Convert RGB image to CMYK and match blacks to rich black

[drgosling]

Hi,

I'm working on a CD packaging which will be printed in 4-colour offset. I have a rich-black background over which is placed an RGB image bitmap image. On one side, the image has a opacity mask so that it fades out over the black background.

The blacks in the RGB image are virtually 0R 0G 0B which gives an overly-saturated black for printing when converted to CMYK.

How do I convert the RGB image to CMYK and lighten the blacks so that they match the rich black of the background (say 30C 30M 30Y 100K) ?

Thanks,

Dave.

[JonathanArias]

why not work in indesign. place your art. make the flat black in indesign export print .pdf and allow indesign do to the converting?

[c.pfaffenbichler]

What is the exact CMYK black?

What are the RGB and CMYK Spaces?

Please post a screenshot of the image.

Depending on the image’s content you may need to correct in the separated file.

[D Fosse]

This is one of those few cases where I might consider working in all CMYK - provided I had the actual CMYK profile. But be very careful to not exceed the total ink limit for the profile!

[Jenz Grove]

I have a similar project which sounds like it is in the same vein as yours. I am creating a huge mural with around 70 black and white portrait photos on a grid. The original photos are RGB but I am converting it to CMYK for the layout. I also want to use a rich black background in Illustrator (C=60 M=40 Y=40 K=100) to place the photos on. Every photo has a black background that needs to match the rich black background in Illustrator. Does anyone have an idea how to adjust the photos in Photoshop? Is there a colour profile that will do this automatically?

Sorry, I don't mean to hijack your question. I just thought we might have similar situations.

[rob day]

Does anyone have an idea how to adjust the photos in Photoshop? Is there a colour profile that will do this automatically?

Rather than trying to match the photo's black point to the Illustrator background build, why not go the other way? Get the 0|0|0 conversion to the CMYK space you are using in Illustrator and use it as the Illustrator CMYK rich black build. If the total ink isn't a problem in the Photoshop file it shouldn't be a problem in Illustrator.

[Jenz Grove]

Do you mean I should use an RGB colour space in Illustrator and place the photos as RGB? Then convert to CMYK for print? Sorry, I am not super clear on what you suggested.

[rob day]

How is the mural being printed?

Illustrator has a document color mode, so if you placed an RGB photoshop file int a CMYK AI doc, its conversion at output should be to the Illustrator file's assigned CMYK space, and Separation Preview would show that.

So here my Illustrator file's color mode is CMYK with GRACol Coated assigned, and I've placed a PSD with a 0|0|0 black circle and a transparent background on a 0|0|0|100 CMYK rectangle. There's no CMY so the mismatch is obvious:

If I sample the Photoshop color the CMYK build is the conversion from 0|0|0 AdobeRGB to GRACol Coated, and if I fill the rectangle the color and the CMYK channels match. If I can't control the conversion later, I could also make the conversion to GRACol over in Photoshop:

The Magenta and Yellow plate

But, you must be printing the mural on some kind of inkjet device right?

In that case you would be better off working in the same RGB space in both PS and AI, with the AI document setup as RGB. Most inkjet printer drivers expect RGB and don't output actual document CMYK values.

[Jenz Grove]

Thank you for that great clarification! Wow. I learnt something new.

I am not sure how it will be printed out but I ask my client to put me in touch with the printer so I can get that information. I hope it's an RGB colour space. It will make the whole process much less painful.