process Density and Dot gain questions

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

  1. The Heidelberg Guy

    The Heidelberg Guy Senior Member

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    If your just running to density alone, as in "just run to the numbers", your repeat jobs and even job to job consistancy will suffer greatly..
     
  2. lildaddy50

    lildaddy50 Member

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    Turbobotom,

    If you don't agree with my post than respectfully disagree. But calling me "ignorant' , Talking out of my ***" and "God help the people that work for someone like you", is uncalled for! I like to laugh and joke around at the work place as much as the next guy. But telling jokes and swapping stories is different than playing silly pranks on each other that always seems to get out of hand.

    The point I was trying to make about dot gain is as follows.

    10 years ago we had dot gain before we even hung the plates. It was already on the plate because we were using film. Using CTP at least we illiminated about 50% of the problem.

    I didn't say that dot gain is still not there, I said that it was "not an issue" By this I mean that an additional 25% of the problem can be corrected in pre- press with the click of a mouse using CTP.My pre-press staff takes into consideration for gain on press depending on the type of stock, coverage, screen tints etc... They call this practice, ( pre-anticipated dot gain conpensation)

    Now ,after all these improvements over the years and if your printing on a good cast coated sheet , (as most high quality shops are), and your press is set up properly in respect to pressures, tack , blankets, packing etc....., then dot gain is "not an issue". At least compared to what it was years ago.

    Rod (not Ron)

    Ps. Your right, I should make sure that I proof read my post before I click "send"
     
  3. Moya

    Moya New Member

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    i'm very new to printing industry...we are using CTcP for Plate making and will dot gain be a problem in CTP...and what will be the stage to correct dot gain...in RIP or before...?
     
  4. Alan C.

    Alan C. Member

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    Use Linear setting. Don't focus on dot gain! Use dot gain more as a tool if your having trouble matching your sample.
     
    Last edited: Aug 20, 2010
  5. Roy Batty

    Roy Batty New Member

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    Ink Density Dot Gain

    If you're on this forum, you obviously love to print and hopefully produce quality work. Don't take anything for granted. Everything involved with pre-press and your press has a direct affect on the final finished product. Keep your plate and or film/plate output device calibrated. Make sure your press has good blankets, correct packing, rollers striped, fresh fountain solution etc... Get your press fingerprinted to match your proofing device. Personally I've run most of my work KCMY, ink densities... K 190, C 135, M 130, Yellow 90. These setting are for most coated stocks. If I'm running un-coated I bump it up a little for dry back. Maybe 3-4 points. Also make sure you're not over-packing blankets and or setting rollers in correctly. These two simple steps cause most printing problems. As far as dot gain, I'm running direct to plate and can manually adjust for dot gain/loss. If we are trying to match a printed sample from another shop that ran film to plate we can adjust up very easily with our rip to match. On press, measure your sheet thickness and add or remove packing accordingly. It's easy if you take the time. Although, I know how it is, some shops I've worked for in the past don't care much about the quality, just quantity produced. Good Luck!
     
  6. DanRemaley

    DanRemaley Senior Member

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    Hello all, I have worked in printing for more than 40 years and can help with color matching issues. The "secret" to color printing is having the 'correct' density and DOT GAIN to match the sepraration. Thankfully, the separations are out of Photoshop and are set up to the following numbers-
    FOR COATED OR MATTE STOCK
    K1.70 C1.30 M1.40 Y1.00 the gain in the midtone should be K22% C20% M20% Y18% (meaning a Cyan 50% will read 70% at press).
    FOR UNCOATED
    K1.25 C1.00 M1.12 Y.95 THE DOT GAINS ARE THE EXACT SAME AS COATED
    Therefore. . .you cannot run 'linear plates', each color must be curved, and you MUST measure 50% gain.
    I have the entire tone scale numbers 1%-99% for each color (e-mail me and I'll share with you).
    Dan Remaley (Google me) danremaley@comcast.net Cell phone 412.889.7643
    Felix Brunner says "80% of print problems are caused by DOT GAIN, only 20% by density. . .what do you measure? 20% of the problem!
     
  7. DanRemaley

    DanRemaley Senior Member

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    process color sequence

    There is a great book by Kelvin Tritton of PIRA (UK) "Color Control in Lithography" that talks and measures color sequence. The best color sequence is K-C-M-Y (K can be first or last) but the other colors need to be in sequence to get the best Red, Green, Blue, Trap. Period.
     
  8. DanRemaley

    DanRemaley Senior Member

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    Printing to Gray Balance (for all)

    Here is an article I wrote on printing to gray balance. . ."Google" for more-
    Printing to Gray Balance. . . .
    Most recently there has been a lot of discussion about “printing to gray balance”. The
    new GRACoL (G7) describes the methods to achieve gray balance at press.
    What’s so important about gray balance at press?
    The concept of gray balance is essential for excellent color reproduction in scanning,
    proofing, and in the pressroom. In scanning, images that are not in gray balance are
    considered “casted.” Images that are casted show a magenta, cyan, or yellow (or
    combinations of M-C-Y) color appearance in the highlights, midtones, and/or shadows.
    Casted images require color correction to remove the unwanted colors. Images that are in
    gray balance only need to be adjusted for specific areas of color enhancement, i.e. greener
    grass, or bluer skies.
    Proofing systems must be able to reproduce neutral gray without any cast as well. If
    the file is correct and the proofer introduces a cast, then all the color is shifted away from
    gray balance. A proof that is casted will require the press to print away from neutral gray to
    match the proof.
    The little “secret” of process color printing at press is that you can only print two
    ways on press - in gray balance or casted - that’s it! You are either neutral throughout the
    tone scale, or you are casted in some way. If you’re casted, color reproduction suffers.
    The fact is that all press operators abide by this principal. Press operators look at a
    printed press sheet and notice casts of too much magenta, cyan, or yellow and reduce
    whichever color is creating the cast. The control for the press operator is more or less ink,
    however the TVI, or dot area, is equally important. The press operator can’t change the size
    of the dots on the plate, but he or she can change the gain by adding or subtracting ink.
    The major problem in printing today is that the values on the plate are incorrect. The
    values on the plate need to be adjusted for all four colors, each color Y-M-C-K, needs its own
    plate curve to reproduce neutral gray at press. A lot of printers have only one plate curve for
    all colors! The other issue is weight - how dark or light is your midtone reproduction? Screen
    builds and Photoshop images are adjusted for around a 20% TVI, or midtone gain, meaning a
    50% patch will print as a 70% value. Most linear plates (50% = 50%), gain around 14 to16%
    on press, and print too light for separations created in Photoshop.
    The majority of printing plants I encounter have this platemaking problem. It is
    impossible for the pressroom to control gray balance and color with the wrong size dots on
    the plates. The procedure is to print a test form with complete tone scales at the required
    density.
    Next, compare the scales against a standard and adjust the plate values accordingly.
    Every color bar should include a three-color gray patch represented by 50C-40M-40Y. This
    patch, when printed at the correct density and dot gain, will appear neutral - without any
    casts. It can also be measured with a reflection densitometer. The densitometer needs to be
    set for “ALL” filter readings, now the yellow, magenta, and cyan inks can be measured as a
    density. When all three filter readings are equal, the patch is neutral. A 0.03 density among
    all three filter readings is the tolerance for an acceptable neutral appearance.
    If you have any questions, or would like me to help you on-site, please call me. at
    Dan Remaley
    Process Controls Consultant
    412.889.7643 Cell
    Email:danremaley@comcast.net
     

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  9. pa printer 3

    pa printer 3 Member

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    You all seem to be right on, the densitometer is a "tool" to get fine results and to get you in the ball park. The customer sees the finished product not the bars nor does he probably care. I try to shoot for my numbers at the same time watching my grey bar usually when that is in balance my densis are there, or very close. I hate watching a guy run that densi across the bar and at same time micro setting the keys and twenty -forty sheets later do the same thing. It takes a bit for these to change especiallly the subtle moves.
     
  10. pressing situation

    pressing situation Member

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    Great forum and info. I am looking for tips and tricks now learning a DI press.
    For 33 years I have run a small one color A.B. Dick to an A.B. Dick with t-head, to Ryobi 3302 twin tower, Digital Xerox so called press, to now learning a 4 color DI press.
    Thrown into them all with the figure it out on your own mentality, however I love a challenge and with a book and help with you great guys on this thread, I will figure it out. The owner of the company is giving me a shot and I want to do all I can to learn from you experts and produce a great job.
    I have done a few 4 color jobs in the past on an A.B. Dick 360 in 4 passes, A Ryobi 3302 in 4 passes two sides with polyester and paper plates.
    I wish to gain more knwoldege about process work. The densitmeter, how it works, what the numbers should read and on various stocks. Any helpfull tips would be greatly appreciated.
    You guys are great and I love to read the tips and tricks and hate to see the put downs on someone just trying to gain knowledge.
     
  11. pressing situation

    pressing situation Member

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    Who can explain in simple terms grey component replacement for process printing.
    Press operators understand, however design departments have no clue what it means.
     
  12. tonyc

    tonyc Member

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    Who can explain in simple terms grey component replacement for process printing.
    Press operators understand, however design departments have no clue what it means.


    grey component replacement (GCR) takes the correct proportion of cyan, magenta and yellow out of the images and replaces this with black. This is based on the knowledge that that these 3 process colours should equal neutral grey or black depending on the amount. This is very similar to UCR which only affects heavy coverage or shadow areas.

    GCR reduces ink usage, improves colour consistency and neutrality. Our printers love this as make readies are quicker on quadratones without the normal colour casts deviation.
     
  13. tonyc

    tonyc Member

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    Should have mentioned that the GCR system we have trialled has affected certain image reproduction which we are trying to address with other software.
     
  14. tonyc

    tonyc Member

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    Going back to the debate on densitometers and dot gain....

    We have to be careful when we give standard weights across different countries.

    America and Britain tend to use different filter sets in their densitometers compared to the rest of Europe in general. USA / Uk use Status T filter set, EUR use Status E filter set. Black, cyan and magenta readings remain the same but their is a different reading for the yellow. There is a large difference which I can't confirm at the moment but a status T reading of 1.00 would read approximately 1.25 on the staus E densitometer.

    Spectrophotometers are even more critical with other settings that need to be quoted to compare results such as observer angle, geometry and light source.

    The debate on dot gain is a no brainer to me. If you want to control colour, you must control all of the print attributes which have an effect on colour. These are substrate, ink hue and density, tone transfer (dot gain), trapping and sequence.

    You can get away altering density and such to cover a dot gain issue on some images but as soon as you have a solid and screen within the same inking zone then something will change compared to the original (proof, print, whatever)

    One problem with setting up a press to match a proofer or vice versa is that both devices will drift. This can result in one of devices being calibrated to a moving target. Another problem is the two devices have different gamuts, i.e the press can not print all the colours the proofer can reproduce. If the reference point or device is stable, never moves and can be be matched by all devices involved then this is preferred.......which is why standards such as ISO 12647-2 are popular with printers and customers. They never move and all the proofers and presses are calibrated to this instead of to each other, ensuring if followed, different printers across the globe can print the same job / colours within a better, closer tolerance.
     
  15. DanRemaley

    DanRemaley Senior Member

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    The "secret" behind dot gain is keeping them in "balance". That way the gray balance becomes lighter or darker but not casted. Fwelix Brunner, the smartest person on earth says 90% of color problems is "dot related" only 10% is from solids. . .what do you measure?
    Dan Remaley
    412.889.7643
     
  16. DanRemaley

    DanRemaley Senior Member

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    E-mail me and I'll send you the "numbers", density and dot gain. I also have an X-Rite 418 refurbished for $600US. and a 518 for $1,000US
    Dan Remaley
    danremaley@comcast.net
    412.889.7643
     
  17. discountprintingservice

    discountprintingservice Senior Member

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    Dan Remaley is right on target about dot gain, gray balance and running to standard ink density...makes much more sense than spending a lot of $$$ on chasing after G7/Gracol/etc. Can't thank you enough Dan!

    In my own shop I printed a dot gain test strip to industry standard densities, recorded the patches with a reflection densitometer using Murray-Davies formula, made curves in our CTP rip for each color, and tweaked the curves for gray balance...what a difference it makes...our press sheets have never looked better!

    And color is easier to control and maintain consistency throughout the run...jobs now magically match previous samples on reorders...why? because dot gain is controlled and now all we have to do is match the standard density numbers...

    The very first job I ran after gray balancing the press was noticeably much easier & faster to get up to color since all I had to do was match the ink density to the standard numbers which by the way makes it much easier doing 4/c work on a 2 color press...took the guess work right out of eye balling the color until it matches...oh and less waste sheets getting color up too...

    But those of you that think you can eyeball quality 4/C work keep on doing it and I will keep getting more clients who want accurate colors without color casts or shifts and as wide a gamut as our press will print....

    This method takes a little time to implement but hands down is well worth the quality improvement...

    Dan is good as gold in my book...:cool:
     
  18. DanRemaley

    DanRemaley Senior Member

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    Thanks for the kind words

    I am ready, willing and able to help, please call me 412.889.7643
    Dan Remaley
    danremaley@comcast.net
    color Print Consultant
     
  19. DanRemaley

    DanRemaley Senior Member

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    Who can explain in simple terms grey component replacement for process printing.
    Press operators understand, however design departments have no clue what it means.[/I]
    .....Yes GCR replaces combinations of y-m-c in with black. What people don't know is that GCR pushes the y-m-c values away from the midtone (where the most change takes place during a press run). The values become more "saturated" (60-70-80%) or less "saturated" (10-20-30%), therefore the color doesn't, and can't. . . be changed on press. Dan Remaley
     

  20. discountprintingservice

    discountprintingservice Senior Member

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    Dan,
    Basically it is just what you said, Gray Component Replacement or GCR is the process of using software, such as Photoshop or a RIP to replace equal amounts of Cyan, Magenta and Yellow with Black based on the theory that equal parts of Cyan Magenta and Yellow produce gray...this became more widely used back in the late 80's through the 90's with wide spread use of common blanket presses, particularly T-heads by Townsend Industries. Townsend used to distribute literate explaining this in great detail and illustrating the difference with a composite and individual CMYK images showing the same image with and without GCR and also UCR (Under Color Removal)...it was an interesting article and I think I still have a copy, if I do I will try to make a PDF of it to post for anyone interested in seeing...

    The main purpose of it I was told was for presses than had difficulty running high Total Ink Limits (300 or higher) on multicolor presses, but particularly useful for common blanket 2 color presses using T-heads or roll back heads to reduce the amount of ink coverage on a common blanket for 4 color process to reduce color contamination by the darker color on the common blanket migrating to the lighter color...Townsend claimed that by reducing the amount of Cyan, Magenta and Yellow you could reduce color migration & contamination and that it made it easier to print 4 color on T-head equipped presses by reducing color casting and help reduce drying times by laying less ink down on the sheet...Keep in mind that Townsend was referring to "pleasing process color" and specifically said it was not meant for "National Geographic type work"...

    As far as how to explain it to pre-press they just need to understand the basic component of replacing the equal amounts of the 3 primary colors with black for gray...but with modern CTP systems I don't see the need for GCR or UCR if you run calibrated plates and your press is dialed in for dot gain and gray balance, unless you are running on a common blanket press then I could see the benefit...

    I remember the days when I printed 4 color on a T-head equipped press and you had to be on you A game to make it look good, tack of inks had to be just right and press and T-head had to be near perfect mechanically...now you couldn't give me a T-head press for 4 color work, I wouldn't trade my 2 color press for anything less than a 4+ color machine...

    Using the calibrated gray balance method you spoke about here, I wonder how good you could make a 4 color job could look on a common blanket 2 color press??? hmmmm....lol
     
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