Posterization in BG, any tips?

I've been running into a problem lately with posterization of my backgrounds when converting to web formats (jpg, png) and its been a bit frustrating. I'll look at my finished image in PS, save for web (Max Jpeg, Bicubic Sharper) and when I look at the jpeg in an image viewer or uploaded to flickr or whatever my once smooth backgrounds have posterized and become blotchy. Looking around the web the only answers I've seen are to add noise. I don't want to add noise, I want smooth backgrounds.

Example:

https://farm4.staticflickr.com/3838/...625c73ac_b.jpgGreater Yellowlegs by No Small Wave, on Flickr

Unfortunately, flickr only has 1024 or 1600 sizing so I've got to use a smaller image than I would like but the blotchiness is still pretty apparent even at this size. In post the only adjustments I've made to the BG are slight noise reduction (ISO 400, didn't need much), slight tone curve, +15 or so saturation bump, and some gaussian blur. The blur was to try to combat the posterization. It does not look this bad in Photoshop. There is slight posterization but its not really visible unless viewed at high resolution.

So, any advice or tips? Am I missing something when converting to jpeg? Or is it something else?

I assume you're shooting in raw? Are you going to PS from the raw convrter in 16 bits? After you make any adjustments in PS, it is important to first flatten the image then convert to 8 bit (Save for Web or Export from LR will do that for you correctly). If you go to 8 bits before flattening, you have lost the tonal overhead advantage of 16 bits, and that advantage will minimize posterization. But at some point the 8 bit JPEG will show posterization that isn't in the 16 bit PS file. And JPEG compression will emphasize it further.

And trying to zoom in on a JPEG will show artifacts that look like posterization. JPEGs just aren't meant to be viewed at more than 100% screen size.

Quote:

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Originally Posted by Diane Miller

I assume you're shooting in raw? Are you going to PS from the raw convrter in 16 bits?

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I read this and was saying to myself "Of course I'm converting from 16 bit, I'm no scrub" but then I checked my settings in ACR and, sure enough, 8 bit. I reinstalled Adobe CC a little while ago and ACR must have defaulted to 8 bit. I hadn't noticed because I usually use DPP to convert but I was browsing photos in Bridge and converted through Camera RAW. Just processed another photo with a ton of soft tonal variations in the BG and its much much better. Thanks, sometimes I just need someone to ask the dumb questions I forget to ask myself. Now I get to go back and redo a bunch of photos. Sigh.

Perhaps its not the case here, but I've found that applying NR to a varying, but smooth BG, can then lead to posterization when downsizing.

I also have notice posterization being more frequently when I have images that have blueish/greenish backgrounds.