Non standard color separation for cyanotype/ink composite

[Dibbd]

I'm quite new to photoshop and having trouble getting it to do what I want.

My idea is to split out the cyanotype colour from a colour photograph. Print everything except the Prussian blue component with a printer. Make a negative of the Prussian blue component and make a cyanotype print on top of the partial colours. Hoping to end up with a full colour image that is part ink part Prussian blue.

I've spent a good few hours trying to get photoshop to produce the separations but I can't figure it out. I'd be very grateful if someone could point me in the right direction. NB a cyanotype isn't cyan. It's Rgb is 0 49 83 so that needs to be extracted proportionally from each pixel as a starting point.

 

[gmikol]

OK...here's a quickie way:

But first an important note: What I describe takes a giant short-cut, which will not produce 100% accurate color. It will probably result in a significant hue-shift towards blue, given the difference between process cyan and prussian blue. But it's a quick way to put together a proof-of-concept, to go through the whole process, test ink/paper/cyano processing compatibility, etc.

1) Take the image you want to print, and in photoshop, use "Convert To Profile..." and select CMYK - "US Web Coated (SWOP) v2"
2) Duplicate the image
2a) In one image, delete the cyan channel in the channel palette
2b) In the other, delete everything but the cyan channel
3) Print the MYK image with your inkjet printer.
4) Make your digital negative from the cyan-only image and print that step

You may need to swap 3 and 4 so that the inkjet inks are not exposed to the cyanotype coating. You'll need to test this.

That's the easy way.

In very broad steps, the hard way is to get a CMYK RIP for your printer so that you can directly control the ink channels (which you're not doing in my example above) and then print out custom profile targets using inkjet MYK and cyanotype, and then create a custom CMYK profile, which you can then use to "Convert To..." in photoshop and then follow the steps above.

Don't forget to take into account possible paper shrinkage and registration (a good reason to print inkjet *after* cyanotype, if you can get away with it.)

 

[Dibbd]

Thanks, that is worth a try for a first attempt to test the process. I will have a go at that.

Is photoshop really incapable of doing the separation I want though? It's a fairly straightforward transformation in many ways. I'm a software engineer by trade and could probably knock something up in Java or C++ to do this but it's outside my normal application area so I'd have to spend a weekend or so getting familiar with the relevant APIs.

 

[Doyle Thomas]

When ready, select:
Image > Mode > CMYK color
On the channels pallet right click on and delete the black, yellow, and magenta channels leaving only cyan.
Next select: Image > Mode > grayscale
And then:
Image > Mode > duo-tone and select monotone
At the color picker select a pure cyan using the table below.
Cyan is: RED = 0**** GREEN = 255 BLUE = 255
Magenta is: RED = 255 GREEN = 0*BLUE = 255
Yellow is: RED = 255 GREEN = 255 BLUE = 0
Black is: RED = 0**** GREEN = 0**** BLUE = 0
Close the dialog and save the image as a copy adding a C to the file name, revert to the original and repeat the process for each of the other channels adding M, Y, and K to each file name respectively.

 

[Doyle Thomas]

When ready, select:
Image > Mode > CMYK color
On the channels pallet right click on and delete the black, yellow, and magenta channels leaving only cyan.
Next select: Image > Mode > grayscale
And then:
Image > Mode > duo-tone and select monotone
At the color picker select a pure cyan using the table below.
Cyan is: RED = 0**** GREEN = 255 BLUE = 255
Magenta is: RED = 255 GREEN = 0*BLUE = 255
Yellow is: RED = 255 GREEN = 255 BLUE = 0
Black is: RED = 0**** GREEN = 0**** BLUE = 0
Close the dialog and save the image as a copy adding a C to the file name, revert to the original and repeat the process for each of the other channels adding M, Y, and K to each file name respectively.

Extracted from my article Dye Transfer done Digitally~http://www.primaryfocusphoto.com/?page_id=16

 

[Doyle Thomas]

http://www.primaryfocusphoto.com/?page_id=16