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Thread: CMYK grey and brown mixes for a digital print. Help please.

  1. #1
    thhought is offline Junior Member
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    Default CMYK grey and brown mixes for a digital print. Help please.

    This is my first post. I hope this isn't posted in the wrong place or isn't a repeat question.

    I work in a label shop and we have two Jetrion, Digital, Roll-to-Roll presses. Something I run into over and over again is brown mixes and gray mixes varying from one head to the other. The problem is magnified if you are printing on top of white when using any material that is not white (silver foil, clear etc.).

    The problem as I understand it is that browns and grays are a mixture of all four colors. Add that to the fact that you have three separate printheads spanning the width of your print that must be working in perfect sync with one another (output of all four colors and their respective percentages) in order for a solid gray or brown to appear consistent. This often results in some areas of the print having more magenta (for example, this applies to all except black). I should mention this is only in jobs that have a solid color background: meaning the label has a gray or brown background with black text(for example: the black text is irrelevant to the discussion). And especially in cases where it is white behind the solid gray or brown.

    I am asking if you have solutions other than to operate in the utopian world where printheads are always aligned and calibrated perfectly, clients know better than to order browns and grays on digital, and unicorns re-set type for me HAHA. In all seriousness though are there certain CMYK mixes that result in more consistent browns and grays?

    I can go into more detail if you guys are unclear but I don't want my query to be ignored for it's lengthiness. Plus if you are experienced in digital production I am sure you have run into the same issue.

    PS I can post a picture of the specific artwork in question. But once again I think that specialist, such as yourselves, will understand that this is a non-artwork specific issue.

    Thank you so much for your time.

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    Stephen Marsh is offline Senior Member
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    When you say "this applies to all except black" - do you mean that the K heads print more consistently than the CMY?

    One can use a higher Grey Component Replacement ratio in your separations, swapping out the grey CMY component for K.

    For example, the common 50c40my neutral midtone grey balance values often used in offset printing can be made with a higher GCR:

    31c24my29k
    5cmy52k
    15c13my44k

    All of these three different sets of GCR values have the same L*a*b* value of 61L 0a 0b as the original CMYK mix that contained no black. These numbers are only used for example, they are based on ISO Coated/F39 conditions, not your inkjet.


    Regards,

    Stephen Marsh
    Last edited by Stephen Marsh; 12-18-2012 at 01:54 PM.

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    thhought is offline Junior Member
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    When you say "this applies to all except black" - do you mean that the K heads print more consistently than the CMY?

    I mean that the grays and brown will be inconsistently A) more magenta in places B)more green in places. I guess this could be an inconsistency in black; where the black is letting those other colors show through more in certain areas. I just don't think that this is the case (and I am no expert in color theory) but black isn't neutralizing those other colors it is only providing tone.

    GCR:
    This is the first I have heard of this. I am after all pretty new to production so I apologize for my lack of knowledge. However, this press is using a UV inkjet system and their ink is proprietary. I will ask if this company has something like this but I am responding with this because I am wondering if we are on the same page. This is not a flexographic or offset press. We do not mix these inks or have anything outside of the CMYK heads and then the white.

    The long and short of it is that I am going to have to do some more research to find out about this. But I wanted to respond and thank you for your time.

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    rich apollo is offline Senior Member
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    The GCR (gray component replacement) is handled at the RIP. The RIP that is driving your Jetrion will have some color management procedures set up as part of the workflow. Files coming in are converted from whatever colorspace they happen to be in to the output color space of your Jetrion. To minimize this inconsistency, the ICC profile describing the colorspace of your Jetrion needs to have a very full black channel. You want to push as much of the file onto the black channel as you can.
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    Stephen Marsh is offline Senior Member
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    I agree with Rich 100% (sorry for the typo, ratio when it should have been replacement).

    Is the Jetrion driven by RIP software, or by a "simple" printer driver?

    If a RIP, see if Jetrion have different ICC profiles or ICC DeviceLink profiles for the Jetrion, that use a higher GCR amount.

    If they don't, you would have to make your own profile that uses heavy to max. GCR. If doing this yourself, you would need a spectrophotometer and ICC profile creation software and the knowledge to use both. This could be costly if you only need to create 1 or 2 custom profiles. Colour consultants can offer this as a service which may be a better option to begin with. You will need to create a separate profile for each substrate (one profile for gloss paper with CMYK, one for self adhesive vinyl with CMYK, another profile for surface print white + CMYK on clear, another profile for reverse print CMYK + white on clear etc).


    Stephen Marsh
    Last edited by Stephen Marsh; 12-18-2012 at 01:55 PM.

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    thhought is offline Junior Member
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    Wow, you guys are awesome!

    I am still looking into it. The RIP software that it uses is EFI fiery and I have already found in color management>output that they have an .icc profile named EFI gray profile. I have kind of been forced to get up to speed on a lot of the intricacies of this machine because the other operator that had been here for a while had to leave.

    But this is much appreciated because now I have a place to start. In the beginning I was curious if it was something that could be prevented in the setup of the artwork files. Now you have specified and narrowed down where I should be looking to correct/better our end product. So much of my college career was not aimed at production and it seems that so many graphic designers (on other online resources I have found) are just content to say "well don't print grays digitally because you can't". But your forum and the community that uses it doesn't offer useless responses and makes sure that you know what you are talking about when you respond.

    Thank you very much Stephen and Rich. I might have other questions as I go along but I think you have given me enough to get on my feet and take it from here.

    Sincerely,
    Thomas

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    thhought is offline Junior Member
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    Wow, you guys are awesome!

    I am still looking into it. The RIP software that it uses is EFI fiery and I have already found in color management>output that they have an .icc profile named EFI gray profile. I have kind of been forced to get up to speed on a lot of the intricacies of this machine because the other operator that had been here for a while had to leave.

    But this is much appreciated because now I have a place to start. In the beginning I was curious if it was something that could be prevented in the setup of the artwork files. Now you have specified and narrowed down where I should be looking to correct/better our end product. So much of my college career was not aimed at production and it seems that so many graphic designers (on other online resources I have found) are just content to say "well don't print grays digitally because you can't". But your forum and the community that uses it doesn't offer useless responses and makes sure that you know what you are talking about when you respond.

    Thank you very much Stephen and Rich. I might have other questions as I go along but I think you have given me enough to get on my feet and take it from here.

    Sincerely,
    Thomas

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    Stephen Marsh is offline Senior Member
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    This is not a flexographic or offset press. We do not mix these inks or have anything outside of the CMYK heads and then the white.

    Hi Thomas, sorry that my OP was not very concise, I wrote that in a hurry while having my morning coffee. I should have posted when I was more awake!

    Although I used offset printing as an example, and "separating" or building a CMYK file or object with higher GCR, as Rich stated - this is also possible and common with digital output being driven by a CMYK RIP. Instead of the source file having higher GCR, the output profile that describes the printer/media is created using heavy or max. GCR.

    Stephen Marsh

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    Correct Color is offline Senior Member
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    tthought,

    Just to expound a little. What you've got there is an inkjet printer, and as such, it needs to be profiled basically just like a large-format printer.

    And what that means is that if you want to solve this problem, you've got to make -- or have made --custom profiles for this machine on the media on which it prints in its environment.

    And I'd deviate just a bit from what these guys are saying to point out that it's not so much GCR that's going to resolve your issue, but the black start point and the black ramp in your profiles. If they're not set to achieve your desired result, all the GCR in the world won't overcome them.


    Mike Adams
    Correct Color
    Last edited by Correct Color; 12-29-2012 at 10:29 AM.

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    Stephen Marsh is offline Senior Member
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    Mike, I would also say that it is a combination of both GCR and black start point and curve/ramp shape. If a device only has one K ink, I would be more wary of starting the black below 20-30% on the grey ramp (the shape of the curve also plays a role here too), than if the device used LK, LLK and K. It also depends on the source colour, what lightness value is the input?

    Stephen Marsh
    Last edited by Stephen Marsh; 12-29-2012 at 06:28 PM.


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