Re: Densitometers and Spectrophotometers
Re: Densitometers and Spectrophotometers
- Subject: Re: Densitometers and Spectrophotometers
- From: Dan Wilson <email@hidden>
- Date: Mon, 11 Feb 2008 09:33:33 +0000
- Thread-topic: Densitometers and Spectrophotometers
Hi Peter,
In a crude explanation, I find it easier to think of Densitometers as black
and white instruments. Inside the densitometer a different colour filter is
put in front of the lens/light when you want to read different colours -
each different filter makes a colour look like black.
For instance, if you got some old red Rubylith film and looked at a Coke
bottle the red and white on the label would largely disappear. If you then
look through the Ruby film at something cyan it would look black. So using
the filters the Densitometer reads the 'blackness' or density of the target
relative to the paper.
Spectros on the other hand read all the wave lengths of light - they are
'full colour' devices. Then smart people on this forum get the paper white
value, the read target value, and apply some fancy maths formula to
calculate the density.
It is also possible to calculate TVI (or Dot Gain) with a Spectro - I think
the ISO should adopt this method as it removes the 'relative-ness' (if that
is a word) of using Densitometers to calculate TVI.
Below is a sample of the data a Spectro collects.
Regards,
Dan Wilson
--
G7 Certified Expert
UGRA Certified Expert/Consultant
--
Prepress I.T. Limited
Dublin, Ireland
Dublin +353 (0)85768 2733
www.prepress-it.com
**************************************************
SAMPLE_ID CMYK_C CMYK_M CMYK_Y CMYK_K LAB_L LAB_A LAB_B
SPECTRAL_400 SPECTRAL_410 SPECTRAL_420 SPECTRAL_430 SPECTRAL_440
SPECTRAL_450 SPECTRAL_460 SPECTRAL_470 SPECTRAL_480 SPECTRAL_490
SPECTRAL_500 SPECTRAL_510 SPECTRAL_520 SPECTRAL_530 SPECTRAL_540
SPECTRAL_550 SPECTRAL_560 SPECTRAL_570 SPECTRAL_580 SPECTRAL_590
SPECTRAL_600 SPECTRAL_610 SPECTRAL_620 SPECTRAL_630 SPECTRAL_640
SPECTRAL_650 SPECTRAL_660 SPECTRAL_670 SPECTRAL_680 SPECTRAL_690
SPECTRAL_700
END_DATA_FORMAT
NUMBER_OF_SETS 275
BEGIN_DATA
1 100 100 100 0
27.36826 0.7248735 2.337503 3.95595
4.856588 5.058892 4.761323 4.455005
4.37118 4.53157 4.196051 4.072113
**************************************************
> ------------------------------
>
> Message: 3
> Date: Fri, 8 Feb 2008 18:13:13 EST
> From: email@hidden
> Subject: Re: Densitometers and Spectrophotometers
> To: email@hidden, email@hidden
> Cc: email@hidden
> Message-ID: <email@hidden>
> Content-Type: text/plain; charset="US-ASCII"
>
>
> In a message dated 08/02/2008 23:09:52 GMT Standard Time,
> email@hidden writes:
>
> I am not as happy with the repeatability of the Eye-One as I was with a
> high end densitometer.
>
>
> Matk sorry to butt in here - but doesn't a spectro calculate density
> differently than a densitometer - or is that just an old wives tale
>
> peter
>
> ------------------------------
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