Densitometer - reading proof color bars

truetype1

Active member
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.
 
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.
 
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?
 
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
 
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
 
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
 
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
 
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)
 
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
 
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/golden-nugget-5…density-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
 
Re: Densitometer - reading proof color bars

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

Peter
 
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.
 
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
 
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!
 
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.
 
Re: Densitometer - reading proof color bars

> {quote:title=Paultheprinter wrote:}{quote}
> 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?

Yes, Paul. That is correct. DeltaH is the difference in the hue of 2 colors.

As to Tim's original thought -

You absolutely CANNOT use a densitometer to verify proofs!!! It is an abomination before the Lord! The book of Leviticus clearly states:

"Thou shalt only verify thy proofs with a blessed spectrophotometer. To use a densitometer for such purpose is an abomination before the Lord. Any transgressor shall be smote."

I can't remember the chapter and verse, but I know it's in there.

rich
 
Re: Densitometer - reading proof color bars

tim~
In my fumbling knowledge of profiling, ((which I think our shop is pretty good for a small quick printer)) I use our densitometer to check that the CMYK isn't too saturated compared to what we're printing on press. I know it's not going to catch a hue shift, that's what the spectrophotometer does, but it works pretty good and in comparing my proofs to Kodak certified proofs, we're pretty much spot on.

We use GRACOL's recommended density's
I've attached the chart.

as for measuring paper white, you should measure the white of the paper you're proofing on because that color can affect the density readings.

Hope this helps.

and please, spare the spamming of how horrible an idea that is! I'm aware it's not the recommended course, but when you're on a budget, you use the tools you have on hand, and make due. A small shop can't afford to spend thousands to have someone come in to profile their shop.
 
Re: Densitometer - reading proof color bars

Paul,
Listen to Preacher Rich Apollo. Densitometers are for printers measuring their ink densities and Gray Balance (and can do as good as if not better job on a press than spectrophotometry). But for proofs, because they don't use the same inks and substrate and there are optical brightners in the inkjet coatings sometimes, density is false worship before the golden calf! (actually a brownish-yellow calf if you try).

You need Spectrophotometry - you need to measure colour not density. The printer will take care of his ink densities and try to match your proofs. You can get combination Spectro-Densitometers such as the X-Rite DTR508. I thought DuPont supplied spectros with all their digital proofers?

Pick your colour standard, pick your press method, measure and adjust colour, profile to same and vary ye not one thing if ye wanteth consistent results. The little Spectro-Eye and Eye-One type products mentioned earlier measuring, say the Gracol, FOGRA, Calathumpian strip or whatever, do a very good job.

If its ISO you're after, you could do a lot worse than contact Alan Dresch of Mellowcolour in UK. www.mellowcolour.com .

(Colour with the 'u' for American friends)
.
Kind regards
Andy in Australia
 
Re: Densitometer - reading proof color bars

Praise the lord ! i thank god for the devine wisdom of your input and shall from this day forth only preach the dark path of densitometery on press, and will enlighten all pre press with the savour of spectrophotometery to rid the free world of inacurate proofs.

Paul the converted
 

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