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how to avoid "color banding" "banding" and "posterization" ?

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  #21  
Old 05-17-2007, 03:16 PM
yuccaview yuccaview is offline
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Re: how to avoid "color banding" "banding" and "posterization" ?

I think anytime you are working in 8 bit and trying to add a graduation you WILL get banding and working in jpg is the worst thing you could do.If you add
noise to the problem area you need to run a MOTION blur not gaussian.
To avoid the problem altogather open the raw file in 16 bit do everything
you need to do with graduations then convert to 8 bit. You will never get a jpg image not to band there just is not enough information in the file.But if you
cannot start over in 16 bit open the channels seperate them add noise to the worst then motion blur the offending area, this will even out the bands somewhat but even this is hit or miss.I would NEVER work in jpg ever for
any retouch no matter how simple the job was, again the way to eliminate
the problem altogether with banding in graduations is 16 bit then convert to 8 bit.
Don
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  #22  
Old 05-17-2007, 03:26 PM
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Re: how to avoid "color banding" "banding" and "posterization" ?

thanks

didnt work in jpg of course, i work in .psd at 8bit, for faster working results
(saved the 2 examples as JPG for faster upload, misunderstanding, sorry)

maybe i really should work in 16bit from raw from now on.
but then i guess i will need a new workstation Mac pro with 4GB RAM, my new imac 24" 2,1 Ghz with 3GB ram wouldnt be capable of 10 or 20 layers in 16bit, fast working, yes?

for the motione blur, may i ask why first adding noise and then motion blurring?
the blurring will erase the noise again. maybe i understand something wrong?

Last edited by pure; 05-17-2007 at 03:33 PM.
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  #23  
Old 05-17-2007, 06:00 PM
yuccaview yuccaview is offline
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Re: how to avoid "color banding" "banding" and "posterization" ?

You only need to work in 16 bit when you do the graduations, apply those then switch to 8 bit,I don't know anyone who has enough horsepower to do everything in 16 bit.Try adding some noise to something then a motion blur
you will see what I am trying to say, try anything file and you will see the noise streak
at what ever angle you set and that sometimes covers the banding.I have to do that on some airbrush work when I am not in 16 bit because of the banding.
It happens on large backgrounds and of course the graduations.
Don
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  #24  
Old 05-25-2007, 08:03 AM
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Re: how to avoid "color banding" "banding" and "posterization" ?

thanks

enclosed is a sample pic.



if anybody could take a look please? i cant get rid of that heavy banding.

i tried adding noise to the sky/clouds which have a major banding, in the foreground is a running person, the sky has been added by myself. (from another source.)

so if i add noise to the banding sky it looks like it is gone for 75%. (the banding) then when i do a motion blur, the banding appears again, as the noise is gone. (45 degress or whatever)

any idea?

thx
Attached Images
File Type: png band.png (67.2 KB, 53 views)
File Type: jpg band2.jpg (23.0 KB, 44 views)

Last edited by pure; 05-25-2007 at 08:13 AM.
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  #25  
Old 05-25-2007, 02:56 PM
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superkoax superkoax is offline
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Re: how to avoid "color banding" "banding" and "posterization" ?

huh? I'm looking at the pictures, but don't see what I'm supposed to see...this is by far the most technical thread I've ever read in RP.com :P

This is something I should learn...man!!! *NERVES*


Gerry
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  #26  
Old 05-25-2007, 03:05 PM
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superkoax superkoax is offline
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Re: how to avoid "color banding" "banding" and "posterization" ?

http://www.graphics.com/modules.php?...icle&artid=288

can this be helpful to you're banding problems?
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  #27  
Old 05-25-2007, 03:17 PM
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Re: how to avoid "color banding" "banding" and "posterization" ?

thanks for your help

its a bit complicate, and some retouching collegues are reporting same thing
even with raw images coming from a h1 or h2 (hasselblad), at 8bit , there is usually some banding in the sky, if it is a "heavy" composition with many sky elements, many layers and 50 or 100 masks and lots of gradients in the mask. and so on... would love to work in 16bit, although i cannot, working speed is too slow and i cant do any corrections in the skys after converting to 8 bit.
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  #28  
Old 05-30-2007, 02:16 PM
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Re: how to avoid "color banding" "banding" and "posterization" ?

here is the same trick a bit different by garyblack. (for whom who is interested)

by the way, today i tested to develop a Raw in 16bit to see if banding is there. before i developed in 8bit and there was banding in the gradient. the shot is a stilllife image, a piece of glass standing on a grey background which fades to black. in the background is banding. the image comes from a 39Mio pixel Hasselblad H2. the 16bit image had the same banding in the image, althoug i didnt touch it. straight after exporting from flexcolor app.

"I am having problems with "banding" in Photoshop. Any suggestions?



Answer:

1. Start by making a new layer in Photoshop, select Overlay mode and check
the "fill with overlay neutral color" radio button in the dialog. You can also use Soft Light for a more subtle application of noise or Hard Light for heavier noise.

2. Apply noise to this neutral gray layer only. In RGB this will be a true 50% gray but in CMYK the channel values depend on the CMYK set-up.

3. Flatten before output

This method has the advantage of ramping the noise off in highlights and shadows with zero noise in black and white values thus preventing a dirty look. This also allows you to add more noise that you might be able to otherwise in the most troublesome areas of banding. You might also experiment with applying slightly different amounts of noise to individual channels (still only on your noise layer) with higher percentages in channels with the most banding."

i will test this tomorrow and report... thx for your attention
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