process Density and Dot gain questions

Discussion in '4-Color Offset Presses +' started by verbena, Apr 22, 2007.

  1. lildaddy50

    lildaddy50 Member

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    your upside down on your cyan -magenta values, but then again what do I know after 30 years. And you say "thats if i use it at all" good luck in the printing industry.

    Rod
     
  2. Data

    Data Senior Member

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    I understand if you don't agree Rod....but there's no need for comments like that.

    Do you think there could be reasons that different values are used?

    For not using desitometers all the time is due to printing 1-2mm from the edge of the sheet. As far as register marks go we dont sell those, so I'd rather fit the job.

    Finally i must thank you for your best wishes. Ive now been in the trade for over 28 years from letterpress to currently running multi-coloured presses, various papers, plastics, conventional/Uv inks coatings and powders.
     
  3. Dan1

    Dan1 Member

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    "Normal" densities in any given shop will depend on what prep has done before you get the plate. They vary from shop to shop, what may work for you may not work for the guy in another shop.
     
  4. RichardK

    RichardK Senior Member

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    You want to advertise... then pay for an ad.
     
  5. DWF

    DWF Member

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    Hi Guys, To Add to this thread although i agree with most posts already, I have run Kmcy for about 20 years and always changed over any shops i have worked at simply because it works best in most applications, We do alot of client passing and they don't care about denso readings they just want a certain look, We run Image control on large jobs or book work but the komori PDCS was a better easier system. Cheers and happy printing
     
  6. lildaddy50

    lildaddy50 Member

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    again "NOTAGOONER is correct.Rod (old school}
     
  7. lildaddy50

    lildaddy50 Member

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    Verbena,

    Ive been doing this for 30 years. Your sequence for process work should be k,c,m,y . Dot gain is not an issue with direct to plate . Forget about re-calibrating your dinsitiometer for every job! your going to break the damn thing. Calibrate it annually.

    Rod (old school)
     
  8. RichardK

    RichardK Senior Member

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    Pretty much of a generalisation there Rod.

    Sequence is job and stock dependant. Absorbant stock, run pretty much what sequence you like. Art stock...then it's K down first, Y down last but the C & M are interchangeable.

    Say you have a dark blue made out of 40K 100C and 60M...on art art stock you're gonna give yourself a hard time trying to get an even lift from the magenta, unless you reduce the tack and even then you're laying up the potential for trouble (ain't about to tell you as you've clearly the experience behind you).

    I suppose the point here is think flexibly and just because you've done something one way for 30 years don't think that's the only way. FWIW I ran KCMY for 15yrs then went to another printshop where I quickly learnt to swap over C & M since the vast majority of process jobs we ran had those reflexy blues much loved by designers.

    Oh and occasionally k last when pale gray tints were in the job to avoid spray powder affecting them.

    As for dot gain not being an issue with CTP. It's less of a problem than it used to be, since the dot generated on the plate is 1st generation, but an incorrect use of dot gain curves in the software can still throw the print off.
     
  9. Stu

    Stu Member

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    The reason all the densities quoted are approximate, is that the industry standards don't quote densities, they quote l.a.b. values. You all know that different inks on different stocks when printed to the same densities, regardless of whether the densitometer has been zero'd on that paper will appear different colours.
    So, if you find out what the lab values are for the standards you are trying to reach, then find out at what densities you most closely achieve these values.
    You will find that 1. The figures are there or there abouts what everybody has been quoting here. and 2. You really don't have time to find all these figures out for every type of paper as it gets in the way of getting the work done. :)
     
  10. Alan C.

    Alan C. Member

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    Forget about dot gain, it will change! follow your startup O.K. sheet & try to hold density.
     
  11. Stu

    Stu Member

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    When I adjust dot gain, I try to get it correct at just the 40% and 80%. If you can't get a good looking curve with these 2 figures approximately right then it's usually an indication something else is amiss.
    Don't obsess too much about density and dot gain, remember, these 'standards' whether they be fogra, swop etc. etc. are all meant to make things easier for us! They aren't some holy grail that is unobtainable.
     
  12. turbotom1052

    turbotom1052 Senior Member

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    dot gain is not an issue with direct to plate??? please tell me what planet your from? i have a newsflash for you ron. prepress is only half of the formula when it comes to dot gain. To think that just because were living in an age of direct to plate that the issue of dot gain is a non issue is ludicrous. The biggest variable when it comes to dot gain happens on press. you keep touting your 30 years of experience but with every post you make it shows your ignorance. I too am am old school, and ive also surpassed your 30 years of experience. I too beleive that densitometers are way overused by lots of people in this trade, ive even referenced this in a previous post of mine but Ron your talkin outa your ***. In one sentance you talk about stop worrying about the densitometer before you break the damn thing and in another sentance you correct someone about what the numbers should be, and what the correct color sequence should be. Id think that someone with your experience would know from years doing the job that there are no hard and fast rules when it comes to these issues. In another post you talked about people acting like their in kindergarten and how if they could grow up their might be a job in it for them from you. God help the people that work for someone like you. I feel for them. Ive read a few of your posts for awhile and have bit my tongue and not said anything but i cant hold back any longer. Ive tried real hard to be kind here and have even read and reread my posting and went as far as to edit it twice and this is the best i can do. My suggestion to you Ron is that you begin to read what you say before hitting that send key. And if you incapable of that then you might want to allow someone else to proofread your posts for intelligence before sending.
     
    Last edited: Jul 26, 2010
  13. The Heidelberg Guy

    The Heidelberg Guy Senior Member

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    I am amazed at some of the suggestions in this thread, to be honest, completely shocked.....

    I have been in hundreds of print shops across the USA and have seen pretty much everything when it comes to sequence, dot gain ect... The "standard" seems to be the BCMY, black being first down. However, this is not to say any other combination is incorrect, quite the contrary. There are quite a few shops that run a lot of purples, violets in process colors traps for corporate colors ect.., that the sequence is BMCY, it works rather well as said previously by Richard. The most common densities are; Black 1.80, Cyan 1.35, Magenta 1.40 and Yellow 1.00.

    Dot gain has always been a thorn in the pressman's side, either they don't quite grasp it, or they cant control it. The TVI (dot gain) we get on press can be effected by literally 100's of things. Any offset press will have dot gain, waterless, DI, Anicolor, conventional ect. All these machines have considerable differences, but have a few similarities as well.

    When reading TVI (dot gain) we need a reference point to shoot for, this data will come when you benchmark, color profile the machine. After the machine is benchmarked and profiled, this is when you read and record your final densities and dot gain patches for reference. If anything changes i.e. paper, blankets, fountain solution, plates, ink, packing, press temperature...... I could go on and on, so will your dot gain. So it is best to profile your machine on the paper you most run, or for the most quality conscience customer, or better yet, make several profiles. I personally like the 40 and 80 percent patches on my color control strip, it gives me a better idea of what's happening on the press sheet. Most color control strips (from Heidelberg) have only one percentage patch, but others may have one with two percentage patches on there. A quick density and dot gain relationship scenario;

    -Magenta target value 1.45 Density, dot gain @ 50% is 19%.
    -Put a job on and run to 1.45, and it looks like it needs more magenta to match the proof, the dot gain @ 50% reads 15%.
    -If you boost the density up a few points to get the dot gain to your target 19%, you will most likely hit the proof.
    -We can do the same to lower the dot gain by lowering the density as well, but we can only go so far with raising and lowering.

    So all in all, density and dot gain monitoring will lead you to more consistent results in the pressroom. I think its great that you want to learn this, it will cause you to have a lot less head aches in the future!

    Tim
     
  14. Stu

    Stu Member

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    Tim are you suggesting controlling dotgain by adjusting density?
     
  15. The Heidelberg Guy

    The Heidelberg Guy Senior Member

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    You can up to a certain point, 3 to 5 percent while maintaining stable ink water balance. I should of been more clear on this in my post.

    Tim
     
  16. Alan C.

    Alan C. Member

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    I also agree with Tim, But I'll say it again. Forget about dot gain, it will change! follow your startup O.K. sheet & try to hold density. Why make things harder? unless you like creating issues.
     
  17. Stu

    Stu Member

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    Of course dot gain can change, there are many variables, but it still needs to be set up in the first place. Say you have 2 presses maybe different manufacturers, ages condition etc. How else will you get them to match if you don't fingerprint them using dot gain? What if you have a solid orange/green/purple type colour that requires 100% of a colour, if you adjust the density to correct the dot gain what will happen to these colours? An inkjet proofing device won't print using varying densities. What if you need the dot gain to be different from the mid tones to the shadow areas? How can adjusting the densities help here?
    If you print to consistent densities, then fingerprint the press to a standard (whatever one you prefer) using the dotgain software. and then profile a proofer to match the press you will make your life so much easier in the long run because;

    1. Your customer receives a proof that is profiled to match the colour gamut of the press.
    2. If the operator is always running to the same densities his press curves will be more accurate
    3. In the scenario that the operator is on a night shift, there is no manager to pass his job and there is no proof present. If he runs to density he can justify this.
    4. If you run to a standard, it is an easy way to see if you have any problems with your press, roller pressures, blankets etc.
     
  18. The Heidelberg Guy

    The Heidelberg Guy Senior Member

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    Of course dot gain can change, there are many variables, but it still needs to be set up in the first place. Say you have 2 presses maybe different manufacturers, ages condition etc. How else will you get them to match if you don't fingerprint them using dot gain? What if you have a solid orange/green/purple type colour that requires 100% of a colour, if you adjust the density to correct the dot gain what will happen to these colours? An inkjet proofing device won't print using varying densities. What if you need the dot gain to be different from the mid tones to the shadow areas? How can adjusting the densities help here?
    If you print to consistent densities, then fingerprint the press to a standard (whatever one you prefer) using the dotgain software. and then profile a proofer to match the press you will make your life so much easier in the long run because;

    1. Your customer receives a proof that is profiled to match the colour gamut of the press.
    2. If the operator is always running to the same densities his press curves will be more accurate
    3. In the scenario that the operator is on a night shift, there is no manager to pass his job and there is no proof present. If he runs to density he can justify this.
    4. If you run to a standard, it is an easy way to see if you have any problems with your press, roller pressures, blankets etc.



    Number one, an offset press will NEVER match any proof 100%, it simply cannot be done. No proofer that I know of can simulate any given spot (PMS) color along with screens accurately, simulations are at best sketchy...

    So as I previously stated, we need to profile (fingerprint) the machine and work from that point. From a larger view, the "tool" we use, density and TVI, can work in some instances, but if the differences are that great to where a match is not possible, something has changed or different than from what we profiled the machine to. From this point, either the stock is different from the profile, or one of many entities on the machine has changed (or prepress hasn't been calibrating their end :-/). For example, I have recently set up a shop where we have multiple profiles for every machine, and these can be instituted by the proofer as well, to match no matter what machine it is on. It works 100% using the density and dot gain as basic tools for achieving color.

    Always running to the same densities is a good start, but if you cant match the proof, the customer isn't going to buy it. One of the biggest culprits in misidentifying a color match problem is roller settings, when a majority of the time it is just a simple error of blanket packing, or ink and water balance...

    As you call it "Running to a standard" is the right thing to do, but if your not reading your dot gain, its like running blind IMO.
     
  19. Stu

    Stu Member

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    ???
     

  20. Stu

    Stu Member

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    ???
     
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