Re: Lith film—Play it again, Sam

 OK, Grasshopper, to become one with the curve......

Sam,

That is a good demonstration of the difference between a 16 bit file and an 8
bit file—how a 16 bit file can withstand the destructiveness of any curve,
but an 8 bit file cannot, without getting the comb-like histogram, or gaps in
tones—since those tones have to go somewhere, you see them piled up on other
levels in the histogram.

First, its a one of the nice improvements with Photoshop CS (8)—it does allow
you to make 16 bit gradients  :).  The Gradient Tool did not work in 16 bit
mode in Photoshop 7.

Regarding 16 bit files being sent to the printer.....

The printer driver does convert the file to 8 bits on the fly. 

In your example below, it is not surprising that the 16 bit gradient printed
smoother than the 8 bit gradient.  When you apply a curve to a 16 bit file,
you have enough tones still left to "fill in the gaps" in the gradient when the
printer driver converts it to 8 bits during printing.

To test this, make two files with the same gradient—one in 16 bit mode and
one in 8 bit mode.  Now, using the 16 bit file, create an adjustment layer for
curves and make the curve of your choice.  Drag this adjustment layer over on
to the gradient that is 8 bit and Flatten Layers.

Now duplicate the 16 bit file, Flatten Layers on it and then convert it to 8
bits.

Flatten Layers on your original 16 bit file.

Open the Histogram Palette.  Successively click on the windows for each of
the files and look at the histograms.  You will notice that the two 8 bit files
do not look the same...the one that was converted from 16 bits will have the
gaps filled in, while the file that was created in 8 bit mode has gaps. So, if
you printed the two 8 bit files, they would look different.  You don't have to
waste a sheet of Pictorico, you can use any paper or just trust the
histograms.

I rest my case, or that's my two bits worth on the topic.

But, you did show me the trick with the Stouffer & Pictorico—and that
Photocopy trick to reduce colour noise....

Mark Nelson

To test your hypothesis,  you have to do something different than this.

In a message dated 12/11/03 5:05:54 PM, stwang1@bellsouth.net writes:

> Mark,
>
> Pardon me, but if the Epson driver converts the 16 bit file to 8 bit on the
> fly, the result is certainly
> different.
>
> I just showed Sandy my tests and he can vouch for me: I created a gradiant
> in 2 separate files, one
> 8 bit and the other 16. Then I made the same curve adjustments on both and
> printed them on
> Pictorico with same settings. The 8 bit file showed posterization while the
> 16 bit file did not - it's
> smooth.
>
> So there is a definite advantage of using 16 bit throughout.
>
> Sam Wang
> PS: Mark, you know how long I waited to be able to find something worth
> saying that you don't
> already know!?
>
>
Received on Thu Dec 11 22:30:02 2003