[PDF] Re: CMYK to Lab

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Robert Zacherl

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Jul 26, 2001, 11:21:10 AM7/26/01
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Hello Bob,

the reason for this is always the same. People save Photoshop CMYK images as EPS files
with the save option "PostScript Colomanagement" turned ON.

What does this mean? If you use this option the device dependent CMYK color space you've
choosen inside Photoshop is converted internally into a device independent PostScript
colorspace as soon as the EPS image runs through a PostScript level 2 or PostScript 3
device.

The bad thing which is happening with Distiller 4.x is that if the Photoshop color space
was CMYK the resulting device independent color space inside the PDF file is not a 4
channel one (DeviceDEFG) but due to a limitation of Distiller 4 it is converted into a 3
channel one, namely Lab!
Why is this so bad. Because a color transformation has happened which can't be reversed
even if the color space is converted back to a device dependent one.

In this respect Distiller 5 is a great step forward because it would convert the same
Photoshop CMYK EPS image into a calibrated DeviceDEFG color space. If you don't like the
calibration you can remove the CSA (the PostScript counterpart of a ICC profile) and will
end up with a normal CMYK image. This removal can be done at print time or with a tool
like PitStop Professional.

Even better, Distiller 5 can replace the embedded PostScript CSA by the appropriate ICC
profile if it exists and lays at the right place.

If you don't like the whole story about device independent color spaces than simply save
your Photoshop EPS images with option "PostScript Colormanagement" turned OFF in the
future.

Best regards,

Robert


Bob Rapuano wrote:


> Date: Wed, 25 Jul 2001 10:16:59 -0400
> From: "Rapuano, Bob"
> Subject: [PDF] CMYK to Lab
>
> Hello All,
> I received a call from my printer this morning informing me that a
> page (file) of mine kept crashing his RIP. I opened the page and did a
> flightcheck with Pitstop, which reported 2 images were Lab colorspace. Okay,
> so I open the images in question in PhotoShop and guess what... CMYK !
>
> Has this happened to anyone and does anybody have any idea as to why
> and when (in Postscripting or distilling) it might have happened?
>
> Bob
>
--

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Robert Zacherl
IMPRESSED GmbH
Tel:++49(0)40/89 71 89-0
Fax:++49(0)40/89 71 89 71
e-Mail: rzac...@impressed.de
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