Dither Gradient

[SmallBear]

Hi

I would like to learn how to remove banding that arises in  combination with gradients. Does anyone have a good trick to make the gradient smooth and what are the steps to do this?

thanks!

[davescm · Accepted solution]

Hi

Two things:

1. Work in 16 bit - there is much less chance of banding in your image. You may still see some on screen as your display will still be 8 bit (or 10 bit for a high end display and card)

2. Add a tiny bit of noise to your image (Filter - Noise -Add noise). It takes very little to hide the banding

Dave

[Terri_Stevens]

Dave have you taken a course in express typing , your far to quick for me lol

[davescm]

Must be the coffee Terri

Dave

[Terri_Stevens]

The usual approach is to use 16 bit images instead of 8 bit and select 'Dithering' when applying the gradient.

[rayek.elfin]

When working in "16pbc" mode in Photoshop, the user must also be aware of a long-standing limitation in Photoshop that creates visual banding on the screen when there actually is no banding at all.

Zooming out in 16pbc mode (in my case around 64% and lower) causes banding due to how Photoshop works with the data when presenting it. So be very careful when you work in 16pbc mode and zoom out: banding will become quite apparent in some cases. Resist the urge to "fix" things in this case, because Photoshop is merely not displaying the image correctly.

This only happens in 16bpc mode, btw.

According to Chris Cox (senior dev for Photoshop):

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.

[Terri_Stevens]

good point , anything other than 100% view or anything divisible by 2 ie 50%, 25%, 12.5% will result in Photoshop averaging the image and be misleading

[rayek.elfin]

Terri, it goes deeper than that: unlike every other image editor on the market, Photoshop's legacy code limits its 16bpc mode somewhat:

1. it is not full 16bpc, but rather a 15bpc one - in short, PS may clip values when a full range HDR image is imported, and saved again. This is problematic for CG/FX/3D purposes.
2. at the time 16bpc was introduced in Photoshop the developers decided to use 8bit down-sampled image data to display 16bpc images when zoomed out, which means that at ~64% and lower zoom levels 8bit image data is used instead of the full 15bpc data to render the image to the screen.

I recorded a quick video (be sure to watch it at 720HD quality and full screen) to demonstrate the effect:

Photoshop 16pc banding - YouTube

No other image editor capable of working with 16bpc image data has similar limitations. It is a bit unfortunate, and a source of confusion in particular when PS users complain about visual banding: is it true banding inherent to the image, or is it caused by Photoshop's limitations, and is the user viewing a zoomed out 16bpc image (probability: high!)?

[davescm]

Yes, good reminder!

Although this thread is about the banding, that preview "pyramid" also impacts blending and the impact of sharpening etc, so in an often repeated mantra in this forum   "always check your image at 100% zoom"

Dave