Posterization problem, need help

[Dan Brown]

I have tried 3 times to post this image in the Avian forum. It looks fine in PS CS3, I upload it and in the preview I have the posterization/jpeg artifacts in the sky? I have tried selectively smoothing the sky with Noise Ninja but I get the same results. I have PP'ed the image with only minor changes in levels, hue/sat and selective color layers. I have tried sharpening before downsizing and after downsizing? The image posted here was sharpened after downsizing using Nik Sharpener Pro. What can I do?


Camera Model: NIKON D200
Shutter speed: 1/1250 sec
Aperture: 5.6
Exposure mode: Manual
Flash: Off
Metering mode: Multi-segment
ISO: 400
Lens: VR 80-400mm f/4.5-5.6D
Focal length: 400mm

[Axel Hildebrandt]

I'm assuming you were working on it while it was a TIFF file. It might be due to compression when saving as jpg because of all the branches. Sharpen after resizing and don't sharpen the BG, just the birds. If necessary you could use NR on the BG. You could make it smaller, 800 pixels for example and see if it still happens.

Aside from this problem, I would clone out the trunk on the right.

[John Chardine]

Dan- Not sure if this applies but I've noticed that more than gentle NR can cause this. If I apply repeated NR with the blur tool and/or Noise Ninja, this will happen. Not sure why as you would expect that you would just get a blurrier and blurrier effect.

[Dan Brown]

Thanks Guys. Here's a repost at 800 with no NR at all and selective sharpening on the birds only. Seems to have done the trick, now to remove the big branch, actually, I kinda like it:p

[Emil Martinec]

Noise actually helps dither tonal transitions, and masks posterization. See http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3.html

[Dave Phillips]

Dan, similar to John and Emil's comment......I have found that if I get to heavy handed with noise reduction on skies that I get that posterization banding

[Fabs Forns]

Did you work the image in 8 bit?

[Dan Brown]

Yes, Fabs the image was worked a 8 bits. Does this potentially add the this problem?

[Roger Clark]

Yes, Fabs the image was worked a 8 bits. Does this potentially add the this problem?

In my opinion, yes. Any change you do in integer processing results in errors of 1 bit. Thus, after processing in 8-bit, you are effectively down to 7 bits, or 128 levels. Posterization as well as noise can become more of an issue. Even when I start to edit an 8-bit image, the first step I do is convert to 16 bits, do all the work, then if I want 8-bit, convert to 8 as a last step. If I am not done, I'll save the 16-bit file. (Disk space is really cheap.)

Generally, I do raw conversions direct to 16-bit tif files and process in 16-bits.

But for posting to BPN, early on we saw a lot of jpeg posterization/compression artifacts, but now with the larger file size allowed, I rarely see such artifacts. So when you save your image for BPN, be sure the compression is high quality that still fits in the allocated size (e.g. 200 KBytes).

Roger

[Bill McCrystyn]

I must second Rogers advice and I'm sure Fabs was getting at the same thing. I learned the hard way and my lesson from Roger. When it comes to sky/clouds I have also found big changes as I work them with "selective color" and/or selective "hue/saturation". This occurs from the 16 versus 8 bit format as Roger mentioned.