CMYK to RGB conversion

[Ross Penn]

Hi folks,

I used PowerPoint 2003 to create a presentation containing some JPEG
images in CMYK format. I'm getting complaints that the images won't
display in PowerPoint 2000, so I need to convert them to RGB.
So I've opened the original CMYK images in Photoshop, converted them to
RGB and saved them. The weird thing is, the RGB versions of the images
look different to the original CMYK images in PowerPoint; the colours
are considerably lighter in the RGB version.
I guess the way PowerPoint converts CMYK to RGB (for display) is
different to the way Photoshop does it. Does anyone have any idea how
PowerPoint does this conversion?

Thanks in advance,

Ross Penn

[Troy @ TLC Creative]

RGB and CMYK use different color space, so when an image is converted it is
changed to that formats color space. In genereal CMYK has a much smaller
color range, as it is for print. When you insert a CMYK image into PPT it is
not being converted, but you are seeing a CMYK image. The problem is early
versions of PPT do not support CMYK images (hence your user problems). When
converting in Photoshop I recomend changing to RGB (IMAGE >> MODE >> RGB),
then adjust with the curves tool (IMAGE >> ADJUSTMENTS >> CURVES) to
"restore" the image as close as possible to the original color space.

--
--
Troy Chollar
TLC Creative Services
<< Microsoft MVP, PowerPoint >>

"Ross Penn" <penn...@googlemail.com> wrote in message
news:1132672322....@o13g2000cwo.googlegroups.com...

[Steve Rindsberg]

In article <1132672322....@o13g2000cwo.googlegroups.com>, Ross Penn
wrote:

Anything you bring into PPT will get converted to RGB, so there's not much
point in feeding it CMYK graphics. And as you've seen, CMYK won't work in some
versions, and in all cases you lose control over the CMYK to RGB conversion.

Since it WILL happen no matter what, it's best to do it yourself first, so you
can see the results.

As to the results being different, Photoshop almost inevitably has some form of
color management engaged, and that alters the way CMYK - RGB conversions turn
out. PPT does a straight conversion by formula, no tricky stuff.

It's pretty easy to tell if this is the case.

Create a small image in Photoshop, flood fill it with CMYK 100 100 0 0
Convert the image to RGB
Sample the color: if no CM is going on, it'll be RGB 0 0 255
Convert it back to CMYK
If no CM is going on, it'll convert back to the original values.
If CM is happenin', the CMYK and RGB colors will wander off in different
directions as you convert back and forth.

-----------------------------------------
Steve Rindsberg, PPT MVP
PPT FAQ: www.pptfaq.com
PPTools: www.pptools.com
================================================

[Ross Penn]

Steve,

Thanks for the hint - that looks like a good place to start figuring
out what's going on.

Ross