Digital BW, The Print

----- Original Message -----
From: "Kevin Gulstene" <kevin@...>
To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
Sent: Sunday, March 16, 2003 10:47 PM
Subject: [Digital BW] Self Inflicted Posterization


> Aaargh-
>
> I've been having problems with posterization introduced into a PS7
> file, that is very slightly visible in the print.
>
> The image has very similar tones around each of the four edges of a
> greyscale image.  To help with the center of focus I want to darkening
> the edges.  To do this I make a rectangular selection, invert the
> selection and then feather it by 50 pixels.  When a curve is applied to
> the selection the feathered edge has 'bands' in it.  It is not a smooth
> looking transition but steps in concentric bands from tone to tone --
> I'm calling this posterization.  It is not that obvious but once I know
> it is really distracting.
>
> Adding a small amount of noise to the image mostly removes the
> posterization but (and it may just be my imagination) leaves a less
> smooth texture to the image.
>
> So, is there a better way to make the selection without introducing the
> banding/posterization?  Is it better to go around the edge with a big
> soft brush and paint it in the selection?  Is there a setting somewhere
> that will introduce some dithering or noise in the feathered area?
>
> I tried making the curves on a 16 bit image after loading the
> selection(s) from the adjustment layers of an 8 bit version but got the
> same results for the most part.
>
> Any suggestions are appreciated.
>
Kevin,

I have encountered the same thing occassionally. Especially in smooth areas
like the sky portion of landscapes. Generally when I want a selection with a
blurred edge I make a selection with the lasso tool (you could paint the
selection as well) and save it as a new alpha channel, turn the selection
off, apply gaussian blur to the alpha channel and then use that to create a
selection which has a blurred edge.

You could also create a duplicate file, resample it to a much lower
resolution and then create your blurred edge mask. Resample back up to the
original resolution and copy the mask or alpha channel into your file.
Resampling up seems to decrease any banding.

You can also work with very large soft brushes. You can try these techniques
in combination.

I wouldn't add any noise to the image since you will lose detail as you
noted.

Martin Wesley