U of S | Mailing List Archive | alt-photo-process-l | Re: digital negative possibilities for gum

Re: digital negative possibilities for gum

Hi Katherine,

I am not sure what you are asking when you said "why?" below.

I also know that a bitmapped negative also can be improved with a curve—based on early work with imagesetter negatives.

You said you "prefer a negative with less density for gum" - this is consistent with the idea that gum has a lower exposure scale than other processes such as pt/pd, so with a continuous tone negative, be it traditional silver negative or digital inkjet, gum requires a negative of less density range.

When you print a bitmapped image with an inkjet printer, the printer dots create all the bitmapped dots such that each bitmapped dot is of the same density range. All that is important is that this "equal density" be equal to or greater than the exposure scale of the alt process. If, however, you make a negative that is not bit mapped, then even though the negative is made up of the printer's dots, the negative is more of the nature of a continuous tone negative with different ink colors dithered together.  In the lowest density areas of the negative, the dots don't quite touch eachother, so you see discreet dots of color and you get more print density because of all the clear space around the printer dots.  One of the things a curve does is smooth out this transition between non overlapped dots and overlapped dots.  As density increases, the dots overlap and intensify and are more continous tone and it is the change in the mix of the color dots and the increased ink that increases the density.

You could make a bit mapped image for a negative and convert it back to RGB and make all the bit mapped dots a color such as pure magenta ink and it would probably fail and not give you a paper white in the most dense areas of solid color.

Best Wishes,
Mark Nelson

Precision Digital Negatives - The System
PDNPrint Forum at Yahoo Groups
Military Commissions Act of 2006 - A STAIN on our Nation's History

In a message dated 10/19/06 6:37:49 PM, kthayer@pacifier.com writes:

On Oct 19, 2006, at 12:36 PM, Ender100@aol.com wrote:

> Hi Charles,
> The bitmap negative is one of those binary types of negatives.. it 
> is either printing with full tone or no tone—the closer the printed 
> dots are together, the more tone.  This is why the negative appears 
> to be more dense—because there is no continuous tone in it.  It 
> would be like an imagesetter negatives.  Printing with dots is 
> fairly foolproof, though not what I would want for PT/PD.  However 
> with full color gum, you have at least 3 printings to get a 
> "dither" of the three colors, which will hide the dots somewhat.

But that still begs the question, why?

At any rate a bitmap that's given a curve correction doesn't look 
that dark.   I've never tried to print an uncorrected bitmap; when I 
started out with bitmaps I was working from Dan's book, and the book 
said a bitmap needs a curve or it will print too dark, and I didn't 
have any reason to doubt him, so I got one of the curves off his CD 
and tried that and it worked pretty good, with some slight 
modification,  and so I always used that on all the bitmap negatives 
I ever printed.  As you can see from the other negative posted, I 
prefer a rather thin negative for gum;  much density doesn't do 
anything for gum, as many people before me have pointed out.