Ender100@aol.com
Date: 11/09/01-03:25:44 PM Z
Hi Jeff,
I am not aware of any printer desktop printer that can print the tonal range
of a 16 bit image. While a an image may be printed in Photoshop while in 16
bit mode, what is actually sent to the printer is 8 bit date... it gets
converted.
Starting with a 16 bit scan and keeping the tweaking to a minimum in
Photoshop would certainly prevent posterization.
"The histogram has nothing to do with posterization. A step wedge can
give a comb-like histogram and continuous tone a smooth line histogram.
But this is only information as to the total number of pieces of certain
tones comprising the image."
A comb-like histogram tells you a lot about how much an image has been
fiddled with—if there are lots of gaps, then that means certain tonalities
are missing.... thus posterization. Of course a step wedge would look like
a severe example of this. if it is a 21 step tablet, then think of all those
tones that are missing... and you are printing a posterized image with 21
tones, if your image has a histogram like a step wedge.
You stated that the image looked posterized...that is why I asked what the
histogram of the image looked like. Even if they started with a nice smooth
16 bit scan, it may have been tweaked to the point that the 8 bit file had
gaps in it. Looking at the histogram of file that generated the negative
would tell you this,
Mark Nelson
In a message dated 11/9/01 2:02:56 PM, jeffrey.d.mathias@worldnet.att.net
writes:
<<
Mark Nelson wrote:
> Could the original image have been posterized in Photoshop prior
> to making the negative? Did the file have a smooth histogram or
> a "comb-like" histogram?
As I mentioned in the previous post, I feel a 16-bit scan should be
used. Then yes, posterization is likely caused by Photoshop. This is
basically by the reduction to 8-bit data. Also several of the
calculations (functions, filters, and such) can increase posterization
(reduce the number of steps). But even if using GIMP 16-bit image
software, the printer (and/or it's driver) and the inks can reduce the
number of steps.
The histogram has nothing to do with posterization. A step wedge can
give a comb-like histogram and continuous tone a smooth line histogram.
But this is only information as to the total number of pieces of certain
tones comprising the image.
An example:
While one might assume that posterization would not be a problem if only
two tones were present in the image, they should be cautious as the two
tones may not be accurately reproduced. The two original tones may be
5% and 80% and due to posterization (like if using 1-bit data) are
printed as 0% and 100%. >>
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