Gradient banding problem

[kevinashworth]

Hello. Got an odd problem with a pic. After using gaussian blur on a shape, theres stripes/bands in the gradient between light and dark. It's stepped rather than smooth. Does anyone know whats going on?

[Pat]

Kevin I don't know if this will be of help to you or not but I've found that if I'm a little too heavy-handed with the gaussian blur to reduce noise in an area of an image with little detail I'll get banding. Apparently a certain amount of random noise is important to give you smooth total gradations particularly when working in 8 bit.

Pat

[Jonas.Wendorf]

Banding occurs because there's too little tonal variation between the start and end point in a given space.

Things to try are for example working in 16bit or adding noise (as suggested) or (and I find that works even better in some cases) using the "Filter"-"Brush Strokes"-"Spatter" with the lowest possible spray radius and a smoothness of 1.
That'll add noise to just the bands, so you don't need to apply it everywhere.

Btw. At what zoom level are you? These bands could be lessened by a Gaussian Blur if it's 100% (although you'll introduce new bands which you could than defeat with the techniques above).

[kevinashworth]

Hi Pat, Hi Jonas

Heres the pic at 100%. It's everywhere! It's definitely gaussian blur thats causing it. Usually i keep a layer of grain at the top to use at the end to overlay over everything. The grain does hide it, but doesn't get rid of it completely. I tried to break up the banding with healing brush, but it just seems to push it around.

It's so odd! I've never had this before, and been using the same methods i usually use. I will switch to 16 bit and see what happens

[kevinashworth]

Wow. 16 bit works!  :wnw:
So does that mean 16bit is higher quality than 8, or less? I can't see any difference in the quality, but the banding has gone! But why?

[Mhayes]

Great post!

Kev, I can't argue that is does look better and appears to work, but the bad news is that you can't convert our original 8 bit jpgs to a 16 bit, because they are not Raw files. The reason being is that jpgs  can only be 8 bit and converting them will not result in a true 16 bit. All photos on copy runs are high quality jpgs, because taking in Raw would have meant huge file size and more work later and not practical. For someone doing very high quality photography work with a Raw files, 16 bit is a good choice. The other thing is that a jpg will not support 16 bit, so the minute you flatten a file be it a tiff or psd and save; it will go to an 8 bit size. Also, some of the features in Photoshop you will not be able to use if your file is 16 bit.

Scott Kelby has published a book for each of the different PS editions and in his latest: The Adobe Photooshop CS5 book for digital photographers; he touches on 8 and 16 bit. He also explains that  more tweaking to a photo will often cause banding. Gradients will not have the smooth transitions in 8 bit that they do in 16 bit. On pg 365 of Scott's book, he recommends going to Filter>Add Noise and set the amount to 4% and click on the Gaussian and Monochromatic checkbox.

Some good links:  http://www.luminous-landscape.com/tutorials/bit-depth.shtml

http://digitaldailydose.wordpress.com/2009/11/17/8-versus-16-bit-what-does-it-really-mean/

Margie

[kevinashworth]

Well Margie the plan is to use any means necessary to get get rid of the problem. I want pure smoothness at any price. I don't want to introduce any amount of noise during restoration. It's got to be smooth. Grain is introduced at the end.

But don't worry, once it's complete i'll save the image as a high quality ping, then re-open a fresh copy of the original jpeg, and import my finished job on a new layer above it and save that as the final jpeg version for uploading. That way it meets all the technical specifications of the original, keeps all the exif data intact, has no banding and looks gorgeous.

[Jonas.Wendorf]

Kevin, well, let's just say, the tonal range in 16bit is 2^15 instead of 2^8 in 8bit.
However some experts argue, that this comes in important in real world images and that it'd be just noticeable in technical images with gradients etc. ;-).
Personally I don't work in 16bit often because I find it overkill and after a long series of tests didn't find the benefits to be huge. Though my computer slowed down considerably -> easy choice ☺.
And, as Margie said, 16bit is most beneficial if you really have a tonal range that is greater than 8bit (e.g. a RAW file).

Margie, while Kelby is right that converting from 8bit to 16bit won't gain you anything, you can still apply certain filters in 16bit which will then create a full tonal range (e.g. the Gaussian Blur will create steps between the values that weren't possible in 8bit).
If you convert the images back to 8bit after that, the image gets interpolated again and therefore the banding is gone in many cases (as can be seen in the screenshot which is 8bit).

[kevinashworth]

Margie thank you for going to the trouble of providing those links, i've just been reading them. I can see why 16 bit has helped here. It increases the tonal range.

At first i tried increasing the size of the image to 200% to create more pixels for the gradient to spread out over, but it didn't work. Now i see why it couldn't work.

Jonas the reinterpolation of pixels is what i was hoping would happen when i import the finished job back into a fresh .psd so it looks like the plan will work. My PC has slowed up a little, but if this new trick gets the results i want i can live with that. Yay! Thanks again you three!

[Hannie]

Great information on 8bit versus 16bit!
I'm not sure when your changed mode to 16bit to get rid of the banding or did you convert before adding Gaussian blur?

Thanks,

Hannie

[kevinashworth]

Hannie yes i did have to convert before applying the blur. the blurred object was held on a layer of it's own. I hadn't merged the object to the main pic, so the gaussian blur wasn't commited (?) yet. If i had continued to work in 8 bit and merged the blurred object to the main pic the banding effect would have been rasterised and irreversible, so i kept it on it's own layer, switched to 16, then the problem disappeared and then i merged it in.

[Mhayes]

Thanks Jonas and Kev, you provided a lot more information on how to use this. I knew that Kev's example looked better, but didn't think it would hold up once he flattened and saved. Jonas your explanation helped a lot.

Margie

[Hannie]

Thanks Kev and Jonas! 

In the past I did a little experiment scanning an old photo in both 8bit(24bit color) and 16bit(48bit color).  I found no significant improvement working in 16bit.  For the size of the photo 8bit was perfect.  Also the size of the 16bit image was huge and slowed down the computer.

The use of a 16bit layer to get rid of banding is great.

Hannie

[kevinashworth]

Thought i'd show you the bigger picture. I think it's ready to upload. What would you say?

Also this is the first ever pic i got to use the FFT filter for, to get rid of the honeycomb texture in the photo. Very much a learning, yet rewarding project.

[Atlantis]

OMG this looks stunning, like brandnew.
Could you please do a step by step tut on your workflow in this one? I'd love to learn.