Color banding in sky

In this <a href="http://www.photo.net/photo/5458311"

>image</a> the sky shows radial color banding in the sky portion. How can I

get rid of this? I am using Photoshop 7. Thanks,

When I see banding like that (a fine photograph by the way) my first guess is that the

photographer used the sRGB color space and shot JPEGS.

 

The way out is to use a larger color space and greater bit depth per channel (Pro Photo at

16 bpc) ,which means shooting "raw".

 

sRGB is a very small color space. It is good for internet posting , & Powerpoint graphics.

The color range (gamut is narrower and very saturated colors are "clamped", "crushed" or

"clipped" to fit its narrow confines. In other words it s a fine output color space if you

know how the image is going to be out put but it is not ideal for original capture unless

you have a subject matter (most portraiture is a good example) with a small gamut as well.

 

Adobe RGB (1998) is a moderately large color space and is a good overall compromise for

most photographic work.

 

But if you have really bright or dark saturated colors (as in your example) you really need

the very large Pro Photo color Space where the gamut is large enough to hold virtually as

much as your eye & brain can see and then some) and Pro Photo definitely needs a 16 bit

per channel approach.

The difference between 8 bits per channel (bpc) and 16 bpc is that in a given color space

(we call it color space because the value of each color can be defined relative to other

colors by a set of three coordinates ) is a matter of fineness of gradation. an 8 bit R, G or

B color channel has 256 steps of color gradation while a 16 bit color channel has over

64,000 steps of gradation. In a small space like sRGB the extra gradations don't make

sense. Adobe RGB (1998) can work either way (but generally better as an 8 bpc) while Pro

Photo is so large that you really do need the finer gradation.

 

Most DSLRs on the market today are actually 12 bpc recording devices --which Photoshop

treats as 16 bpc. and a healthy human eye sees in the area of 9 bpc for a well illuminated

subject. Part of the benefit of working with 16 bpc images is that there is enough "over

head" that editing done in photoshop still leaves enough information there to prevent

things like pasteurization and banding.

 

JPEG compression doesn't help either: one of the ways JPEG compression works is by sort

of averaging similar color values and rounding them up or down to an averaged value so

when the color changes enough you get an abrupt jump in color or tone.

I would go back to your initial capture and see if it is there too. One way of fixing this is to

convert to lab and add a small amount of "noise" to the luminance channel. See if you can

add enough to decrease the banding but not show grain in your final output.

Ellis & David,<p>I will give both of these methods a try. Thanks for your help.

Looks like Ellis had a little accident with spell checking. The word is posterization not pasteurization for those in the audience not backgrounded enough to puzzle that out.

Actually I hit the wrong button in my spell checker and then did not double check the results!

 

OW!

Pasteurization - good for milk, bad for photos. I wonder, if in his youth, to make a bit of extra money, Pasteur was a poster paster? Hmmm...

In his youth it is true that Pasteur was a poster paster, but only when passing a pisser in a

pasture.

That probably explains why Pasteur's posters always read "Don't piss in the pasture." Perhaps Pasteur himself was a pasture pisser in his past, after drinking too much pastis, even pissing on the pasture posts where he later pasted his posters, but then had to amend his ways when he got caught by the pastor.

This thread got weird.

 

Anyways, thank you Ellis for that explanation. I never really knew or even thought about sRGB and Adobe RGB. Now I'll always shoot with at least Adobe RGB.

No, shoot in Raw. Then you have the choice of an 8 or 16 bit image and whichever colour space you wish when you process the image in the raw converter.

bad curve or level adjustment can do this too to a file. A too strong gradient mask also (as it look you use it). JPEG and sRGB could be also the problem.

<I>bad curve or level adjustment can do this too to a file. A too strong gradient mask also

(as it look you use it). JPEG and sRGB could be also the problem.</I>True, but shooting raw

and porcessing as a 16 bpc Pro Photo TIFF opr PSD file mitigates virtually all of those

problems which can also be seen as gaps in the histogram of the processed iamge as well as

banding in the sky.