how to change RGB to CMYK?

I have a children's book with lots of brightly coloured illustrations ready for the printers.
I used Corel Print-house/Photo-house programme for image editing and adding text.
The end result [of many months work] is in RGB format.
I have converted all the files to CMYK format as knew the Offset-printing in Malaysia uses this format.
But the printer now tells me the resulting colour printing will be different to the original, not so 'colourful' because the initial work wasn't done in CMYK format!
Does anyone know how I can overcome this problem?

 

Some colors you simply won't be able to print as brightly in 4 color, for example bright bright greens. The CMYK color space is not as wide as the RGB colorspace. But within the realm of what's possible for your budget, use the correct color profile to convert based on what your printer tells you and then tweak the cmyk images to adjust color tones, saturations, etc. as necessary as there is no software as smart as your eyes and brain to do the final tweak. If you're still not able to capture the vivid richness you're after, you then have to budget for more (colors) than standard 4-color offset printing to capture a wider colorspace.

P.S. I like corel apps a lot - I use coreldraw and corel photopaint all day, but I do like photoshop a bit better for rgb to cmyk conversion. You can download a free trial of photoshop to give it a spin if you can't get what you're after with what you're using.

 

Thank you Jeff, not sure i understand all what you say as i'm only just learning about all this different format business. but do i get it right that if i open my RGB files in adobe-photoshop and then convert to CMYK i will get a better result?

 

I'm not familiar with the software you're using, so I'm not sure what control you have now. But it will at least give you a second option and will give you the tools to control how the cmyk image looks.

Going from RGB to CMYK you will not be able to produce the full range of RGB colors because the CMYK gamut is smaller.

So:

1.) are you doing the "automatic" RGB -> CMYK conversion correctly and not throwing out the baby with the bath water... (check with your press for basic optimal values and then plug these in under edit: color settings in Photoshop or the corresponding area in your application, e.g. us coated vs. uncoated.)

2.) once you've converted to cmyk, now within the more limited confines of the CMYK space, you can manually tweak problematic colors to be more pleasing by manually adjusting the CMYK levels for those colors.

3.) if you can't work within the gamut limits, then it depends on the type of art how to proceed (and budget) Additional colors can be added to increase the overall gamut or spot colors if there are a few specific bright colors that need to be addressed for example... but adding plates (colors) will definitely increase your cost, so before considering this see how pleasing a result you can obtain manually adjusting the cmyk images in step #2.

Now as an added complication, when you say "But the printer now tells me the resulting colour printing will be different to the original, not so 'colourful' because the initial work wasn't done in CMYK format!" there are two things at play. First the major RGB to CMYK conversion where some colors will not reproduce exactly and some tweaking may be required to get a nice pleasing result. Second, the color calibration of the system you're working on. Optimally if you have a color profile / your monitor is profiled you can get the closest match of the cmyk image on screen to what their proof looks like which is what they'll shoot for on press. It wouldn't be bad at the start to make sure you're close; otherwise spend the $ to profile your system if you're a long way off.)

 

A quick video might be worth a thousand words - have a look at :
around 4 to 4 1/2 minutes in
(I don't have any association or experience with PressCats but thought they did a nice clear and simple intro video)

 

Thank you Jeff, your suggestions and the video are a great help...beginning to see a bit of light now!

Rita

 

you should, if your doing this type of work, get rid of corel printhouse, which is designed for home users as something different from msoft, and upgrade and get a decent version of corel, then you will see the light. (trust me, i first started with printhouse, i had it on the computer for ooo about 2 days before i scrapped it)

 

well, actually i'm just now trying adobe photoshop CS4, but i'm stuck...have just posted this question around [perhaps you can help]:

'Converting RGB to CMYK: I am very new to Adobe PhotoshopCS4 and need some urgent help to talk me through converting imported RGB graphic files to usable CMYK graphic files [illustrations not photos], for giving to commercial offset-printing company who are waiting to print…hope someone out there can help?'

 

I may be able to help...

First, you really need a calibrated monitor. Without that you are kind of poking holes in the dark (guessing) for color.

If you use a Mac you can get Gamma Control - a freeware application... just google it. I think there are other simailar apps. for PCs too.

But first you need your monitor optimized by some hardware device like SpyderII.

Once you've completed all the steps calibrating... and yes I can talk you through those if you need help, you need to set the Photoshop color prefs which I can also help with.

Once you have a clean representation of a target then what ever you bring up on the screen is what you will see coming off press.

I use Gamma Control and have targets for each printer I use whether it be my Epson, a photo lab (all those are RGB) or in CMYK for any one of several printing companies I use in my brokering. I turn on the profile for the output and see an accurate rendition of what to expect. It's magic!

I can be reached at 309-678-0653

 

The images to CMYK mode to export tif format images, then this tif image import, color will not be any change.

 

IF You have good color on a calibrated moitor, then making the conversion in Photoshop using the correct settings in the color preferences

Just using the conversion from RGB to CMYK in Photoshop will not guarantee good color conversion because there are so many RGB colors that are not printable using CMYK.

That is why you need to have a calibrated monitor so you can see with your eyes what colors change when you do the conversion.

Exporting to tif, or jpeg has nothing to do with color, other than a jpeg file can have more hi-light loss due to clipping from file size reduction.

Monitor calibration is very important. If you can accurately see the color before you print and it is wrong - you can fix it.

See the attached color settings jpeg.

 

Thanks!