# Rastering of image in CC PS



## sanjosedave (Jul 26, 2014)

I'm probably using the wrong term, rasterizing, but I'm trying to understand what is happening to my image

Using CC Photoshop, I select the sky, apply field blur, click ok, and bring it back into PS. The sky that has been blurred is wavy, like gradients.

Any tips would be appreciated

Thanks


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## Skirball (Jul 31, 2014)

What do you mean "bring it back into PS"? You mean, just from the field blur filter?

Banding and posterization can be caused by several issues, sometimes it's even just an optical illusion because you're monitor can't display the amount of colors in the actual image - though this is easily checked by zooming in to 100% and seeing if it's still there.

Are you editing in 16 bit or 8 bit? I recommend 16 bit, though you can still get banding there (and a common fix is to downsample to 8 and come back).

I don't use field blur, but I often get banding in dark tonal areas when using a Gaussian blur. The fix is to simply add noise, which I do anyway so that it matches the rest of the picture. Very little, like 1% or less is usually sufficient. As I mentioned above, I know people that downsample to 8 bit and come back, but I prefer to not downsample until I'm done with my edits.

Edit: I should add that for sky's like this (which is usually where I encounter banding as well) I will usually use a soft brush at low fill (on a new layer) to even out and add some randomness. I just sample colors from various points in the banding. Then I run a noise filter on this layer.


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## mackguyver (Jul 31, 2014)

It looks like you're using a JPEG or processing in 8-bit as Skirball says. The terms you're looking for are "posterization" or "banding" and they are caused by low-bit capture (JPEG) and/or overprocessing, especially in 8-bit, which means you are processing it, saving it, then processing it again and again. If your histogram is spiky instead of smooth, you have overprocessed your photo. Try to do as much as you can in RAW or at least in 16-bit TIFF to avoid that. You may need to start over with this photo.


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## Skirball (Jul 31, 2014)

It just dawned on me that Field Blur is probably one of those filters that only works in 8-bit mode.


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## Skirball (Jul 31, 2014)

mackguyver said:


> You may need to start over with this photo.



You can definately fix it using the method I mention above. But if you're haven't put much time into post processing you might as well start over and do it right instead of fixing it. In the future, shoot in RAW, edit in 16 bit.


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## mackguyver (Jul 31, 2014)

Skirball said:


> mackguyver said:
> 
> 
> > You may need to start over with this photo.
> ...


Yes, and sorry to gloss over that. My comment was specifically around the photo being totally overprocessed which has more serious issues that a banded sky alone. RAW/16-bit is the way to go for sure.


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