PMS -> CMYK, problems with screens

[bhartzell]

Hi,

I'm printing something on a digital press with a large gradient of a blue PMS. When it converts to CMYK, it looks great at 100% but at about 40-50% screen it takes on a purplish hue, and then returns to a nice blue below 40%. The rip on the press will allow me to adjust the colors for the entire page, but I can't adjust the one PMS color (so as not to affect the other photos).

Can you suggest any prepress steps? The source file is InDesign CS3. We have Acrobat 8 and Acrobat 9 (for mac) installed with pitstop professional 8.

Thanks,
Ben

 

[michaelejahn]

No one calls it PMS anymore

No one calls it PMS anymore

Hi,

I'm printing something on a digital press with a large gradient of a blue PMS. When it converts to CMYK, it looks great at 100% but at about 40-50% screen it takes on a purplish hue, and then returns to a nice blue below 40%. The rip on the press will allow me to adjust the colors for the entire page, but I can't adjust the one PMS color (so as not to affect the other photos).

Can you suggest any prepress steps? The source file is InDesign CS3. We have Acrobat 8 and Acrobat 9 (for mac) installed with pitstop professional 8.

Thanks,
Ben

Hi Ben.

well, gee wiz. Not sure what "Blue PMS" is (Pantone i will assume?) or what your CMYK "hope" is, but the fact is that you really can't achieve a nice rich saturated blue very well using CMYK inks - not sure what your "RIP on the Press" actually means - is this a digital press (iGen, HP Indigo, Nexpress?)

if you want to know "why";

Welcome to Bruce Lindbloom's Web Site

hope that helps (probably didn't very much)

I would suggest you purchase a Pantone COlor Bridge book - that way you could (in the future) see what happens to a specifc Pantone color when it is "converted" to CMYK, and stay away from ones that look cruddy (if possible) - a great example is Pantone 151 - a very bright saturated orange (like little Nemo) - or cheese doodle Orange - looks great as a Pantone spot color, and greyish dirty ink as CMYK.

 

[bhartzell]

Michael (and anyone else):

I was omitting details I didn't feel were particularly relevant, but obviously I was wrong. Here you go:
• The color I'm matching is Pantone 301 C.
• The press is an HP Indigo 3050. The "RIP on the press" refers to the built-in RIP.
• We found our starting CMYK using the icc profile generated by our gretagmacbeth eye-one. The results are the same by the way if we use the color bridge values and just use the icc profile as our output intent.

It matches fine at 100% and I'm perfectly happy with that. It doesn't match at 40-50% and I don't expect it to match. However, I don't want it to look purple either. The sort of solution I'm hoping to find is something that does something similar to this, but in InDesign or Acrobat: If I had just this separation (Pantone 301) in Photoshop and converted it to CMYK, I could adjust the magenta/cyan with a curve to make sure the gradient appears "blue" in the way through the gradient but still maintains the 100% CMYK values we like.

Thanks, hope that gives you enough to go on.

 

[Luc St-Pierre]

I am afraid that trying to adjust part of the gradient in Photoshop or anywhere else will just move the color cast somewhere else. You are experimenting a typical hue shift in the tonal. Even some custom inks such as Pantone based color mixes will show such a color shift down the tonal in a one-color gradient !!!
Some shades do it more than others. When we short-cut the gamut by using CMYK extensively, there are some compromises to be done. I don't think my comments make you smile. Good luck

 

[Tech]

Where is this PMS 301 converted to CMYK? InDesign layout?

If you have design elements on layout applied with this screen of 40-50%, why not create the exact CMYK swatch for it at 100%. If you want to add more to magenta/cyan, just modify the swatch.

 

[bhartzell]

Right now, it's converted in Acrobat, but I could convert in layout if it helped. But, the problem is that it's a gradient so I don't have specific control over the 40-50% point since the gradient runs 0-100%.

-Ben

 

[Lukas Engqvist]

The problem of colour shifts in a gradient is probably due to a the shape of the Cyan and Magenta TVI curves. Your base colur probably has twice as much Cyan as Magenta.
If you want to see how curves affect the hue shift just open a shade in photoshop and play a little with your cuan and magenta curves, you will get banding in different hues.
How to solve it? Well what you are upsett about is the excess of magenta in mid blues? If so add a little step point in the gradient (In indesign or illustrator is easiest) and in the are where you have too much purple, take the magenta down. Now that is the fix.
Try printing a gradation of a neutral grey in RGB and see if it stays neutral if not, try and work on your TVI curves, or you will have to make an ICC profile for your printer and convert jobs from a standard profile to your profile to maintain visual integrity.