inDesign: Printing a photo with only two spot colors, and highlights - will it work?

Question

I have a project in inDesign that was only budgeted for 2 colors, Pantone Orange and Black. I've read that to print photos with only 2 spot colors, you'd need to have the photo set to a grayscale color mode and then in indesign, set the fill of the bounding box with the photo to your spot color. This works, but there are no highlights.

I was wondering if I create a second image in a greyscale color mode, with only white and alpha values, and then place that over my spot colored orange and black image, will it print just fine?

Here is the grayscale image:

Here is what it looks like using two spot colors in design:

Here is an all-white fill with an alpha mask of only the highlights of the original image (photoshop screenshot for clarity):

Here is what it looks like in indesign with the white image over the black and orange image:

I guess I'm just asking for assurance, but will this work? Or would it be better to just image-trace the white image be a vector? And that way it's guaranteed to work.

Answer 1

For the highlights to work, you need to poke a hole in the orange, (Although it could work, I would not overlay another layer as in your example)

A duotone is normally the same image with some modification on the curves to emphasize different zones.

Here is a modification I made on your same image for the orange channel.

The curve has 3 zones:

1. I am crushing all the dark gray tones to have a flat orange

2. To keep them smooth I made the middle section as a curve.

3. I crushed the very light tones flattening the last portion of the curve, so I have clean whites.

The right image is a simulation combining orange and black ink.

It still could have a bit of tweaking; I would like pure white on both, black and orange channels.

As the black ink is a big grayish on the highlights It also needs some white crushing. But also I Lighten up the overall image so more orange shows in the image making it "glow". Here is the black ink modified.

If you have the original RGB image, try using different channels for different inks. Here is a full explanation: Preparing design for duotone printing?