Full Analog Prints With Digital Tweaking

[Mr Bill]

A mini-lab system of about 10 years ago already did what some posters are suggesting. It was during the transition from optical to digital printing exposures that Agfa came out with a "digital mini-lab".

Basically, Agfa put a transparent LCD image display between the light source and negative. This was used for automated masking, to correct deficiencies in the neg. Basically, it was similar to L Gebhart's method (low res scan, printed onto transparency film, use as mask) except that this mask could be immediately changed for every neg, at normal, automated mini-lab printing speed.

It seemed like an ideal method, but it became obsolete with the adoption of full digital exposure.

 

[Mike1234]

You can disassemble a cheap old LCD panel so that it's a transparent panel with no backlight or anythng behind it. You can then put that above the print; its height will mean it's just out of focus. That would allow you to do arbitrary contrast masking cheaply and repeatably since old 17" panels are regularly discarded, particularly when their backlight fails...

Ahh... okay so one uses the monitor as a mask with an external light source. Very interesting... I can see how this would work for contact prints but wouldn't this affect enlarged print sharpness?

 

[Kirk Keyes]

I have been following this thread and did not mention contour mapping as the OP observations lead to the possibliity of burning in as well as dodging which contour mapping or inkjet mask would not allow you to do. You still have to manually burn in the highlight areas for effect.

Actually both the frosted mylar and inkjet mask technique do allow for burning. You can cut holes into a sheet of frosted mylar over the areas to be burned, and for the inkjet, you make the mask to have a base grey over the neg and then you add density to the base grey for dodging as mentioned above, and subtract density for the areas to be burned. The amount of burn is dependant on the density of the base grey used.

Also, if you want to get fancy, you can use yellow and magenta ink to print adjust contrast when using VC paper.

The only issue I find is that it increases exposure times by several stops.

 

[Bob Carnie]

Kirk
You are absolutely right, why I didn't think of that vexes me.
Bob

Actually both the frosted mylar and inkjet mask technique do allow for burning. You can cut holes into a sheet of frosted mylar over the areas to be burned, and for the inkjet, you make the mask to have a base grey over the neg and then you add density to the base grey for dodging as mentioned above, and subtract density for the areas to be burned. The amount of burn is dependant on the density of the base grey used.

Also, if you want to get fancy, you can use yellow and magenta ink to print adjust contrast when using VC paper.

The only issue I find is that it increases exposure times by several stops.

 

[PeteZ8]

I'm not as worried about pixelation as posterization of the tone emitted by the screen. If the tone curve of the mask isn't smooth then the silver paper will emphasize that for sure. My point is just that with dithering any tone can be rendered, even in the very worst case of only 1-bit white or black screen pixels.

Anyway... it just has to be tried

Gotcha, I see what you mean now.

 

[Vaughn]

They were, by screwing them in or out.

And I believe the bulbs around the outer edge were closer to the neg than the inner ones -- supposively to "burn in" the edges of the image. But it has been perhaps 20 years since I was in AA's Carmel darkroom.

Vaughn

 

[polyglot]

Quantisation in the dodging/burning is not the same as quantisation of the whole image and will not result in loss of continuity of tone. Consider a typical burn I might do: 8s base exposure and then 4s additional exposure on one part of the image - these levels can be represented with only two bits and are therefore extremely heavily quantised. But of course, the original image is being applied during that time, so it doesn't mean we're quantising the image to two bits. There would be an issue if the dodge/burn tool was focused in the print but as long as the edge is sufficiently defocused, there won't be a hard line of changing tone.

Same principle applies to dodging or burning using a digitally printed mask and/or LCD. You could do it with only 3 or 4 different densities and the effect would be quite as good as any dodging or burning someone does by hand as long as the pixels in the mask are not focused in the print.

I'm not sure how putting an LCD under the enlarging lens will affect sharpness - could be terrible or it might have no effect at all, depending on what the surface finish is. Putting it a few mm above the negative should be fine under any circumstance though. I had a bit of a look on mouser and there are suitably sized (for MF) TFTs available with controller for about $120. It would require you be an EE to interface it with a PC though, which is where the larger VGA modules that plug straight into a computer would be much much easier.

Using an LED array above a negative could work I guess, but I think it would be very difficult to get uniform illumination due to the way the light beams from the LEDs overlap. And you'll get way more resolution from an LCD anyway.