Dither Gradients Preference and Gradient Banding?

[dhayton]

FYI, this question has to do with AP:

 

Looking at a recent image, I noticed some faint banding that was visible when I applied a color gradient (maybe it was there in the B&W version, but I couldn't see it). See the darker of these two images: https://forum.affinity.serif.com/index.php?/topic/20687-photos-from-a-mountaintop/(FWIW, I see the banding on my non-retina, late 2013 iMac; I haven't checked on other machines).

 

Searching the forums I came across a comment about the "Dither Gradients" preference and the different effects if you are working in 8-bit or 16-bit (see MEB's comments in this thread: https://forum.affinity.serif.com/index.php?/topic/13742-unwanted-noise-in-gradients).

 

So, my question: If I'm working in 16-bit, is it better to leave "Dither Gradients" preference checked? Or unchecked?

 

Thanks,

Darin

 

[MEB]

Hi Darin,

It's better to leave Dither Gradients checked as this will help to remove/eliminate the banding when creating gradients no matter if you are working with 8 bit or 16 bit images (although you will get better results with 16bit + dither).

[scottkane]

Hi, I have dither gradients, and no matter what I do I have banding, I tried also to work in 16bits, then convert to 8bits (flattened image), and nothing fixes the banding, when you work in 16bits in photoshop and then you flaten image and convert to 8 bits, it applies a perfect dither and no banding is there. This gradient is added from a layer style, is there possible to fix this?

Edited March 26, 2020 by scottkane

[Armelline]

Also having this issue when creating a gradient. No matter what I try I can't get rid of gthe obvious banding. Anyone figured this out since it was last posted?

[NotMyFault]

There are multiple possible reasons why you get banding during rendering in Photo (how the file is displayed in Photo). This is only  preview which might differ from exported files.

First of all, if you export the image (as PNG to avoid jpeg compression artifacts), does the export have a banding issue when opened with a web browser? If yes, the banding might be caused by limitations of your system (Monitor / display adapter / driver / OS settings). It could be limited to 8 bit per color channel, whereas other settings or configurations might be able to display 10 or 12 bit color depth.

I recreated your test image. In Photo, you can activate "Dither Gradients". This smooths gradients, but only for display in Photo. It has no impact to exported files. For me, this settings removes any visible banding. Even when disabled, the gradient is much smoother vs. your screenshot.

PNG file with 16 bit, showing almost no banding

Screenshots (limited to 8 bit color depth by OS, so showing more banding than reality)

banding test.afphoto

[Paul Coddington]

I'm seeing an odd pattern of banding with gradient overlay in Designer at the moment, that ripples badly while adjusting settings, even in 16-bit document with 10-bit video output to calibrated monitor, not just while editing but also after export to PNG 32.

Not seeing banding in SVG files imported into Affinity from elsewhere (eg: from Wikimedia Commons), but rather only in objects I create. I have emailed support tonight, but just realized my attached document was accidentally set to 8-bit (however, re-testing with a 16-bit document does not solve the problem).

There has been some major optimization with the latest version, so I'm wondering if this is a new problem others are encountering?

But I might have made a silly error due to fatigue, so I am not jumping to conclusions yet. I have not seen this problem before now, but I haven't used gradients much until this week (I've been doing 'old school' animation-cel style art and simple icons for software). That gradients are smooth for SVG imported into Affinity, both when edited and exported to PNG, but not for vectors created from scratch within Affinity using gradient overlay FX is an interesting puzzle. Likewise, those SVG files are smooth in photo viewers and web browsers.

[NotMyFault]

Hi Paul,

There are open issues regarding banding. But it depends how the gradient has been created. Can you share an document to reproduce the issue?

I have no issues creating smooth gradients, if a avoid some of the cliffs like merging, 8-bit color mode, staying away from advanced functions from Layer FX like profiles etc.

 

 

[Paul Coddington]

Hi NotMyFault,

After I posted, I realized that what had happened was that my gradient had been accidentally created in an 8-bit document, but remained seemingly stuck in 8-bit when the document was corrected later to 16-bit, which seemed unexpected behavior for what I had assumed about the nature of vectors.

When I recreated the overlay in 16-bit, it greatly improved, although not quite as smooth as the imported SVG version I had tried to reproduce (as practice and learning curve), but people would have trouble seeing the remaining banding on an average monitor, I think. So, I can still see some very slight gradient banding on objects I create, but not on imported SVG, which indicates things could be a little better, but the problem is not enough for anyone to really notice unless really squinting.

Interestingly, when I had the gradient object visible, PNG would export as 32-bit (unexpected, so was not noticed at first), but when I had it hidden, PNG would export as 64-bit. Unfortunately, I have already corrected the problem and moved on to getting my Windows 11 upgrade underway and the files I emailed in are probably not much help after all, given my initial take on the problem was erroneous.

But today I learned that not all vectors (or rather effects applied to them) in a document take on the bit depth of the document, and the bit depth of the export can depend on which objects are visible. Not sure if that is expected behavior or a glitch, but at least it can be worked around once understood.

[borntobe]

Hey, I have 8-bit png image rendered in 3D software with perfect gradient transition, but when I drag it to affinity photo for postproduction and use your Develop Persona it always gets these nasty dither gradients bandings, that's really disappointing...

[Old Bruce]

What happens if you don't use the Develop Persona? If you are starting with an 8 bit PNG I would just open it, change the bit depth to 16 and work in the ordinary Photo Persona. I can't see any advantage to working with an 8 bit PNG in the Develop Persona.

[NotMyFault]

9 hours ago, borntobe said:

Hey, I have 8-bit png image rendered in 3D software with perfect gradient transition, but when I drag it to affinity photo for postproduction and use your Develop Persona it always gets these nasty dither gradients bandings, that's really disappointing...

It depends on what operations you are using. 8 bit color depth does not leave much room for color stretching. Develop Persona is for RAW files, which are 32 bit normally. There is no reason to use the Develop Persona for non-RAW images, as all relevant operations can be done in Photo Persona, and non-destructively. I would not expect you need one of the rare functions only available in Develop, e.g. chromatic aberration removal, for rendered files.

Can you upload the actual file, or a relevant part of it, and list your edit steps?

[borntobe]

I tried whatever you suggested, but then even if I just import and export it without touching anything, still get these gradient bandings...

that's when comparing the two images in windows 11 image preview

[NotMyFault]

We would need the actual files in PNG format to investigate deeper.

Possible causes:

• export settings differ from source file
• palettised export
• Color profile changes

A PNG file can be read and exported losslessly in Affinity Photo. If the export differs, there is a reason.

[borntobe]

Sure, here are the files, thank you!

[NotMyFault]

21 minutes ago, borntobe said:

Sure, here are the files, thank you!

 

 

 

Interesting. The before / after files are visually identical (when opened in Affinity Photo, on MacOS). The 3rd file showing both side by side shows differences. What application are you using for the 3rd image?

[borntobe]

Thanks for the prompt replies - it's just windows 11 image preview windows that have the option to compare multiple images...

[NotMyFault]

I have no clue, and can't test under Windows 11. maybe OS specific issue.

Can you try to use the file compare cmd line utility (fc.exe) under Windows? Maybe a bug in Windows 11 how it renders PNG files. 

 

Can you please try:

1. Open Photo
2. New Stack
3. add before  after image
4. deactivate alignment
5. execute
6. when document opens, remove both images from stack (move them out of stack, above)
7. select top layer
8. set blend mode to "difference"
9. the rendering goes black
10. add levels adjustment on top, above all existing layers
11. set "white level" to 0. If there is any difference between layers, it will be emphasised and clearly visible. On MacOs, no difference!

stack of image for differences.afphoto

[Pšenda]

Yes - before and after is "same" image (same file data - see content comparison, for example Total Commander).

[borntobe]

Ok, thanks, but if they are the same why do all renders look seamless, but after being exported with AP getting these gradient bandings on windows preview? Windows bug? so what to say to the person I'll be sending these - if the images look bad it's because of your Windows. or maybe just don't use Affinity Photo for the post-production?
Also if they are the same, why the render is 2.24 MB and after AP export 1.74 MB

[Pšenda]

17 minutes ago, borntobe said:

Also if they are the same, why the render is 2.24 MB and after AP export 1.74 MB

The files you put here are exactly the same size.

[NotMyFault]

Can you make screenshots of the exact export settings, including „more“?

 

[borntobe]

hm, that's strange, because on my end they are not the same size, please check out the image and I add them to zip file this time...

hm.rar

[Old Bruce]

Mac doesn't like RAR files, unable to open it.

41 minutes ago, borntobe said:

check out the image and I add them to zip file this time...

Aside from that I noticed that there is no Profile in the ones you posted earlier and there is an Alpha channel.

[walt.farrell]

9 minutes ago, Old Bruce said:

Mac doesn't like RAR files, unable to open it.

You would need an app like Unarchiver (or possibly others) from the MAS.

[NotMyFault]

I posted a false conclusion and deleted that post to avoid further confusion.

on Mac, both files look identical, both in photo, and in Preview.below my screenshot of both files side by side in preview.

Initially it looked different, but that was caused by color burn-in of my LG display (which will be healed automatically every day when in sleep mode).

I do not trust Windows Photo / Preview: it was never able to correctly handle color profiles.