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

Re: digital negative possibilities for gum


Yes, I do understand your point very clearly: it is diffusion dither.

In looking at my negs, they do not look like your bitmap/regular neg comparison on your website. I have a 2400 Epson, hence the difference, I would think. My bitmap negs are less dense than my regular negs. I suppose this is the whole essence of learning a custom curve process--this printer is different than that printer is different than...

The bitmap dots under loupe look like they lay down much less ink, too. It is just all around...less dense.

To clarify my original point: I am not advocating bitmap negatives as a replacement for any other type of neg. I am only surprised (greatly) that such fine detail would even come from a lowly bitmap neg. It is just one more thing to add to my arsenal of gum possibilities, but I have been quite satisfied with going the more complex route with separate blue, magenta, and yellow curves for tricolor RGB negs printed in colored ink only. That's not going to change. But in a quickie gum demo and with those who want to try gum for the first time, it could be useful for sure. In fact, my idea is to explore that softness and slight "grain" more, just as I advocate using a grainy film developed with Rodinal in my Experimental Photography classes to get students away from a Tmax-100-only mindset.

KT said:
You're welcome, but I'm not sure you understood my point. There's one more branch beyond Image>Mode>Bitmap: you still need to specify >type of bitmap ( diffusion dither, pattern dither, custom dither, halftone screen, or whatever). When I open the dialog box, "diffusion dither" is the option that's selected on that menu so I'm guessing, though I don't know for sure, that diffusion dither is the default, and since you didn't mention having chosen another option, I'm also guessing that diffusion dither is probably the kind of bitmap you made, by default. Diffusion dither is a stochastic dot, the same kind of pattern you get from your Epson printer. So if that's what you used, you're just comparing one kind of stochastic dot printed with a different kind of stochastic dot, to the usual stochastic , which is not the same as, say, comparing a halftone screen (with a round dot and the screen angles set to deposit the different gum colors in different sections of the dot) to a stochastic dot.

Today I printed a bitmap negative from an image I printed in gum yesterday (from a normal inkjet negative) choosing Image>mode>bitmap>360>diffusion dither, from a file that was 360 ppi. Both negatives were printed on cheapie inkjet film (something nameless I bought online for something like $16 for a box of 50). I've uploaded scans of both of these negatives, with prints made from them.

What amazes me is that you got such a good print from uncurved bitmaps, because in my experience printing gum from dififusion dither bitmaps, this kind of file requires an extreme curve, otherwise the negative will be way too dense and print with too much contrast. As you can see from the example, the uncurved bitmap was so dense in the face area that most of the details of the face washed away almost immediately (the two negatives were given the same exposure time, as per your protocol) just as I would have expected. So I'm fascinated that you were able to print uncurved bitmaps with apparently no problem, and maybe my guess that they were diffusion dither bitmaps is mistaken. (But if not, then what?) At any rate, I would strongly suggest to anyone considering diffusion dither bitmaps (although I'm sure I don't know why anyone would) that you use a curve. The curve on Dan's CD (first edition) for preparing a bitmap for the imagesetter for silver printing was the one I used, with some modification, when I was printing bitmaps for the laser printer for gum printing.

Marek, you can see how grainy the bitmap negative is. It's not quite as easy to see the dots on the print in the jpeg, although they can be seen by eye. And through the 8x loupe they are very pronounced. People who have come to alt-photo fairly recently might stop and consider that earlier in my days of gum printing, this was the best one could do as far as making negatives with a desktop printer (imagesetters, which Dan and his followers used so effectively in those days, weren't available within 100 miles of here, so I made do with what I had at hand). I don't see any point to making this kind of negative now when you can do so much better with today's inkjet printers using a normal file, even on cheap transparencies.

Yes, I had to use bitmaps when I was printing negatives on a laser printer, but it was the ONLY way to get a stochastic dot on a laser printer. Now we've got printers that produce stochastic dots, and much smaller and finer ones at that, all by themselves. As your comparison shows, even on a cheap transparency the unbitmapped negative prints gum at least as well as the bitmapped, and in my example there's no comparison; the unbitmapped is far superior to the bitmapped. And even if it were properly curved, there would still be the grittiness in the print. So I'm scratching my head to try to understand what possible advantage could accrue from using bitmaps now.

I looked through an 8x loupe at the two kinds of negatives; they look quite similar, except that the bitmap one looks like a magnification and intensification of the other one. The dots are similar in shape, except the ones on the bitmap seem a little more square (pixel- shaped) and the regular ones seem maybe a little more rounded, but I'd need a 10X loupe, as Marek says, to be sure about that, since they're so much smaller. But as I said, the bitmap looks like a magnification of the regular negative. The dots are bigger and darker, as I would expect in an uncurved bitmap, but the shape and distribution of the dots seems quite similar. (BTW, I'm curious what's the basis for saying that bitmap uses less ink? I would say it uses way more, especially an uncurved bitmap.)

Oh, the URL. This is a big jpeg, so will take a bit to load, and for that reason also it won't stay on the site long, as bitmaps don't seem terribly relevant to modern-day printing, to me anyway, so it's not something I'm willing to give that much space to longterm.