Re: gum curve testing

[Camden Hardy <camden@hardyphotography.net>]

Laura,

Curves can be intimidating at first, especially if you've never really
used them before jumping into digital negatives.  Curves in general are
simply an advanced form of contrast control, where you can change the
values of a given tonal range (i.e. lighten up the shadows, while leaving
the highlights as they are).

The important thing to keep in mind, as Dan mentioned, is that when
applying a curve to a digital negative, you're simply matching the tones
you're getting on screen with what the process is capable of printing. 
It's a means of standardizing a printing process.  So, to answer one of
your questions, the curve creation process is for a given process, not for
each image you print.  Once you nail down your curve for lamp black gum,
you shouldn't have to worry about making a new one until you change a
variable in your workflow (exposure time, paper, etc.).

It's interesting that Dan's platinum curve gave you the best results for
gum.  The tricky thing about curving digital negatives, which I believe is
evident in your test prints, is that there are so many variables in alt
process printing that when you use someone else's curve (unless you work
under exactly the same conditions) it most likely won't give you an
accurate "translation" from the computer screen to the print, although
they can be close.  If you're looking for a perfectly accurate curve, your
best bet is to create your own using one (or any combination) of the many
digital negative systems out there, or simply by "guess and check".


Camden Hardy

camden[at]hardyphotography[dot]net
http://www.hardyphotography.net


On Wed, January 31, 2007 4:21 pm, Laura Valentino wrote:
> I figured I would never grasp the concept of curves or how to use them
> unless I did some testing on my own. Now that I've done that, I'm still
> not totally clear, but at least I have a starting point to refer to.
> What I did was download a couple of curves, as I really didn't have a
> clue what to shoot for. One was designed specifically for gum printing,
> but I noticed later that it was supposed to be used for a color
> separated image, and I was just making one neg, so that might be why it
> didn't print very well. The other curve I downloaded was from Dan
> Burkholder's site, and was designed for platinum, but optimized for my
> printer type and media. Then for fun I created a 3rd curve, sort of a
> halfway between the other 2 curves, and I called this one 'whatever'.
> The thing that baffles me the most about curves is how when applied they
> make a perfectly good image look really awful on screen...!
>
> If anyone is interested in my results they are here:
> http://lavatop.com/gum_curve_test/   and I welcome all comments! The top
> 4 images are how the image looked onscreen (very close to how they print
> on my inkjet), and the bottom 4 images are the scanned gum prints.
> Remember, I'm still a beginner (how long do I get to call myself that?)
> so the gum prints are a bit bumpy...I haven't mastered my brushing
> technique yet. I also took a brush to the development to help it along
> as it was taking so long, but I tried to brush them all equally to be
> scientific about it :) Is 30 minutes a normal development time?
>
> Looking at the printed step wedges, I'd say the platinum curve was the
> winner here for range of grays (good job, Dan!) However, I don't see any
> difference between 90 and 100%. But then these are all just one layer of
> lamp black. Should I go another layer or 2 before I can really decide?
>
> Also, I'm assuming that each different image I print might get a
> different curve...or is it really possible to design a 'one size fits
> all' curve optimized for my working methods?
>
> Best Regards,
> Laura
>
>