Spot Process / Simulated Process

[claytonperry]

I am looking for the best way to break down a raster CMYK or RGB image into spot colors. For instance converting a CMYK image of a strawberry into a Red, Yellow, Black, & Green. Does anyone have any suggestions for me? I have been using the "Select Color Range" feature in Photoshop.

Thanks

Clayton

 

[Lukas Engqvist]

Place it in illustrator, Live trace it and use Live colour, limiting to pantone library (you can even limit to a specific number of colours). If you need you can then superimpose a greyscale image and use opacity mask with a greyscale to get the details of the image if necessary.

 

[Deleted member 16349]

Place it in illustrator, Live trace it and use Live colour, limiting to pantone library (you can even limit to a specific number of colours). If you need you can then superimpose a greyscale image and use opacity mask with a greyscale to get the details of the image if necessary.

Lucas,

Would this method provide a separation where there was no overprinting of inks?

Curious.

Erik

 

[gordo]

You could also work in CMYK in PShop. Assign each process color to represent one of your spot colors: e.g. M= Red, C=Green, Yellow =Yellow, Black = Black.
In the old days, if you wanted a closer approximation as to how the image will look then you could change the L*a*b* values of the CMYK hues to match those of the spot colors - but I don't think that's possible anymore.
Don't forget that spot colors are not designed to be over printed, nor screened.

best, gordon p

my print blog here: Quality In Print current topic: gray balance unbalanced

 

[Deleted member 16349]

Don't forget that spot colors are not designed to be over printed, nor screened.

best, gordon p

Gordon,

In the process that is in discussion, which is Dry Offset for container printing, spot colours are often screened but in general should not be overprinted. Overprinting is not desired due to the common blanket press designs that are used and not for the traditional reasons why spot colours are not overprinted.

The goal is to make an image look reasonably like a process print but do it with a limited (6 to 8) spot inks that are printed close to each other but are not overprinted.

 

[Lukas Engqvist]

Yes. The Live trace makes opaque illustrator objects. You can make it into a "photographic resemblance" by choosing say 256 colours or more.
Then using live colour you can reduce the number of colours, still no transparency or over printing involved, and choose to limit to a number of colours with a specific libary. I will attempt to show a photo of my son in that way,
I have just taken a plain photo... probably could vastly improve result by prepping the image a tad. (I never done this, just aware of the functions and thinking out loud ;p)

I'm not going into the details on how to use the functions but here is an example

And reduced to 3 colours (Pantone 7546, 419, 4975... you can choose manually or let the computer pick, also you can move what colours are going to what place. I think actually you can live trace to a specific colour group, but never done it in that order) Colours are mapped to tint, so choosing a dark saturated colour will give you a better range with less colours.

 

[meddington]

In the old days, if you wanted a closer approximation as to how the image will look then you could change the L*a*b* values of the CMYK hues to match those of the spot colors - but I don't think that's possible anymore.

The Lab value of CMYK hues would be locked into the particular CMYK working space profile, perhaps this is why it isn't possible in CMYK mode? Switching to multichannel mode, you then have this ability. Is this what your referring to?

 

[alang66]

There is no easy way to do it. It will take some cutting out (depending on separation of original scan). If it's a strawberry, I would look at the magenta channel for the red, duplicate that channel as a spot red channel and clean up outside of the strawberry anywhere that does not need red. Increase channel data so that there is a full tonal range and that strawberry is solid red in places. For leaves, try cyan channel, duplicate, clean up any areas that do not need to be green and adjust strength to give full tonal range. Not sure what you need the yellow for unless it's the seeds/pips on outside of the strawberry. If so, choose bets channel to duplicate. Once done, clear all data from CMY channels. Convert empty CMY and original K channel to grayscale document with 3 spots. That's how I would do it.

 

[Deleted member 16349]

Yes. The Live trace makes opaque illustrator objects. You can make it into a "photographic resemblance" by choosing say 256 colours or more.
Then using live colour you can reduce the number of colours, still no transparency or over printing involved, and choose to limit to a number of colours with a specific libary. I will attempt to show a photo of my son in that way,
I have just taken a plain photo... probably could vastly improve result by prepping the image a tad. (I never done this, just aware of the functions and thinking out loud ;p)
View attachment 497
I'm not going into the details on how to use the functions but here is an example
View attachment 498
And reduced to 3 colours (Pantone 7546, 419, 4975... you can choose manually or let the computer pick, also you can move what colours are going to what place. I think actually you can live trace to a specific colour group, but never done it in that order) Colours are mapped to tint, so choosing a dark saturated colour will give you a better range with less colours.
View attachment 499

Lukas,

At first, I thought this was a potential method but after some more thinking about it, I am suspecting that there is a flaw in the method that would cause problems.

The method you use implies that a reasonable match is possible but that method is working in the RGB space of the monitor. Even if the monitor is colour managed, this IMO does not ensure that the match will be produced in some set of Pantone coloured inks.

As I understand it, one can not model colour of complicated print structures, when dealing with Lab or even the XYZ tristumulus values. On a monitor, which is dealing with colours related to the rgb of the monitor itself, one can model the colour of what the monitor will produce but not of real inks.

The Lab value of individual inks is not sufficient information to use it to model the colour of multiple inks when printed next to each other of with overprinting.

When dealing with real inks, one would need to obtain the reflection spectral curves for each printed ink. Then one could combine all the reflection spectral curves for a combination of printed inks in a local image in order to determine the total reflected spectral curve. Then from this the XYZ values could be determined and then the Lab values.

Seeing a nice match on the monitor is most likely giving a false view of how real inks will perform.

I think that any software that would have reasonable predictability of desplaying how a simulated process print would look, would have to take into consideration the spectral curves.

An added complication with Dry Offset is that screens can often print with a much greater hue shift than one is used to in conventional offset. This is due to the uneven ink films which is a result of the flexo style plate and the spectral curves of some of the Pantone inks.

It is an interesting process but also in some ways more complicated than normal offset.

 

[michaelejahn]

@ claytonperry

I am looking for the best way to break down a raster CMYK or RGB image into spot colors. For instance converting a CMYK image of a strawberry into a Red, Yellow, Black, & Green. Does anyone have any suggestions for me? I have been using the "Select Color Range" feature in Photoshop

If you were trying to accomplish some Andy Warhol effect, so your photo is converted into a silkscreen look, well I guess Lukas Engqvist live trace offers an approach that would work - I once had to convert a 'type on fire" Photoshop image into something that could be silk screened in 3 colors, and this Adobe Illustratords live trace did that perfectly.

But if you really are interested in converting an image from one color space to a set of DeviceN color separations, I would contact Glynn Hartley
email -- [email protected]

Specialcolor
ICISS - CoCo - nColor
25 Redcliffe Road
Nottingham, NG3 5BW UK
Tel. +44 115 962 6060

Specialcolor - Worldwide distributors and implementers of color separation and color correction tools

I have not seen a better tool for selective color correction than CoCo Multi Channel (which is different than CoCo RGB-CMYK)

When Specialcolor refers to CoCo Multi Channel and "separation", that is usually for bump plates, spot colors, t-shirts, ceramics . . . . . . )

Also - Specialcolor uses a different Photoshop plug-in that enableds the user to creat multi channel separating with any profile, (since January 1997), is called nColor Converter.

Specialcolor sells plenty of nColor Converters for other purposes.

Also - when a user desires nColor separation for any files for any situation, I suggest people to consider ICISS (and a bundled CoCo Multi Channel).

Specialcolor works on a one-to-one basis. As Erik Nikkanen suggests - this is complicated with complex issues that relate to selecting the proper inks and setting up a proofing method. My friend Scot R Fernandez at Hallmark uses this, and also uses Apago PDF Enhancer to generate proper 5 / 7 color PDF files and send them to suppliers - In addition to this - Scot shared at a conference I attended how to make color moves using HSB tools (using a Photoshop Plug-in) which provided advantages when coupled with a custom RGB profile and "DeviceN PDF out" strategy. This is a bit different than what the original post is about, but I share this in the case that you needed a way to send PDF outside your shop.

Hope this helps !
__________________
Michael Jahn - Slightly used PDF Evangelist
Simi Valley California