Need help

[aquakiwi]

Every now and then after a little playing around in Photoshop I get these rings in the blue background(see image). Its never on the original. only after some processing.

[KenByrne]

I've seen that as well. As best I understand it when you're lightening or darkening (mainly lightening) an image you've exceeded the number of shades that the software can encode into the number of bits available. Shooting in RAW and processing in 16 bit mode for as much of the post processing as possible can help. In 8 bit mode you've only 256 shades of blue available.

[Cerianthus]

It also depends a bit on the jpg quality setting, you might bump into this earlier if you dont use the highest setting.

Since " everybody" has fast internet these days, and harddisks are relatively cheap, i tend to leave it on 100%

Also: apparantly jpg quality reduces if you save an image several times.

[Mike W]

Ken and Gerard are both right - the best way to avoid this in is to open the original, create a duplicate and save as a TIFF, then carry out any Photoshopping on the TIFF not the original jpeg. The TIFF format is uncompressed and these rings won't appear.

When you're happy save the changes to the TIFF.

When you want to use an image - on the web, for example - open the TIFF, downsize as appropriate and save the result as a jpeg. I use images between 500 and 800 pixels on the horizontal dimension and save as level 5 or 6 jpegs if that's any help.

The TIFF remains unchanged on the hard-drive as the reference/best version of the pic.

[Cussy]

Ah, but......

I've seen this in Lightroom when working on RAW! I've only seen it on photos that I would say need to be "over-processed" in order to end up with anything anywhere near acceptable. This I would then put down to hitting the limits of the sensor and what it could record. As an example, I have a few pictures of Pike taken from below where I've burnt out the jaw. In order to correct I end up seeing this. This is when I've burnt out, so I wonder if these blues have been clipped (what is the opposite of burn out).
Rob

[KenByrne]

I first saw this effect post processing scanned slides, usually in the blues and where there is a wide range of tones from light to dark. There are some shots that you just can't do anything with and the bands appear even in 16 bit mode, that said it could be a monitor issue when using 16 bit mode as most monitors if not all are 8 bit devices.

[aquakiwi]

Thanks for all the help, I allways save the original to disc in both Raw and Jpeg. I noticed after creating a copy in Tiff that I cant do much processing.
I get the message that I need to go down from 16 bit to 8 bit which is where the problem seems to begin. Heres the same shot which a touch of lightening saved from Raw then converted to Tiff and finaly downsizes to a Jpeg.