Simple & Stupid Curve Generator for Digital Negatives

Hi Don,

I) Determine your exposure time for black (using a blank negative and
bracketing, just like silver-gelatine printing).
II) Expose your paper with a digital 100 step tablet using the time you
found in step I (I made the 100 step tablet in Photoshop; 10x10 squares,
starting with 1% luminosity - ending with 100% luminosity, each square
2x2cm @ 360dpi - you may use a less accurate scale if you like)
III) Inspect the print and determine the first clear square - this will
be your 100% density value. Use the eye dropper on the 100 step tablet
file to determine the 100% density value equivalent in the 256 scale.
IV) Use the value you found in step III as "Max Value" in the following
Excel file:
http://www.geocities.com/loris_medici/loris_curve_generator_for_digital_
negatives.xls and create a curve using values in A column as input, and
values in D column as output.
V) This will give you a good starting point (assuming you're printing
black-only or quadtone and your B&W output is pretty linear), print a
photo which also includes 21-step wedge, evaluate & fiddle a couple of
times.

Hope this helps - I made my cyanotype curve using this method; it works
for me.

Regards,
Loris.

> -----Original Message-----
> From: Silver Plated [mailto:dstevenbryant@mindspring.com]
> Sent: Thursday, May 27, 2004 8:27 PM
> To: alt-photo-process-l@sask.usask.ca
> Subject: Building PS curves for alternative processes with
> the Inkjet Companion
>
>
> Good Afternoon Everyone,
>
> Recently I purchased an Epson 2200 (an a 1280) and this past
> weekend I had an opportunity to make a digital inkjet
> negative to try printing as a toned kallitype print. Before I
> go in to the particulars of my results and questions let me
> point out that to make the negative I used Dan Burkholder's
> Inkjet Companion Template, using his curve for palladium
> prints. Additionally my monitor is calibrated and profiled
> and I'm using Pictorico OHP for the inkjet negative
> substrate. I choose the kallitype process since it is
> relatively inexpensive.
>
> I knew that using Dan's curve would most likely require
> adjustments to produce a good result, in fact I hoped that
> the print would need adjustment to provide myself with the
> opportunity to learn how to make adjustments to curves for
> various processes. The final print was extremely flat. There
> was very little differentiation in most of the steps in the
> included step wedge on the print. This is in contrast to the
> quad tone print I made as a proof.
>
> The 0% step read about .09 and the 100% step read about 1.35
> on my densitometer. Most of the mid-tone steps had a reading
> of about .25 to .35 (I'm working from memory here).
> Additionally I have not established the minimum print time
> for black but I assume I'm pretty close since the 100% step
> was 1.35. I plan on establishing the minimum black time this
> weekend with a blank piece of OHP.
>
> My question today is; is there a way to correlate my
> densitometric readings that will result in the desired
> changes in the PS curve to produce good separation. Also how
> much difference in log density values should one expect to
> see in the step wedge mid-tones? Also if I read the
> transmissive values on the negative are there aim points for
> the differences from step to step that one should observe?
>
> Hopefully my questions seem rational and clear, if not,
> someone, anyone please correct me!
>
> Also as time permits I plan to test Keith Schriber's
> colorization values and curves along with several other
> curves different individuals have sent me.
>
> Thanks,
>
> Don Bryant
Received on Fri May 28 01:48:21 2004