Changing a color photo to print in black and one additional color only

I have some color photographs that I'd like to print using only two colors: black, and some shade of red. For example, here's a full-color image:

I've used Photoshop extensively, but only for certain tasks, and this is beyond what I've been able to figure out.

Is there a straightforward way to select a red color out of this image, and produce a new image that has only:
a black layer (or channel, or whatever, I'm out of my league) and
a red layer,
and see what the printed image would look like?

Thanks in advance for any suggestions.
--Steve D.
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David BruggeCommented:
Ah ha! You want to send this image to a printer who will then print it as a two color job-black and red.

First off. Your image is at 72 ppi. Your printer is likely to want artwork that is 300 ppi. That means you image will print at just over two and a half inches wide. If that is not what you want, you can either find a higher resolution image, or settle on a lower quality product. You can probably go as low as 200 ppi, but lower than that will start to look rough. No sense spending money on a two color job without a good image to print.

What the printer is looking for is a file set up with "spot" colors instead of CMYK or RGB.

You're on the right track, selecting the red, but as you discovered, the degree of "redness" gets sort of iffy around the edges of a selection, and there is also a bit of red that shows up in the color of the tray.

So, the others have demonstrated how to select the red in the dice (I like to use the Refine Edge to fine tune my selections.)

What you want to do after you have the red isolated it to go to the Channels Pallet and in the drop down panel on the right, choose New Spot Channel. Lucky for you the default color is red.

Next, go to Image > Mode > Grayscale to remove all of the color and make a black ink channel for your printer along with a separate red channel.

But, the red looks muddy because of the black image printing on top of it. To fix that, make your spot color channel active in the colors pallet and click the dotted line circle icon at the bottom of the pallet. This will load your red channel info as a selection.

Not click on your black and white channel to make it active and zoom in on the dice. Should see the marching ants marking the selection. You want to hide these "ants" for a moment, so press Ctrl + H (for Hide). Now open a layers dialogue by pressing Ctrl + L (for Levels). Grab the far right arrow under the histogram and slowly move it to the left.

As you move it, the black and white over the red will start to lighten. You don't want to remove all of the black because the red ink is not dark enough to carry the shadows in this area. You want to remove just enough to show a little shading but not enough to dirty up the red.

Save it, you're done.

Take this to the printer, pick out the shade of red you want for the ink, go home and wait for the printer to send a proof (usually a pdf) for you to approve.

Look the proof over carefully because this is your last chance to fix anything. Hopefully everything is the way you want it.

Best of luck.
Don't know about doing two colors in one go but you could create two layers and merge
From the Select menu, click Color Range
With the eyedropper select the color to keep, and OK
Right click in one of the color selections (they have the dotted line around them) and select Layer via copy

You should now have a new layer with just the color you selected.
StevenMilesAuthor Commented:
Hi, Cathal,

Thanks. I guess I should have stated what I've tried so far, because it's similar to what you said.  I took the original image. I used "Select... Color Range ..." and selected a bunch of the red, with high fuzziness. I copied that selected-red and saved it onto a new image. Then I changed the mode to greyscale on the original image to dump out the color, changed it back to RGB color so I could add color again, and pasted the red-only-image back in.

Here's what I came up with (the before on top, the "two-color" version on bottom):

It looks pretty good, but there may be lots of different reds in there, and the printer might say it's still a "four-color" image.

Did I explain things better this time?
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So you are basically wanting to get rid of all shading of the colors so it is just one solid color - red and black and the whites/grays
StevenMilesAuthor Commented:
I think so. So that using only black and all the greys, and some shade of red (to be determined) and all the different percentages of that shade of red, I get as close as I can to the original image, but the printer only needs two ink colors: black, and the one shade of red that I specify, based on my analysis of the photo.
So something like this
Here I have just set Tolerance to 100, no anti alias or continguous, fill method Color and paintbucket the red on the new layer
my $0.02

Heres another method for creating the two colour print job.

My first step was to create a good greyscale image from the master.

I then added the new spot colour, in my case i chose Pantone 185 as its a great red

I copied the original greyscale channel and pasted it into the red channel

I selected the areas i wanted red using the pen tool and made a selection deleting (filling with white) the areas

I adjusted the curves in the red channel to give me the contrast required and then adjusted the opacity of the red channel in the channel palette.

If you are going to use this method or D_Brugges method, you will need to talk to a printer before delivering this type of coloured file. This type of image can be difficult for printers to handle as the Oldskool way of deliverying two colour tifs/eps/dcs files was as DCS (desktop colour seperations) 

DCS file use to give me the caniptions when i had to do work for customers and i don't think there are any ways to handle the DCS type files anymore.

A method you may have to try if you don't have any luck with a single file is to create two tif file, one grey and one red. Stack them in Indesign with the red file on top. Set the tranparency of the red file to multiply and you get the same result and modern printers will be able to deal with the file.

Good luck

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