Changing cmyk photo to pure 100% black

[dominique]

I am trying to change CMYK photos in Photoshop. I have the files as 300dpi psd documents.

The image is of a person and the background shadows appear gray and white. I need to make the entire back ground (a white blanket and white back ground) K only (no CMY).

This will be printed flexo on a plastic substrate. The printer requires at least 2% K in all of the white areas. I have masked the human so it will print CMYK. But when I tried to make the background grayscale in K only it won't work. It keeps all the color channels to create the grayscale.

I tried desaturating...to no avail. I also opened the document separately changing it to grayscale. I have also tried making it a bitmap (but this won't work as it loses the photo quality my client wants)

I am desperately trying to figure out how to do this.

Does anyone know how to help without explaining too much on the printer end since I am just a graphic designer trying to make sure I give them EXACTLY what they need!

I appreciate the help!

 

[Stephen Marsh]

Two quick tips when working in CMYK mode:

Use a channel mixer adjustment layer and layer mask, set the channel mixer to grayscale, double check that all tones where required are K only.

Select the K channel only, then paste in the data that was converted to grayscale - rather than pasting into the composite CMYK channel. Again, you will likely need a mask to isolate the CMYK areas from the K only areas.

EDIT: There should be enough K data in the CMYK area so that misregistration "white gaps" will not show against the K only areas, even more so for flexo work where registration tolerances are greater.

It sounds like your role is not just "graphic designer" - as you are being asked to perform prepress duties (precise CMYK builds), so you will have to learn "stuff at the printer end".


Hope this helps,

Stephen Marsh

 

[John Clifford]

In photoshop go to image-->mode-->grayscale.

This will turn the file into K and tints of K only (grayscale).

If you want more control. Use the adjustment called Black and White. This will allow you to control how different colors will convert to gray. Once you've got it how you want it, then convert to grayscale.

Grayscale creates a black (K) plate only.

 

[gordo]

If I understand what you're trying to do correctly...here it is in 5 steps:

1 Copy your CMYK image to a new document

2 Convert the new document to a grayscale image - quickest way, just do a mode change

Do a "Select All" and "Copy" your grayscale image

Go to your CMYK image

3 Select the backgound (what you want grayscale only. Go to the Channels and choose the Black Channel only

4 Paste the grayscale image from memory into that selected area of the black channel

What you've done is created a new black printer in your CMYK image where you want black only.

5 With the background still selected - deselect the black channel and select the CM and Y channels

Then delete. That deletes C,M,Y from where you only want black, but leaves the original black where you want it in the CMYK color part of the image.

Then flatten the image and do a save as and give it a different name.

hope this helps - gordon p

 

[John Clifford]

Sorry, I misread the original post. Gordon, you've done a masterful explanation.

 

[Verdant]

Yes, and I'd like to re-iterate that you must have the channel selected when pasting, otherwise the image may not place in the exact spot you want it to. I've had issues before when pasting in channels, and it's always boiled down to what is selected when doing the pasting.

 

[dominique]

Thank you all! Gordon and Stephen I followed your instructions and everything turned out great! I just got the news from the printer! I am sorry it took my so long to thank you! I appreciate your expertise!
Sincerely, Dominique

 

[gordo]

Thank you all! Gordon and Stephen I followed your instructions and everything turned out great! I just got the news from the printer! I am sorry it took my so long to thank you! I appreciate your expertise!

Your consideration is appreciated.

Sometimes the magic works.

best, gordon p

 

[pmkprog]

You can also copy and paste the image into a separate alpha channel.
Then that channel can be used to make a selection.
On a different layer you can then fill that selection with the 100k value and it will appear only on the black.
Also, if the shadows or background need to overprint, then you set that channel to multiply in Photoshop.
Then make sure the white base channel is gone before you save and place in InDesign.

 

[KevinC@EFI]

If I understand what you're trying to do correctly...here it is in 5 steps:

1 Copy your CMYK image to a new document

2 Convert the new document to a grayscale image - quickest way, just do a mode change

<snip>

Gordo's suggestion should work fine - my only suggestion would be to avoid using the default convert-to-grayscale option in Photoshop for most images - especially if they include skintones. The result is usually pretty flat and dull compared to what you'd probably want.

The better option in many cases is to conver the image to LAB color space first, then use just the "L" (Lightness) channel as your grayscale image. It should provide a more dynamic result, with better gradation - especially in difficult areas like skintones.

(years ago I was a certified Photoshop instructor... YMMV)

Kevin.

 

[gordo]

To Kevin-

I wrote that it was the "simplest" way to go from CMYK to grayscale - not necessarily the "best" way. I thought it best to answer the OPs specific question. Going into what could become a complicated description of all the different ways to generate a grayscale from a CMYK image would have added unnecessary complication.

gordon p

 

[reyhub]

Lossless conversion of RGB or CMYK to perfect Grayscale...

Lossless conversion of RGB or CMYK to perfect Grayscale...

For a quick and easy and most importantly Lossless conversion of an RGB/CMYK photo to Grayscale do the following:

Step 1. Create a copy of your photo
Step 2. Change your photo from RGB/CMYK to "Lab Color" mode
Step 3. Go to Channels and click on Lightness
Step 4. Change your photo from Lab Color to "Grayscale"
Step 5. You will be asked if you want to discard the other channels. Click o.k.

You now have a perfect grayscale photo. Save it using "Save As" in whatever format you require. TIFF or whatever. This is a little known secret trick (among many) that has always existed in Photoshop for Lossless Manipulation of photographs. Enjoy! Reyn Hubbard