Banding issues visible in photoshop CS6

[beautyb1]

I have only used this forum once before and I am hoping they can help with this query and appreciate the support. 

I seem to have more banding issues when using gradients or painting solid colours after I upgraded my RAM from standard 8 mb to 24 mb.  Perhaps just a coincidence or maybe something in the PS preferences needs changed ?

I have attached a file below (1) which is saved as 8 bit jpeg, it was created from 16 bit file and then I used a soft round brush to roughly paint three colours RGB 0/0/0, 65/65/65 and 128/128/128.  This has more banding visible in photoshop than I expected but would appreciated the forums view ?

I then created a blank document (2 below) in photoshop, 8 bit, gradient map black to white, then added Levels layer and set output to 120 to 140, added another Levels layer and set input to 120 to 140 to see level of banding. 

I then repeated this (3 below) but only difference was in a 16 bit file and I expected to see a smoother gradient and less banding but no real difference on my display in photoshop which seems strange on my iMac 27" 2013.  But it does look different below when both saved as 8 bit JPEGs.  I thought I would see a difference on my display rather than just when I finally saved down as 8 bit JPEG ?

Any support much appreciated. 

Thanks

Mark

1) Paint 000, 65 and 128

2) 8 bit

3) 16 bit

[D Fosse]

Short answer: In a 16-bit file, any banding you see is in your display system (panel, profile, calibration tables, more rarely video driver).

The only exception is for jpegs, where the compression algorithm can introduce banding. But this is most often color banding, not luminance banding.

I don't see anything out of the ordinary in your examples. Keep in mind that even if you work in 16 bit depth, the display usually operates in 8 bit depth. So you will always see the 256 individual steps.

This is usually not visible in photographs, because even the most fine-grained photo contains just enough noise to break up the banding. It only shows with synthetic gradients.

[beautyb1]

Thanks D Fosse, I really appreciate you taking time out, explaining and confirming.

Can I please ask a couple of follow on questions to deepen my understanding ?

You confirmed that ........... In a 16-bit file, any banding you see is in your display system (panel, profile, calibration tables, more rarely video driver).

The only exception is for jpegs, where the compression algorithm can introduce banding. But this is most often color banding, not luminance banding.

1) When you mention displays usually only operate at 8 bit depth, hence I assume I would not see much difference on my display in photoshop if I worked on 2 identical images, albeit one was 8 bit and one was 16 bit. 

When I saved these 2 images in my original post i.e. images 2) and 3) as 8 bit JPEGs I could see a marked improvement in the 16 bit original image which is what i expected.  Why can I not see this difference in Photoshop but I can when they are converted to 8 bit JPEGs and viewed in Preview or a photo application ?  Is it because you only see the full impact of the layers in photoshop when you flatten the image ? Is there a way to see the real impact in PS before flattening ?

2) Do you have any good tips on how to add gradients or paint with solid colours and avoid creating banding in photoshop ?  I am aware of adding a small amount of noise but wondering if you can do something when painting rather than fix after with adding noise ?

Thanks for sharing your thoughts so far, much appreciated.  I just wanted to check the above before marking your response as the correct answer.

[D Fosse · Accepted solution]

8 bit banding is cumulative. If the original is 8 bit, and then viewed in an 8 bit display system, you won't see any additional banding if the RGB numbers are sent directly and unchanged to the display. But in a color managed environment that doesn't happen, the numbers are converted - altered - into your display profile. The result is odd intervals.

With a 16 bit file you don't get this cumulative effect, and the result should ideally be a clean transformation into 256 equally distributed steps. A 16 bit file has roughly 16000 individual steps from black to white. There is no banding there.

The video chain operates in 8 bit depth from video card to monitor (unless you have a high-end 10 bit display system and monitor). Any calibration adjustments in the video card again offsets 8 bit values against each other. A faulty display profile or a low-quality display panel (such as a laptop screen) can have inherent banding issues.

The only way to avoid banding in synthetic gradients - aside from investing in a 10 bit-capable monitor and video card - is to add noise. Very little is needed, well below any obviously visible threshold. Again, consider a very fine-grained, low ISO photo. It's virtually noise-free - but still enough to break up any on-screen banding.

[beautyb1]

Thanks D Fosse