*Urgent* Photoshop CMYK question

I am having some advertising flyers printed - just a little bigger than postcard size and I want one side printed in B&W (greyscale).

The printer needs the .psd file in CMYK format (no problem there) but has said that if I want it to be "true" black & white (i.e. with no possible colour cast) - I should select each of the C,Y & M channels in turn and cut them (not delete, just Ctrl+A to select the canvas then Ctrl+X to cut it, having first set the background colour to white) from the image - this will then leave just the K (black) channel.

I'm absolutely fine to this point.

However, by doing this I loose just about any detail there is in the image - most, if not all, the "greyscale" has then dissapeared. (which seems obvious to me that this would happen - but hey, you have to humour these guys!)

I have about 4-5 hours from now in which to nail this and get the artwork to him, does anyone have any better suggestions on how I might retain detail in a desaturated image (in CMYK mode), without the worry of the possibility of there being a slight cast over the final printed work?

Thanks

TJ

Did they specify a dot gain or gray gamma profile?

It seems to me (I have not tried this) that converting the RGB to grayscale with some particular dot gain profile or gray gamma would be the first step before turning off the CMY colors. I do not think that you can verify this on your printer because it expects to receive image data in RGB format and then does its own internal conversion to CMYK.

Bill, no, nothing was specified.

The main file is made up of three layers, a greyscale "background", an image of a Bride - also in greyscale, and a top layer containing just her flowers in colour.

Removing the CMY channels from the background image is not perfect, but acceptable. Doing the same to the Bride is aweful. There is very little left of the image if I do that.

To the eye, there appears to maybe be a "very slight" hint of magenta on a laser printout (albeit thats in RGB) - but you have to look, look away, then look again to see it (if you know what I mean!)

I could go with leaving the image of the Bride in colour, with the B&W background - but that isn't really what I want. I feel tempted to just run with it the way it is.

What are the chances of any cast spoiling the final copy?

TJ

I wrote about this just yesterday - https://photography-on-the.net/forum/showthre​ad.php?t=544482

Please write back immediately if you need further explanation.

Your printer sounds like a goose - that's the worst advice I've ever heard. If you must do it his way, you need to:

1. Make a duplicate of your RGB file, so you have two copies on screen.

2. Convert one to greyscale (20% dot gain unless you have specific information to the contrary)

3. Convert the other one to CMYK (doesn't matter what profile)

4. Completely delete everything in the CMYK one, so it's just a blank white file

5. Choose the greyscale one, Ctrl A, Ctrl C to select and copy the greyscale image

6. Go back to the CMYK one, go to your channels palette, and choose just the Black channel

7. Paste the greyscale image onto the black channel.

8. Save the CMYK file.

Damien, Thank you, I'll take a look now and come back if I need further help.

TJ

No worries, I'll be here for an hour or so ...

A public "Thank you" to Damien, your instructions worked extremely well.

...and Bill - I think that's what you were pointing to as well.

TJ