Digital BW, The Print

> From: Steve Kale [mailto:stevekale@...]
>
> Hi. I am just working up an image from my new digital camera and
> have come across
> something that is puzzling me.  The colour image looks great - no
> posterization and no
> apparent clipping in any channel.  From the RAW file I used
> Capture One Pro with high
> contrast setting and simply slid the RGB black point slider up to
> the left of the red
> histogram and then processed (no other adjustments).  In PS, I
> then used the split
> channels technique to work up a B&W version.  The image is of a
> sand dune against a dark
> (blue) sky.  My problem is that the red channel appears (on
> screen - I have not printed it
> yet) to be posterized in the sky.  I want to use the red channel
> because it is giving me the
> dark sky.  Any ideas as to why this would be?  I can go back to
> the original RAW file if need
> be.

If you have a very quiet camera, like a Canon 20D, and you make the mistake
of converting to an 8-bit image, and then apply a curve, you may be able to
see posterization. Noisier cameras provide enough dithering to break up the
bands. Make sure you use 16-bit mode, at least until you're finished with
any significant exposure or curve correction.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@...