Duotones in Aperture

Question

Is there a possible way to do a true "duotone" image in Aperture? I know you can export a TIFF to Photoshop to do this, but I thought there might be a tricky way to back door this in Aperture. What I want to accomplish is to change the image to a monochrome image, with the darker details tinted say blue, and the lighter details say yellow.

Answer 1

I know you can export a TIFF to Photoshop to do this, but I thought there might be a tricky way to back door this in Aperture. What I want to accomplish is to change the image to a monochrome image, with the darker details tinted say blue, and the lighter details say yellow.
Better know why you would not want to do device dependent duotones in the first place, and what device independent ways of toning are available to you.
The idea in a duotone is to start with a grayscale which is either printed in the colour of the black process ink or in the colour of a premixed spot black ink.
One then adds other premixed spot inks, whether from the warm gray or the cool gray or some other range of premixed spot inks.
In order to be able to preview this, the premixed spot inks have to have a colour definition. You have to know what colours they are solid and tinted and combined in several orders, and on top of that you have to know the lightness and tint of the paper itself.
The trouble with duotones, tritones and so forth is that you don't have that colour information. The premixed spot inks are intended to be laid down solid on a specific paper at a specific tone value increase whereas in a duotone/tritone etc. one wants to lay them down in tints, in combinations and on other papers.
If you want to colour manage this device dependent process, you basically need to convert to a large and linear RGB colour space. Since the start, the ICC specification has had a device independent solution to this device dependent problem. Its called an ABST Abstract profile which is a colour change within CIELa*b D50 to CIELa*b D50 as opposed to a device profile.
When you build a colour correction in Apple Quartz, you are building an ABST Abstract profile. Try starting the Apple ColorSync Utility, click Profiles, click Lab Profiles and e.g. click Blue Tone. On the right you will see that the class is ABST Abstract and the colour connection space is CIELa*b. Whether you create toning in a large and linear RGB space or in La*b itself, you can colour manage the colours you create. But if you try to create toning with device dependent colours intended to be laid down solid on a specific paper at a specific tone value increase, what seems simple on the surface is seriously complicated below the surface.
/hh