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RGBCMYK I need your help. I am trying to convert my RGB poster into a printable CMYK poster. But when I change the "neon like" headline to CMYK colours and the document color mode in illustrator the Blur effects becomes grey. The same thing goes with the blur and transparent effect in indesign when I transform the document and colours to CMYK. The background picture is converted to CMYK also, but when I activate proof setup at proof colors, the colors becomes flat like a grey overlay was added.

What am I doing wrong? Please help!

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A common problem.

CMYK print processes cannot produce as bright and colorful looking colors as the usual sRGB screen. Some programs can make usefully accurate predictions on the screen what CMYK printing would produce. Adobe products and CorelDraw have got their position in the industry because that capability. There are some free and low cost alternatives which also understand CMYK printing: Krita, Scribus, Serif Affinity series. But GIMP knows nothing of it.

To get reliable results for ex. in Photoshop you must use right RGB and CMYK color profiles which know how your monitor and how the forthcoming CMYK printing handle color. Unfortunately low cost office printers do not have such profiles, they present themselves to Photoshop as perfect sRGB capable printers which is of course a lie and the result will be something like in your 2nd image.

Learn the color management concept from the numerous available sources, for ex. Adobe's manuals. Design the colors of your art so that the colors are printable. If that's done properly the result can still look good as you can see in magazines.

In your current case the image obviously has several layers. Transparent layers in CMYK are combined differently with the background in CMYK images than in RGB images. The suggestion given in a comment "flatten the image before converting it to CMYK" is good.

See the next image which has a little too saturated red on brown. The red cannot be shown properly in the used CMYK printing color profile which makes it as dull as in your image.

enter image description here

In the left there are the same shapes as in the right, but flattened before converting the image from RGB to CMYK. In the right the glow is a separate layer.

The glow suffers baldly due the different layer mixing priciple. In RGB the transparent glow adds color on the background, in CMYK it takes color off. The result becomes even worse if you use some layer blending mode other than Normal, for ex. Screen which is common in glow effects.

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  • When you say flatten what do you want me to flatten? Do you mean the whole poster or just the headline? The background image is produced in photoshop, and then placed into indesign. The headline is made in Illustrator and then placed into indesign, the rest of the text is made in indesign. But where do you want me to flatten it? I am not aware of a flatten effect in indesign? Please help – ida_design Sep 28 '20 at 10:51
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    Make the text + the glow in Photoshop or paste it to Photoshop. onto the background image. High enough resolution prevents quality loss. Do not use unprintable red. Flatten the image to single layer and then change the color mode to CMYK. If you have in color settings the right CMYK printing color profile you have a possibility to see what's the outcome. View > Gamut warning makes unprintable areas grey. You can still adjust colors to get it into the printable range. Your printer should tell what color settings should be used for the printing. And learn the color management concept!!! – user287001 Sep 28 '20 at 11:07
  • Thank You! What does happen if you flatten a RGB red, and then make the document CMYK? Does the document convert all colors to CMYK or will this be a problem in print? – ida_design Sep 28 '20 at 11:17
  • You should place the image to InD after you have converted it to CMYK and saved it (keep also the original just for safety). If your InD work is started as for CMYK printing you'll get a warning of still existing RGB objects at last when you try to make a print PDF. – user287001 Sep 28 '20 at 11:23
  • Thank you! I really appreciate it. Have a nice day :) – ida_design Sep 28 '20 at 11:26

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