Participant

Question

A CMYK curve to convert between two color profiles?

Forum|Forum|7 years ago
July 27, 2018
4 replies
1711 views

Our printer recently changed their press and have assigned us a new color profile for us to use. We have a few decades worth of image assets (archives) that were converted to CMYK using the "old" color profile. We will need to reprint our "old" archived images on the new press. However, not surprisingly, if we run our "old" photos on the new press, keeping the CMYK numbers the same, they will print relatively darker than our "new" photos.

Since we have both of the profile settings, I'm thinking that there is a curve that could be applied to our old CMYK images that would convert the color values to simulate how the new color profile would have converted them. But I'm not sure how to determine the curves or difference between the two profiles.

At first I thought this would be easy. In my head I assumed that if the original image contained, lets say 100% black, the "old" color profile might convert that to 80% black. I could test the entire black color range and plot it in as curve. Do the same for the "new" color profile and then make a third "adjustment" curve based on the difference of the first two curve. However, obviously this doesn't work because images are converted from RGB to CMYK. There is no 100% C,M,Y or K in RGB to easily set a benchmark.

Does anyone have thoughts on how to to create a curve based on two profile settings?

And yes, I know it's not ideal to use curves and degrade the images another step, but we want to avoid going back and color correcting the original RGB photo to save us time and money.

Thanks

This topic has been closed for replies.

G

G_Hoffmann

Inspiring

In my opinion the printer should use a Device Link Profile. Either he can create this

himself by RIP software or buy it from an external service:

https://www.google.de/search?hl=de&as_q=Device+link+profile&as_epq=&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=lang_en&cr=&as_qdr=…

In my RIP, device link profiles are internally used, but not explitcitly available as files.

No customer should have to convert old files himself.

The manipulation of curves for CMYK channels is a hopeless case because of the

impossibility to maintain gray balance over the whole range. Not only in my opinion,

but also by experience.

Best regards --Gernot Hoffmann

c.pfaffenbichler

Community Expert

The manipulation of curves for CMYK channels is a hopeless case because of the
impossibility to maintain gray balance over the whole range.

Amen.

The hope that a Curves Adjustment could, in a meaningful fashion, perform the task of transferring a CMYK image to appear identically in another CMYK space that might have different GCR and TAC would appear unfounded.

No customer should have to convert old files himself.

A customer that decided to work in CMYK or at least only store CMYK images might be responsible for their problems in large part themselves.

In any case the print provider would be justified in charging for the conversions if they are entrusted with them.

Stephen Marsh

Community Expert

Can you provide a download link to both CMYK profiles?

DeviceLinks are likely the best bet, however you may be able to get acceptable results via a simple curve edit to each separate channel. DeviceLink profile may be created using a simple TVI curve or using colorimetric data.

Norman Sanders

Legend

Since I have no firsthand experience with this type of conversion, please consider the following suggestion with some skepticism. Theory does not necessarily play out well in practice. The suggestion is that you convert the current-profile CMYK file to device-independent Lab Color Mode. Once there, convert it back to CMYK carrying the new profile. It may be worth a test.

On the subject of profile conversion and tests, it seems odd that your lithographer did not provide the instructions for making the conversion. It should be easy to convince him that running this and similar tests would benefit not only you but his other clients, as well, assuring their continued loyalty. (Imagine if another equally talented lithographer in town offered a conversion method to their profiles. Enough said.)

D Fosse

Community Expert

The problem is that any normal conversion (including to Lab) will turn K only black into 4 color black.

Device link profiles are made to avoid this.

Conrad_C

Community Expert

A curve is probably not the best solution. It sounds like you need a device link profile, which is typically used for converting between two CMYK profiles. One of the reasons to use a device link profile is to properly preserve black generation. You can read more about it at the link below; scroll down to the heading Device Link Profiles.

4.8 Beyond Output Profiling: Display, Input, and Device Link Profiles – Graphic Design and Print Production Fundamentals

As it says there:

"A device link profile combines two output profiles to provide the specific conversion instructions between two particular devices. It provides the opportunity to maintain black and other separation purity…"

In the Convert to Profile dialog box in Photoshop, there is a Device Link option that's revealed if you click the Advanced button.

That's just about all I know about them…you should probably ask the printer if they've made such a profile to ease reprinting of jobs originally printed on an older press.

Sign up

To post, reply, or follow discussions, please sign in with your Adobe ID.

Sign in to Adobe Community

To post, reply, or follow discussions, please sign in with your Adobe ID.

Scanning file for viruses.

This file cannot be downloaded