PHOTOSHOP - image cache level setting can make banding more visible in 16 bit/channel images

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  • Updated 4 years ago
  • (Edited)
input file is a 16 bit tiff file.
i just made it brighter in different editing tools.

it ́s not a question that even 16 bit files can show banding.
the problem is that photoshop, as the most used image application on earth, has some real issues when using the default settings.

the results are quite devasting for photoshop.
in fact every shareware tool i tested did this better.

i don ́t want to imagine how many images i edited where i thought it ́s a tonal problem and i added (unnesessary) noise to the image to get rid of the banding.

this is GRAVE GRAVE issue!!!

the cache level setting should not influence the appearance of an image!



on the left photoshop .. on the right acdsee.

when i set the cache level in photoshop CC preferences to 1 the result looks much smoother and cleaner:



it doesn ́t matter for the problem if i use "exposure" or a "levels" or "curve" adjustment.

i am using:

win7 64bit sp1
intel i7
24gb ram
nvidia 980 gtx (latest drivers)

photoshop is the latest 64 bit CC version.

i also tested this on my notebook with a nvidia 430 graphics card. the result was the same.

the default cache level of "4" showed massive and ugly banding (i did not test higher cache levels).
reducing the cache level to 1 showed much smoother images. all other image editing tools i tested don ́t show this massive banding issues. only photoshop has this problem.

this issue was always labeld an "user error" in the past by adobe employees (advice was : add more noise to avoid banding").

this example clearly shows that it is NOT an user error.
i can reproduce this behavior on my systems and i asked friends who can also reproduce this with photoshop CC.

more info here:

https://forums.adobe.com/message/7530...

grettings from germany.
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Tanja Schulte

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Posted 4 years ago

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Chris Cox

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Official Response
Yes, that is expected because the upper levels of the image pyramid are 8 bit/channel to improve performance. I think there is already a feature request to change the upper levels to 16 bit/channel for 16 bit/channel images (losing performance, but gaining a little bit in quality depending on the exact image and adjustments used).

Yes, the image cache setting can affect the appearance, because of noisy images or subtle changes applied to the image not being preserved in the downsampled levels of the image pyramid.

The true appearance of the image can only be judged at 100% zoom, for many reasons.

And yes, the solution to 99.9% of banding problems is to add a small amount of noise to break up the smooth edges that make the banding (quantization) visible.
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Tanja Schulte

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"(losing performance, but gaining a little bit in quality depending on the exact image and adjustments used).
"

A LITTLE BIT?

sorry but this is plain and simply unacceptable in my opinion.

where is this written in the documentation?
this info is completely new to me and im using photoshop since version 4. there should be a warning or some info in the preference dialog.

i use PS for editing... and only photoshop ...for years.
i always thought the banding issues had something to do with the tonal range of the IMAGES.... now i learn it ́s in many cases an issue with how photoshop is handling the image data. :(

and nowhere did i read a warning about this behavior.
and when people mentioned this all adobe employees answered was "add more noise",

"The true appearance of the image can only be judged at 100% zoom, for many reasons."

now what has the zoom to do with the cache level settings?
where is this info about cache levels above 1 decreasing image quality? and why is the default a setting that cripples image quality?

how should people know this? i sure don ́t and i read a lot and watched a lot of PS tutorials over the years!

of course i know that i can only judge the image quality at 100%... but it never occured to me that photoshop is destroying image data (when displaying images) in such a massive way when i use these settings.

with todays image resolutions you have to zoom out more often then not. i can work on details at 100% but i can ́t edit 36MP files at 100% all the time. even worse are my rendered image who are 60-80+ megapixel.

i also know that banding is a problem with gradients and smooth transitions. and adding noise can help to avoid banding. i work a lot with CGI files and banding is often an issue.

but this CLEARLY is a photoshop issue!
at least there should be a clear warning about this.

i bet often i did not had to add more noise in the past, if only photoshop would display the actual image data and not some ugly approximation.

i know... i know...when not displayed at 100% it ́s always an approximation. unfortunately for adobe other tools do this better!!
and i can ́t judge, for example, the sky of an 36MP image while looking at a small part of it. but when i zoom out then i see this ugly banding that is introduced by photoshop.

how can i judge what im doing when photoshop is not showing me the actuall image data?

people jump to loops to get 10 bit workflow and then this?

so your claim that 99% of the time adding more noise is not the right solution. not when the image you see is destroyed by photoshops internal data handling.

shareware tools i get for free are doing this better.

ps: it ́s not only 16 bit images.
8 bit images are affected too when zoomed.
not as visible as 16 bit files but the banding of 8 bit files is also noticable increased by the cache level setting.
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Chris Cox

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I'm sorry to hear that you don't understand all the issues involved.

Yes, each part is explained in the documentation, but the documentation cannot spell out all the consequences of all possible settings changes and image editing choices.

Yes, the solution to real image banding (quantization) is to add a small amount of noise to break up the visibility of the edges. But first you have to understand where the banding is coming from (image data, display, color conversion, etc.). You want to break up quantization issues in the image, and not be compensating for a bad display or color conversions.

No, shareware tools rarely get this right, and most are much worse when you compare the accuracy and quality of the previews.

Yes, 10 bit/channel display support is still problematic due to video card driver issues and the need for specific displays that can support 10 bit/channel. We will keep working with the display and GPU vendors to make this easier to accomplish.

The image zoom factor has everything to do with the image pyramid/cache levels. When you are at 100% or greater you are looking at the true image. When you zoom out to 50% or less you are looking at the downsampled image pyramid. 16 bit/channel images use an 8 bit/channel image pyramid to improve performance when you are zoomed out. In 8 bit/channel images and 32 bit/channel images this is not a problem, because the pyramid level bit depth matches the base level bit depth. Though in 1 bit/channel images the upper levels are 8 bit/channel, and can cause some confusion when bilevel images start showing averaged gray levels.
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Tanja Schulte

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"Yes, each part is explained in the documentation, but the documentation cannot spell out all the consequences of all possible settings changes and image editing choices."

can you point me to that?
you don ́t have to explain all possible consequences just the grave ones who causes a lot of confusion would be enough.

what i read is.. "increase cache level for better performance".... the downside.. well i NEVER read that it can increase banding!

in fact the help says using a cache level of 1 does not yield the highest quality results for some PS functions.
what does that mean.. best performance or best image quality?

what quality suffers with cache level set to 1?
setting cache level to 1 sure helps avoid banding, as we have seen.

https://helpx.adobe.com/photoshop/kb/...

is there an updated page for CC?

about the quality of the photoshop display....

look at my screenshots from acdsee and photoshop.. tell me photoshop does not look much worse... can you do that with a honest face?

i can give you screenshots from other applications too.

i understand the cause of banding .. what i don ́t understand is why photoshop is using such a image quality decreasing features as DEFAULT.

and as you can see in the thread i linked above (where you did not give this answer by the way.... all you said is "add more noise") many others have the same issues with this photoshop behavior.

" In 8 bit/channel images and 32 bit/channel images this is not a problem"

unfortunately i found this not to be true.

it is LESS visible for 8 bit images but is is still visible.
i can see clearly when cache level is set to 1 or 4 on problematic images.
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Tanja Schulte

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anyone who can answer the question about this statement in the online help?

"...a cache level of 1 does not yield the highest quality results for some PS functions...."
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Chris Cox

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Using cache level of one will slow down many operations (previews, healing, alignment, some filters, some resizing, etc.), and result in lower quality in many operations (healing, quick select, etc.). Using a cache level of one really isn't a great idea unless you really know what you are doing.
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Tanja Schulte

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thanks. i still don ́t get why disabling a preview cache makes the image quality worse. but i have to believe that.
the internal PS calculations (for filters and the healing brush etc.) rely on the cache level for the preview?

so what IS a great idea to get rid of that ugly banding when a higher cache level is used?

i can ́t always zoom to 100% .. it ́s not practical.
with todays photo resolutions you have to zoom out.
and for judging an image i need to see it as whole.
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Chris Cox

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zoom in to 100%, or keep a second window for the document open at 100%.
Even in other bit depths, you need to judge the final quality of your images at 100% zoom.
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Tanja Schulte

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unortunatley that seems to be true ....except when i use other programs who don ́t have the issues photoshop has.

i would really advice to rethink this approach and work on making this banding go away. that it is possible are shown by other tools who behave much better than photoshop.

people buy 30inch 2560x1600 pixel monitors and all they see at at fullscreen view in photoshop is some ugly approximation. :(

again im aware that you have to redcuce the resolution when you display a 24 or 36MP image on a 2560x1600 pixel display. the issue i have with PS is the quality in that photoshop does it (as demonstrated above).

this simply sux:

https://d2r1vs3d9006ap.cloudfront.net...
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Chris Cox

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No, it is true in all applications. As long as you are looking at subsampled values, you can't see the accurate result of your adjustments. The worst case sample of this is a 2x2 checkerboard of black and white pixels -- at any subsampled level you will see 50% gray, and any adjustments will not look correct applied to 50% gray.