Banding problems... why?

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Fri, 13 March 2009 08:53 Go to next message
Smurfy (Photoshop expert)
A file I'm working on has heavy banding when greys fade to black. Even
applying a blur on this banding will not fix it (oddly enough, it seems to
make it worse).

It's a straight up, high-res, 8-bit per channel RGB file. Nothing unusual
about the gradient. Not sure what circumstances are causing the banding
here, but it's there, in this file. And the more we turn up the brightness,
the more obvious it becomes.

Anyone have any clue what I can do about this? I gotta send this off to a
printer, for a 10'x10' booth display, and I'm afraid the banding will come
through.

Using CS4.
Fri, 13 March 2009 11:46 Go to previous messageGo to next message
jaSPAMc (Photoshop expert)
"Adam" <no@thanks.com> found these unused words:

>A file I'm working on has heavy banding when greys fade to black. Even
>applying a blur on this banding will not fix it (oddly enough, it seems to
>make it worse).
>
>It's a straight up, high-res, 8-bit per channel RGB file. Nothing unusual
>about the gradient. Not sure what circumstances are causing the banding
>here, but it's there, in this file. And the more we turn up the brightness,
>the more obvious it becomes.
>
>Anyone have any clue what I can do about this? I gotta send this off to a
>printer, for a 10'x10' booth display, and I'm afraid the banding will come
>through.
>
>Using CS4.
>
Might try a low setting of grain. If it's 'pure grey' then there's nothing
to break up the perception of the step. Nature isn't 'pure' so we get
smoother 'steps' in 8 bit.
Fri, 13 March 2009 18:56 Go to previous messageGo to next message
gowanoh (Photoshop expert)
Without having any idea what you are seeing:
Some processing steps/filters add banding that is more prominent in some
images than others.
If the image originated as a jpeg and has banding I don't what can be done
about it.
A freshly opened raw image should not have banding, barring some major
camera problem, so the banding has to have been added somewhere in your
processing steps.
Fri, 13 March 2009 20:56 Go to previous messageGo to next message
Geoff J (Advanced Photoshop user)
"Adam" wrote in message...
>A file I'm working on has heavy banding when greys fade to black. Even
>applying a blur on this banding will not fix it (oddly enough, it seems to
>make it worse).
>
> It's a straight up, high-res, 8-bit per channel RGB file. Nothing unusual
> about the gradient. Not sure what circumstances are causing the banding
> here, but it's there, in this file. And the more we turn up the
> brightness, the more obvious it becomes.
>
> Anyone have any clue what I can do about this? I gotta send this off to a
> printer, for a 10'x10' booth display, and I'm afraid the banding will come
> through.
>
> Using CS4.
>

Are you sure it is not your monitor that is wrong? The reason I ask is that
a few weeks ago I was advising someone who reported a similar problem that
turned out to be caused by his display somehow getting changed from 32 bit
to 16 bit. Try looking at others images on your screen or your file on
another computer, if only to rule out the problem being with your display.

--
Geoff J.
Sat, 14 March 2009 04:19 Go to previous message
Mike Russell (Photoshop expert)
On Fri, 13 Mar 2009 08:53:51 -0400, Adam wrote:
Good advice from others. I would add a couple of points by way of
clarification.

> A file I'm working on has heavy banding when greys fade to black. Even
> applying a blur on this banding will not fix it (oddly enough, it seems to
> make it worse).

Yes - banding is a low frequency phenomenon and is not easily removed by
blurring.

> It's a straight up, high-res, 8-bit per channel RGB file. Nothing unusual
> about the gradient. Not sure what circumstances are causing the banding
> here, but it's there, in this file. And the more we turn up the brightness,
> the more obvious it becomes.

Is it a photograph or an artificially generated image? Can you see the
banding in one channel, or is it in all the channels? Making the image
artificially brighter is not necessarily an indication of what will happen
in print.

> Anyone have any clue what I can do about this? I gotta send this off to a
> printer, for a 10'x10' booth display, and I'm afraid the banding will come
> through.

As a general rule, remove banding by adding noise to the channel that has
the problem, perhaps using a mask to restrict the noise to the shadows,
though this is not generally necessary because the noise will affect mainly
the shadows. After that, it may be appropriate to blur.
--
Mike Russell - http://www.curvemeister.com
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