[rollei_list] OT: Inverting an image digitally, was: Wooden Tripods


On Oct 31, 2007, at 5:21 PM, Mark Rabiner wrote:
Thing is don't you have to make a film positive then from that make a film 
negative? That's what kills me.
No, with Photoshop or other image manipulation programs, you can invert the greyscale values in your image to create the negative directly. In Photoshop the hotkey is cmd-i on Macintosh, not sure about Windows. Probably Ctrl-i. Someone wrote a book a few years ago on the subject of preparing images using Photoshop for output on an offset press using transparency material to produce a large-format negative that is then contact printed. At the time, it was important to use a professional offset printer since the resolution was an order of magnitude (or more) higher than what you could get from an inkjet printer printing onto transparency material. Although inkjet printers with DPI ratings of above 5000 now exist, they typically are only rated for a maximum of 300 DPI when printing onto transparency material. Another thing that it is necessary to do before printing out your "negative" is to adjust the contrast curve of the digital image to adapt it to the curve of the (silver halide) printing paper you will be using. Once the curve of the paper is established, a custom curve can be set up and saved in Photoshop, and reused on each new image. 

Here is a link to the site of the book mentioned above:

http://www.danburkholder.com/Pages/main_pages/book_info_main_page1.htm
I've never gotten around to trying this technique, although I do find it intriguing. 

Best regards,
Aaron Reece
Oswego, NY, USA
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