Losing Color Intensity

I am trying to provide an image to an ad company for printing. When I change the color mode from RGB to CMYK, I lose the beautiful intense blue of the sky. I have tried to get this intensity back through photo filters, curves, levels, saturation, variations, color balance, selective color, and the channel mixer to no avail. Can anyone give me some tips on this? (I freely admit that my solution will probably be found in some combination of the above!)

I am using PS CS2 on WXP xp2.

Thanks!

Susan

Susan,

here are some informations about sky blue:
<http://www.fho-emden.de/~hoffmann/skyblue14072008.pdf>
Color space for the images is sRGB.

In short: postcards and travel agency brochures are
showing often fully saturated dark blues which I didn't
ever encounter in real life.
Blue sky at a sunny day, over the haze of the horizon, is
rather light and, concerning the hue, between blue and
cyan. The doc contains color ranges in Lab instead of RGB.

A light saturated blue is not available in any CMYK space.
Try to tweak the RGB image and check often the appearance
in CMYK by View > Proof Colors and View > Gamut Warning,
using your preferred CMYK space.

The improved sky blue colors in my doc are all printable
by ISO Coated, eventually with tiny deviations.

Best regards --Gernot Hoffmann

Gernot,

THANK YOU! This information will be incredibly helpful and I have already been able to make some tweaks that are better than what I was doing before.

My biggest frustration is that I took the photo I am working on and I know that the sky was a much more vibrant blue than what the CMYK rendering was showing.

Thank you for responding - and for sharing these tips with me. I am certain that I will be much happier with the end result now.

Susan

Nice document, Gernot.

Saved! for future reference.

They know their stuff in Ostfriesland!

Thanks to everybody for the pleasant feedback.
You may search by Google for Norbert Kustos,
the photographer. He had contributed the photos
to many books (most famous: Heidelberg, Mallorca,
Toscana etc.). We have friendly discussions about
the touristic sky blue ...

Best regards --Gernot Hoffmann

If anyone missed it in the references part of the Sky Blue pdf, there is a link to Mr. Hoffman's CIELab Color Space pdf that is at least as helpful (at least for the LAB-challenged, such as myself).

Thank you very much for those.

Good comments and documentation from Gernot, as always. I would add that
blue is notoriously the most difficult color to get right in CMYK, and
people have devised any number of tricks to get around this. It is crucial
to use the Info Palette to ensure that the other parts of the image do not
have a blue cast. Adding a small amount of yellow to the non sky portions
of the image will kick up the blue, but stop short of yellow clouds.
Making the sky darker, as Gernot hints, is also an effective way to get
more blue into the sky.