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  • Densitometer - reading proof color bars

    Im trying to implement a system where we will read the color bars on our proofs with a densitometer to make sure they are staying in spec. I have an older xrite densitometer. I have used one of these a little in the past but I really need a refresher. I dont know where to start as far as what good densities would be. I could calibrate my dupont and then read the color patches, but Im clueless about how high or low I could allow the densites to go before we say its out of spec. Any help is greatly appreciated.

  • #2
    Re: Densitometer - reading proof color bars

    Tim
    In the UK and it must be the same in the US - we use the liitle Spectro Eye one which fits into a usb port on a PC and software (cost about $500 ) The little spectro fits on a plastic rail and we measure special patches in one swipe - and then a dymo label printer - prints a label which we stick on the proof.

    http://www.bodoni.co.uk/ - have a look at their proofsign software for an idea.

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    • #3
      Re: Densitometer - reading proof color bars

      I think i may not have been clear. We calibrate our dupont and we know what the delta numbers are. what im looking to do is read the color bar that proofs with each page. I want to know that that the color coming off the proofer is still falling in acceptable ranges. I just dont know what those ranges should be for each of the 4 colors. I need to find out for both a publication and commercial stock. That being said, when I "zero out" for paper white would I zero on the publication paper or a known value white?

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      • #4
        Re: Densitometer - reading proof color bars

        Tim
        All my proofs a validated to a particular printing condition on different paper types using the Spectro

        I think this is what you are tring to do

        Peter

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        • #5
          Re: Densitometer - reading proof color bars

          Tim
          I thought the G7 guys would be all over you - modern day thinking (great words) is that our proofs and presses are set up a standard. This standrad really should be the standard ,that the colour profiles used to convert rgb to cmyk were produced from. As far as proofing goes all you do is up load the profiles and you have a proof - on your presses ( spend loads of money) and match the proofs.

          Peter

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          • #6
            Re: Densitometer - reading proof color bars

            The densitometer won't tell you if the color is still in spec because it doesn't measure color. Your densities and dot gains can remain in spec while the color shifts. A spectro will tell you if your color is in spec. I think that's why the other responders were mentioning their use of a spectro for QC purposes.

            best, gordo

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            • #7
              Re: Densitometer - reading proof color bars

              Hi there, i hope this post helps in clearing up some issues, it may not as all i have learnt is form asking questions on these forums and not from gaining actual results. Firstly if you are using actual LAB values to check calibration of each proof then the general run tollerance is 5 delta e, but the G7 specification states something like for calibration purposes it should be more like half of any run tollerance so 2.5 delta e. All measurements for G7 and iso 12647 are all absoloute which means that the colour which is being measured includes the papers effect upon it, if you zero to paper you will skew any results ( There is a reply form a mr Eddington on this site from one of my posts under the title ISO 12647 who explains this).
              As for the difference in stocks, it should not matter as long as you use the right set of ISO values dependent on stock as target refs (unless the paper doesnt comply to iso standards) the delta difference is the same independent on stock.

              Hopefully some of the info above is right if not please post and correct me. but i think it ok.

              All this is assuming the term "densitometer" is actually ment to be spectrophotometer, but i always call it a densitometer.

              Paul

              Edited by: Paul Green on Jan 18, 2008 7:18 PM

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              • #8
                Re: Densitometer - reading proof color bars

                Paul
                There is a seperate ISO proofing standard 126747-8 this measures DeltaE and DeltaH ( Gordo may help explain what Delta H is) -

                As I am sure you know there are two main camps where proofing is concerned -

                THe first traditional one is setting up your proofer to mirror what the job will look like on press. This is the most forgiving as clients dont have anyone elses proofs to compare it with. You can just proof on different colour of papers to match what you do - we have all done it for years and it sort of works.

                The Other is where we proof to the same printing conditions and paper colour that was used to create the profiles we recommend -in our case ISOCoated and ISOuncoated - this is much more difficult - because our proof have what is called the Fogra Media wedge on - and this is the agreed European measuring colour bar. Most of the large magazine companies will not except adverts unless they have a proof validated .
                Having a common standard for proofs is great - but every one has problem with the paper colours - in the web market lots of money is spent repurposing files using CMYK to CMYK profile conversion software - to try and get the same visual appearance as the proof regardless of stock colour.

                Peter
                WE (The BPIF) are looking to organise a technical colour workshop in Birmingham in April (in an evening) - if you would like I will try and get you an invitation (it will be free)

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                • #9
                  Re: Densitometer - reading proof color bars

                  Peter, thankyou for the reply, i did not know about seperate proofing standard for ISO, i shall google that later. As for the proofing methods, we have used the first method for years now but have not adopted the idea of producing proofs within any international standard although i have tried to push this issue. My company is going through a rough time at the moment with a buyout taking place so hopefully if im still employed i might get a chance to push things forward later on this year. If at all possible i would be intrested in joining any technical colour workshop to gain some more knowledge so an invitation would be very welcome.

                  Cheers Paul

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                  • #10
                    Re: Densitometer - reading proof color bars

                    Almost three years ago I wrote about the Density/TVI & L*a*b* considerations when measuring proofs.

                    My thoughts can be found at:

                    http://jimraffel.com/2005/07/13/gold...ty-tvi-or-lab/

                    My general thoughts are that density and TVI of ink jet proofs are virtually meaningless numbers. I support this statement in the above post on my blog.

                    Just wanted to get my 2 cents in on a very cold Saturday morning in Wisconsin

                    Jim Raffel
                    CEO - ColorMetrix Technologies, LLC
                    http://www.colormetrix.com
                    http://www.jimraffel.com
                    Jim Raffel - CEO ColorMetrix
                    http://ColorMetrix.com/blog | Twitter: @raffel

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                    • #11
                      Re: Densitometer - reading proof color bars

                      Paul
                      sorry to hear about the uncertainty - it is really tough out there at the moment -

                      Peter

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                      • #12
                        Re: Densitometer - reading proof color bars

                        My very basic understanding of the difference between delta e and delta h...

                        Delta e - is how close/far out the colour is (as a mathematical representation of measuremetn - distance between the reference colour and the measured colour)

                        delta h - is in which direction (measured/represented as an angle)

                        so for instance, if measuring a reflex blue, the delta e value tells you how close or far the colour is. the delta h will tell you whether it is out in the black, cyan or magenta channel.

                        hope this makes sense

                        Peter A - if the april workshop is anything like the conference that was run in birmingham last year, then it will be well worth attending.

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                        • #13
                          Re: Densitometer - reading proof color bars

                          Peter A - if the april workshop is anything like the conference that was run in birmingham last year, then it will be well worth attending.

                          THanks for that - it was a gamble - but as the say - "the boys did well" This one is going to be focused on implementaion - with much more time for Q and A at the end with a panel of printers etc -

                          I just ran out of time in Birmingham.

                          Peter

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                          • #14
                            Re: Densitometer - reading proof color bars

                            thanks seejay is h bassed on the LCH colour space then. as i think that gives the H co-ordinate as a degrees co-ordinate e.g 0 to 360?

                            thanks paul

                            off to the pub!

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                            • #15
                              Re: Densitometer - reading proof color bars

                              Delta H is based on the LAB values - it is the angle between the reference and measured lab values.

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