Digital BW, The Print

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. 

Steve 

(I have ordered the 3 channels as follows:  base Green at 100%, red on top at 90%, then 
blue with pinlight for extra contrast on top at 40%.  Although the posterization is evident 
just looking at the red channel.)

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Steve Kale" 
<stevekale@b...> wrote:
>... 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....

Have you tried NOT adjusting the red histogram? Then what file format 
did you pass from Capture One to PS? What bit depth? I'm sure you may 
have already looked at these variables but if all are ok then may be 
it's just your monitor display properties. Just some thoughts.

--nick

> 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@...

hi Steve -

I don't work with Capture One so I can't help on that specifically. But
here is a trick that may prove helpful, probably in combination with
other corrective measures you may already have found.

Before you convert to b&w, use Select Color Range to select the blue
sky. Save this selection as an alpha-channel mask. 

Then when you're editing your b&w image, use Load Selection to reload
that mask. This will re-select the sky. While the sky is selected, add a
curves adjustment layer (the selection will become the layer mask). By
manipulating the sky curve, you'll be able to adjust the tone of the sky
quite precisely -- without changing the sand dunes. 

You'll want to do this in 16 bit mode. And if you do see any dithering
in the sky, a little Gaussian blur (while the sky is selected, of
course) will take care of it. Also, note that reloading the sky mask
will not work if you've cropped or resized the image since you saved it.

Hope this helps,
Richard Wolfson
Fine Art Photographer & Digital Imaging Consultant

> -----Original Message-----
> From: Steve Kale [mailto:stevekale@...] 
> Sent: Monday, January 10, 2005 1:33 PM
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Subject: [Digital BW] Posterization in red channel
> 
> 
> 
> 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. 
> 
> Steve 
> 
> (I have ordered the 3 channels as follows:  base Green at 
> 100%, red on top at 90%, then blue with pinlight for extra 
> contrast on top at 40%.  Although the posterization is 
> evident just looking at the red channel.)
>

Tiff at 16 bit.  I went back and redid it with the shadow warning on.  Seems
that the warning kicks in (when set to 0) well before the RGB (not red)
black point reaches any of the left most points of individual channel
histograms (is this understandable?  I mean I am adjusting the levels in RGB
but watching the 4 histograms overlaid on each other - RGB, R, G, and B).
The image is much better but the notion of visually dragging the RGB black
(and white) points to the edge of the histograms seems to be flawed.

> From: "Nick H. Nugent" <nghin@...>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Mon, 10 Jan 2005 21:08:10 -0000
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Subject: [Digital BW] Re: Posterization in red channel
> 
> 
> 
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Steve Kale"
> <stevekale@b...> wrote:
>> ... 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....
> 
> Have you tried NOT adjusting the red histogram? Then what file format
> did you pass from Capture One to PS? What bit depth? I'm sure you may
> have already looked at these variables but if all are ok then may be
> it's just your monitor display properties. Just some thoughts.
> 
> --nick

1Ds MK II all work in 16 bit.

> From: "Paul D. DeRocco" <pderocco@...>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Mon, 10 Jan 2005 13:58:17 -0800
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Subject: RE: [Digital BW] Posterization in red channel
> 
> 
>> 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@...

Thanks.  Will give this a go.

> From: Richard Wolfson <rw@...>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Mon, 10 Jan 2005 17:32:00 -0500
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Cc: <stevekale@...>
> Subject: RE: [Digital BW] Posterization in red channel
> 
> 
> hi Steve -
> 
> I don't work with Capture One so I can't help on that specifically. But
> here is a trick that may prove helpful, probably in combination with
> other corrective measures you may already have found.
> 
> Before you convert to b&w, use Select Color Range to select the blue
> sky. Save this selection as an alpha-channel mask.
> 
> Then when you're editing your b&w image, use Load Selection to reload
> that mask. This will re-select the sky. While the sky is selected, add a
> curves adjustment layer (the selection will become the layer mask). By
> manipulating the sky curve, you'll be able to adjust the tone of the sky
> quite precisely -- without changing the sand dunes.
> 
> You'll want to do this in 16 bit mode. And if you do see any dithering
> in the sky, a little Gaussian blur (while the sky is selected, of
> course) will take care of it. Also, note that reloading the sky mask
> will not work if you've cropped or resized the image since you saved it.
> 
> Hope this helps,
> Richard Wolfson
> Fine Art Photographer & Digital Imaging Consultant

> From: Steve Kale [mailto:stevekale@...]
>
> 1Ds MK II all work in 16 bit.

Well, it's hard to imagine a quieter camera than that, and it's with
low-noise images that posterization is more likely to be a problem. I wonder
if there was some operation in your workflow that's really performed on
8-bit data, even though it claims to be 16-bit. That's about all I can think
of.

--

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

Maybe on a clear day in the desert (blue sky, sand dunes) there's just
not much red light coming from the sky?

Richard Wolfson
Fine Art Photographer & Digital Imaging Consultant

> -----Original Message-----
> From: Paul D. DeRocco [mailto:pderocco@...] 
> Sent: Monday, January 10, 2005 7:41 PM
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Subject: RE: [Digital BW] Posterization in red channel
> 
> 
> > From: Steve Kale [mailto:stevekale@...]
> >
> > 1Ds MK II all work in 16 bit.
> 
> Well, it's hard to imagine a quieter camera than that, and 
> it's with low-noise images that posterization is more likely 
> to be a problem. I wonder if there was some operation in your 
> workflow that's really performed on 8-bit data, even though 
> it claims to be 16-bit. That's about all I can think of.
> 
> --
> 
> Ciao,               Paul D. DeRocco
> Paul                mailto:pderocco@...

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Steve Kale" 
<stevekale@b...> wrote:
> 
> 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. 
> 
> Steve 
> 

Most scanner and digital camera technology today has problems 
rendering certain shades of red correctly, meaning that several 
shades as you see them will turn into a single hue when digitally 
captured, which may not be obvious at first until you start playing 
around with the curves and levels. I have had many problems with 
this myself while scanning or photographing some of my artwork, 
where the reds can turn out to be way off, particularly for a shade 
very close to pure red and a bit towards yellow, which all becomes a 
pure red in the scan or photo.

Hakon
www.hakonsoreide.com
mail@...

Yes and hence my choice of the red channel to get a very dark sky.  I am
just surprised that I get a shadow warning when the black point is nowhere
near the edge of the red (or blue or green histograms).  Maybe I am missing
something basic here....I will keep experimenting.

> From: Richard Wolfson <rw@...>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Mon, 10 Jan 2005 19:49:27 -0500
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Subject: RE: [Digital BW] Posterization in red channel
> 
> 
> Maybe on a clear day in the desert (blue sky, sand dunes) there's just
> not much red light coming from the sky?
> 
> Richard Wolfson
> Fine Art Photographer & Digital Imaging Consultant
>

Hi Steve,

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Steve Kale 
<stevekale@b...> wrote:
> Yes and hence my choice of the red channel to get a very dark sky.  
> I am just surprised that I get a shadow warning when the black 
> point is nowhere near the edge of the red (or blue or green 
> histograms).  Maybe I am missing something basic here....I will 
> keep experimenting.

There may be pixels that are clipped though you don't see them in the 
histogram. Picture Window Pro has a High Histogram Expansion mode so 
even a very small pixel count will become visible. Capture One may be 
very much like PS in that the count for a particular pixel value is 
shown as a percentage of a maximum value.  So though the slider is no 
where near the histogram edge, there are pixels there.

I think Capture One may be performing an 8 bit operation there 
because I have no other explanation for the posterization.

To verify this you may want to bring the red channel into PS as is in 
16 bit and perform your histogram adjustment there to see if 
posterization occurs.

--nick