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Exported picture from Zerene stacker looks faded

 
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MarkSturtevant



Joined: 21 Nov 2015
Posts: 605
Location: Michigan, U.S.A.

PostPosted: Sat Aug 17, 2019 7:55 pm    Post subject: Exported picture from Zerene stacker looks faded Reply with quote

I have been getting into stacking with Zerene stacker. There will be more questions later, I am sure, but right now I have a mystery. My preliminary stacks are turning out ok, and when I export them as .jpg they have also looked like the image in zerene stacker. Except for this last one, which is of a weird insect (a Derbid planthopper). You can see the PMax stack on the left, and the jpg of that PMax stack on the right. The jpg is clearly faded.
I tried exporting several times and got the same result. I have only done a few stacks so far, and earlier jpg exports of those were fine.
So... what is going on with this one?

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rjlittlefield
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Joined: 01 Aug 2006
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Location: Richland, Washington State, USA

PostPosted: Sat Aug 17, 2019 8:08 pm    Post subject: Reply with quote

From the Zerene Stacker website FAQs page:

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.

What does "Retain extended dynamic range" mean?
As background, you need to know that the PMax stacking method often causes contrast to increase, pushing darks darker and brights brighter. If your source images are already high contrast, then the increase can internally push pixel values to “darker than black” or “brighter than white”. Such values cannot be saved in ordinary image files. By default, Zerene Stacker clips these pixels to exactly black or white when the file is saved, thus throwing away some information you might like to keep. Placing a checkmark on “Retain extended dynamic range” essentially does a “levels adjustment” that reduces contrast and possibly brightens the image, exactly enough to occupy the full range of allowed pixel values, 0-255 in an 8-bit image. This preserves all the computed pixel values so that you can apply your own levels or curves adjustment in Photoshop or any similar tool to get whatever appearance you like best. When using “Retain extended dynamic range”, it's also a good idea to use 16-bit TIFF output, so as to preserve good gradation that might be lost if the extra dynamic range were compressed into 8 bits.

In your case the offending region is probably that small very dark area under the abdomen, which became blacker-than-black as a result of interaction with the light areas around it.

--Rik
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MarkSturtevant



Joined: 21 Nov 2015
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Location: Michigan, U.S.A.

PostPosted: Sun Aug 18, 2019 7:39 am    Post subject: Reply with quote

Ah! Thank you!
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Bob-O-Rama



Joined: 06 Dec 2014
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PostPosted: Wed Aug 21, 2019 2:14 pm    Post subject: And its good to keep the DR and export as TIFF Reply with quote

Hi,

Its also better to keep the DR and export as higher bit depth TIFF. Its washed out in JPG because it compresses the levels to squish them into an 8-bit / channel container.
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rjlittlefield
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PostPosted: Wed Aug 21, 2019 3:28 pm    Post subject: Reply with quote

(From the fellow who wrote the software...)

The image would look equally washed out if saved as 16-bit TIFF. That's because exactly the same squishing is done, into a 0-to-1 floating point space, prior to quantizing the pixel values to 8- or 16-bit integers.

To make the image look right again, you would need to add a curves or levels adjustment, perhaps with some assistance from HDR processing, to restore contrast in the bulk of the image that was not originally brighter-than-white or darker-than-black. The big advantage of 16-bit TIFF is that finer gradation is preserved, so it's possible to do those adjustments without introducing visible banding (posterization).

--Rik
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MarkSturtevant



Joined: 21 Nov 2015
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PostPosted: Wed Aug 21, 2019 8:34 pm    Post subject: Reply with quote

Thanks, again! I will start using Tiff.
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