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You are here: MacNN Forums > Enthusiast Zone > Art & Graphic Design > b/w RGB to the K in CMYK. Dot gain?

b/w RGB to the K in CMYK. Dot gain?
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cla
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May 31, 2005, 07:06 AM
 
I'm creating an ad for a magazine, in which the background is almost black (83-93%). My employer is also printing 250 000+ paper cups with this dark background, so it's important I get it right.

I've found a good way of converting dark black and white RGBs to CMYK, by simply copying the RGB version of the image and pasting it into the black (K) channel. This way I get a cleaner CMYK,
as Photoshops auto-convert sets _every_ channel (CMYK) to values between 80% and 100%, which will probably smudge in the offset press.

My problem is, when I activate the other channels the image turns brighter. Even though the other channels are empty. Why is this? I think it's related to dot gain, though I'd feel like asking for trouble if I were to start altering color profiles ad hoc (my monitor is embarrasingly enough not calibrated).
     
cla  (op)
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Jun 2, 2005, 07:28 PM
 
Never mind, the deadline just went out... =/
     
budster101
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Jun 3, 2005, 09:48 AM
 
Did it all come out ok?
     
cla  (op)
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Jun 3, 2005, 03:09 PM
 
Thanks for your concern,

I don't know yet - they're printing it as we speak. I understand they charge about $0.15 per cup, 250 000 cups, so we'll see if I still have a job next week... =)
     
Corys
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Jun 8, 2005, 04:23 PM
 
that kind of money and no one is press checking? wow
www.prepressforums.com
News & Information for the Prepress Industry
     
cla  (op)
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Jun 8, 2005, 06:12 PM
 
=(

Unfortunately the deadline turned the whole deal into a panic thing. Especially now when the printers of the cups just cancelled the job - their key account manager actually told us he's "sick and tired" of us, and that we should never call them again.

This has never happend to me, and we have absolutely NO IDEA why he did this! Could it be that he'd rather loose us as a customer than miss a deadline?!? (Or as he expressed it himself: "You're not even a B-client!!")

I really have no clue. As of now, we're trying to get the cups printed in China and then fly the stuff over to Europe. They are really nice, but the fact that they couldn't open "that strange thing named something-pe-de-eff" and asked us to send them a jpeg makes me suspect I've got more to worry about than the colors of the background...

They also said they need three days to "make the plates"... Three days? Why so long??

This thread is turning out to something of a diary... :>
     
KeriVit
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Jun 8, 2005, 10:34 PM
 
Originally Posted by cla
=(



This thread is turning out to something of a diary... :>
And much like a soap opera to me... more details?
     
budster101
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Jun 9, 2005, 09:30 AM
 
China? Great. If it turns to crap, blame them.
     
CaptainHaddock
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Jun 10, 2005, 12:06 AM
 
I've had awful experiences with clients who used Chinese printers. Communication is impossible, their equipment is outdated, and even the simplest things get messed up. So I know a bit of what you're dealing with!

As for your original question:
My problem is, when I activate the other channels the image turns brighter. Even though the other channels are empty. Why is this?

The reason is that black process ink is actually more like a dark grey when printed on white paper. That's why most programs like Photoshop will convert RGB's true black to CMYK "rich black", which mixes black with the other inks to make it darker. When you turn on the other channels in Photoshop, it simulates what the print job will look like on paper, which means lightening the black to dark grey.

If you want a nice dark black, you could also paste your RBG image into the CMY channels at, say, 20% opacity. Or if the item is being printed with black only, you can run it through the press twice (double-hitting it).
     
budster101
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Jun 10, 2005, 09:29 AM
 
Is Kinkos owned by China?

They suck.
     
cla  (op)
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Jun 10, 2005, 10:29 AM
 
Thanks Haddock. Your answer was so great I'll pay homage with a fan shot:


Anyway, here's the next episode:
I sent the chinese the original, which by the way looks like this:


I know barely anyone at the printers' speak English, so I had no idea as to how to send them printing instructions. The only solution I could think of was to render a 3D preview of the cup, so that they'd understand that the logo should be on the vertical middle, and that the italian stripes should be on the inside of the underside of the cup.

I sent them this:


Then they were suppose to warp the print original to go with their cup making machine... this is what I got back (converted from TIFF):


I have no idea what they did to the colors... Probably the (RGB) TIFF they sent lacked a color profile. Unfortunately, we had to approve it right away (deadline...).
     
CaptainHaddock
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Jun 10, 2005, 04:24 PM
 
Well, however it turns out, your design is quite nice. And I enjoyed the picture of my namesake. Thundering typhoons!
     
   
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