Gaussian blur banding question

[WraithBand]

Hello,

I have an issue when applying gaussian blur on my photos.

I'm working in 16 bits, that means when I export photos from lightroom to photoshop my export parameters are all in 16 bits under lightroom.

I checked that my image => mode is in 16 bits aswell under photoshop. I'm working in Prophoto RGB colour mode.

My screen is a BenQ SW2700 calibrated with a spyder pro 5. That means a 12 bit compatibility screen.

The problem is when I apply a Gaussian blur on Photoshop, even a small one (let's say 30 px) banding appears on my picture.

Is there something I didnt set up correctly ?

PS :

- My photoshop version is 21.0.0 and Lightroom is 8.4.1

- I'm working on W10

- My GC is a Geforce 1060 6Gb

[davescm]

Unless you have set up 30 bit display in Photoshop >Preferences >Performance >GPU Advanced and have a display chain that supports 30 bits all the way through  i.e. GPU card and driver (open GL), monitor and use of the correct ports  then you will be using 8 bits /channel for display. If any link in that chain is not capapble then you will only have 8 bits/channel.

Note : Lightroom uses dithering to hide banding even on 8 bit displays so do not assume that because you see no banding in Lightroom you are using more than 8 bits for display

Dave

[WraithBand]

Many thanks Dave for your explanations.

I think ports isnt a problem nor my monitor but maybe the GC.

Under NVIDIA control panel I can't change to 10bpc (it's greyed out to 8 bpc).

I 'll try to find out why.

Anyway I'm just surprised that a simple gaussian blur (even a small one) triggers so much banding !! I wanted to try adding a small orton effect to one of my photo and it's a total mess (banding). I'm just wondering if there isn't another issue on my Photoshop settup. That means one cannot apply a gaussian blur in 8 bit without banding...

[D Fosse]

What Dave is saying is that banding is in your display system, not in the data.

Photoshop works in 16 bit depth, but the display chain is 8 bit depth only, and that's where the banding happens - unless you have a 10-bit capable system.

And yes, Lightroom uses dithering. It does not support 10-bit display at all.

[WraithBand]

If it's not in the data, can you explain to me why when I post the result on whatsapp with my mobile, the banding is still here ?

I suppose mobile phones are 10 bit compliant ?

[D Fosse]

That's an 8 bit jpeg (or png).

The whole point here is that banding happens in 8 bit color depth, not 16. At 8 bit depth, like in your display pipeline, you only have 256 discrete steps per channel. With a narrow gradient, banding cannot be avoided.

In addition, jpeg compression is very aggressive and very destructive, and introduces its own banding.

Oh, BTW, why would phone screens be 10-bit capable, when only the most expensive desktop monitors are?

[davescm]

As D.Fosse said, when you post on facebook, whatsapp etc you will be using a jpeg file which only supports 8 bits/channel. So even on the best monitor in the world , it will still only be 8 bits.

As an aside, don't believe all the marketing hype about phone displays. A phone display is one of the most unreliable displays around. It is often wide gamut i.e. displays a wider range of colours, but does not use colour management to ensure those colours are displayed correctly (that applies to both iOS and Android) resulting in over-saturated colour. It will also be using 8 bits/channel.

Dave

[WraithBand]

Ok, I suppose I need to work in 8-bit so if I want to post my photos on FB or Insta I see the same.

Thank you very much for all explanations !!!

[D Fosse]

The standard way to remove banding in 8 bit data is to add a tiny bit of noise. Not much, just enough to break up the banding. This is identical to the dithering that Lightroom does.

This is also why you normally don't see banding in photographs. Even the most fine-grained low ISO shots contain just enough noise to conceal any banding.

[WraithBand]

Ok I'll try that ! 

I found a tutorial on a photogeaphy website :

1. Create a new Overlay layer filled with 50% gray by clicking Control+Shift+N and setting mode to Overlay and checking “Fill with Overlay-neutral color (50% gray).
2. Add noise to this overlay layer by selecting Filter => Noise => Add Noise. Make sure that distribution is set to Gaussian and the amount of noise needed will depend on how severe the banding in your particular image is, but usually it’s in the range of 1-5%.