to inactive, just my 2 cents.


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rjlittlefield
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PostPosted: Thu Sep 20, 2018 10:53 am    Post subject: Reply with quote

mjkzz wrote:
can color change that much -- from almost black to hazy black. I really doubt it, but if that is the case, maybe the option to make it happen should be defaulted to inactive

What is shown looks like a typical mild effect of "Retain extended dynamic range", which does default to inactive (= not selected).

But it could also be due to Brightness correction, combined with a deep stack.

If it is due to Brightness correction, then I disagree that the default setting should be changed. That's because quite a few stacks have exposure variation that messes up DMap without correction. But certainly some code could be added to detect a potential problem and issue some warning. Or the correction code could be made more sophisticated so as to reduce frame-to-frame variation while still preserving the global shapes of the contrast & brightness curves. (All of this has been true for the last 9 years, BTW.)

In any case, the ultimate solution must lie with people learning how to use the controls. I am not skilled enough to protect everyone from everything by default.

--Rik
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mjkzz



Joined: 01 Jul 2015
Posts: 945
Location: California/Shenzhen

PostPosted: Thu Sep 20, 2018 2:29 pm    Post subject: Reply with quote

Rik wrote:

What is shown looks like a typical mild effect of "Retain extended dynamic range", which does default to inactive (= not selected).


The user unchecked that when saving and seems to work well. I am glad it is unchecked by default (for 9 years)

Rik wrote:

In any case, the ultimate solution must lie with people learning how to use the controls. I am not skilled enough to protect everyone from everything by default.


Thanks Rik, I think this IS user's RTFM (read the freaking manual) issue Very Happy
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