4-Color printing lesson for a single or 2/color press

Discussion in '1-Color and 2-Color Offset Presses' started by DanRemaley, Mar 11, 2017.

  1. DanRemaley

    DanRemaley Member

    Joined:
    Oct 2010
    Messages:
    54
    Location:
    Pittsburgh, PA
    The correct color sequence is K-C-M-Y. This "layer" of ink, gets the best secondary R-G-B overprint colors. Color from a single or 2/C press is actually better than multicolor press because the traps are "dry".
    I suggest printing B/C then M/Y. The secret is to create a midtone gain of 20% - this means the plates need to be adjusted so when printed at density a 50% patch on file - measures 70% on press (for coated & uncoated - although the uncoated densities are lower. If you have printed K/C the Cyan gain will vary as you print from (say 70% to 74%). The secret here is to mark those changes in the run and match the Magenta gain to match those numbers from the Cyan. If the C/M gains are the same - the color will be accurate (in Gray Balance) the 74% will be a little darker but still correct. (Yellow's target is 68% and Black is 72%).
    In order to do the plate correction correctly you need to print a complete tone scale at the correct density - measure the dot area of each patch. I can send you the "Wanted Values". You enter these into the pre-press RIP and it calculates the difference of "Measured" vs "Wanted". The plates will have smaller dots so that the dot area will be correct and match the "Wanted" numbers - Done.
    You will be the BEST printer in your area - GATF trained!!!
    Questions? Dan Remaley 412.889.7643 <danremaley@comcast.net>
     

    Attached Files:

  2. emet

    emet Member

    Joined:
    Sep 2015
    Messages:
    44
    Location:
    Devon, United Kingdom
    I am very interested in what you are saying here.
    I am a "volunteer" printer not a professional. I am printing 4 colour with a GTO46. I don't have a really professional setup. I print inkjet film using a RIP and then expose positive plates. I am quite happy with the results but always like to understand more.
    I printed halftone swatches on film and then ran them on the press. I measured them with my densitometer and then used photoshop to make a curve so what I see on the screen is what i get on the press. A 50% on the screen is a 50% on the press. If I am to understand you rightly that is not how I should do it. Are you suggesting that a 50% on the screen should print 70%. This is consistent with something I heard from a friend who ran a shop with web presses. I never really understood what he was saying though. He said you want some gain or it will look dull.
    Can you help me better understand all of this.
    Thank you
     
  3. mantman

    mantman Senior Member

    Joined:
    Nov 2015
    Messages:
    152
    Location:
    Greece
    I think its best to start with C/M then Y/K in single or 2 color machines, that way you almost simulate a 4 col machine and you get better register at the two primary colors of C+M and it is easier to see and control, any kind of cast towards cyan or magenta, besides Y+K do not affect images as much as C+M. Also you can check up on uncle googlie bdvm mediastandard 2016 for TVI color curve and many interesting information, imho you can omit the hard to find papers mentioned in there.

    emet printing linear is not a good thing, your friend was right meaning your prints will be totally flat.
    You must be absolutely sure that your halftone swatches on film are what they say -50% is 50% not 51 or 48 as the rest-. Your RIP should have a program to make calibration curves, usually 3 curves are used: current -what you print now with increment patches of from 5% to 100% with uncalibrated plates or fingerprinting-, target -what you want to achieve from a proof machine/profile- and calibration curve -if you measured 60% in 50% patch and you target is 68% software will try to match that 68%-.

    Silly question but...when you measure dot area for fingerprint you exclude paper white or not?
     
  4. emet

    emet Member

    Joined:
    Sep 2015
    Messages:
    44
    Location:
    Devon, United Kingdom
    Thank you mantman for your reply.
    When I measure the dot area I have a densitometer that makes me read the paper and then a solid, then it is ready to measure dot. That is a vipdens C9. So I think I am adjusting for the paper. I hope this answers your question. I am not trained in this realm, just had to figure it out mostly for my self. This is partly because the rip I am using is for screenprinting. It has the capability of adjusting it so your film and be accurate but what I do is use it to calibrate for the end result of the printed sheet. I don't have a good proof machine, just a desktop inkjet so I don't have to calibrate for that.
    If you gave me a good idea of what to shoot for I think I could give it a go. Like -- when it says 25 on screen make it 35 and when 50 make it 65 etc etc
    So far I am not displeased with what I am printing. I would generally like things to be more vibrant but I am mostly printing on cheap copier paper (the stuff you get from staples on sale). I have printed a couple of times on coated and it definitely was more vibrant.
    Just so you know I have a single colour GTO.
     
  5. emet

    emet Member

    Joined:
    Sep 2015
    Messages:
    44
    Location:
    Devon, United Kingdom
    Hello,
    Mantman, I hope I did not create confusion or offend. I am really interested in what you were saying and would love to have a target curve to shoot for. I feel confident that if you say a 50% on the screen needs to be 65% (or whatever) on the press then I can make that happen.
     
  6. DanRemaley

    DanRemaley Member

    Joined:
    Oct 2010
    Messages:
    54
    Location:
    Pittsburgh, PA
    Dot area and dot gain are measured
    (-paper). Density measurements are (including) paper.
    Start with linear plates or film. Print the entire tone scale at the correct density. Measure these tone scales values. You can use BVDM curves or contact me and I can send you them.
     
  7. emet

    emet Member

    Joined:
    Sep 2015
    Messages:
    44
    Location:
    Devon, United Kingdom
    Thank you for your reply.
    I only print occasionally so I am hoping to do the whole process in one shot.
    From what I understand I need to be able to get what is 50% on the computer monitor to be 50% on the plate. That is linear right?
    Then I need to take that plate and print on my press to see what it's dot gain is for the entire tone scale at the correct density.
    The next step would seem to be to make a correction if need be to hit what would be a "target" dot gain. It seems like if I knew what that was I could do the whole process in one go. I think I have enough understanding of the process to do that. I just don't have a target yet. Does that make sense?
    Is there a way to get a target set of values. A set of values that show how much dot gain you want for each tone value. So it would say for example "for a 25 on the computer monitor make it 32% on the paper (a random example)"
     
  8. DanRemaley

    DanRemaley Member

    Joined:
    Oct 2010
    Messages:
    54
    Location:
    Pittsburgh, PA
    Attached- “wanted” tone values.
    Print “wet” 1.03Y 1.33C 1.43M 1.75K
    This allows for dryback.
     

    Attached Files:

  9. emet

    emet Member

    Joined:
    Sep 2015
    Messages:
    44
    Location:
    Devon, United Kingdom
    Thank you so much.
    I usually print on uncoated paper. Is there other values for that? At least other densities?
    I have been printing pretty close to linear on the press. From the values you have given me I would think things will be a lot more colorful now. I am surprised by how much gain you want.
    Also I was surprised to see that there are different values for each colour. Am I going to notice a lot of problem if I use the same curve for all colours? My setup is not very good for handling that.
     
  10. DanRemaley

    DanRemaley Member

    Joined:
    Oct 2010
    Messages:
    54
    Location:
    Pittsburgh, PA
    Yes, u need 4 separate curves-Y-M-C-K
    The “wanted” is the same for uncoated ( because all scans are the same - since no one knows if the job is coated or uncoated). Here’s the densities for uncoated Y.95 C1.10 M1.15 K1.40
    You’ll print the BEST uncoated sheet in your area!
     
  11. emet

    emet Member

    Joined:
    Sep 2015
    Messages:
    44
    Location:
    Devon, United Kingdom
    Whooppeeee!
    I can't wait.
    Thank you so much for your help
     
  12. DanRemaley

    DanRemaley Member

    Joined:
    Oct 2010
    Messages:
    54
    Location:
    Pittsburgh, PA
    Your welcome - call anytime with any questions 412.889.7643
     

    Attached Files:

  13. DanRemaley

    DanRemaley Member

    Joined:
    Oct 2010
    Messages:
    54
    Location:
    Pittsburgh, PA
    . . .one other thought - you could have your ink co. Adjust the ink to create more/less gain per color. (I don’t recommend but if u can’t create 4 curves - it’s an option)
     
  14. mantman

    mantman Senior Member

    Joined:
    Nov 2015
    Messages:
    152
    Location:
    Greece
    Dan, I prefer magenta over cyan myself, to avoid the green cast, but i believe you forgot to mention the status of densitometer, E, G or T? Though i think status affects only the measurement of yellow.
    One more question densities and l*a*b* values go together?
    Also, if you have a spot color that read l50 a+30 b+20 and your target is l50 a+10 b+20, how do you "remove" the reddish cast, can you add the opposite in the color circle -green in this example-, i am fairly new to colorimetry and would like some advice thank you in advance
     
  15. DanRemaley

    DanRemaley Member

    Joined:
    Oct 2010
    Messages:
    54
    Location:
    Pittsburgh, PA
    Yes, these are status ‘T’ - and Yes the Yelo reading will be the largest difference (if status ‘E’)
    We assume the inks are ISO - these numbers will give u gray balance throughout the tone scale AND will match the Pantone screen build book.
     

    Attached Files:

  16. emet

    emet Member

    Joined:
    Sep 2015
    Messages:
    44
    Location:
    Devon, United Kingdom
    Another question I have is how my choice of GCR (ie, max, heavy, medium etc) will effect colour.
    I like maximum or heavy because I print 4 colour on a single colour press on cheap paper so max gcr is great for making the print sharper but I thought I would lose on the way the colour is
     
  17. DanRemaley

    DanRemaley Member

    Joined:
    Oct 2010
    Messages:
    54
    Location:
    Pittsburgh, PA
    GCR - replaces black for any tri-chromatic (y-m-c) color. It subtracts Y-M-C and places more black.
    The press normal variation is +/- 4% dot gain - GCR prevents color from changing. (See PC refrence I sent previously). If your curves are set correctly, GCR is fine. If you have to move or “correct” color - you can’t!
    Also GCR is a MUST for a 4/color - black & white image.
     

    Attached Files:

  18. emet

    emet Member

    Joined:
    Sep 2015
    Messages:
    44
    Location:
    Devon, United Kingdom
    I did do a 3 1/2 year stint as a pressman on a newspaper press for a small newspaper in Tennessee. The pre press man did not know about GCR but I had learned a little when I had tried doing 4 colour on a Ryobi 3200 w/ T head. The web press we ran did not have the greatest registration over the whole sheet so I advised him to sometimes use max GCR. One negative thing I noticed was that the pictures could look a little flat. When the blacks were made of all the colours they were denser and thus the photos tended to have more depth. That is why I have shied away from MAX GCR on my GTO 46. Any thoughts??
     
  19. DanRemaley

    DanRemaley Member

    Joined:
    Oct 2010
    Messages:
    54
    Location:
    Pittsburgh, PA
    When selecting GCR you can select UCA (under color addition) this adds y-m-c under shadow areas creating more contrast.
     

  20. emet

    emet Member

    Joined:
    Sep 2015
    Messages:
    44
    Location:
    Devon, United Kingdom
    I never knew what UCA was. Hmmmm.. How is that different than just choosing medium GCR rather than maximum GCR.
    Thank you so much for sharing what you know. This is so interesting!
     
Loading...